I’m working on a off-season drive train project for our team. It takes some cues from the WCD.
It’s made from 3 X 3" .120" box tube and uses the VEX ball shifter with a modified 3 stage with 34:50 gearing. The rear VersaWheel is directly driven and then chained to the middle VersaWheel with two sprockets, This wheel is then chained to the 3rd.
The top of the chain runs inside the tube on and outside on the bottom chain for easy tensioning.
Has anyone done anything similar to this? Any comments?
This reminds me of the Rock Box Chassis Rail from 221 Systems. The Rock Box has a very nice solution to chain tensioning in this case that you could draw inspiration from in your own projects.
chain inside box tube is a pain in the @$$ to work with. unless you have access holes that i’m not seeing, its going to be really hard to get chain on the sprockets.
i was not really impressed with the versa wheels. in my experience they wear down really fast. my team ran them for about an hour of practice driving and 10 matches before they pretty much balded. picture (i understand that other teams have not had the same issues with the versa wheels wearing down that fast)
Wouldn’t it be better to run the chain on the outside over the top, and on the inside on the bottom? Might make it easier to tension, rather than having to get under the robot. And also might avoid any issues with the chain damaging field elements/game pieces?
Oh, and yes, similar things have been made before, Andymark has been selling these for a couple years now.
Wow that wear is staggering, how was the traction when they were balded?
The Chain runs outside the tube for half it’s run so it shouldn’t be two hard. I’ll be adding more lightening holes soon so it should make it easier to access.
The wheels are too small to do that sadly but the chain height would be the same as putting the versawheels on the vexpro chassis
what is the advantage of this over cantilevering wheels?
Might i suggest adapting this for eight wheels? Also, I think Plaction Wheels (or the VexPro Equivalent) with roughtop would be much better suited to this. We have roughtop tread on our wheels and the traction is tremendous.
its lighter as you don’t need the blocks and it leaves a little more space inside the robot. You also don’t have to worry about wires getting caught in it as much.
You might want to consider some way of tensioning chain
I noticed that the vexpro chassis doesn’t have any way of tensioning the chain and I’m hoping the relatively large sprocket surface will prevent the chain from slipping. If it becomes a big issue I will probably add a sliding delrin slider or implement something like the rockbox.
While definitions of WCDs vary, virtually all include cantilevered wheel shafts and sliding bearing blocks for chain tensioning.
I designed a similar system (technical term/name for this style of drive is ‘nested tube’, see notes about WCD above) in 2011 when I was on 816 and it worked reasonably well, although servicing it was a complete pain - or at least when servicing anything out of the norm. Here are some pictures:
Frame: http://www.chiefdelphi.com/media/photos/36107
Completed Chassis: http://www.chiefdelphi.com/media/photos/36163
Some general specs:
Drop Center 6WD
6" AM Plaction Wheels, Roughtop Tread
AM Super Shifters, Standard Gearing
Direct Drive Center Wheel, #35 Chain to outer wheels.
That drive didn’t have any method of tensioning* and we never had any issues with the chain tension through two regionals and the off season. The drive only ever had one major failure that I can remember - the tread on one of the wheels came off and lodged itself in between the wheel and the tube… Other wise, aside from needing to swap out the roll pins in the Super Shifters for 4-40 screws (or the other way around, it’s been a while) the drive was solid.
Another note on dead spacing in drive applications, I only recommend doing so if one of the wheels is direct driven from a transmission. If one wheel is direct driven and all other wheels are chain driven a lost chain shouldn’t render the entire drive useless for the rest of the match.
WCDs also typically direct drive the center wheel off the transmission. This means that both chains must fail to lose both additional wheels. Will you able to quickly replace wheels on this chassis? (WCD cantilevering speeds up wheel replacements).
Each module is only about 60$ of parts without the shifter and we can machine it in our school so if we were to implement it in a comp bot we could just build backup modules. The wheels shouldn’t be that tricky to replace, once the chain is removed you just slide it out of the bottom.
wow, could you explain more about how to dead space the chain?
You can use a calculator like this one to figure out exactly how far apart your sprockets should be to perfectly take up the slack in the chain.
With a CNC Plasma, I would consider doing drivetrains similar to 610. They have very nifty flat plate drivetrains, and is probably much easier to access and service. They cut their’s on a CNC router.
http://www.chiefdelphi.com/forums/showthread.php?t=111975&highlight=610
http://www.chiefdelphi.com/forums/showthread.php?t=101692&highlight=610
+1 on this. I really really really want to get a CNC router for 1306 so we can make stuff like this.
I would but sheet metal is really expensive, I’m not sure if its just Canada but two 6061 6x37 .125 sheets would be double what the 3x3x37 .120 box tube costs. Plasma cut metal also takes a long time to finish and isn’t as precise. Does anyone know how 610 hold’s there sheetmetal in place on there router? I cant think of a way to do it without using wood as a relief material but it looks like there using something else in there pictures.
