I have yet to encounter a RX that demonstrates anomalies while operating on 5 cells. I use 5cell packs wherever possible. I do recall within the IMAC world an OEM (regular case size) servo that jittered on anything above ~6.3V. That has been corrected.
Although the physical size of the regulating IC may seem small, advances in design mean the losses associated with gating current/voltage are significantly less, thereby less mass is required to dissipate the heat generated due to those (internal) losses. Size versus performance, in this case, results in an inaccurate comparison.
Not sure of your statement "Seems like long thin wires would become more of an instability factor at the higher current levels". Given typical F3x wiring, either 22 or 24awg is employed. The series-resistance from RX to servo invariably lowers the working voltage as seen by the servo motor (remember, battery V is seen by the RX buss and the servo motor - although this was not always the case).
Your premise that a "switched regulator" would be advantageous is misleading. If you are actually referring to a switching versus linear regulator, the opposite is true. Although a switching regulator operates more efficiently, it also introduces significant EMI/RFI, whereas a linear regulator will not.
Again the internal regulator on modern RX's is very robust. It does not require regulation upstream until one wishes to run more than 5 cells.
Where regulation becomes subjective is the premise that a consistent (regulated) voltage will offer some sort of benefit. This debate continues on the large scale aerobatic lists, where the premise is an unwavering V somehow allows a pilot to fly more consistently.
One can safely assume that the voltage excursions on a 40% aerobat with as many as 10 (regular cased) digital servos are WAY more than any F3X ship being flown with as much vigor as possible. The one thing any regulator can NOT do is control the V-drop downstream. As a servo motor is demanding more current to hold or move to a commanded position, the lower the voltage to perform the task. One fella is going to install regulators at the I/P of every servo. This will then allow a consistent V. However for every servo there is now (3) more points of mechanical failure.
Bill H wrote:
<snip>
Having never used a 5 cell reciever pack I would wonder about some possible problems.
Has anyone had a receiver or servo become unstable at the higher voltages? Seems like long thin wires would become more of an instability factor at the higher current levels.
Recievers might fail (the cheaper ones maybe) due to burnout of the internal voltage regulator. I find that the voltage regulators which regulate the voltage to the reciever internal circuits (3.5 to 4 volts or so) to be a small one. Increased voltage drop would cause increased heating there, increased by the square of the increase of the voltage applied: P = I\2 / R.
Most recievers pass the raw battery voltage to the power lead of the servo, and from what I have seen they do not usually have an internal voltage regulator. If they did, we would probably see a few less twittering servos :-) But, this is how the increase in voltage is able to effect an increase in power at all.
Also as to: (Motors use less current at higher voltage to drive a given load)
In electric flight and switching type controllers this may or may not be true, because we load the motor to the power we want by changing props for example. Use the same prop at a lower voltage, apply a higher voltage and notice an increase in rpm. This would indicate an increase in power dissapation. At full throttle the motor will draw more current and dissipate more power at a higher voltage than a lower voltage. Just like RC Cars would. We can change that by changing the load (prop or gear ratio) of course.
I can see a real asset in using a 5 cell pack with a switched regulator to regulate the voltage to your RC system at 5.5 or 5.8 volts. Your power source would be stable and consistant until the pack is near death and solve the rare problems caused by battery voltages that vary under load. It would also be safer for your reciever's internal regulator.
btw, How many here got to take their ham test (and pass) in front of an FCC field office examiner? Back then you didn't get the questions ahead of time :-)
Bill Heishman
N5HNN, Extra Class, ham since 1969
packDate: Thu, 12 Feb 2004 08:36:14 -0500 From: Rick Eckel <[EMAIL PROTECTED]> To: Simon Van Leeuwen <[EMAIL PROTECTED]>, Bob Pope <[EMAIL PROTECTED]> Cc: Bill Malvey <[EMAIL PROTECTED]>,soaring <[EMAIL PROTECTED]> Subject: Re: [RCSE] 5 cell current limiter Message-ID: <[EMAIL PROTECTED]>
You might want to rethink that Simon.
A 4-1000mah cell pack is nominally 4.8 watt/hours. The 5-1000mah cell
is nominally 6.0 watt/hours. Clearly the 5 cell pack has more power.Simplistically
It is unclear to me why the 5 cell pack wears down quicker.
with a pure resistive load Ohm's law would explain it. The receiver and servos present a bit more complicated load..... Motors use less current at higher voltage to drive a given load. Except for minor efficiency effects the motor uses the same amount of power.
However I'm willing to accept that a 5 cell pack will be used up faster in a given system based on the user experience reported here.
Hope this helps Rick
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