EV Digest 4459
Topics covered in this issue include:
1) Re: Acceleration Calculations
by David Dymaxion <[EMAIL PROTECTED]>
2) Re: on Ebay: 2004 Toyota Prius Wrecked Salvage
by "David Chapman" <[EMAIL PROTECTED]>
3) Re: ComutaCar "rescue"
by "David Chapman" <[EMAIL PROTECTED]>
4) Re: Antique hybrid idea
by Victor Tikhonov <[EMAIL PROTECTED]>
5) Re: on Ebay: 2004 Toyota Prius Wrecked Salvage
by Henry Davis <[EMAIL PROTECTED]>
6) Re: Modern hybrids, Re: Antique hybrid idea
by Victor Tikhonov <[EMAIL PROTECTED]>
7) Re: Looking for a smarter E-meter
by Victor Tikhonov <[EMAIL PROTECTED]>
8) Re: Antique hybrid idea
by David Dymaxion <[EMAIL PROTECTED]>
9) Re: Acceleration Calculations
by Victor Tikhonov <[EMAIL PROTECTED]>
10) RE: Acceleration Calculations
by "Don Cameron" <[EMAIL PROTECTED]>
11) RE: Acceleration Calculations
by "Don Cameron" <[EMAIL PROTECTED]>
12) RE: Acceleration Calculations
by David Dymaxion <[EMAIL PROTECTED]>
13) Re: Acceleration Calculations
by Victor Tikhonov <[EMAIL PROTECTED]>
14) Re: Need Charger Recommendation
by "Lawrence Rhodes" <[EMAIL PROTECTED]>
15) RE: Acceleration Calculations
by "Don Cameron" <[EMAIL PROTECTED]>
--- Begin Message ---
Have you plotted your calculated acceleration vs. speed? I like to
divide by 9.8 m/s^2 to get the answer in g's of acceleration. For a
FWD you'd expect about 0.5 g max. Much more than that and you just
have wheelspin.
When I first did a sim I got amazing acceleration, too, and found I
was starting out with several g's of acceleration! So you need an
"if" test similar to this:
// If acceleration calculates to be above traction limit
if ((a/9.8) > 0.5)
a = 0.5 * 9.8; // Set max accel to traction limit
else
a = f(rpm);
a -= a_aero;
a -= a_drag;
A sanity check you can do:
a ~ Current * Voltage * 0.6 / (mass * velocity)
for higher rpm (rpm above current limit).
--- Don Cameron <[EMAIL PROTECTED]> wrote:
> I am revisiting my calculations for acceleration and power and I
> seem to
> find they are overly optimistic. I have compared them to other
> spreadsheets
> and estimations and the results are wrong. If anyone else is doing
> something similar, do you mind taking a look?
>
>
>
> The approach is to base it on time:
> 1. Start with time t0,
> 2. determine velocity based on RPM,
> 3. calc force available to accelerate from motor graph,
> 4. adjust for aero drag and rolling resistance,
> 5. calculate max acceleration
> 6. then determine finish velocity for time increment.
> 7. go back to step 2, and use this velocity for the next time
> t0+0.5sec.
>
>
> Here is the detail:
>
> Given:
> The car has fixed gearing (no transmission) overall gear ratio
> (R)
> the tire diameter
> the frontal area of the car (A)
> the aerodynamic drag (Cd)
> the drive train efficiency (Cdt)
> tire rolling resistance (Crr)
> vehicle mass (m)
>
>
> Starting with times from 0 seconds to 90 seconds in 0.5 second
> increments
>
> 1. At time t, use the previous time's calculated final velocity V0
> 2. Determine the RPM of the motor based on the velocity, gear ratio
> and
> wheel diameter: RPM = (V0 * OverallGearRatio)/(pi * WheelDiameter)
> * 60
> 3. Using the motor torque graph, determine the motor torque at the
> specified
> RPM
> 4. Determine the force of the motor from the torque: F = (Torque *
> OverallGearRatio) / (WheelDiameter/2)
> 5. Correct the force for drive efficiency: F(corrected) = F *
> DriveTrainEfficiency
> 6. Force to overcome rolling resistance F(roll) = VehicleMass * 9.8
> (gravitational acceleration) * TireRollingResistanceCoeff
> 7. Force to overcome air resistance at velolcity V0 F(air) = 1/2 *
> DragCoeff
> * FrontalAreaOfCar * AirDensity * V0^2
> 8 Total force available for acceleration: F(total) = F(corrected)
> - F(roll)
> - F(air)
> 9. Acceleration: a = F(total) / VehicleMass
> 10. Final velocity for time period : V1 = a * t + V0
> 11. Go back to step one for next time period, using V1 as the next
> time's V0
>
> Since I use metric no real unit conversions were required. I have
> tried to
> keep units out of this wherever possible.
>
> If anyplace has an error, I think it is around step 9, 10 or 11.
> All the
> other calculations appear to be OK.
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--- Begin Message ---
Interesting find Mike, but for those interested would suggest you tread
lightly. Its got a salvage title which means that it was a structural total.
From experiance this can mean major value issues (loan value, diminished
resale value, etc) and insurability issues. I also think the "lightly
wrecked" statement is being very charitable.
David Chapman
Arizona Electropulsion / Fine-Junque
http://stores.ebay.com/theworldoffinejunque
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Monday, June 27, 2005 9:41 AM
Subject: on Ebay: 2004 Toyota Prius Wrecked Salvage
I just found this on Ebay, thought someone in Califoria might be
interested.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7983492807&category=6763
--------------
"This is a lightly wrecked 2004 Prius with 15,372 miles. "
Current bid: US $10.50
Time left: 4 days 10 hours
Item location: Carmichael, California
---------------
Michael Shipway
Maryland, USA
--- End Message ---
--- Begin Message ---
The `67 Rambler app sounds about right David. Once one figures out what the
original app was I have had very good luck finding odd old and unusual at a
very good price from www.rockauto.com For instance just got a M/C for a `57
Chevy 150 wagon from them, brand new Raybestos item and cheaper than any of
my other suppliers even with shipping.
David Chapman
Arizona Electropulsion / Fine-Junque
http://stores.ebay.com/theworldoffinejunque
----- Original Message -----
From: "David Roden" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Sunday, June 26, 2005 11:13 PM
Subject: Re: ComutaCar "rescue"
On 26 Jun 2005 at 21:25, Nick Viera wrote:
So here's a question to end my long-winded story: where do you find
brake components for these ComutaCars? For example, is the master
cylinder a pretty standard part or something that is going to be hard to
find
a replacement for? How about wheel cylinders?
I found wheel cylinders for mine at a local Cushman scooter workshop. The
counterman kindly matched mine up with stock, but didn't tell me which
Cushman model they were to suit. I don't recall the cost, but seem to
remember thinking at the time that it was pretty steep.
According to the auto parts jobber who matched it up for me, the master
cylinder is the same as the one used in a 1967 Rambler Ambassador with
drum
brakes.
This was all in 1989; I don't know how readily available these parts are
today.
BTW, the problem is that when these cars are stored, moisture gets into
the
brake systems and plays hob with the metal parts.
David Roden - Akron, Ohio, USA
EV List Assistant Administrator
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--- End Message ---
--- Begin Message ---
A PWM seems to be modern implementation of this principle,
full on and full off; thus high efficiency of SMPS compare to
linear power supplies.
View ICE as "analog" rheostat - controlled EV, efficiency of such
an EV is probably not much higher than that of the ICE engine,
in contrast of high efficiency of modern switch mode controllers.
As of Prius, if your capacitor bank is large enough to
propel it for, say, one mile with the drive system
accommodating to the diminishing voltage while maintaining
the speed, indeed an ICE could re-start about once a minute for
a few seconds at full throttle to recharge the caps and then
shut off.
It is more efficient than present Prius system but the
fumtamental problem I see is it is still an ICE.
Even prtimized and running at peak power only, it is unlikely
to exceed 35% efficiency.
Victor
Lee Hart wrote:
I like old technology, and went to an antique engine show. They have
lots of antique cars, tractors, and engines of all sorts. Steam engines,
electric motors, diesels, and all sorts of odd gasoline engines from
days gone by.
The "hit-n-miss" or "dam-dam" engines were interesting. This is a
sort-of-normal small engine like you might find in a lawnmower. However,
they have an unusually large flywheel, and a valve mechanism that can be
disengaged. With the valves working, it runs like a normal engine. With
the valves off, it just freewheels -- the piston moves up and down, but
there are no pumping losses. The trapped air in the combustion chamber
just acts like a spring, returning the energy it takes for compression
on the downstroke.
The dam-dam engine is unique in that it always runs at full throttle.
The spark, timing, carburation, cam etc. are all optimized for
full-power only. Then they duty-cycle modulate it to get the actual
power desired. At "idle" it is actually spinning at full speed. It fires
once; and the freewheels for many seconds, fires again, freewheels many
seconds, etc. The sound it makes while doing this is is where the name
"hit-n-miss" or "dam-dam" comes from. Because of this mode of operation,
the part-load fuel economy is very good.
In practice, a governor senses flywheel speed, and engages the valve
train when it falls below a certain rpm; and disengages it above a
certain rpm. So engine rpm oscillates back and forth between these
speeds.
What caught my attention is that someone had one connected to a
generator, and used it as a battery charger. It looked like an old Ford
model A generator was coupled directly to the flywheel, and used its old
relay-type voltage regulator to control battery voltage and charging.
When there was no load on the battery, it charged at a couple amps, and
the dam-dam engine just fired once every 5 seconds or so. When he put a
load on the battery, the voltage sagged; the regulator called for more
current; the generator increased its load on the flywheel, and the
engine fired more and more often to maintain speed. A highly fuel
efficient hybrid power plant, built in the 1930's!
I wonder if this idea was ever used in a car? I wonder if it would be
practical today?
On the Prius (and most other normal cars), you get the best gas mileage
by "pulse mode" driving. This is how you win mileage contests. You
accellerate so the engine is at its peak efficiency point, which is
usually somewhere near full throttle. Then shut off the engine and let
the car coast down in speed. When it gets slow enough, restart the
engine and do it again. The Prius does this automatically, running on
batteries between times so you can actually maintain speed. On
conventional cars, you (and the drivers behind you :-) have to put up
with the constant speed-up and slow-down.
The dam-dam engine and a generator can do this, too. Ony they are doing
it at a far faster PWM frequency (many more on/off cycles per minute).
Thus, you shouldn't have the large speed changes during the cycle.
Any thoughts?
--
Victor
'91 ACRX - something different
--- End Message ---
--- Begin Message ---
--On Monday, June 27, 2005 10:32 AM -0700 David Chapman
<[EMAIL PROTECTED]> wrote:
Interesting find Mike, but for those interested would suggest you tread
lightly. Its got a salvage title which means that it was a structural
total.
Salvage titles in California do not necessarily imply any structural damage
at all. I own one vehicle with a salvage title with absolutely no damage
what so ever. The salvage title is because the original owner died, the
vehicle was towed, and then sold at auction. I also have another vehicle
with a salvage title - the insurance company totaled the motorhome because
of vandalism to the engine.
Henry
--- End Message ---
--- Begin Message ---
Granted, when the engine is off yo as well disengage it
with electric clutch similar to that used for A/C compressors
to avoid internal ICE friction all together.
Victor
Somewhat as some engines now use cyl cut off to
lower fuel consumption but you still have all that
internal friction that can add up to 20hp in many cars
wheher it's moving or not, enough to drive a car on
flat ground to 60-75mph depending on the car. And that
doesn't include ascessories. This is a big part of why
ICE's only get 7% of the fuels energy to the road and
an EV gets 20%.
Now instead use a 20hp engine that only has 3hp of
friction because it is much smaller, 1/5-1/10th the
normal size and the saving is great. Also on a
gasoline motor running at full power, doesn't have
trottle loses.
On the Prius (and most other normal cars), you get
the best gas mileage
by "pulse mode" driving. This is how you win mileage
contests. You
accellerate so the engine is at its peak efficiency
point, which is
usually somewhere near full throttle. Then shut off
the engine and let
the car coast down in speed. When it gets slow
enough, restart the
engine and do it again. The Prius does this
automatically, running on
batteries between times so you can actually maintain
speed. On
conventional cars, you (and the drivers behind you
:-) have to put up
with the constant speed-up and slow-down.
Any thoughts?
By running full all the time whenever the gas
hybrid motor is needed, the eff is so much higher that
it isn't even worth directly hooking it to the
driveshaft if 90% eff gen/ e drive motor is used
saving much weight, complication and costs. This
allows greater flexability too.
It's this kind of hybrid that will be our future
with a 100hp EV drive and 20hp gen in a 2,000lbs car
that can easily get 100mpg if aero for long distance
with a 50 mile range batt pack for most driving.
Jerry Dycus
--
Ring the bells that you can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in
-- Leonard Cohen, from "Anthem"
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377,
leeahart_at_earthlink.net
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--
Victor
'91 ACRX - something different
--- End Message ---
--- Begin Message ---
BRUSA Ah counter does this.
... I was about to describe details, but this this device is
unpopular among people on this list as not conforming to 12/80
principle. Well, just FYI, Ah counter has logic transition output
at "battery full" cindition you can hook a relay to.
Victor
Christopher Zach wrote:
Does anyone know if there is an E-meter device that can turn a relay on
when the SOC reaches 0% and turn the relay off when SOC reaches 100%?
Based on an AH count up and down modified by a charge efficience factor
and perkeurt factor like the E-meter?
I suppose I could just hook the RS232 output to a STAMP computer and
watch for 100% and 0% SOC.
Chris
--
Victor
'91 ACRX - something different
--- End Message ---
--- Begin Message ---
That's neat stuff. Cadillac did something similar with its 4-6-8
engine (it would lift two half-camshafts).
If you had selenoid operated valves you could do it even every other
crankshaft rotation.
Since 4 vs. 6 vs. 8 cylinder engines don't get much different gas
mileage in the same car, I'd wager you could get nearly as much
benefit with higher gearing. Half the cylinders firing half the
pumping losses, or half the rpm half the pumping losses.
--- Lee Hart <[EMAIL PROTECTED]> wrote:
> I like old technology, and went to an antique engine show. They
> have
> lots of antique cars, tractors, and engines of all sorts. Steam
> engines,
> electric motors, diesels, and all sorts of odd gasoline engines
> from
> days gone by.
>
> The "hit-n-miss" or "dam-dam" engines were interesting. This is a
> sort-of-normal small engine like you might find in a lawnmower.
> However,
> they have an unusually large flywheel, and a valve mechanism that
> can be
> disengaged. With the valves working, it runs like a normal engine.
> With
> the valves off, it just freewheels -- the piston moves up and down,
> but
> there are no pumping losses. The trapped air in the combustion
> chamber
> just acts like a spring, returning the energy it takes for
> compression
> on the downstroke.
>
> The dam-dam engine is unique in that it always runs at full
> throttle.
> The spark, timing, carburation, cam etc. are all optimized for
> full-power only. Then they duty-cycle modulate it to get the actual
> power desired. At "idle" it is actually spinning at full speed. It
> fires
> once; and the freewheels for many seconds, fires again, freewheels
> many
> seconds, etc. The sound it makes while doing this is is where the
> name
> "hit-n-miss" or "dam-dam" comes from. Because of this mode of
> operation,
> the part-load fuel economy is very good.
>
> In practice, a governor senses flywheel speed, and engages the
> valve
> train when it falls below a certain rpm; and disengages it above a
> certain rpm. So engine rpm oscillates back and forth between these
> speeds.
>
> What caught my attention is that someone had one connected to a
> generator, and used it as a battery charger. It looked like an old
> Ford
> model A generator was coupled directly to the flywheel, and used
> its old
> relay-type voltage regulator to control battery voltage and
> charging.
>
> When there was no load on the battery, it charged at a couple amps,
> and
> the dam-dam engine just fired once every 5 seconds or so. When he
> put a
> load on the battery, the voltage sagged; the regulator called for
> more
> current; the generator increased its load on the flywheel, and the
> engine fired more and more often to maintain speed. A highly fuel
> efficient hybrid power plant, built in the 1930's!
>
> I wonder if this idea was ever used in a car? I wonder if it would
> be
> practical today?
>
> On the Prius (and most other normal cars), you get the best gas
> mileage
> by "pulse mode" driving. This is how you win mileage contests. You
> accellerate so the engine is at its peak efficiency point, which is
> usually somewhere near full throttle. Then shut off the engine and
> let
> the car coast down in speed. When it gets slow enough, restart the
> engine and do it again. The Prius does this automatically, running
> on
> batteries between times so you can actually maintain speed. On
> conventional cars, you (and the drivers behind you :-) have to put
> up
> with the constant speed-up and slow-down.
>
> The dam-dam engine and a generator can do this, too. Ony they are
> doing
> it at a far faster PWM frequency (many more on/off cycles per
> minute).
> Thus, you shouldn't have the large speed changes during the cycle.
>
> Any thoughts?
__________________________________________________
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Tired of spam? Yahoo! Mail has the best spam protection around
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--- End Message ---
--- Begin Message ---
It will be interesting to compare your actual results with my
simulation software output. Could I get basic specs on your
car again (I think you've sent them to me once)?
Then I can tell you where your calcs are off.
Victor
Don Cameron wrote:
Phil, thanks for the quick reply.
I use a couple of web site's brute force calculators. I think they
simplistically do it by cube root of power and weight.
I also have a spread sheet from an associate that was used for other
projects.
In both cases, they estimate a 18 sec 1/4 mile (400m) and a 6 second 0-60
(0-90kmh). Mine has a 12.5 second 1/4 mile and a 3 second 0-60 (seems
pretty darn quick, but it is a 1500lb race car with a 220Nm torque motor).
I calculated torque by entering the actual chart for the motor in a spread
sheet in 300 rpm. Then I use a linear interpretation to calculate a value
between the points. I validated the numbers by comparing the charts between
the real motor and the spreadsheet.
I will go through it calculation by calculation and look for typos...
thanks
P.S. Any chance you can send me your worksheet?
Victoria, BC, Canada
See the New Beetle EV Conversion Web Site at
www.cameronsoftware.com/ev/
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Philip Marino
Sent: June 27, 2005 9:44 AM
To: [email protected]
Subject: RE: Acceleration Calculations
Hi, Don
Everything looks fine to me. In fact, I put together a very similar model
(also using a spreadsheet) when I was deciding what motor/batts/controller I
would use for my Echo.
The only thing I did different (and this would be a very small effect) was
to add a brake/bearing drag term.
Are you seeing a difference by comparing this model with real data, or other
peoples' models? How much difference are you seeing? ( a few percent ? a
factor of 10?) How consistent are the other peoples' models to each other?
The places I would look for errors ( or, differences compared to other
models) would be :
1. The torque calculation - can you give us more detail of how you calculate
torque? Are you assuming a constant voltage available at the motor
terminals, or are you limiting the current. etc ??
2. A typo in the spread sheet calculations ( I do this a LOT) where the
wrong entry is used in a calculation. One way to check this would be to do
the entire calcuation for one time step by hand, (example - start at the
spread sheet's predicted speed at 2 seconds) , and calculate by hand the
predicted speed at the next time step and see how that compares to the
spread sheet result. That would also check your calculations for the last
three steps, although they look pretty straightforward, and your equations
are certainly correct.
Good luck, and keep us posted on this
Phil
From: "Don Cameron" <[EMAIL PROTECTED]>
Reply-To: [email protected]
To: <[email protected]>
Subject: Acceleration Calculations
Date: Mon, 27 Jun 2005 09:08:06 -0700
I am revisiting my calculations for acceleration and power and I seem to
find they are overly optimistic. I have compared them to other
spreadsheets
and estimations and the results are wrong. If anyone else is doing
something similar, do you mind taking a look?
The approach is to base it on time:
1. Start with time t0,
2. determine velocity based on RPM,
3. calc force available to accelerate from motor graph,
4. adjust for aero drag and rolling resistance,
5. calculate max acceleration
6. then determine finish velocity for time increment.
7. go back to step 2, and use this velocity for the next time t0+0.5sec.
Here is the detail:
Given:
The car has fixed gearing (no transmission) overall gear ratio (R)
the tire diameter
the frontal area of the car (A)
the aerodynamic drag (Cd)
the drive train efficiency (Cdt)
tire rolling resistance (Crr)
vehicle mass (m)
Starting with times from 0 seconds to 90 seconds in 0.5 second increments
1. At time t, use the previous time's calculated final velocity V0
2. Determine the RPM of the motor based on the velocity, gear ratio and
wheel diameter: RPM = (V0 * OverallGearRatio)/(pi * WheelDiameter) * 60
3. Using the motor torque graph, determine the motor torque at the
specified
RPM
4. Determine the force of the motor from the torque: F = (Torque *
OverallGearRatio) / (WheelDiameter/2)
5. Correct the force for drive efficiency: F(corrected) = F *
DriveTrainEfficiency
6. Force to overcome rolling resistance F(roll) = VehicleMass * 9.8
(gravitational acceleration) * TireRollingResistanceCoeff
7. Force to overcome air resistance at velolcity V0 F(air) = 1/2 *
DragCoeff
* FrontalAreaOfCar * AirDensity * V0^2
8 Total force available for acceleration: F(total) = F(corrected) -
F(roll)
- F(air)
9. Acceleration: a = F(total) / VehicleMass
10. Final velocity for time period : V1 = a * t + V0
11. Go back to step one for next time period, using V1 as the next time's
V0
Since I use metric no real unit conversions were required. I have tried to
keep units out of this wherever possible.
If anyplace has an error, I think it is around step 9, 10 or 11. All the
other calculations appear to be OK.
thanks
Don
_________________________________________________________________
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--
Victor
'91 ACRX - something different
--- End Message ---
--- Begin Message ---
Thanks Victor, this is for a new little race car. The specs are:
Vehicle Mass (kg) 680
Wheel Diameter (m) 0.58
Total Gear Ratio 4.3
Drivetrian Efficiency Coeff 0.9
Drag Coeff 0.38 (intentionally set high)
Frontal Area Of Car (m^2) 2.39 (intentionally set large)
Air Density (kg/m^3) 1.2
Tire Rolling Resistance Coeff 0.015
Percent Grade of Hill 0
Max RPM 8500
Max Traction (g's) 0.6
I am modelling it using the MES 200-175 motor torque curve as per your web
site. (I estimated the 0 and 300 RPM torque numbers).
RPM Torque (Nm)
0 220
300 220
600 218
900 212
1200 207
1500 190
1800 172
2100 158
2400 145
2700 133
3000 120
3300 112
3600 102
3900 91
4200 85
4500 80
4800 74
5100 70
5400 64
5700 60
6000 55
6300 52
6600 50
6900 47
7200 44
7500 42
7800 40
8100 37
8400 34
8700 30
9000 27
Don
Victoria, BC, Canada
See the New Beetle EV Conversion Web Site at
www.cameronsoftware.com/ev/
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Victor Tikhonov
Sent: June 27, 2005 11:13 AM
To: [email protected]
Subject: Re: Acceleration Calculations
It will be interesting to compare your actual results with my simulation
software output. Could I get basic specs on your car again (I think you've
sent them to me once)?
Then I can tell you where your calcs are off.
Victor
Don Cameron wrote:
> Phil, thanks for the quick reply.
>
> I use a couple of web site's brute force calculators. I think they
> simplistically do it by cube root of power and weight.
>
> I also have a spread sheet from an associate that was used for other
> projects.
>
> In both cases, they estimate a 18 sec 1/4 mile (400m) and a 6 second
> 0-60 (0-90kmh). Mine has a 12.5 second 1/4 mile and a 3 second 0-60
> (seems pretty darn quick, but it is a 1500lb race car with a 220Nm torque
motor).
>
> I calculated torque by entering the actual chart for the motor in a
> spread sheet in 300 rpm. Then I use a linear interpretation to
> calculate a value between the points. I validated the numbers by
> comparing the charts between the real motor and the spreadsheet.
>
> I will go through it calculation by calculation and look for typos...
>
> thanks
>
>
> P.S. Any chance you can send me your worksheet?
>
>
> Victoria, BC, Canada
>
> See the New Beetle EV Conversion Web Site at
> www.cameronsoftware.com/ev/
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
> On Behalf Of Philip Marino
> Sent: June 27, 2005 9:44 AM
> To: [email protected]
> Subject: RE: Acceleration Calculations
>
> Hi, Don
>
> Everything looks fine to me. In fact, I put together a very similar
> model (also using a spreadsheet) when I was deciding what
> motor/batts/controller I would use for my Echo.
>
> The only thing I did different (and this would be a very small effect)
> was to add a brake/bearing drag term.
>
>
> Are you seeing a difference by comparing this model with real data, or
> other
>
> peoples' models? How much difference are you seeing? ( a few
> percent ? a
>
> factor of 10?) How consistent are the other peoples' models to each
other?
>
>
> The places I would look for errors ( or, differences compared to other
> models) would be :
>
> 1. The torque calculation - can you give us more detail of how you
> calculate
>
> torque? Are you assuming a constant voltage available at the motor
> terminals, or are you limiting the current. etc ??
>
> 2. A typo in the spread sheet calculations ( I do this a LOT) where
> the wrong entry is used in a calculation. One way to check this would
> be to do the entire calcuation for one time step by hand, (example -
> start at the spread sheet's predicted speed at 2 seconds) , and
> calculate by hand the predicted speed at the next time step and see how
that compares to the
> spread sheet result. That would also check your calculations for the
last
> three steps, although they look pretty straightforward, and your
> equations are certainly correct.
>
> Good luck, and keep us posted on this
>
> Phil
>
>
>
>
>>From: "Don Cameron" <[EMAIL PROTECTED]>
>>Reply-To: [email protected]
>>To: <[email protected]>
>>Subject: Acceleration Calculations
>>Date: Mon, 27 Jun 2005 09:08:06 -0700
>>
>>I am revisiting my calculations for acceleration and power and I seem
>>to find they are overly optimistic. I have compared them to other
>>spreadsheets and estimations and the results are wrong. If anyone
>>else is doing something similar, do you mind taking a look?
>>
>>
>>
>>The approach is to base it on time:
>>1. Start with time t0,
>>2. determine velocity based on RPM,
>>3. calc force available to accelerate from motor graph, 4. adjust for
>>aero drag and rolling resistance, 5. calculate max acceleration 6.
>>then determine finish velocity for time increment.
>>7. go back to step 2, and use this velocity for the next time t0+0.5sec.
>>
>>
>>Here is the detail:
>>
>>Given:
>> The car has fixed gearing (no transmission) overall gear ratio (R)
>> the tire diameter
>> the frontal area of the car (A)
>> the aerodynamic drag (Cd)
>> the drive train efficiency (Cdt)
>> tire rolling resistance (Crr)
>> vehicle mass (m)
>>
>>
>>Starting with times from 0 seconds to 90 seconds in 0.5 second
>>increments
>>
>>1. At time t, use the previous time's calculated final velocity V0 2.
>>Determine the RPM of the motor based on the velocity, gear ratio and
>>wheel diameter: RPM = (V0 * OverallGearRatio)/(pi * WheelDiameter) *
>>60 3. Using the motor torque graph, determine the motor torque at the
>>specified RPM 4. Determine the force of the motor from the torque: F =
>>(Torque *
>>OverallGearRatio) / (WheelDiameter/2)
>>5. Correct the force for drive efficiency: F(corrected) = F *
>>DriveTrainEfficiency 6. Force to overcome rolling resistance F(roll) =
>>VehicleMass * 9.8 (gravitational acceleration) *
>>TireRollingResistanceCoeff 7. Force to overcome air resistance at
>>velolcity V0 F(air) = 1/2 * DragCoeff
>>* FrontalAreaOfCar * AirDensity * V0^2
>>8 Total force available for acceleration: F(total) = F(corrected) -
>>F(roll)
>>- F(air)
>>9. Acceleration: a = F(total) / VehicleMass 10. Final velocity for
>>time period : V1 = a * t + V0 11. Go back to step one for next time
>>period, using V1 as the next time's V0
>>
>>Since I use metric no real unit conversions were required. I have
>>tried to keep units out of this wherever possible.
>>
>>If anyplace has an error, I think it is around step 9, 10 or 11. All
>>the other calculations appear to be OK.
>>
>>thanks
>>
>>Don
>>
>>
>
>
> _________________________________________________________________
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--
Victor
'91 ACRX - something different
--- End Message ---
--- Begin Message ---
David, thanks for the input - good idea about the traction and sanity check.
I have put them both into the spreadsheet. However, I do not see any
wheelspin (?!??!?). Not wanting to load down the list with a bunch of
numbers, here are the first few calculations for T=0, 0.5, 1 and 1.5)
Time (secs) 0.001 0.5
1 1.5
V0 (m/s) 0 0.004170444
2.089392547 6.256338411
V0 (km/h) 0 0.015013599
7.521813168 22.52281828
Angular Velocity V0 (RPM) 0 0.590505908
295.8434587 885.8540236
Torque at V0 (Nm) 220 220
220 212.2829195
Motor Force at V0 (N) 3262.068966 3262.068966
3262.068966 3147.64329
Corrected Force (N) 2935.862069 2935.862069
2935.862069 2832.878961
Force to overcome incline (N) 0 0
0 0
Force to overcome rolling resistance at V0 (N)
99.96 99.96
99.96 99.96
Aero Drag at V0 (N) 0 9.47758E-06
2.378881617 21.32913348
Total Force available for Acceleration (N)
2835.902069 2835.902059
2833.523187 2711.589827
Acceleration (m/s^2) 4.170444219 4.170444205
4.166945864 3.987632099
Adjusted acceleration for max traction
4.170444219 4.170444205
4.166945864 3.987632099
Sanity #DIV/0! 4584.07931
9.149858933 3.05572458
Final Velocity (m/s) 0.004170444 2.089392547
6.256338411 12.23778656
Distance travelled (m) 4.17044E-06 1.042611051
4.170780257 10.28967354
The specs (as just sent to Victor) are:
Vehicle Mass (kg) 680
Wheel Diameter (m) 0.58
Total Gear Ratio 4.3
Drivetrian Efficiency Coeff 0.9
Drag Coeff 0.38 (intentionally set high)
Frontal Area Of Car (m^2) 2.39 (intentionally set large)
Air Density (kg/m^3) 1.2
Tire Rolling Resistance Coeff 0.015
Percent Grade of Hill 0
Max RPM 8500
Max Traction (g's) 0.6
I am modelling it using the MES 200-175 motor torque curve as per Victor's
web site. (I estimated the 0 and 300 RPM torque numbers).
RPM Torque (Nm)
0 220
300 220
600 218
900 212
1200 207
1500 190
1800 172
2100 158
2400 145
2700 133
3000 120
3300 112
3600 102
3900 91
4200 85
4500 80
4800 74
5100 70
5400 64
5700 60
6000 55
6300 52
6600 50
6900 47
7200 44
7500 42
7800 40
8100 37
8400 34
8700 30
9000 27
Victoria, BC, Canada
See the New Beetle EV Conversion Web Site at
www.cameronsoftware.com/ev/
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of David Dymaxion
Sent: June 27, 2005 10:31 AM
To: [email protected]
Subject: Re: Acceleration Calculations
Have you plotted your calculated acceleration vs. speed? I like to divide by
9.8 m/s^2 to get the answer in g's of acceleration. For a FWD you'd expect
about 0.5 g max. Much more than that and you just have wheelspin.
When I first did a sim I got amazing acceleration, too, and found I was
starting out with several g's of acceleration! So you need an "if" test
similar to this:
// If acceleration calculates to be above traction limit
if ((a/9.8) > 0.5)
a = 0.5 * 9.8; // Set max accel to traction limit
else
a = f(rpm);
a -= a_aero;
a -= a_drag;
A sanity check you can do:
a ~ Current * Voltage * 0.6 / (mass * velocity)
for higher rpm (rpm above current limit).
--- Don Cameron <[EMAIL PROTECTED]> wrote:
> I am revisiting my calculations for acceleration and power and I seem
> to find they are overly optimistic. I have compared them to other
> spreadsheets and estimations and the results are wrong. If anyone
> else is doing something similar, do you mind taking a look?
>
>
>
> The approach is to base it on time:
> 1. Start with time t0,
> 2. determine velocity based on RPM,
> 3. calc force available to accelerate from motor graph, 4. adjust for
> aero drag and rolling resistance, 5. calculate max acceleration 6.
> then determine finish velocity for time increment.
> 7. go back to step 2, and use this velocity for the next time
> t0+0.5sec.
>
>
> Here is the detail:
>
> Given:
> The car has fixed gearing (no transmission) overall gear ratio
> (R)
> the tire diameter
> the frontal area of the car (A)
> the aerodynamic drag (Cd)
> the drive train efficiency (Cdt)
> tire rolling resistance (Crr)
> vehicle mass (m)
>
>
> Starting with times from 0 seconds to 90 seconds in 0.5 second
> increments
>
> 1. At time t, use the previous time's calculated final velocity V0 2.
> Determine the RPM of the motor based on the velocity, gear ratio and
> wheel diameter: RPM = (V0 * OverallGearRatio)/(pi * WheelDiameter)
> * 60
> 3. Using the motor torque graph, determine the motor torque at the
> specified RPM 4. Determine the force of the motor from the torque: F =
> (Torque *
> OverallGearRatio) / (WheelDiameter/2)
> 5. Correct the force for drive efficiency: F(corrected) = F *
> DriveTrainEfficiency 6. Force to overcome rolling resistance F(roll) =
> VehicleMass * 9.8 (gravitational acceleration) *
> TireRollingResistanceCoeff 7. Force to overcome air resistance at
> velolcity V0 F(air) = 1/2 * DragCoeff
> * FrontalAreaOfCar * AirDensity * V0^2
> 8 Total force available for acceleration: F(total) = F(corrected)
> - F(roll)
> - F(air)
> 9. Acceleration: a = F(total) / VehicleMass 10. Final velocity for
> time period : V1 = a * t + V0 11. Go back to step one for next time
> period, using V1 as the next time's V0
>
> Since I use metric no real unit conversions were required. I have
> tried to keep units out of this wherever possible.
>
> If anyplace has an error, I think it is around step 9, 10 or 11.
> All the
> other calculations appear to be OK.
__________________________________________________
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--- End Message ---
--- Begin Message ---
Your acceleration numbers look good, a ~ 4 m/s^2 would give a 0 to 60
mph of about 7 seconds.
Since acceleration is fairly constant, your velocities should be
going up linearly, but they don't look like they are:
~t ~v
0.0 0
0.5 2 // v goes up 2 units in 0.5 s
1.0 6 // v goes up 4 units in 0.5 s
1.5 12 // v goes up 6 units in 0.5 s
a ~ dv/dt should be pretty constant
2 m/s / 0.5 s = 4 m/s^2
4 m/s / 0.5 s = 8 m/s^2
12 m/s / 0.5 s = 24 m/s^2
Maybe you accidentally have t^2 in the velocity equation?
--- Don Cameron <[EMAIL PROTECTED]> wrote:
> David, thanks for the input - good idea about the traction and
> sanity check.
> I have put them both into the spreadsheet. However, I do not see
> any
> wheelspin (?!??!?). Not wanting to load down the list with a bunch
> of
> numbers, here are the first few calculations for T=0, 0.5, 1 and
> 1.5)
>
>
> Time (secs) 0.001 0.5
> 1 1.5
> V0 (m/s) 0 0.004170444
> 2.089392547 6.256338411
> V0 (km/h) 0 0.015013599
> 7.521813168 22.52281828
> Angular Velocity V0 (RPM) 0 0.590505908
> 295.8434587 885.8540236
> Torque at V0 (Nm) 220 220
> 220 212.2829195
> Motor Force at V0 (N) 3262.068966 3262.068966
> 3262.068966 3147.64329
> Corrected Force (N) 2935.862069 2935.862069
> 2935.862069 2832.878961
> Force to overcome incline (N) 0 0
> 0 0
> Force to overcome rolling resistance at V0 (N)
> 99.96 99.96
> 99.96 99.96
> Aero Drag at V0 (N) 0 9.47758E-06
> 2.378881617 21.32913348
> Total Force available for Acceleration (N)
> 2835.902069 2835.902059
> 2833.523187 2711.589827
> Acceleration (m/s^2) 4.170444219 4.170444205
> 4.166945864 3.987632099
> Adjusted acceleration for max traction
> 4.170444219 4.170444205
> 4.166945864 3.987632099
> Sanity #DIV/0! 4584.07931
> 9.149858933 3.05572458
> Final Velocity (m/s) 0.004170444 2.089392547
> 6.256338411 12.23778656
> Distance travelled (m) 4.17044E-06 1.042611051
> 4.170780257 10.28967354
>
>
> The specs (as just sent to Victor) are:
>
> Vehicle Mass (kg) 680
> Wheel Diameter (m) 0.58
> Total Gear Ratio 4.3
> Drivetrian Efficiency Coeff 0.9
> Drag Coeff 0.38 (intentionally set high)
> Frontal Area Of Car (m^2) 2.39 (intentionally set large)
> Air Density (kg/m^3) 1.2
> Tire Rolling Resistance Coeff 0.015
> Percent Grade of Hill 0
> Max RPM 8500
> Max Traction (g's) 0.6
>
>
> I am modelling it using the MES 200-175 motor torque curve as per
> Victor's
> web site. (I estimated the 0 and 300 RPM torque numbers).
>
> RPM Torque (Nm)
> 0 220
> 300 220
> 600 218
> 900 212
> 1200 207
> 1500 190
> 1800 172
> 2100 158
> 2400 145
> 2700 133
> 3000 120
> 3300 112
> 3600 102
> 3900 91
> 4200 85
> 4500 80
> 4800 74
> 5100 70
> 5400 64
> 5700 60
> 6000 55
> 6300 52
> 6600 50
> 6900 47
> 7200 44
> 7500 42
> 7800 40
> 8100 37
> 8400 34
> 8700 30
> 9000 27
__________________________________
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--- End Message ---
--- Begin Message ---
Don,
I need gear ratios for all 5 speeds and also diferential. If you want
to use only 2 (or 1) speed, the software still expects to see 5
numbers for gears; they can be identical if you fool
it to simulate 1 real gear. Also, I'll simulate with Optimas
instrad of your Deka,s since I have fairly accurate software model
for that battery.
How many batteries do you use?
WHat is the flider weight (estim.) without batteries, entire
drive system, you and cargo? I usually estimate 100kg for the
driver and some cargo.
Victor
Don Cameron wrote:
Thanks Victor, this is for a new little race car. The specs are:
Vehicle Mass (kg) 680
Wheel Diameter (m) 0.58
Total Gear Ratio 4.3
Drivetrian Efficiency Coeff 0.9
Drag Coeff 0.38 (intentionally set high)
Frontal Area Of Car (m^2) 2.39 (intentionally set large)
Air Density (kg/m^3) 1.2
Tire Rolling Resistance Coeff 0.015
Percent Grade of Hill 0
Max RPM 8500
Max Traction (g's) 0.6
--- End Message ---
--- Begin Message ---
That takes care of the small stuff. Are you guys planning a commercial 440v
or higher monster charger? If the govenator's plan goes through(hydrogen
highway) we are trying to attach conditions like offering all alternate
fuels at each station. That means there will be oportunities for bio,
electrical, cng etc as well as hydrogen. Let the marketplace
decide......LR..........
----- Original Message -----
From: "Joe Smalley" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Sunday, June 26, 2005 11:26 PM
Subject: Re: Need Charger Recommendation
It takes about 80 amps to charge an Optima to 80% in 20 minutes. They
taper
down to 15 amps at 20 minutes.
You will need at least a PFC-50B to do it.
Joe Smalley
Rural Kitsap County WA
Fiesta 48 volts
NEDRA 48 volt street conversion record holder
[EMAIL PROTECTED]
----- Original Message -----
From: "Lawrence Rhodes" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Sunday, June 26, 2005 10:04 PM
Subject: Re: Need Charger Recommendation
This charger and my motorcycle. 4 optimas. About 20 minutes to 80%
charge
or would that take a PFC 50? Seeing this new fast charging technology
promising 15 to 20 minutes to 80% (well not new just out there) what
would
it take to get that performance in a big pack using PFC technology? 440
three phase. 10k of charger? I'd sure like to know. Lawrence
Rhodes....
> PFC20B
> $1800 list.
> 5 days lead time from order.
>
> 12 to 450 volts output
> 110VAC to 240 VAC input. 30 amps output with 240 VAC and a 20 amp feed.
>
> Or just check the Manzanitamicro.com Website
>
> Rich Rudman
> Manzanita Micro
>
--- End Message ---
--- Begin Message ---
Excellent! That was it!
I was multiplying the acceleration by the elapsed time, not the dT.
thanks!
Don
Victoria, BC, Canada
See the New Beetle EV Conversion Web Site at
www.cameronsoftware.com/ev/
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of David Dymaxion
Sent: June 27, 2005 12:43 PM
To: [email protected]
Subject: RE: Acceleration Calculations
Your acceleration numbers look good, a ~ 4 m/s^2 would give a 0 to 60 mph of
about 7 seconds.
Since acceleration is fairly constant, your velocities should be going up
linearly, but they don't look like they are:
~t ~v
0.0 0
0.5 2 // v goes up 2 units in 0.5 s
1.0 6 // v goes up 4 units in 0.5 s
1.5 12 // v goes up 6 units in 0.5 s
a ~ dv/dt should be pretty constant
2 m/s / 0.5 s = 4 m/s^2
4 m/s / 0.5 s = 8 m/s^2
12 m/s / 0.5 s = 24 m/s^2
Maybe you accidentally have t^2 in the velocity equation?
--- Don Cameron <[EMAIL PROTECTED]> wrote:
> David, thanks for the input - good idea about the traction and sanity
> check.
> I have put them both into the spreadsheet. However, I do not see any
> wheelspin (?!??!?). Not wanting to load down the list with a bunch of
> numbers, here are the first few calculations for T=0, 0.5, 1 and
> 1.5)
>
>
> Time (secs) 0.001 0.5
> 1 1.5
> V0 (m/s) 0 0.004170444
> 2.089392547 6.256338411
> V0 (km/h) 0 0.015013599
> 7.521813168 22.52281828
> Angular Velocity V0 (RPM) 0 0.590505908
> 295.8434587 885.8540236
> Torque at V0 (Nm) 220 220
> 220 212.2829195
> Motor Force at V0 (N) 3262.068966 3262.068966
> 3262.068966 3147.64329
> Corrected Force (N) 2935.862069 2935.862069
> 2935.862069 2832.878961
> Force to overcome incline (N) 0 0
> 0 0
> Force to overcome rolling resistance at V0 (N)
> 99.96 99.96
> 99.96 99.96
> Aero Drag at V0 (N) 0 9.47758E-06
> 2.378881617 21.32913348
> Total Force available for Acceleration (N)
> 2835.902069 2835.902059
> 2833.523187 2711.589827
> Acceleration (m/s^2) 4.170444219 4.170444205
> 4.166945864 3.987632099
> Adjusted acceleration for max traction
> 4.170444219 4.170444205
> 4.166945864 3.987632099
> Sanity #DIV/0! 4584.07931
> 9.149858933 3.05572458
> Final Velocity (m/s) 0.004170444 2.089392547
> 6.256338411 12.23778656
> Distance travelled (m) 4.17044E-06 1.042611051
> 4.170780257 10.28967354
>
>
> The specs (as just sent to Victor) are:
>
> Vehicle Mass (kg) 680
> Wheel Diameter (m) 0.58
> Total Gear Ratio 4.3
> Drivetrian Efficiency Coeff 0.9
> Drag Coeff 0.38 (intentionally set high)
> Frontal Area Of Car (m^2) 2.39 (intentionally set large)
> Air Density (kg/m^3) 1.2
> Tire Rolling Resistance Coeff 0.015
> Percent Grade of Hill 0
> Max RPM 8500
> Max Traction (g's) 0.6
>
>
> I am modelling it using the MES 200-175 motor torque curve as per
> Victor's web site. (I estimated the 0 and 300 RPM torque numbers).
>
> RPM Torque (Nm)
> 0 220
> 300 220
> 600 218
> 900 212
> 1200 207
> 1500 190
> 1800 172
> 2100 158
> 2400 145
> 2700 133
> 3000 120
> 3300 112
> 3600 102
> 3900 91
> 4200 85
> 4500 80
> 4800 74
> 5100 70
> 5400 64
> 5700 60
> 6000 55
> 6300 52
> 6600 50
> 6900 47
> 7200 44
> 7500 42
> 7800 40
> 8100 37
> 8400 34
> 8700 30
> 9000 27
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