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Unread 09-01-2012, 22:56
chi-town-biker chi-town-biker is offline
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Using an encoder with a two CIM gearbox

We’re considering using CAN this year for the position mode during hybrid and speed mode during teleop.

I noticed that there were several discussions last year on how to use an encoder with a two CIM gearbox. Some suggesting splitting the encoder wires but the ground wires needed to be isolated. Others suggesting connecting the encoder to the master jaguar and then using the voltage output of the master as the input into the slave jaguar but that sometimes created problems. I may have missed other methods. Is there any consensus on the “correct” way to use an encoder with a two CIM gearbox?

Thanks
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Unread 10-01-2012, 00:29
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Re: Using an encoder with a two CIM gearbox

If I can remember, the encoder gets installed on the back side of the main shaft. So you would do it with any other way.
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Unread 10-01-2012, 01:29
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Re: Using an encoder with a two CIM gearbox

The correct way to do this on board the Jaguar is to have the Jaguar firmware modified to include a "follow me" mode so you can implement a master and a slave Jaguar. Since that didn't happen for this year, the correct answer is to connect the encoder to the cRIO and to run the PID algorithm on the cRIO.

-Joe
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Unread 10-01-2012, 09:22
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Re: Using an encoder with a two CIM gearbox

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...the correct answer is to connect the encoder to the cRIO and to run the PID algorithm on the cRIO.
Consensus achieved.
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Unread 12-01-2012, 11:02
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Re: Using an encoder with a two CIM gearbox

is it posable to attatch one encoder to two Jags with diodes so it wont get feedback to the other one?
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Unread 24-01-2012, 12:37
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Re: Using an encoder with a two CIM gearbox

Re: Doc543

If you use diodes the forward voltage drop will reduce the output voltage from the encoder (0.3VDC - 0.7VDC) and if you look at the encoder under that load you'll discover that might not be desirable.

More importantly you won't really get noise isolation from that.
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Unread 25-01-2012, 01:46
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Re: Using an encoder with a two CIM gearbox

Quote:
Originally Posted by jhersh View Post
The correct way to do this on board the Jaguar is to have the Jaguar firmware modified to include a "follow me" mode so you can implement a master and a slave Jaguar. Since that didn't happen for this year, the correct answer is to connect the encoder to the cRIO and to run the PID algorithm on the cRIO.

-Joe
Just to share our experience from last year. We ran into the same encoder splitting issue on our lift and drive train... We were not successful in splitting one encoder to two Jags but were able to get something to work that's along the lines of what you're describing as a "follow me" mode.

We set one motor controller up in a speed control mode over CAN. We then queried that "Master" controller's output voltage. Then commanded the "Slave" motor controller (in VBus mode) to the Masters' voltage.

This obviously is not ideal as the slave controller will undoubtedly lag the master, however it worked in our testing. That said, we ended up not implementing closed loop control on the Jags for other reasons, and ended up not driving the motors in this configuration during the competition season.

If you are tempted to use this method of Master/Slave control, be conscious of the traffic generated on the CAN bus, especially if you're using the RS232 bridge
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Unread 25-01-2012, 08:23
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Re: Using an encoder with a two CIM gearbox

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we ended up not implementing closed loop control on the Jags for other reasons
What were the other reasons?

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Unread 26-01-2012, 10:33
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Re: Using an encoder with a two CIM gearbox

what if you set one Jag to run the closed loop speed control and have the other Jag copy the output voltage of the first one?
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Unread 26-01-2012, 11:18
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Re: Using an encoder with a two CIM gearbox

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what if you set one Jag to run the closed loop speed control and have the other Jag copy the output voltage of the first one?
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Unread 26-01-2012, 13:48
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Re: Using an encoder with a two CIM gearbox

We tried a number of different approaches, and like other teams we ended up running the PID loop on the cRIO. The best results we got was running a master/slave setup, but I didn't like it so we went back to just running the control loop on the cRIO.

You can successfully split the encoder, and we in fact ran them to both Jaguars and to the cRIO. But as I said, we ended up ignoring the inputs to the Jaguars.

Ideally, it would have been nice to have a firmware update that would have let us do this on the Jaguars, but no such luck. There was some talk that it might happen, and I was hopeful when there was a firmware update. Maybe next year.
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Unread 26-01-2012, 19:37
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Re: Using an encoder with a two CIM gearbox

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The best results we got was running a master/slave setup, but I didn't like it...
Why didn't you like it?

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Unread 26-01-2012, 22:51
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Re: Using an encoder with a two CIM gearbox

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Originally Posted by Ether View Post
What were the other reasons?

Time, and we had it working implemented on the cRIO...
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