Talon SRX CAN Daisy-Chain Wiring

[prifken]

Hello,

Can somebody please confirm that the wiring schematic in the attached image would work?

To maintain symmetry in our wiring, we would like the PDP to be in the center of the electrical bed, with two Talon SRX on either end. I know 120 Ohm termination is required on this bus, it's just not clear if we need a second if already using the PDF in the center.

Thanks in advance for the help,

Peter

[cgmv123]

This setup will work, but the termination resistor is required to be at the end of the chain, and the termination resistor on the PDP needs to be bypassed (jumper set to off).

[prifken]

Jumper set to "off" - that makes sense, we'll try that. Thanks for the help!

[kiettyyyy]

This should work fine.

Just a heads up, if you took a close look at the Talon SRX PCB, there is really no "daisy chaining".

Both yellow wires and green wires are soldered directly to the respective high and low pads.

I wouldn't worry about throwing on your own terminating resistor and instead, use the terminating resistor on the PDP.

Either will work.

[cgmv123]

Originally Posted by kiettyyyy

I wouldn't worry about throwing on your own terminating resistor and instead, use the terminating resistor on the PDP..

The termination resistor in the PDP only works if the PDP is at the end of the CAN bus. They don't want to put it at the end of the bus.

[kiettyyyy]

Originally Posted by cgmv123

The termination resistor in the PDP only works if the PDP is at the end of the CAN bus. They don't want to put it at the end of the bus.

Again, I'd recommend taking a closer look at the SRX PCB.

[ozrien]

kiettyyyy, the intent of the original posters question was asking how to best setup CAN specifically when the PDP is in the middle.

The previously posted answer for turning off term.res jumper and terminating manually with a 120Ω resistor is correct. Since the CAN harness is just two wires it's pretty easy to solder a single resistor and heatshrink it.

kiettyyyy, did you void your TALON SRX's warranty on purpose?

To kiettyyy's point, it's nice putting the PDP at the end instead (I like effortless solutions!). But I understand not every robot has the luxury of having the PDP at the end of the chain. I'm sure prifken's team will make the best decision based on what they want to do.

[philso]

Originally Posted by ozrien

kiettyyyy, the intent of the original posters question was asking how to best setup CAN specifically when the PDP is in the middle.

The previously posted answer for turning off term.res jumper and terminating manually with a 120Ω resistor is correct. Since the CAN harness is just two wires it's pretty easy to solder a single resistor and heatshrink it.

kiettyyyy, did you void your TALON SRX's warranty on purpose?

To kiettyyy's point, it's nice putting the PDP at the end instead (I like effortless solutions!). But I understand not every robot has the luxury of having the PDP at the end of the chain. I'm sure prifken's team will make the best decision based on what they want to do.

The physical location of the CAN device does not have to correspond to it's place in the daisy-chain. The OP could have installed the PDP with two motor controllers on either side, connected from the RoboRio to one motor controller then from motor controller to motor controller until he reached the fourth then connected the fourth motor controller to the CAN Bus terminals of the PDP and enabled the termination resistor on the PDP. The CAN Bus wires would be looping back from one of the motor controllers at the end.

[prifken]

Thanks all for the feedback. While terminating the motors with the PDB would be convenient (avoid the solder + heat shrink of a resistor), our specific design requires the PDB to be in the center of the electronics bed, with the SRX CAN motor controllers at opposite ends.

I will say that the CAN configuration is very straight forward. The Software Reference Manual CTR puts out (http://bit.ly/1zlnRLU) explains the process of changing your controller's device ID very clearly. I would also recommend taking a look at the PDB manual as it explains how to use the jumper for termination.

Good luck everyone.

[Al Skierkiewicz]

prifken,
phil was telling you that the CAN buss wiring can loop back to the PDP to allow you to use the termination there. The physical location does not matter as long as the last point in the chain is terminated.
The single biggest problem for CAN use in the past has been teams making an error in the termination resistor. The buss is actually a 50 ohm buss terminated at both ends. The RoboRio supplies the first termination and the PDP gives you a convenient second termination. Since the PDP has to be connected anyway, you might as well just add the few inches of wire to get the CAN buss back to the PDP as the last point in the chain and use that termination. CAN buss wiring has little loss so it is not like power wiring where you want to make it as short as possible.

[philso]

Originally Posted by Al Skierkiewicz

prifken,
phil was telling you that the CAN buss wiring can loop back to the PDP to allow you to use the termination there. The physical location does not matter as long as the last point in the chain is terminated.
The single biggest problem for CAN use in the past has been teams making an error in the termination resistor. The buss is actually a 50 ohm buss terminated at both ends. The RoboRio supplies the first termination and the PDP gives you a convenient second termination. Since the PDP has to be connected anyway, you might as well just add the few inches of wire to get the CAN buss back to the PDP as the last point in the chain and use that termination. CAN buss wiring has little loss so it is not like power wiring where you want to make it as short as possible.

Thanks, Al for restating my post more clearly.

My suggestion was made with the assumption that it would be easier and less trouble for your team to splice wire on to the CAN Bus wires from the motor controller than it would be to find an appropriate resistor and install it properly.

[timytamy]

Originally Posted by Al Skierkiewicz

The buss is actually a 50 ohm buss terminated at both ends.

Is that a typo? The PDP manual states it has a 120 ohm terminator resistor (selectable via jumper). If it is indeed a 50 ohm bus, I'd be very interested in reading more about it?

[Ether]

Originally Posted by timytamy

Is that a typo? The PDP manual states it has a 120 ohm terminator resistor (selectable via jumper). If it is indeed a 50 ohm bus, I'd be very interested in reading more about it?

http://www.ti.com/lit/an/slla270/slla270.pdf Page5

[Daniel_LaFleur]

Originally Posted by cgmv123

The termination resistor in the PDP only works if the PDP is at the end of the CAN bus.

Please state where your proof is.
CANbus can work with the terminating resistors not at the end of the bus, but it is more prone to errors.

[cgmv123]

Originally Posted by Daniel_LaFleur

Please state where your proof is.
CANbus can work with the terminating resistors not at the end of the bus, but it is more prone to errors.

Originally Posted by Ether

http://www.ti.com/lit/an/slla270/slla270.pdf Page5]

Attachment 18056

Notice how it says "terminated at both ends".