WCD Versablock vs. WCP Side Bearing Block

#21

Without a cam or something similar, sliding bearing blocks are still held in place by clamping force/friction. The cam only prevents the block from sliding back. Consider that vices and other fixtures on mills are often held in place this way too.

At the very least, this works out in the short term with Versablocks. I’ve made a handful of prototypes using Versablocks without cams + #35 chain without issues, and Team Copioli did the same with 9 [mm] wide, 5 [mm] pitch HTD belts. Of course, it’s best practice to use the cams and not leave things to chance.

#22

Is the pocket height the same as the bearing block diameter or did you provide some clearance? If so, how much?

#23

The pocket height should be the same height as the rectangular protrusion on the inside of the bearing block. The pocket width should be wider to allow for sliding tensioning.

#24

Vertically, we had it milled to the exact measurement of the block, and then filed as necessary.

#25

Exactly. We just torqued down the two bolts through the block. We would have to go back and retension them every other match or so, but it wasn’t too much of a hassle. Granted, if we had known about the cams, we definitely would’ve used them.

#26

Jesus how long did that take him?

#27

Probably depends on what attachment he had on there, how much power he applied, and how much force he used. Wouldn’t be all THAT hard to use a cutoff wheel to take out a block slightly smaller than required on each side, then grind the rest of the way and file the fine details.

I also wouldn’t recommend the approach, but I will admit to using it on (non-FRC) stuff. You need a steady hand, a firmly-held workpiece, and patience. Once you get the feel for it, it’s pretty doable–maybe a couple of hours once the initial cuts are out of the way?

#28

Bingo. IIRC, it was a cutting disc for most of the work, and then one of the thin little milling attachments for cleaning up the corners and the like afterwards. It wasn’t the prettiest thing, but it did ultimately work.

#29

1675 has now made 3 different versions of WCD with Versablocks and Side Bearing Blocks. I’ll share my thoughts with you all but I am also looking for some advice.

2014:
3CIM WCP Shifter with versablock on the outside of the 2x1 with fasteners through VB, through the tube, and into the outer gearbox plate
6wd 4" wheels with center drop
Versablocks on outer wheels
9mm belts
Gearbox was very rigid for the drive (not so much for our alternative use of the third motor slot to run our arm, but that’s a different story https://www.chiefdelphi.com/media/photos/39499). 9mm belts were a problem (snapped 8 or more during the course of the season, I believe, and with them being internal to the gearbox, replacement was a big pain). Versablocks were a good solution for us but we observed some “twisting” due to the eccentricity between the cam and the belt which caused the belts to walk a little bit and actually pop the flanges off several pulleys (which lead to some of the belt failures).

2017:
3CIM Ballshifter with WCP Bearing Block attachment to 2x1
4WD with 3.25"
WCP Side bearing blocks on non gearbox wheels
15mm belts outside the frame
Gearbox was very rigid. No broken belts. Never had to adjust the tension all year. Had some issues doing the machining for the blocks but it was worth it.

2018:
3CIM Ballshifter with outside plate fastened to half of a versablock and then clamped to the 2x1 with the other half of the versablock.
4WD 6" wheels traction + omni
Versablocks on the non gearbox wheels (the omnis)
#25 chain integral to the gearbox.
Gearbox was not as rigid as past iterations but not to the point to cause any problems. No broken chains. Did have to adjust tension throughout the season. 2014 issue of twisting did appear again, in both versablock wheels and gearbox wheels. This led to sprockets walking, shafts walking, and one wheel dangerous close to coming off a shaft during a match.

I really like the idea of the Versablocks but I can’t help but wonder if we are doing something wrong because I have not seen anyone else refer to these twisting issues that we have experienced. Is it possible we are overtensioning? I can’t recall what our metric in 2014 was for measuring tension (something like deflecting the belt 10% the span length when pushing in the middle with a given pressure) but it was comparable to other C-C belts we’ve done before.This year the typical chain tension was enough to keep it from flapping on the bellypan but not overly tight. We saw noticeable camber on both the gearbox shaft and the shaft on the other end; we removed the gearboxes and tightened everything and reinstalled but saw the problem persist afterwards.

I’ll be doing some deeper analysis into the problem this weekend but it makes sense to me - even with a small eccentricity between the pull of the chain/belt and the point of contact with the cam, there will be a moment created in the shaft. Because the cam and the inner bearing of the versablock pair are essentially collinear, the moment really is only transferred to the bearing on the outer half of the versablock and is then resisted by the campling force of the two bolts holding the block halves together onto the 2x1 tube. We only use 2 bolts two hold the blocks together, not four, so perhaps that is our problem, but that is what is recommended in the versaframe documentation. It seems like the real solution would be to add a counter cam on the outside block but that just feels wrong.

#30

We used the versa blocks for the first time this year, and we’ve encounter the same issues. We first saw it on our practice bot, so for our real robot we tried to use four bolts on each instead of two. This was a poor choice as for one, we were unable to access many of the bolts that were on once we installed our bellypan when we needed to remove a bearing to replace (the chain was overtightened) and we also seemed to necessarily strip the heads of these bolts ever time we removed them. Not entirely sure the cause, but we tried some bolt from Bolts N’ Nuts (A local hardware chain, not sure of the grade) in addition to the included bolts from vex, both ended up with a stripped head. A counter cam might work, but I agree that may also introduce some other issues.

#31

Sorry to necro the thread, but I just wanted to clarify on some stuff said in this thread. The VersaBlock’s biggest advantage is that it doesn’t require as precise machining. The advantage to the WCP clamping bearing block is that it looks a lot more cleaner. Our team has never used either one but I am assuming that performance wise they both perform equally as well. Am I correct to believe this? The other thing I am thinking is that the extra space “freed up” by the absence of the versablock wouldn’t really be of benefit since if you were to use a WCP bearing block or even c-c bearing holes, you still couldn’t really mount anything structural since there would be a hex shaft running through the holes. Is this also correct to believe?