Reducing wheel slop

If the plastic inserts on your wheels are getting rounded out, you can replace them with metal gear inserts. I have not tried this, but the hole size is the same (1/4"). The plastic inserts are just glued in, and one of them actually came loose on one of our wheels, so it shouldn’t be very hard to remove them.
wheel insert removal.jpg

You could boil them to assist in removing :smiley:

But apparently that is illegal now cause it may “Hyper-Hydrate” the wheels making them better haha :eek:

We did this last year (not boiling, they just fell out since they were 3 year old wheels) but it allowed us to put a screw through the wheel and then we were able to cantilever our front wheels. But that isn’t needed in Toss Up because you don’t need a 15 inch wide intake haha.

Cantilevered wheels? Kyle approves.

Is it just a coincidence that you used 15 inches, which happens to be about the size of the large balls?

Some inserts are easy to remove but some are really stubborn, resulting in more than just the insert being removed! Seumas is the master at this operation, while the rest of us hope the wheels survive the ordeal. It is very difficult to get the metal inserts fitted perfectly central on both sides, so our wheels have ended up with slight, but still annoying, degrees of “wobble”.

Future improvement suggestion
We find the plastic wheel inserts invariable get flogged out with use. We now have a lot of redundant high strength gears, as the metal inserts for the gears have been pinched for the wheels. It would be great if all wheels could be supplied without any inserts fitted and come as a kit with the option of square centre metal inserts and round centre plastic inserts, just as the high strength gear kits are supplied.

Thanks, Paul

I’ve decided I’d better finally make a post, as opposed to just lurking on the forums as I have done for a while. :smiley:

By the way, I’m Seumas from 2941B during Sack Attack, and 2941 during Gateway and Round Up. :slight_smile:

I found that some of the plastic inserts can be particularly difficult to remove. Sometimes, as already stated, they just wear out with use, and come out quite easily. However, for more stubborn ones, I just persist with the pliers, and gouge out the insert (it doesn’t really matter if not all of it is removed). From this side I then use something like a long nail to chisel out the other side (which usually pops out after a good knock with a hammer), and then if necessary clean up the inside. Sometimes, if the metal inserts refuse to go in, hot water can help (to soften the plastic).

ALSO: The smaller 2.75" diameter omnis have one solid insert which goes all the way through, and so my attempts at removing it were unsuccessful.

Just be warned, that for doing this with all of your wheels, you may soon find that none of your high strength gears have inserts any more… :rolleyes:

This is a wheely good way to deal with slop. :wink:


The forum name may require obligatory puns with every post.

Reducing wheel slop is something that I have done a reasonable amount of testing with… (you could say I have turned it into a science, I am so obsessed with it).

We changed some of our wheels to have metal High Strength gear inserts in Round Up, but that wasn’t because the plastic ones had worn out/fell out, but more that we wanted to reduce the backlash. This meant that the wheels and the encoders actually rotated together perfectly, helping our autonomous. We got this trick from Massey University back then, who then the next year found that by using the metal inserts it had in fact started to slowly wear the plastic of the wheel where the inserts go in.

In Sack Attack I started switching the wheels to have bar locks around them, so that the shaft was still firmly attached to the wheel with little wiggle, but also so that there was virtually no possible way that the wheel could wear out (of course it’s possible, but it would be incredibly hard to do). This helped a huge amount. Far better than the metal inserts. What’s better is that you now have mounting holes for the wheels, so you can bolt sprockets/gears directly to the wheel! That’s what I did after Asia Pacific and it is as though the wheel and sprocket I used is one solid piece. No wobble at all.


Seumas :smiley:

My team had to buy 3 high strength gear kits just for the metal inserts. I notice a lot faster stopping and changing of direction after this mod.

He said 15 because that was the width of three sacks last year so most teams tried to make as wide of an intake as possible.

We pulled out our inserts to put the green ones in and cantilever our wheels on screws as well. Pulling out the inserts really sucked on every one we tried. None of them were easy…

How do you use the wheels with bar locks?

I believe you place an axle through the outer square holes and apply a screw through a round hole. Once the screw is in, you can place a spacer which fits perfectly between the holes of a wheel.

I’m just mind blown by this forum post. I’ve noticed wheels run down, but I never thought it was possible to remove the holes like inserts of a gear. Do you just push the center out?

Should I make a video of the process?

My chasis has 6 omnis with this mod on them and it helps a lot of acceleration and deceleration.

Some inserts slide out easily while others I chisel away at with an axle and a mallet. :mad:
Its a pretty ridiculous process but well worth it.

if it’s something that vex originally intended, then i can look at some wheels and figure it out. However if it requires some cutting and stuff, i’m not interested. But, i would still like watching the video.

Sure. I’d be interested in doing this if you guys say that it improves the performance of the robot.

We just use the metal inserts from the High Strength Gears Kit? With 16 inserts per kit (and I’m assuming two per wheel), you can only build two or three chassis with one, right? Is the performance boost worth $30 per robot?

Basically, you have a bar lock on either side of the wheel. Put a bolt through the bar locks and tighten together (I would recommend a nylock for this, I think regular nuts would come loose quite easily). You could put spacers between the two sides, but tbh I didn’t really find them necessary. Here is a photo:


Haha that’s pretty clever, and probably easier that removing inserts.

Not sure if anyone’s already discussed this but back in Gateway I made these polycarbonate shapes to help reduce wheel slop. Sorry, the image is a little too bright.

It has two little flanges that you bend inward to grab the wheel’s spokes and it has two holes that line up with a gear or sprocket. It seems like it’d be pretty loose but once you put the screws in and space it out properly + tighten the screws down it’s a secure connection. Mostly we liked that you could directly link the wheel to its driving gear/sprocket. Not sure how useful this is anymore now that I know you can get the plastic insert out and put the metal ones in.

We were never able to get the plastic insert out of the wheel, so this was our solution. It’s cool that you CAN remove the insert though, that’d let you put the plastic circular insert in the wheel, and use this polycarbonate shape to make a dead axle drive if you really wanted to.

Still have the CAD around somewhere if anyone wants it for whatever reason.

That is what I am talking about. A lot of the vex omni wheel inserts dont come out easily so I was offering to show how to remove them and put in the metal inserts.

My robot comes to a dead stop when I cut power. Sure that sounds cool for driving but imagine autonomous. Never need To slowly decrease power as you approach target. Never have to send reverse power to counteract momentum like 599 did when they won programming skills in Gateway.

Unless your robot is very, very light, it probably would still drift a bit when power is cut off. I don’t really think that is what is being made better by doing this to the wheels. What is made better is the amount of “unknown” error, in that without this fix, using older wheels, they would rock back and forth on the shafts, allowing a certain amount of error (which was usually quite large, in my experience) that you had no way to detect using an IME or a shaft encoder. With this fix, that “rocking” is just about eliminated, which means that any movement of the wheels would cause the axle to turn right along with them, which means that it can be accurately detected by a sensor.

This also leads me to wonder if teams should do this for sprockets in their “continuous chain run” drives. You could use George’s method of bolting bar locks to either side of each sprocket. Or do the sprockets not tend to rock much/at all? I don’t remember. Another way to reduce rocking (especially if you are using IMEs, or a shaft encoder that is not directly on the wheel’s shaft) is to make sure that your chain run is not too loose. Of course, you do not want it at all tight, but minimize the slack in the chain as much as possible.


The sprockets don’t have the same issue in my experience.
I believe this is due to them being 1 piece of plastic while the omni wheels have a plastic insert inside of the plastic wheel. The inner plastic is made of more malleable plastic so it bends and twists while the outer plastic doesn’t spin.