How do you fit a #35 sprocket with the WCD Versa 3 Cim Ballshifter? Obviously a single hub 12t vex sprocket fits, but I’d like to have two sets of chain running to the gearbox. This seems to fit with #25 chain (Versa’s example guide for a wcd uses #25), but spacing seems to be an issue with two single hub 12t #35’s or one double hub 12t #35. Using plate sprockets from WCP is an option but the smallest teeth number for #35 is 22t which would lead to speeds (with 6" wheels) that are too great, according to JVN calculator. Can’t seem to gear them down enough without additional external gearing either. I’d like to keep 6" wheels and 8" wheels as an option, so standardizing to 4" is out of the question.
You could find one length of their stand offs that is correct or a bit longer and cut and re-tap it. The spacer should be an easy to find a pipe/tubing that can be cut down…Add a longer bolt and you are good to go.
Any questions PM me, I have these around the shop and many Vex EDR parts and can build one if you like.
Let us know how it goes,
Aloha!
Added: Another possible option is to take the single sprockets and cut down the hub down a bit…
We ended up using the same gearbox as you did this season. We ended up making custom plates to replace the one on the 3rd stage to make it easier (at least for us) to mount. See here: https://www.chiefdelphi.com/media/photos/45663
Double hub still leaves chain brushing against the gears and the mounting plate.
I’m afraid that there’s no other option than to mill down two single hub #35 sprockets. Modifying the standoffs is an interesting proposal, but it would not be the best solution for us, specifically. The gearboxes take up quite a bit of space, and it’s already tough enough to fit the battery and electronics where we want them. Good idea though!
I’m surprised that Vex sells the gearbox as compatible with #35. They have a 12t double hub sprocket as wcd sprocket option! https://www.vexrobotics.com/3cimballshifter.html Yet #35 sprockets can’t fit without additional modifications? Am I missing something, or is it false advertising?
Modifying the stand off seems the least work. I think you will probably only need an 1/2 inch per transmission, if that…
I am very surprised the double sprocket didn’t work by design… We ended up modifying our standoffs when we use those transmissions. As of the late we have not used the Vex model and have been using the WCP dog shifters… It is easy to modify those as it uses a much larger tube for a spacer and it doesn’t use a threaded standoff as part of the casing assembly.
It is odd that the double sprocket hasn’t been modified by now. It has far too much spacing between the sprockets than needed and could easily be half as wide…
Another thought is the Andy Mark 12t double sprocket is .770 wide versus the VexPro sprocket is .841 wide… Might be able to use a hex broach similar to how AM did on their hubbed 12t sprocket. https://www.andymark.com/product-p/am-2375.htm
Not a lot of difference but might be enough.
If you can squeeze an inch from the battery/electronics changing the stand offs is probably easier than milling the hubs…
If you need more space, you need to make the standoffs longer. If that’s too much work, you could also install small spacers between the standoffs and 3rd stage plate, it has the same effect. McMaster has a ton of spacers available to do this, but it will always be cheaper to make them yourself.
Based on the original thread that you linked, it looks like you have the transmissions fixed at the rear of the robot, and chains to power the middle wheel and front wheel on each side. With that setup, you can potentially just use one sprocket on the transmission, a double sprocket on the middle wheel, and a single sprocket on the front wheel. The rear would drive the middle, and the middle would drive the front.
The size of the sprocket should not affect the speed of the drivetrain. The speed of the wheel on the output shaft of the transmission is determined by the gears of the transmission. As long as the sprocket on the transmission output shaft has the same number of teeth as the sprocket on the other wheel you are driving, they will both go the same speed.
From the JVN calc, using “Vexpro 3-CIM Ball Shifter Drivetrain” tab, it should look something like this. You have to adjust the gear sizes in the “Chosen Gearing Config” section to match the option you want from Vexpro.
I usually use #35 chain for most chain applications because I’m always afraid of the sprocket coplanar tolerance with 25. #35 can take a lot more misalignment before throwing the chain. How does #25H stack up in that regard?
It would have to be really bad to start causing problems. I don’t have any exact value for you, but there is approximately 0.010-0.015 total side clearance between the sprocket web and the chain plates. In a typical 6 wheel DT configuration I would only expect problems to start happening with planar misalignment greater than 0.125”, you will be losing some efficiency and have increased wear if you’re alignment is that bad, but it will still run for a long time as long as you keep it tensioned. Misalignment of less than a 1/16th isn’t going to cause you issues. If you don’t believe me, set up a chain run and intensionally misalign it until you start to feel it go from turning smoothly to turning with a popping feel as each tooth catches a little bit on the chain links.
Now in regards to the strength of 25, #25H, and #35 ANSI roller chain it does seem that I was misremembering the amounts, but I figured out why. The following are the values for Ultimate Tensile Strength. For reference Roller Chain Size Chart With Dimensions & Specifications 25 chain: 930 pounds #25H chain: 1010 pounds #35 chain: 2320 pounds
Now that is how much you can apply before it snaps, not the working load. 25 chain: 85 pounds (McMaster) #25H chain: 154 pounds (VexPro) #35 chain: 190 (McMaster), 419 (VexPro)
And there is where my statement came from, from before Vex listed both working values side by side.
All this being said, I am strongly of the opinion that if you are running into issues where you are worrying about snapping #25H chain then you should be changing your design so it can’t happen. Just using a slightly larger sprocket significantly reduces the load on your chains, same when you reduce your wheel size. My opinion on #35 chain does change if for some reason you use larger than 6 inch drive wheels as the torque becomes far larger.
Can you get 18or 20 ft/sec with 6" wheels with out brown out? I am not doing well with this JVN spreadsheet. How much current Draw per gearbox is to much?
From what I remember from when we ordered these this season, Vex ships the kits with both sizes of standoffs included. I remember us thinking that we’d need to cut our own, but we were pleasantly surprised when they were included in the box. We did, however, order the ball shifter kit separately from the 3rd stage kit due to a mistake while ordering, so it is possible that the longer standoffs are only included with the separate kit.
We noticed the same thing. At first we kept looking for the different mounting kits, because thats how they used to be advertised/sold. But it appears VEX kitted the 25 and #35 chain standoffs and bolts together when you buy the WCD 3rd stage.
Edit: Looks like VEX advertises that the WCD 3rd stage “…kit contains parts from 217-4246 and is compatible with both 25 and #35 chain.” https://www.vexrobotics.com/217-4247.html
But 25 chain does work for most drivetrain applications. 35 is usually a bit overkill.