Low Res Optical Encoders for Speed Control

[Ether]

Originally Posted by KrazyCarl92

I'll talk to the guys who did that and see what they actually did

Can you share what you found out?

[KrazyCarl92]

Originally Posted by Ether

Can you share what you found out?

Our meeting last week was cancelled, but we are meeting tonight to work on this exactly. I will post it here when I find out. Thanks for the reminder.

[KrazyCarl92]

So it turns out the wire we used is 22 AWG shielded cable which the mentor says is available from Digikey. It has five 22-gauge wires (we only used 4) and these are wrapped with aluminum foil. Around the aluminum is more insolation. The aluminum foil is twisted at one of the ends of the cable, and grounded to the source ground (the jaguar 5 pin connector's ground in this case). It is important to only ground one side of the cable and not both, otherwise you could create a closed circuit, which may cause EMI if there is current going through the foil. My sources say you could also get away with grounding to the frame, but I don't think this is legal and it is usually better practice to ground it to a source anyway.

"[R38]
All wiring and electrical devices, including all control system components, shall be electrically isolated from the Robot frame. The Robot frame must not be used to carry electrical current."

I could see how both sides could be argued. I don't quite know if the aluminum is considered part of the "wiring", or if this would be considered carrying electrical current by the frame, but this is a tangent anyway since it can be grounded to a source.

I wouldn't usually think about the EMI on our robots, but looking at the number of sensors, motors, and other electrical components on that robot in comparison with our past robots, it's not surprising that this would be the one out of all of them to benefit from shielded sensor wires. I could post pictures if anyone is interested.

[KrazyCarl92]

By the way, we were able to get the robot shooting about 50% last night without speed control. This was using the camera feed to the driver station for manual aiming and we had driver voltage control on the shooter motors. We may work toward integrating a simple non-PID speed control algorithm and vision processing from there. The vision processing part was complete during the build season, we just need speed control that works in PWM or to get our CAN working.

[Ether]

Originally Posted by KrazyCarl92

We may work toward integrating a simple non-PID speed control algorithm

Were you thinking of trying a bang-bang controller, or perhaps a take-back-half?

[KrazyCarl92]

Originally Posted by Ether

Were you thinking of trying a bang-bang controller, or perhaps a take-back-half?

We haven't decided exactly yet. Haven't hooked the encoder backup since we stopped using it in competition, so that's the first step along with verifying that it works.

I had thought of a bang-bang approach where we base the original voltage on motor curves, then if the speed drops X% below the target speed, raise the voltage by Y%, or if the speed exceeds the target by X%, lower the voltage by Y%. X would be the max allowable deviation from the target speed and Y would be an experimentally determined voltage correction. If its between 100-X % and 100+X %, we would apply no voltage correction.

I'd also like to see what the students come up with. After reading about take back half control here:
http://www.edn.com/design/analog/432...ence-algorithm
that seems like a good option. It looks like a good opportunity to explore different speed control options so we may try multiple approaches to see what gives us the best results (at least that's what I would like to see).

[Ether]

Originally Posted by KrazyCarl92

I had thought of a bang-bang approach where we base the original voltage on motor curves, then if the speed drops X% below the target speed, raise the voltage by Y%, or if the speed exceeds the target by X%, lower the voltage by Y%. X would be the max allowable deviation from the target speed and Y would be an experimentally determined voltage correction. If its between 100-X % and 100+X %, we would apply no voltage correction.

There's a lengthy discussion (and paper) of bang-bang here, if you haven't seen it yet:

http://www.chiefdelphi.com/forums/sh...d.php?t=105679


Here's a thread (and paper) on take-back-half:

http://www.chiefdelphi.com/forums/sh...d.php?t=105965

[Ether]

Originally Posted by KrazyCarl92

I could post pictures if anyone is interested.

If it's not too much trouble, please do.

[KrazyCarl92]

Originally Posted by Ether

If it's not too much trouble, please do.

posted here, there are 3 pictures:
http://www.chiefdelphi.com/media/photos/38088?

[Ether]

Originally Posted by KrazyCarl92

posted here, there are 3 pictures:
http://www.chiefdelphi.com/media/photos/38088?

Thanks. You got a lot of hits. I guess there was some interest :-)