Sync Two Jags

[Hugh Meyer]

Originally Posted by Gary Bonner

Am I correct that the solution discussed here is to wire the encoder to two Jaguars and run both Jags independently in closed loop speed mode? Can you elaborate or provide a schematic of how the encoders and opto isolators are wired? Do you think this would work in position mode?

Thanks.

Gary,

Yes, that is what I am suggesting. It seems to be working for us, but as others in this thread have mentioned it is not the "Ideal" solution. Other solutions presented will have delay in the synchronization process.

I do not know if it would work in position mode.

I will try to get a schematic posted, but as you know it is very close to ship date and we are very busy. It is on paper (aka napkin sketch) and not easily uploaded.

-Hugh

[mocibot]

Originally Posted by kamocat

That's an interesting method of doing it. It would probably be best to get the %Output status, not the Vout status, because the voltage would have to be scaled down anyway.
Then again, I don't know what your "getVoltage" function does. Has it been modified to get the actual voltage, or does it return %Output?

I think it would make sense to monitor it first and see if any problems arise.

I have a question on this, How do you get %Output status?

[jhersh]

Originally Posted by mocibot

I have a question on this, How do you get %Output status?

There isn't currently a status for that in the library, but the Jag supports it. It should be easy to add that to the library. Just follow the pattern of the other status messages.

-Joe

[techhelpbb]

Originally Posted by Hugh Meyer

If you connect the two GND wires together you can expect to have ground loop issues. This is only a problem with heavy loads where the motors are drawing significant current. We saw this issue last year in the CAN bus ground wire. We have an opto isolator in the circuit to prevent the ground loop.

So far the motors drive well. We see some unbalance, but not very much. We are still investigating if this unbalance is real, or inherit in our logging scheme.

Attached are two step response graphs from recent testing, one showing current and the other showing speed, both from the same run.

-Hugh

We originally split the encoder wires as I described before.

When we did this...

1. We found the chains from the gear boxes to the rear tires snagged and caused tuning issues, so we removed the chains.

2. We found one of the CIMs would always fault it's Jaguar...even unloaded and we replaced it (old CIMs....long hard life)

3. With the only drive wheels in the air we could tune the Jaguars with the cable split and it worked.

When we finished the actual robot instead of the kit of parts...

We had problems tuning one side with the split cables.

The side with issues, as it turned out, had the bad CIM back on it (this time it found a garbage can ).

Even without the bad CIM we still had issues with that side and occasionally with the other.

What we ended up doing to fix it:

We created an optoisolator board with Schmitt trigger TTL input and 74HC TTL output...actually we have several versions of this and I'm not sure we need all of the circuit for this. We wanted to make sure we considered all the possible twists so we went for overkill. This board requires 5V from the digital side car in it's current form and when I hand wired it, I put 7805 on it with a 4,700uF capacitor just to make comparisons with the sidecar's power.

Basically at this point, the encoder channels are each driving merely 1 TTL input, and that input is a Schmitt trigger with hysteresis. The Jaguars are each powering merely a single 74HC04 inverter and their channel inputs are the only thing connected to the inverter outputs.

It's entirely reasonable we could do without most if not all the TTL logic with careful selection of components.

As the final product gets power from the digital side car and doesn't actually reduce the cRIO's control, I think this *might* be legal. Guess we'll find out the hard way. If it's a problem, the PCB has the same headers at the cRIO digital I/O ports...so we could just connect to the cRIO and run the Jaguars like the Victor 884s via the CAN bus.

Regardless when I get a chance I'll put the schematics and documentation some place accessible.

The only thing I do wish we had was some motor capacitors, but even without them we made this work using mere 4 wire telephone wire to the encoders right next to the CIMs.

[taichichuan]

Originally Posted by techhelpbb

We originally split the encoder wires as I described before.

When we did this...

1. We found the chains from the gear boxes to the rear tires snagged and caused tuning issues, so we removed the chains.

2. We found one of the CIMs would always fault it's Jaguar...even unloaded and we replaced it (old CIMs....long hard life)

3. With the only drive wheels in the air we could tune the Jaguars with the cable split and it worked.

When we finished the actual robot instead of the kit of parts...

We had problems tuning one side with the split cables.

The side with issues, as it turned out, had the bad CIM back on it (this time it found a garbage can ).

Even without the bad CIM we still had issues with that side and occasionally with the other.

What we ended up doing to fix it:

We created an optoisolator board with Schmitt trigger TTL input and 74HC TTL output...actually we have several versions of this and I'm not sure we need all of the circuit for this. We wanted to make sure we considered all the possible twists so we went for overkill. This board requires 5V from the digital side car in it's current form and when I hand wired it, I put 7805 on it with a 4,700uF capacitor just to make comparisons with the sidecar's power.

Basically at this point, the encoder channels are each driving merely 1 TTL input, and that input is a Schmitt trigger with hysteresis. The Jaguars are each powering merely a single 74HC04 inverter and their channel inputs are the only thing connected to the inverter outputs.

It's entirely reasonable we could do without most if not all the TTL logic with careful selection of components.

As the final product gets power from the digital side car and doesn't actually reduce the cRIO's control, I think this *might* be legal. Guess we'll find out the hard way. If it's a problem, the PCB has the same headers at the cRIO digital I/O ports...so we could just connect to the cRIO and run the Jaguars like the Victor 884s via the CAN bus.

Regardless when I get a chance I'll put the schematics and documentation some place accessible.

The only thing I do wish we had was some motor capacitors, but even without them we made this work using mere 4 wire telephone wire to the encoders right next to the CIMs.

Please post the schematics to the group when you can. We're all waiting with baited breath...

TIA,

Mike