Controlling/synchronizing a lift system in ROBOTC?

VEX V5 Technical Support UNOFFICIAL Tech Support
1

So, my team and I have a bit of an issue. We’ve been trying to quickly bring our robot together for a gateway competition tomorrow.

You can see our mostly-assembled robot in the picture below (note that the picture is slightly outdated, and we have moved some motors around and removed the two pieces of metal that run between the lift system, but it should give a general idea):

The issue we’re having is with the four-bar linkage designed to lift the conveyor-belt intake system (that would pick up, hold, and drop game objects).

We have a motor powering each of the four bars, where they are connected to the rest of the chassis; the two motors towards the front of the robot are both high power motors, while the two motors towards the back of the robot are regular motors. We also have a potentiometer to monitor each of the two front motors, and an encoder for each of the two back motors (and we don’t have the time or space to change this arrangement).

Unfortunately, sometimes the bars run out of sync, which causes some big issues with our conveyor-belt intake system. So, our goal was to use the two encoders and two potentiometers to attempt to synchronize the four motors (but not necessarily at the same speed, just at an appropriate speed). How could this be done? And if we were to use PID, how should that be configured, what should be the input and where should the output be applied?

2

I would gear (or chain) the connection points on each side together so it’s physically impossible for the bars to run out of sync. As well as maybe Y-cable motors together so that they (theoretically) run in tandem.

I’m a builder not a programmer, so my solutions are usually physical, but I’m sure someone else here on the forums can give you advice on the software side of things. Hope you guys do well tomorrow!

3

If possible, I would connect an axle all the way accross the two sides of the lift to keep them in sync.

4

I know that one of my teammates managed to do this in easyC using potentiometers.
What he did was got the potentiometers on both sides as close as possible, then if they went out of a certain tolerance range, one of the sides would slow down to sync up. I’ll see if I can get him to try and answer more in depth tomorrow.

5

Perhaps you guys shouldn’t have removed the linkage between each arm? Oh, and I forgot to say this, but I really like the design. :slight_smile: Reminds me of Green egg’s elevation robot.

6

It might not be possible to sync it up with a bar because of the gear ratio. I know that my team could have put a bar connecting the two lifts, but it would have just ended up being bent in half. 1:15 too strong :frowning: