I want to build a 4 way motorized adjustable masking system. I’m thinking about 4 stepper motors (two with power off brakes: https://www.robotdigg.com/product/558/B … -or-Nema23), 4 limit stops and a 24v relay for turning the brake off. Code would run each motor to it’s limit stop. I’d then have arrow commands from the remote to advance each motor until a desired position is achieved. I’d record the step positions for several different aspect ratios and then define some remote commands that would go directly to those aspect ratios.
I’m more comfortable with Python than C++ so would like to use a Raspberry Pi to run the code to control it all (also was planning to have the bluetooth on the Pi be used to control the system from a Harmony hub remote).
What would you recommend for accomplishing this? Would I be better off going just arduino and sucking it up and brushing up on C++ coding?
If you’re using steppers, you’re definitely going to need an Arduino or other uC to manage your motors and remember how many steps a particular aspect ratio needs per motor. You would also need a stepper motor driver for each motor and some logic to turn the brakes on and off when appropriate.
Now if you use DC gear motors, you could run those into multiple limit switches and just activate the correct switch for each aspect ratio. You might also be able to find DC gear motors that work well and are less expensive than steppers. If the gear ratio is high enough, you won’t need a brake, the motors just won’t turn when not powered. You could even put an encoder on your gear motor to keep track of it’s position and eliminate most of the limit switches.
As they say, there’s more than one way to skin a cat but in any case, I think you’re going to need an Arduino unless you’re comfortable building a controller with tons of logic chips. The Arduino would be cheaper and easier to use and you’re always free to change the code if you don’t like how something works.
I didn’t know having an encoder on a dc motor was an option. If I’m understanding correctly a PiPlates motor plate (https://www.sparkfun.com/products/14149) paired with the right motor and 4 limit stops connected to 4 gpio pins would allow me to accomplish my goal.
If the motor is geared correctly and I have the masks counter weighted effectively, the encoder would allow me to track travel more than accurately enough for positioning screen masks after zeroing them on a limit stop. I need mm precision on the mask movement, not micron precision for a 3d printer.
I’m thinking about rolling the mask onto a roller. Then having a flat bar sewn into the end of the mask. On each end I’ll have a pulley positioned above/below the farthest point I want the mask to extend to. Then I’ll coil a cable in the opposite direction of the mask material on the roller, run it out to the pulley above/below the farthest I want the mask to extend to and attach it to the flat bar with a tensioning spring. I’ll also have a couple pulleys positioned above the top mask roller. that I’ll run a cable from each end of each flat bar up to, and then to a counter weight so I can make the masks appear nice and light to the motor.
Any advice on where to look for an appropriate motors to use with the MotorPlate?
Would something like this be what I’d want?
https://www.robotshop.com/ca/en/gm37-ge … 56rpm.html
Rigged up to spin the roller 1:1 and assuming a 1.5" diameter roller should result in a little over 4" of travel per second of the mask, which seems like a reasonable speed to me. And then I think I could only hook up one of the encoder leads, giving 16 steps per motor revolution. With a 90:1 gearbox that would make 1440 per shaft revolution which should mean mask movement resolution of well under 1/32".
How would I figure out how light the mask would need to appear to be so they would stay put after the motor is done moving?
That looks like it should work with the MotorPlate, it only needs 0.5 amp and the MotorPlate can supply 1.2.
You’d need to contact the motor manufacturer to see how much static torque it takes to move the motor when it’s off but I would imagine if your applying enough force to make the motor move without power you’re probably damaging the gear train. As long as things are counter balanced, I don’t think you’re going to have too much to worry about.