Some more VersaChassis Questions
 

Hi everyone.

I made a thread like this with some initial questions about the VersaChassis, and with a (now) much better understanding, I come bearing some final questions before my team commits and gets ready to order the parts we need!

So, to my understanding, these are the parts one needs to make a VersaChassis:

1. 2" x 1" tubing (proper length)
2. 6 VersaBlocks
3. 1/2" hex shafts
4. 1/2" hex bearings
5. 6 Wheels, w/ accompanying 1/2" hex hubs
6. 4 belts
7. 2 15mm pulleys
8. 4 9mm pulleys
9. gussets
10. WCP gearbox
11. CAM tensioners
12. 1/2" hex spacers (useful)

Is there anything I'm missing? Something that I mentioned that isn't actually necessary?

Further, I have some small questions.
1) The VersaBlock, to my understanding, holds bearings on both sides for the shafts of the outer wheels. What in the world is the Side Bearing Block Kit (http://www.vexrobotics.com/media/cat.../file_1_11.png) and the Gearbox Bearing Block (http://www.vexrobotics.com/media/cat...ile_1_13.png)?

2) How does the WCP gearbox mount onto the square tubing? I heard something about a 1/2 VersaBlock but wasn't really sure what this meant. Do you take an actual versablock and unbolt half of it? Is there a special unit? Is that really enough to hold such a massive gearbox down?

3) CAM Tensioning. I understanding how it works and all, but have a slight inquiry. If the CAM is meant to be rotated to push against the VersaBlock to tension belts, are the bolts on the VersaBlock supposed to be loosened when this is done? Or do they stay tight so as to clamp the VersaBlock on the tubing, yet the CAM overcomes this friction and pushes the block anyway? Are the bolts on the Versablock even meant to be tightened, or are they properly tolerenced in length that the VB is just meant to slide on and be that way?

4) Similar to #2, but the gearbox has me a bit confused. The outer wheels have VersaBlocks to hold the shaft straight, what is there for the gearbox? Obviously it has its own bearing, but on the other end of the tubing where the wheel is, is there a special piece to mount onto the tubing to hold the shaft straight?

5) What in the world is this? http://www.vexrobotics.com/217-3636.html

As always, pictures are super appreciated, as I think that's the best way to understand this.

I'm sorry if I have a lot of questions, I just want to get this down to a science so that I know what to do come Jan 4th! Thanks everyone, you've been really helpful!

Re: Some more VersaChassis Questions
 

I think that you add this part to the three CIM wcp gearbox to add a power takeoff. You can mount a pulley, sprocket or gear to the versahub thing with the dog pattern in it. You can find a cad drawing of the three CIM gearbox with the pto on the wcp 3 CIM shifter page. I think (but not sure) that with this setup both the pto shaft and normal drive shaft are powered when the pto is engaged, which is different from how some other teams (118, 254) have done it.

Re: Some more VersaChassis Questions
 

Excellent questions!

1) The two other bearing blocks you linked to are for more "traditional" West Coast Drives. These are bearing blocks that mount through the inside of the 2x1 and not on the top and bottom like the VersaBlocks do. These typically require more machining resources, hence why the VersaBlocks were created. You do not need them if you are using the VersaBlocks.

2) Tough to explain in words - hope these pictures make sense.

3) You can loosen the bolts to tighten the CAM, though personally whenever I run an extremely similar setup, if you tighten the bolts on the blocks enough you won't ever need to tension (was using belts).

4) As seen in the pictures I posted above, the inner end of the shaft is supported by the bearing in the back plate of the transmission, and also by the bearing in the outer VersaBlock, and these two together keep the shaft straight (hint: Don't put a bearing on the outer transmission plate - you don't need 3 bearings on the same shaft because it could potentially cause problems).

5) That is the Power Take Off addition to the WCP 3 CIM shifter. Basically it allows you a "third" speed that routs the power from your 6 CIMs to another mechanism, like a climbing mechanism or a part that needs a lot of power. Teams like 254 used Power Take Off this year to use their drive motors to pull them up the pyramid.


Hope these answer your questions. If you have any more, please feel free to pm me. I'd also be happy to send you a CAD file of my drivetrain for you to look over (It's in Solidworks, so if you use anything else it'll be a STEP file).

Re: Some more VersaChassis Questions
 

Thanks Andrew, that was pretty thorough.

As far as the gearbox mounting goes, I see the two bolts through the VersaBlock into the front transmission plate, as well as two socket-cap screws that seem to go into the front plate from the inside of the tubing - could you clarify?

I'm pretty sure the two on the VersaBlock go all the way through and mount on the transmission plate, but are those other two bolts on the sides meant to mount the gearbox to the channel as well? It would seem like they are, because there seems to be a hole drilled on the outside for Hex key access to the bolt, but at the same time I don't see how the bolt would get into the inside of the tubing.

All of your other answers totally answered my questions, thanks!

Also, I'd love to see the CAD if you could send me that, Thanks - I too use SolidWorks.

Re: Some more VersaChassis Questions
 

You've got it correct. The bolts on the VersaBlock go through to the tubing and screw into the 10-32 tap on the gearbox plate. The outer bolts on the gearbox connect through the inner plate in the tubing. You need a larger hole on the outside for access.

I'll pm you a link to my model in a few minutes - just need to tidy up some things that I've been working on.

Re: Some more VersaChassis Questions
 

Is this a replacement for the current shifting mechanism on the 2 speed 3 cim shifting mechanism or is it a separate addition to the gearbox?

Re: Some more VersaChassis Questions
 

Really? That's somewhat surprising - in the past when I've used 80/20 to mount wheels, no matter how much I tightened the bolts the wheels eventually walked enough to loosen the belts. Admittedly, that was with plastic IGUS bearing blocks pressing against a t-slot, and not with aluminum plates clamping around a piece of 2x1, but I'd have expected the physics to be similar for similar-strength bolts with similar amounts of tension on them.

That said, there are holes in the VersaBlocks for mounting directly through the 2x1, right? So in practice you could simply slide the block until your belts are tight and then match-drill through the framing member and bolt it in place for all time. Won't work as well with chain, which expands, but with belt it should be a very good solution.

Re: Some more VersaChassis Questions
 

An addition which can be seen better on top of the transmission here.

Re: Some more VersaChassis Questions
 

The PTO Add-on Kit is an auxilary mechanism that's added to the 2-Speed 3 Cim Box. If you look at this picture it should make a bit more sense. In the standard configuration, Shaft connecting the upper most CIM with the two below, does nothing other than transmit power from the top CIM to the bottom. In the PTO configuration, this shaft serves two purposes, the original one (connecting the lower CIM pair with the upper) and serves as a Power Take Off for the transmission.

Re: Some more VersaChassis Questions
 

This was just my experience. Of course the CAM helped in preventing the block from sliding back as well.

You could in theory do what you're saying. I haven't tried it so I can't provide any data on this, but I see no reason why if you use belts (because chain stretches), you can't just do that.

Re: Some more VersaChassis Questions
 

Thanks, that makes a lot more sense than what I was thinking.

Re: Some more VersaChassis Questions
 

I'll give a counterpoint to Andrew here and say that you're correct, at least in my experience. If you tension your bearing blocks with a clamp, say, and then try to tighten them down, even really really tight, they will slide eventually. Maybe not in the first two matches, but I'd bet they'd slide in the first twenty. We ran a setup very similar to the VersaChassis last year, one in the regular season without cams, and one in the season with. The one for the regular season we had to check almost every match and retention frequently (we were running chain and 4" wheels) as it slipped fairly regularly, even when tightened super hard and locktited down . In the offseason, we ran 6" wheels with slightly larger sprockets and cams, and the bearing blocks never slipped. Never.

After the first installation cams aren't really there to provide an easy tensioning method. They're there to keep the bearing block from moving back. Basically, (and I've seen this on many of our robots) if you don't have a cam, the screws holding the wheel truck will vibrate loose, and the block will slip. When these things are in a drivetrain without cams, they will slip sooner or later.

So, please, just buy four cams. They aren't that expensive, and they will save you from a lot of sweat, blood, tears, and losses in the season. I know for a fact that they could have prevented one of our lost matches.

Re: Some more VersaChassis Questions
 

Yeah, this was my exact experience with bearing blocks on 80/20 sliders. "Re-tension belts/chains" was the number-one drive item on our pit checklist every year we did that, because they simply would not stay put. It wasn't a bad setup, but it doesn't compare to a really good system where you set it up and don't have to touch it again.

The cams look really nice for chain, but I prefer belt and I think simply putting a single bolt through the frame material would probably be easier (and have marginally less weight/complexity) there.

Unfortunately, I won't get to see any of this in practice this year because 449 had already purchased framing material before VersaChassis was unveiled, and 4464 is (overwhelmingly likely) gonna stick with the kitbot chassis. There's always next year, though.

Re: Some more VersaChassis Questions
 

Are four bolts really enough to hold a gearbox and 2-3 CIM's onto the tubing? Seems iffy. Does anyone put any kind of support bars between the gearboxes similar to how the kitbot has hex tubing between the CIMple boxes?

Re: Some more VersaChassis Questions
 

Tighten them well enough and it's more than enough support. In fact our offseason bot only used the two outer bolts and the transmissions held on perfectly.