As far as I know many west coast teams drill a hole into the drive shaft, push the encoder into the hole, and then zip tie the wire to the belly pan. No mount is needed.
It’s how we did it for our offseason robot. It’s great. The only word of caution is to make sure you’ve got a good fit between the hole and the encoder shaft. If its too loose, it will easily fall out. If its too tight, you’ll bend the shaft when trying to insert it. We marred up the encoder shafts using vise grips to make it easier to get a nice press fit.
Correct, we do this almost everywhere.
Sometimes we use a standoff as a post next to the encoder body to make it easier to lock torsionally.
So if I’m understanding this correctly, the encoder is just floating or resting on something?
It’s generally just floating, with whatever’s holding onto the wire (typically a ziptie) providing the tiny amount of force needed to keep the encoder from spinning with the axle.
The idea behind this is to not mechanically over-constrain the encoder, as rigidly mounting the encoder as well as pressing its shaft into the axle would do.
Do you guys have any pictures of said West Side sorcery? We East Side folks be wondering. 
You can sort of see it here. Look at the last picture in the original post. There’s no mount. The bore for the encoder is a tight fit (just under press fit) and the encoder wire is zip tied to the baseplate.
That looks mighty…sketchy. I suppose the fact that so many people use this method speaks to its validity, but doesn’t the encoder want to spin with the axle? While I expect that the zipped down wires help some of that, I can’t help but think that there’s a little wiggle in there.
- Sunny G.
Even if it does wiggle, it really can’t wiggle enough to mess up 15 seconds of driving.
These are the ball bearing S4 encoders. This will not work with the bushing ones. We do not use the bushing ones anywhere. We typically hot glue the connector and add additional strain relief to the wire to prevent damage to the wire/connector. If done properly there is no “wiggle” as the bearing drag is the only friction that exists and is quite minimal. We have done this (on 254/968) for as long as I can remember using encoders (nearly 10 years now).
I thought it was rather bizarre as well until I learned it while on 968. It really works a treat, and ensures that there is no binding or misalignment anywhere. As Travis mentioned, the bearing friction is very minimal, so there is no real load on the wires.
It’s also really nice in that it’s darn short axially. Lets you sneak them in on a lot of things real easy.
This year we used a couple 050 brackets to prevent the encoder from rotating. The idea was to connect the 2 pieces with a loose bolt so the encoder was prevented from rotating but still allowed to translate based on the alignment. The idea worked well until at some point the students found a “loose bolt” and tightened it. This led to 2 broken S4 ball bearing shafts.
One thing I learned was the shaft on the S4 is actually only 1/8" in diameter when it necks through the ball bearing. See images below.
I’m liking the wire + zip-tie idea!
Sorry to keep derailing this thread…I called to order the S4 from US Digital, it seems that they are having a manufacturing problem and as such they will only sell their current inventory to customers who have ordered them in the past.
Being that we haven’t used them in the past it looks like we can’t order them. Does anyone have an alternative encoder we can use?
Kelly
We had great performance from the Grayhill encoders recommended by VexPro for their ball shifters. We got ours from DigiKey.
http://www.vexrobotics.com/vexpro/gearboxes/ball-shifter.html
Great idea Travis, Thanks for sharing.
This year Team 751 is going to try using an organization tool called Trello. This is a an open source project management system popular amongst new product developers here in Silicon Valley.
Instead of a blog, which tells you what was done, this is a task tracking system were people can tackle unknown problems and collaborate and monitor progress on the task. I am pretty sure it will work well as a mobile app for Android or iOS.
“The motto of all the mongoose family is, “Run and find out,” and Rikki-tikki was a true mongoose.”
― Rudyard Kipling, Rikki-Tikki-Tavi