Encoders for 2015 Season

[ozrien]

Originally Posted by marshall

Word of caution about absolute encoders with the Talon SRX... most of them that provide analog output seem to require 5v power instead of 3.3v power which the Talon SRX must have for analog input. DO NOT connect 5v to the Talon's analog in. It might not end well.

CTRE is releasing a converter board and we are making some custom ones. We have a student working on a write-up of how we created ours along with details.

It might be neat to see the Talon SRX controllers support gray code in the future in addition to analog output for absolute encoders but that would likely require a firmware update and some serious coding witchcraft for the Talons.

Breakouts are available at andymark and vex. Search for analog breakout for 5v analog signals.

Why greycode ? CANBus has strong error detection.

[Sh1ine]

Originally Posted by Qbot2640

Excuse my lack of experience - we have never used encoders, and I desperately want to this year. The Grayhill models referenced above look like potentiometers, for lack of a better description...How are they installed? Do you just couple the shaft to the gearbox shaft?

I understand how the US Digital one's install - in fact, we installed a pair on our robot this fall for the off-season, but never figured out how to wire them up or program them.

We use Grayhill Encoder 63R128 (http://www.digikey.com/product-detai...3069-ND/304478) They are terrific encoder, and Digi key sells them at a good price. We use 128 count encoders for our drive train, and since we have them laying around, they get used for other systems frequently as well. In order to to attach our encoder to our output shaft we use 1/4 OD and 3/16 ID surgical tubing. It sounds sketchy, but works great, it also helps absorb some slight misalignment issues that you might have. Simply slip the tubing over the .250 part of a AM output shaft and the other side slips onto the encoder. Create a bracket to hold it in place and you are good to go.

Here is an image:

https://drive.google.com/file/d/0B02...ew?usp=sharing

Hope this helps!

[marshall]

Originally Posted by ozrien

Breakouts are available at andymark and vex. Search for analog breakout for 5v analog signals.

Why greycode ? CANBus has strong error detection.

Mainly because we could then get 3.3v absolute encoders. It's hard to find those things other than 5v. Most of the ones I saw that supported 3.3v were using gray code as output instead of analog. I just want to be able to interface the encoder without peripheral circuitry.

EDIT:

Links to the CTRE breakouts from Vex. I could not find them at AndyMark:

http://www.vexrobotics.com/217-4398.html
http://www.vexrobotics.com/217-4401.html

[The_Drive_DR]

We are using the CUI encoders (http://www.cui.com/product/component...ar/amt10-v-kit) and they work great!

[Bruceb]

with the Grayhill encoders, how do you wire them? Do you use the same connector as the AM USDigital encoders?
May seem like a dumb question but I am not an electronics guy.
Thanks

[ozrien]

Originally Posted by marshall

Mainly because we could then get 3.3v absolute encoders. It's hard to find those things other than 5v. Most of the ones I saw that supported 3.3v were using gray code as output instead of analog. I just want to be able to interface the encoder without peripheral circuitry.

EDIT:

Links to the CTRE breakouts from Vex. I could not find them at AndyMark:

http://www.vexrobotics.com/217-4398.html
http://www.vexrobotics.com/217-4401.html

Yeah but 2bit grey code is the same as quadrature, unless I'm missing something.
I'm always interested in new sensors, send me a data sheet if you can.

[wmarshall11]

Originally Posted by Bruceb

with the Grayhill encoders, how do you wire them? Do you use the same connector as the AM USDigital encoders?
May seem like a dumb question but I am not an electronics guy.
Thanks

You can get them with wires attached or with .1in pins. Getting the pins tends to be more feasible. You can either solder to them or attach standard .1 female connectors (same as pwm) and run cable back to your control board.

[Bruceb]

Originally Posted by wmarshall11

You can get them with wires attached or with .1in pins. Getting the pins tends to be more feasible. You can either solder to them or attach standard .1 female connectors (same as pwm) and run cable back to your control board.

With the USdigital encoders there were 4 wires, with these I see 5 pins.
What do they get wired to?
Thanks

[marshall]

Originally Posted by ozrien

Yeah but 2bit grey code is the same as quadrature, unless I'm missing something.
I'm always interested in new sensors, send me a data sheet if you can.

Is it?!?! I didn't know that. I will find some spec sheets and send them your way for the ones we were looking at. There is also a CAN based sensor from a BMW steering wheel that looked promising...

[Alan Anderson]

Originally Posted by Bruceb

With the USdigital encoders there were 4 wires, with these I see 5 pins.
What do they get wired to?

The data sheet shows the pinout. Pin 4 is not connected.

[Alan Anderson]

Originally Posted by ozrien

Yeah but 2bit grey code is the same as quadrature, unless I'm missing something.

Marshall wants absolute sensors.

[marshall]

Originally Posted by Alan Anderson

Marshall wants absolute sensors.

It's true. I also want a pony.... perhaps even a striped one with a horn on it.

[juchong]

Originally Posted by marshall

It's true. I also want a pony.... perhaps even a striped one with a horn on it.

YAY PONIES!

Every time that we've used encoders for swerve drive, we've coupled them with a 360 degree potentiometer for initial calibration. This way, you (almost) always know where your wheels are pointing and how much you're slipping.

If you throw a well-calibrated Gyro into the mix then you've got field-oriented drive + drift compensation!

We've also had great results using the US Robotics encoders included in previous KOPs. One for steering, and one for drive.

[ozrien]

That's an interesting idea.

With a custom breakout/cable you could wire out both the potentiometer and quadrature encoder for each wheel for each Talon SRX (since SRX decodes both at the same time and puts both on CAN bus).

Originally Posted by juchong

YAY PONIES!

Every time that we've used encoders for swerve drive, we've coupled them with a 360 degree potentiometer for initial calibration. This way, you (almost) always know where your wheels are pointing and how much you're slipping.

If you throw a well-calibrated Gyro into the mix then you've got field-oriented drive + drift compensation!

We've also had great results using the US Robotics encoders included in previous KOPs. One for steering, and one for drive.

[marshall]

Originally Posted by ozrien

That's an interesting idea.

With a custom breakout/cable you could wire out both the potentiometer and quadrature encoder for each wheel for each Talon SRX (since SRX decodes both at the same time and puts both on CAN bus).

That's a complicated mess though. Mounting one of these widgets is bad enough. I really just want someone to start selling 3.3v absolute encoders instead of 5v ones.

We are already building a custom breakout to do the conversion... it's just extra circuitry that I'd love to get rid of.