Does having potentiometers on arms really help in sack attack?
We don’t have potentiometers, but our Motor Encoders do the same thing. They help immensely in both autonomous and operator-auto, where they are used for PID arm holding. For us, it helps hold sacks up and descore, things which are immensely important.
I think it does really help. Many teams use the potentiometer with control loops like the PID controller in both driver control and autonomous to maintain arm height, especially because sacks are rather heavy. For example, a long time ago, we used to just run a small amount of power to help maintain height when we had objects in our feed. This didn’t suffice when objects got heavier/we built for larger capacities. Running PID for the arm right now helps us get to and stay at the same height from 0 to ~15 sacks. After 15, it starts to become inaccurate. The PID loop with potentiometer really helps when our driver is descoring. He can maintain the same height without having to think about it even if suddenly a large amount of sacks suddenly drop into our tray. If you don’t know what PID is, there are plenty of posts and tutorials that have great information on how it works and how to use it.
If you want exact arm placement in autonomous, then either that or some motor encoder (IME or quad) can tell you how far you are in the rotation.
Limit switches can be used for top & bottom hard stops, but the potentiometer or encoder lets you set exact values for certain heights.
Having your program use these top/bottom limit values to not even allow you to jam into the floor or go way over the top and possibly tip over are two other advantages.
Downside to potentiometers are recalibration needs as they loosen every once and a while as well as they only go 270 degrees (and break easily if you go past that too often - good thing they are cheap). The top and bottom values might move a bit if the screw holding it on loosens up or shifts. So you should recalibrate in the debugger the values of top, bottom, and your critical hold points before a tournament.
Can you please tell me how you have used potentiometers in your operator control code?
I am using EasyC v4 for programming.
When using sensors, you should find what you want to do first, then figure out which sensor is the best, rather than saying “I want to use Sensor A, what can I do with it?”
To answer your question, potentiometers are really good if you have a mechanism that spins a limited number of degrees (i.e. a lift). Potentiometers will report a value of 0 to 2500 (10 units is one degree). Potentiometers differ from optical encoders in that it will always report the same number for the same rotation. For example, if you were to use optical encoders and turn off your robot at a certain height (say 100 ticks), when you turn your robot back on, the encoder will read 0 ticks, not 100. A potentiometer would. As I said, the trade off with a potentiometer is that it only goes 250 degrees.
hell yeh ! … for autonomous selectors, for wrist/arm restrictions … helps in autonomous/programming skills …