Now that many teams have completed their first competition, and many of them are going on to their second competition, I’d like to address something. It’s the most vile-looking clumps of worse-than-kitty-hairballs known to open-gearbox roboteers everywhere:
Carpet Gunk (noun, informal) unpleasantly sticky or messy substance consisting, in part, of carpet fibers, robot aluminum filings, and/or dirt
Our average distance traveled this season is approximately 4 full-field cycles, peaking at 5. I suspect plenty of other robots have similar performances. We use the (open) WCP-WCD-DS gearboxes with with lithium grease. Plenty of other teams use similar setups. So how do we easily maintain these gearboxes?
At what point of build-up does carpet gunk become a major
problem - one that disables a robot, or worse, causes excessive wear on gears? 1. What are some tips to clean this stuff out without completely removing the gearboxes? (tweezers? freshmen with toothbrushes? etc?)
*]Suppose we have shields protecting the open bottom of the gearbox. How else can we minimize carpet gunk intake? (Use XYZ enclosed gearbox isn’t an option for this year)
Enclose the gearbox through the use of large amounts of duct tape. Granted, my team hasn’t used anything quite so open as those, but we have used gearboxes with some openings on them, and sealing them with duct tape really did a good job keeping dirt out and grease in.
If you want to preserve the appearance of the exposed gearboxes, you could experiment with clear packing tape. If applied with some attention to detail, it may be possible to keep them looking nice.
In the past we used some thing polycarb to wrap around the gear box and then secured it with electrical tape at the seam and edge. I don’t remember the exact thickness but I see my local supplier normally stocks it in .030 and .060 so I’d say we used .030.
For the EVO shifters (I know, different gearboxes, same principle though), 'Snow Problem bent some .03" clear polycarbonate around them. This has held up pretty well and helped us avoid splattering grease all over our electronics. In the past I’ve done 3D printer gearbox covers as well. Both bent polycarbonate and the 3D printed designs have done their jobs quite well.
Re the other questions, gunk is a sliding scale of issues. On the lowest end, you’re just losing a bit of efficiency. On the highest end it becomes extremely difficult to drive straight, your battery is draining quicker, and your motors are getting too hot. In any case, the best medicine here is prevention-- gunk of a variety of forms is a pain to clean any way you cut it. You don’t need to use a gearbox that is sold enclosed to cover up.
In the past I’ve used and seen used a number of things. For stringier carpet stuff, a knife can be good. For more powdery or mixed grease/grit, a toothbrush (or other small, decently stiff brush) can be good.
We have 0.03" polycarb shields on the underside of the gearboxes. The zip ties that attach it are about 3/16" off the carpet. One of the shields has a massive gash in it, leading us to believe it prevented major failure from field debris. It seems like the fibers get in via the chains and potentially the part of the shield side which aren’t perfectly flush with the curvature of the gearbox.
I think we’ll work up a 3D printed Nylon shield that rivets (or rivnuts) to the underside of the frame rail and zip ties to the opposite plate. If we get something done in time, I’ll post it to Thingiverse/CD.
Cool, thanks for the advice! I’ll make sure we pack a variety of brushes.
We had an exquisite amount of this gunk in our WCP gearboxes after our first district, as in addition to the carpet our CIMs had been mounted incorrectly in the outboard position and thus had been prodigiously chewing through the aluminum gears (a potential downside of having good closed-loop drive control is that it’s harder to spot things like this from robot performance alone).
We’re going to look at the VexPro shifters next year, for this reason and others - I’ve heard that the external stage mounting on those is prone to “sag” over time, though.
Somewhere during final rebuild we missed the tiny stops we usually put in place for the WCP gearboxes. We Had an issue at the very end of Q40 with the bottom CIMs re-positioning, but we had plenty of time to do some gearbox surgery using chiseled wood. We re-added stops during unbag. In the future I think I’ll just use 14T pinions and shave down Colsons to the right size. Ha.
Though come to think of it, the gunk wasn’t an issue at that point of the competition. I’ll have to inspect things again this Thursday to see what may have changed.
Yeah, we just changed to 14T pinions. We figure we could use the increased speed, anyhow, given that we’re autoshifting.
A solution we found last year for holding the motors in the inboard position is to wrap a hose clamp around the CIMs (preferably as close to the gearbox plate as possible).
We built custom gearboxes this year, and made bent 1/16" polycarb covers that wrap all the way around the gearboxes and tie-wrap closed at the top. The gearbox is incredibly close to the ground so this cover was a necessity and it has done a great job so far.
Yes, I forgot to mention that. This drivetrain was highly influenced by the need to save space, but it also conveniently helps protect our chains and gearboxs.
When we were using chain drive, it’s was a bit difficult to clean up. Wipe out everything from chain and reapply grease at each event. Now with rots, just vacuu. Keep a steel brush handy to clean wheels.
We used WCP open gearboxes on our practice driveframe, and the large amounts of carpet gunk don’t seem to affect performance. This may be more because it’s a practice bot, though.
I highly suggest spending a little extra on your grease and getting this grease designed for firearms. We put a light coating on all of our gear to gear contacts and anywhere else we are concerned about friction.
I have used this personally for over 13 years on many different applications and it works.
I have taken to 3d printing shrouds that replace the spacers. This seems to make it more rigid and protects against unwelcome parts entering the gear box. That said the shrouds only ever go on top, having access to the bottem of the gear box is very valuable for maintenance.
We have been using WD-40 brand lown viscosity While lithium grease and it works well and has not been attracting dirt.
