The Best Encoders for Drivetrain

[asid61]

We drill the end of the shaft with 1/4" hole and add a nylon-tip set screw to keep the encoder from spinning. Encoder mounts are made from 1/16" thick clear polycarbonate. Works okay as long as the shaft remains reasonably concentric with the encoder.

[Dunngeon]

Originally Posted by Munchskull

Question for the people using grey hill encoders. Why don't you use a more structurely sound mounting method or an encoder that let's a shaft in to it?

Because the ball bearings in the 63r give enough support to cantilever the remainder of the encoder in space. As far as I've seen, this method of mounting is the simplest, and consumes the least amount of weight.

Obviously you wouldn't do this on a machine seeing 100's ( or even 10's) of hours of run time because it wouldn't be sufficient. On FRC bots, it's acceptable.

[audietron]

Originally Posted by Owen Busler

For those of you using the Grayhill 63R, how do you connect your shafts to the encoder?

Just making sure im looking at the right one

http://www.futureelectronics.com/en/...R256.aspx?IM=0

I usually design the gear plate with a 1/2" hole in it for mounting. Then 3d print a pinion to press fit on to the .25" shaft and another to slide on to the 3/8 hex shaft (usually the first stage).

[SJaladi]

Originally Posted by Owen Busler

For those of you using the Grayhill 63R, how do you connect your shafts to the encoder?

Just making sure im looking at the right one

http://www.futureelectronics.com/en/...R256.aspx?IM=0

I can second the surgical tubing and zipties method. We used this method to successfully mate the encoder shaft to the drive gearbox output shaft. We also found a way to use surgical tubing to mate the encoder shaft to a 1/2" hex shaft. We inserted thinner surgical tubing which snugly fit over the encoder shaft inside of a thicker piece of surgical tubing which snugly fit over the 1/2" hex shaft. Then we just used a bunch of zipties to hold the whole thing together and so far its been working perfectly.

[BSV]

Originally Posted by SJaladi

I can second the surgical tubing and zipties method. We used this method to successfully mate the encoder shaft to the drive gearbox output shaft. We also found a way to use surgical tubing to mate the encoder shaft to a 1/2" hex shaft. We inserted thinner surgical tubing which snugly fit over the encoder shaft inside of a thicker piece of surgical tubing which snugly fit over the 1/2" hex shaft. Then we just used a bunch of zipties to hold the whole thing together and so far its been working perfectly.

Dumb newbie question: So what would be the best way to add one (okay, actually two) of these to a kit bot? Any special mounting needed? Thanks!

[SJaladi]

Originally Posted by BSV

Dumb newbie question: So what would be the best way to add one (okay, actually two) of these to a kit bot? Any special mounting needed? Thanks!

Looking at this drawing you can see that there is a portion of the main output shaft sticking out of the back of the gearbox. You can slide a piece of surgical tubing over that portion of the shaft and then use a small ziptie to cinch it so that it stays on the shaft. Then you can fabricate some kind of simple plate to secure the Grayhill encoder to. It can be really simple we made ours with a small scrap of polycarbonate and a hand drill. then once the encoder is secure you can simple slide the other end of the surgical tubing over the encoder shaft and secure with a ziptie and you should be all set. It's also interesting to note that by using the surgical tubing method you don't have to make the shaft of the encoder and the gearbox exactly concentric. A few mm either way won't hurt the function of the encoder.

[BSV]

Originally Posted by SJaladi

Looking at this drawing you can see that there is a portion of the main output shaft sticking out of the back of the gearbox. You can slide a piece of surgical tubing over that portion of the shaft and then use a small ziptie to cinch it so that it stays on the shaft. Then you can fabricate some kind of simple plate to secure the Grayhill encoder to. It can be really simple we made ours with a small scrap of polycarbonate and a hand drill. then once the encoder is secure you can simple slide the other end of the surgical tubing over the encoder shaft and secure with a ziptie and you should be all set. It's also interesting to note that by using the surgical tubing method you don't have to make the shaft of the encoder and the gearbox exactly concentric. A few mm either way won't hurt the function of the encoder.

Thank you, yes, I can see how that would work. I will share this with our team.

[ice.berg]

Originally Posted by SJaladi

I can second the surgical tubing and zipties method.

Third on the surgical tubing method.

Only instead of zipties we use spray paint.
Spray some inside the surgical tubing and slide it on. Acts like a lubricant while its still wet only then when it dries its like a glue. One of our mentors uses the same technique to put handlebar grips on his dirt bike. So far we haven't had any problems with the system.

[tr6scott]

We had some issues with surgical tubing this year on our elevator, when doing quick direction changes, we had some issues with the surgical tubing twisting and this small error would give rise to a noticeable "bounce" in the elevator as the pid corrected it.

I picked up a foot of 3/16" id fuel line from local auto parts store for a $1.26 and all of the bounce went away.

[btcshields6]

Thank you all for your responses and advice! I'll look over this information with my team and figure out what will work best for us.

Benjamin

[Bruceb]

you can also use pneumatic tubing. Just heat it a bit with a heat gun and slip it on. It is stiff enough to eliminate that twisting as well.

[Batterink]

Can someone post a picture of this surgical tubing method? I think I understand how it works, but I'd like to confirm my understanding.

[Joe Ross]

Originally Posted by Batterink

Can someone post a picture of this surgical tubing method? I think I understand how it works, but I'd like to confirm my understanding.

There's a picture in this whitepaper: http://www.chiefdelphi.com/media/papers/1743

[marshall]

We use a total of 8 encoders on our drivetrain this year. We've got a mix of the CUI quadrature and the US Digital analog encoders. It's a pretty solid setup. We use the Helical (I think that's the brand name) shaft couplers on the US Digitals to couple them to the outputs of some versa planetary gearboxes. The outputs on the versa planetary gearboxes are not always perfectly straight from our observations so the couplers help a lot with the alignment issues. I suspect the surgical tubing will also help with alignment issues. It's clever. Surgical tubing is definitely more cost effective than the couplers.

We also had to switch out the set screws on the couplers to something with a cone tip and higher grip.

This has been our first year with the CUI encoders and we're pretty happy with them but the grounding issue is a serious problem for FRC teams. We had to get creative with some nylon 4-40 bolts to get everything nice and isolated but it worked. It's just something to be mindful of when mounting them.

EDIT: Also worth mentioning is Pololu's pre-terminated .1" cables. They are awesome and saved us a ton of fiddly crimping this year for wiring all of our encoders.

[SJaladi]

Just a side note from drivetrain encoders; when using encoders for a mechanism like an elevator where there is a finite end to the travel (i.e. the top and the bottom) it is good practice to have a limit switch at either each end or at least one end of the travel. This encoder can serve two purposes, an electronic limit on the travel as well as a way of resetting the encoder count at a fixed point. For example on our elevator this year we have a limit switch at the bottom of the elevator that acts as an electronic limit if the operator is manually lowering the elevator, but it also serves as a zero point for if the operator wants to "recalibrate" the elevator encoder to zero.