Open ethanjurman opened 9 years ago
khanny17
commented
9 years ago The raspberry pi only has one PWM pin. If we use sensors to determine position this wouldn't be a problem as we can do a software emulated PWM, but the advantage of using servos is that they know how far they've gone so the mouse laser might not actually be necessary. In this case though, we might want a real hardware PWM, and for that we'd need a microcontroller like an Arduino. I will look into this more
JRJurman
commented
9 years ago A BeagleBone Black may be a good alternative to a RaspberryPi and Arduino...
khanny17
commented
9 years ago The BeagleBone is totally totally awesome but also more expensive and kind of overkill for what we're trying to do. I did some more research and I think software PWM will be fine for what we need.
My previous statement was a little wonky so let me just start over:
If we use servos, we don't need a mouse laser to determine how far we've gone. it should be accurate enough. That should be taken off.
We can probably use the Raspberry pi without even needing an Arduino.
We might need a gear system of some kind to ramp up the torque. This is something we will probably need to experiment with before deciding on though, so we shouldn't include it here for Mark 1.
With the battery, keep in mind the motors will probably run on 12V while the pi will (I believe) need 5V.
Lastly, we should fabricate a robot that works on flat surfaces first before jumping straight to the whiteboard, so I would say leave the magnets out for now and focus on getting a working turtle interpreter.
My recommended revised parts list for iteration 1 would be: 5 Servo motors (1 smaller for the marker) 4 Wheels 1 Raspberry Pi(w/SD) Wood (for fabricating chassis) Assorted batteries(AA, 9V, etc) TBD
JRJurman
commented
9 years ago I don't believe we can plug the motors straight into the Raspberry Pi, but we may not have to go as far as an arduino board. Plugging in the motors straight into the Raspberry Pi, as far as I understand, would require a bit too much power.
khanny17
commented
9 years ago The raspi doesn't power the servos, it only provides a signal to control the direction. The actual power that drives the motors will be an external source with a higher voltage than the pi operates at. There will not be any problems controlling the servos from the raspberry pi.
See here for details: https://learn.adafruit.com/downloads/pdf/adafruits-raspberry-pi-lesson-8-using-a-servo-motor.pdf
On page 8 you can see the power pins are connected to the battery pack while the control pins are connected to the pi.
If people can provide link(s) to the following items so we can construct some sort of budget, that'd be most excellent! This is not a strict list, so if more items belong here or need to be taken off please do so (with an explanation as to why).