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Unread 01-16-2011, 02:58 PM
NetPlanet NetPlanet is offline
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1 Encoder, 2 Jaguars

Our team is new to CAN, but would like to use the speed control function using encoders. The chassis team is thinking of using two toughboxes with two motors each, therefore requiring two jaguars each. But the problem is these toughboxes only have one encoder each. How should we wire or program so that each encoder is used by two jaguars?
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Unread 01-16-2011, 03:09 PM
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Re: 1 Encoder, 2 Jaguars

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Originally Posted by NetPlanet View Post
Our team is new to CAN, but would like to use the speed control function using encoders. The chassis team is thinking of using two toughboxes with two motors each, therefore requiring two jaguars each. But the problem is these toughboxes only have one encoder each. How should we wire or program so that each encoder is used by two jaguars?
What you don't want to do is try to close the loop on speed with each of the two separate jags/motors controlling the same gearbox. This is not the right way to balance the load on the motors.

Instead, close the loop on speed with one Jag, read how much motor voltage (or current) that Jag is supplying, and feed the other motor the same voltage (or current).


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Unread 01-16-2011, 03:44 PM
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Re: 1 Encoder, 2 Jaguars

Thank you, we will certainly try this out
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Unread 01-16-2011, 10:31 PM
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Re: 1 Encoder, 2 Jaguars

Something along the lines of this . . .

Code:
Jag2.set(Jag1.getOutputVoltage() / Jag1.getBusVoltage()); //For voltage control mode
Jag2.set(Jag1.getOutputCurrent()); //For current control mode
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Unread 01-17-2011, 09:09 AM
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Re: 1 Encoder, 2 Jaguars

TI told me that they would consider something to do this automatically for next year.
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Unread 01-22-2011, 06:45 PM
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Re: 1 Encoder, 2 Jaguars

Just to put my two cents in, we'd definitely like to see this happen as well...

A "slave" Jaguar that automatically mimicks the outputs of a "master" Jaguar would be nice!
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Unread 01-22-2011, 09:44 PM
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Re: 1 Encoder, 2 Jaguars

I was testing this today (driving the slave Jaguar with Vcomp mode), and had little success. The slave motor kept jumping all around. The ramp didn't help.

I think the issue is inaccuracy in the voltage measurement of the Jaguar. The one situation where it worked well was at full power.
Another issue may be bugs in the Vcomp mode.

Perhaps the %Vbus mode will work better.
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Last edited by kamocat : 01-22-2011 at 09:46 PM.
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Unread 01-22-2011, 10:16 PM
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Re: 1 Encoder, 2 Jaguars

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Originally Posted by kamocat View Post
Perhaps the %Vbus mode will work better.
The %Vbus mode is the only one that I would try.
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Unread 01-22-2011, 10:22 PM
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Re: 1 Encoder, 2 Jaguars

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Originally Posted by s1900ahon View Post
The %Vbus mode is the only one that I would try.
Why is that?

EDIT:
I just tried, but noticed no difference. It's still very jerky on the secondary motors.
Now, understand that in my test, I am not actually putting both motors on the same gearbox. If I did that, I wouldn't be able to see what each motor is actually doing. Instead, I have each motor on an identical gearbox.
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Unread 01-22-2011, 11:35 PM
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Re: 1 Encoder, 2 Jaguars

Here's an interesting graph:


It shows what my speed-mode Jaguars are reporting as their % voltage output, every 20ms.
This corresponds to what I see my secondary motors doing.

The important part here is that the speed mode Jaguars are, in actuality, driving the motors at a constant speed (approximately half of full-speed).

This leads me to believe there is an issue with how Jaguars report their output when they are in internal closed-loop control. They may be reporting what they are doing instantaneously, but that is not a useful value at 50hz.

If this is not remedied, my only option is to wire the quadrature encoder channels to both Jaguars.
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Unread 01-23-2011, 12:11 PM
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Re: 1 Encoder, 2 Jaguars

Here's a way to get around the issue of putting two motors on the same transmission:
Use only Tan Jaguars.

The reason is, Tan Jaguars switch between 12v and open (coast) in their switching.
Black Jaguars switch between 12v and 0v (brake).

Thus, if one motor is driving the other faster, they won't conflict; the slower motor will simply coast along.

This means an encoder can be split off and wired to two Tan Jaguars for closed-loop control without issue.
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Unread 02-09-2011, 05:25 PM
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Re: 1 Encoder, 2 Jaguars

Quote:
Originally Posted by NetPlanet View Post
Our team is new to CAN, but would like to use the speed control function using encoders. The chassis team is thinking of using two toughboxes with two motors each, therefore requiring two jaguars each. But the problem is these toughboxes only have one encoder each. How should we wire or program so that each encoder is used by two jaguars?
Our team is trying to do the same thing and we haven't found anything yet, so anything you guys find out would be a huge help!
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Unread 02-09-2011, 05:49 PM
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Re: 1 Encoder, 2 Jaguars

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Originally Posted by N1njAgam3R View Post
Our team is trying to do the same thing and we haven't found anything yet, so anything you guys find out would be a huge help!

check out this other thread:

http://www.chiefdelphi.com/forums/sh...ad.php?t=91130


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