Encoders for 2015 Season

[Mecanum Wheel]

Originally Posted by Twins Inc.

From our experience with the CUI encoders, we have had only a positive experienceso for. They seem to be more reliable becuase the actual disk is enclosed and magnetic, not optical. They and mount in a very similar way to the E4P, and could be used for a variety of similar uses.

We used E4Ps for our mechanum last year. Because they were hard to reach under the robot and thus even harder to install/replace during a breakdown, we will probably use all CUI encoders for future mechanum drives. BUT. Be warned:

"*We recommend no more than three cycles of mounting and
removal of the AMT top cover base. Multiple cycles of mounting
and removing the top cover can cause base fatigue over time
and affect encoder performance."

....Its easy to exceed this recommendation if you are careful and treat the plastic tabs and axle mount nicely, but every time you do you risk damaging the disk inside and breaking the plastic mount.
How delicate is the magnetic disk anyways?

Mind, the encoders in the FIRST Choice are a little different then the ones in our picture from the OP, they are "straight radial" pins while the FC ones are "right-angle axial" ones.

mecanum*

[IndySam]

What specific Grayhill encoder is best to purchace from Digi-Key for a drive using a Talon SRX?

[wmarshall11]

Originally Posted by IndySam

What specific Grayhill encoder is best to purchace from Digi-Key for a drive using a Talon SRX?

I'm a fan of the 63R Series. Specifically, the 63R128 and 63R256 are good picks.

[Dunngeon]

Originally Posted by IndySam

What specific Grayhill encoder is best to purchace from Digi-Key for a drive using a Talon SRX?

I don't know if there is a specific encoder that works *better* with the SRX than any other. That said, as in the post above the Grayhill 63R-xxx series has been the most reliable encoder Team 955 has ever used.

[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.

[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.

[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

[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.

[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 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.