On 7/10/20 8:13 PM, Chris Albertson wrote:
Stepper motors are good for this. A stepper has the most torque at zero
RPM and the torque falls as speed increases while a DC brushed motor has
very little power when moving slowly. You need more gearing with the DC
motor.
that is exactly right, that is why I wanted to try going that route
The problem is you need to generate precise pulses. If the pulse spacing
is not accurate then you are asking a large telescope to accelerate and
decelerate instantly. So to generat pulses need either
1) a hardware solution like a microcontroller or FPGA or pulse generator.
2) A real time kernel on the Linux system or
3) A PID loop to supervise a non-real-time software pulse generator
yes I agree on the first part.. :) BUT this is not a high speed
thing and changes at high speed are more "disruptive" then changes at
something that goes rather slow
the 3 solutions you mention work if you really want to be on top. The
thing is.. it is not really that bad if you're a fraction of a second
off, with an amature telescope.
(but perfect is cool :) )
When I build stuff, my preference is the microcontroller. I design it so
the microcontroller can work independent of a larger Linux computer or take
commands from a large Linux computer. I want some basic functionality when
power is applied then adding the Linux PC adds more functionality.
Yes definitely... a micro controller would be something "small" that
works predictable BUT it is hard to interact with and make adjustments.
I worked with micro controllers, they are great for repetitive stuff
that don't need interaction/correction
Linux CNC uses a slightly different idea they either go with Real-Time
Linux or use a very simple pulse generator running in an FPGA.
right. I use linux cnc and really like it for my mill and lathe.
Actually, if you abstract it.. a telescope is sort of a machine that
points at "something" similar like a mill does.
the degrees of freedom are different, but not that different. I think a
telescope can be sort of "defined" with 4 degrees of freedom, however,
2 of them (orbit and rotation of the earth) are constrained. If you
look at it, it would be like a 4 or 5 axis mill running a program
doing nothing except pointing at some star, which is the same
functionality as it milling some "object"
That is not why I posed the question here though. I did because I
knew that Linux CNC knows how to work with drivers and steppers, and I
am trying to do something similar with the hardware that I use in my
little mill and lathe and mill, running linux cnc
Reading up to three quadrature encoders with just a Raspberry Pi might
work, or not. I don't know. A lot depends on the speed of the encoders.
well the speed of rotation is not that high, so one is not as much
measuring speed, but more position... so that would be a few hundred
pulses per revolution
I tried a few scenarios... it doesn't seem to be a real problem to get
a few hundred pulses in a few seconds at all.
On Fri, Jul 10, 2020 at 6:45 PM R C <cjv...@gmail.com> wrote:
I don't think anyone did, but I know that's how most do it...
But that's just too easy :) I would just like to see if I can do it,
killing time
On 7/10/20 7:39 PM, Ken Strauss wrote:
I haven't been following this closely but has anyone suggested that you
use a
DC motor with an encoder? With a PID loop and PWM power to the motor you
could
run the motor continuously. DC motors with integrated encoder and
planetary
gearbox are readily available for a few dollars. Just a thought.
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