New Talon SRX and CAN with the 2015 Control System

[nixiebunny]

A CAN Bus does not have increased latency when more devices are added. They are all wired in parallel. The addressing is dealt with when the address is placed on the bus.

The only worry is that a dead device or bad cable can kill the entire bus, so troubleshooting a dead bus is a matter of splitting the bus into sections to see when it starts working.

[Alan Anderson]

Originally Posted by nixiebunny

The only worry is that a dead device or bad cable can kill the entire bus,...

A dead device should act just like a disconnected device. It won't have any affect on the rest of the CAN bus. While a live but badly misbehaving device does have the electrical ability to jam the bus with spurious signals, such a failure is extremely unlikely.

Changing from the Jaguar's RJ12 connectors to the Weidmuller terminals is going to reduce cable and wiring issues significantly.

[jhersh]

Originally Posted by Alan Anderson

A dead device should act just like a disconnected device. It won't have any affect on the rest of the CAN bus. While a live but badly misbehaving device does have the electrical ability to jam the bus with spurious signals, such a failure is extremely unlikely.

It seems to me that a short between the two wires will be the most likely failure mode in the new system. We have diagnostics that report roboRIO's CAN TX overrun which should catch long to intermittent shorts.

Originally Posted by Alan Anderson

Changing from the Jaguar's RJ12 connectors to the Weidmuller terminals is going to reduce cable and wiring issues significantly.

Of course the Talon SRX has no Weidmuller connector, so Talon to Talon will just be twisted or soldered or some custom connector. would be good if there were a Weidmuller block created that allowed a bunch of them to be all connected.

[Alan Anderson]

Originally Posted by jhersh

Of course the Talon SRX has no Weidmuller connector, so Talon to Talon will just be twisted or soldered or some custom connector.

I should probably just have said "Changing from the Jaguar's RJ12 connectors will cut down significantly on wiring-related problems."

would be good if there were a Weidmuller block created that allowed a bunch of them to be all connected.

5-port Wago lever nuts?

The Talon SRX has two sets of CAN pigtails. I don't really see that working well in a star topology, alas.

[jhersh]

Originally Posted by Alan Anderson

5-port Wago lever nuts?

The Talon SRX has two sets of CAN pigtails. I don't really see that working well in a star topology, alas.

That actually probably a decent solution... in most cases the Talons will be close to each other where only the pigtail length is needed. I think a star would work great with such short lengths... you can just ignore one pigtail. If you used those little blocks you could even use one of the extra pigtails to jump to the next cluster of 4.

[FrankJ]

The CAN spec calls a line structure. You might get away with a star topology, but it is not recommended by specification.

[jhersh]

Originally Posted by FrankJ

The CAN spec calls a line structure. You might get away with a star topology, but it is not recommended by specification.

It also allows for taps up to a foot. I believe this should be acceptable for this application.

http://digital.ni.com/public.nsf/all...25795A000FC025

[FrankJ]

Originally Posted by jhersh

It also allows for taps up to a foot. I believe this should be acceptable for this application.

http://digital.ni.com/public.nsf/all...25795A000FC025

Thanks for the references. The physical layer spec (CiA 102) only says in effect that they should be as short as possible. It is nice to have actual numbers.

[nixiebunny]

I was just looking at a pile of Talon SRXs that we bought for this year's robot. Those green/yellow pigtails sure look like a nuisance to connect!

They want to be daisy chained, so an "in" and an "out" connector as male/female pairs make sense to use.

I'd love a standardized connector for CAN bus on these robots, but it looks like the folks at CTRE didn't think this was important.

Can we make one? I like those crimp terminals that go into Hirose, Molex, TE or whatever housings, but there are unfortunately about a hundred incompatible types out there.

Suggestions? How do you plan to connect Talon CAN wires to each other?

[Alan Anderson]

Originally Posted by nixiebunny

How do you plan to connect Talon CAN wires to each other?

We're going to do our initial wiring using Wago Lever-nuts. Perhaps in a few weeks we'll have come up with an array of Weidmuller terminal blocks on a simple circuit board.

[FRC2501]

Originally Posted by nixiebunny

I was just looking at a pile of Talon SRXs that we bought for this year's robot. Those green/yellow pigtails sure look like a nuisance to connect!

They want to be daisy chained, so an "in" and an "out" connector as male/female pairs make sense to use.

I'd love a standardized connector for CAN bus on these robots, but it looks like the folks at CTRE didn't think this was important.

Can we make one? I like those crimp terminals that go into Hirose, Molex, TE or whatever housings, but there are unfortunately about a hundred incompatible types out there.

Suggestions? How do you plan to connect Talon CAN wires to each other?

Our team is using the PWM cable connectors (2 wire) and crimping them on the SRX CAN wires