paper: DIY 'encoder stage' for VersaPlanetary

[cbale2000]

Wow, very cool way to add an encoder. I hope Vex seriously considers adding something like this as an option for VersaPlanetarys in the future.

The only concern I have (aside from the potential issues others have already pointed out regarding high RPM applications) is that, though this setup does track rotations at the motor, it isn't fault tolerant if some other part of the gearbox breaks.

One of the nice things about most gearbox-mounted encoders is that they are usually connected directly to the output shaft and show its actual rotation (short of a shaft failure, I suppose). With this, if you strip (or partially strip) a gear, the sensor has no way of detecting or compensating for it. Granted, I have never experienced this failure mode on a VersaPlanetary (actually, the only failure I've ever had with one was the input coupler itself), but it seems like it could be plausible.

Or I could just be paranoid.

[Joe Ross]

Originally Posted by AllenGregoryIV

As I'm still looking at this, does anyone know the max encoder rate for the roboRIO and Talon SRX? With 21 or 30 counts/rev at 20000+ RPM we may be coming pretty close to or surpassing that spec. For the cRIO I think we are over the spec. For lower speeds it would be fine and we could also possibly remove some teeth, but I'm not sure how easy that would be.

The RoboRIO samples faster and has much higher bandwidth then the cRIO. 30 cpr at 20,000 rpm is still well within the capabilities of the roboRIO.

[AdamHeard]

Originally Posted by Joe Ross

The RoboRIO samples faster and has much higher bandwidth then the cRIO. 30 cpr at 20,000 rpm is still well within the capabilities of the roboRIO.

What is the limit? Would 10000 cpr at 5krpm work?

[Gdeaver]

Great work. Inspired to look at this sensor for our swerve module. Question. How were the pull up resistor and caps added?

[Nate Laverdure]

Originally Posted by Nate Laverdure

We ran the sensor off regulated 12V from the VRM.

Oops, I have a correction from one of our electrical & controls mentors:

Nate,

Both optical [US Digital S5] and the Hall effect [Allegro] sensor were powered with the 5V from the RoboRIOs DIO ports.

There was another question about sensing direction - yes the sensor has both A and B channels going to the DIO just like a quadrature sensor.