now seeing as you will be driving the 2 enable inputs on the L293D for speed control using pwm you will be needing a digital input signal.If you want to drive something that requires a digital input, you must use a pullup resistor from the drive pin to your logic level to create the full waveform.
I want to control the RA and DEC on a telescope so would like as much accuracy as possible.IanS wrote: ↑Tue Jan 16, 2018 9:41 amDo you really need 16bit PWM hardware control for driving two motors?
I have a python script which just uses pigpio to control the speed of up to four motors simultaneously through L298N drivers by pulsing the enable line. The direction lines are hardwired in my case as I only need a single direction, but I could control the direction too through additional GPIO pins.
Yes you are correct, it will be (auto) guided by a camera tracking a star and adjusting speed accordingly.
pigpio general PWM (for want of a better term) is DMA timed and defaults to 250 steps, not quite 8 bits.
I'm just driving the motors in an old Meade LX10, I did it with an Arduino and a L293, with 8 bit pwm, l wanted to see if 16bit improved it. Not worth £30,000IanS wrote: ↑Wed Jan 17, 2018 11:24 amI assume you are driving the motors in the telescope mount, so there will be be a gear chain following it, which means that you can drive the motor at a moderate speed and the gears turn this into the very slow motion required. Higher speeds would be used to slew to a new target. Trying to drive a normal motor accurately at a very slow speed is difficult, and stepper motors would be better, with micro-stepping to smooth out the motion.
If you are using an equatorial mount then most of the tracking will be in a constant direction on just the RA motor, so there is no need to worry about gear-chain backlash once the motion has started. Any tweaks on the Dec axis could be in either direction, so you may need to allow for taking up the backlash when reversing direction. You may also find that there are imperfections in the gearing which lead to the mount movement slowing/jumping at particular points. I know mine does, which has ruined many a photo. Some controllers are smart enough to learn about these points and compensate for them, but you then have to only move the mount via the controller, or it loses track of where it is in relation to the problem areas.
I did once see a demo of a direct driven (no high ratio gear chain) scope mount that could take a 20kg telescope, slew from one side of the sky to the opposite in under 2 seconds, and still maintain tracking accuracy at the arc-second level. Just what I was looking for. Shame about the £30,000 price tag.
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