Attatching an axel to a wheel

I know the tile sounds a little childish, but I was wondering how do you guys attach your axels to your wheels so that the axel isn’t free moving?

best way is with a slotted axel and a key.

Dont even think of using a set screw!

unless it holds the key stock in place

Exactly. Set screws can be quite good if used properly.

696 has always keyed the axle (and bore of the wheel) with a standard straight key/keyway. A few teams use a hex shaft and matching hex bore in the wheel. Other teams allow the wheel to free spin on the the shaft and affix a sprocket or whatever directly to the wheel.

Shaft collars, flanged bearings, e-clips, and whatnot are all good ways to keep a wheel from moving linearly along the shaft too.

Let me know if you have any more questions. :slight_smile:

According to Mr. Bill (team Hammond, 71), if you don’t want it to move, weld it. While this may be difficult due to the material the wheel hub is made of, some teams will weld the sprocket to the axle and then bolt the wheel to the welded sprocket.

This is an extremely robust method of attachment, though if anything breaks, the whole axle must be replaced including the sprocket.

If you want to avoid broaching a slot a round pin can be used. Examples can be seen Here.
Check out 2006 Robot CAD. Look at the wheel and shaft.

Pins are one of the weakest ways to go. Its difficult to calculate the impact shear forces a pin will see, in a collision for example.

Ive seen many axel pins break, and Ive seen a 0.5" diameter axel break where the pin was located, due to the reduction in cross sectional area the hole produces in the shaft.

BTW, they use pins on the props for small outboard motors - and they call them shear pins - they are intended to break if the prop hits a rock - saves the prop

A robot with failed drive train, motors spinning and bot going nowhere, is one of the most common failures you see at FIRST competitions.

Are you are speaking of a pin located perpendicular to a shaft, as is the case of a prop shear pin, or a pin located parallel to the shaft, as the drawings show? I do not disagree with you, just want a clarification.

I was referring to perpendicular pins that take all the torque applied to the wheel. I have spent many hours replaceing those at competitions.

I clicked into the drawings and I think I found what you are talking about. The pin is wedged between the wheel and the shaft, to hold the key tight on the opposite side?

Why not tap the shaft and put a small bolt with a large washer on the end, to keep the key from slideing out? that would make it easier to remove / replace the wheel.

The shaft is tapped and there is a bolt on the wheel to hold it on.
Look again.

so whats the purpose of the pin then?

we actually had to drill and tap hole at comp so $@#$@#$@# to keep the wheel from coming off the c clip channel was not deep enough and our wheel had about an 1/8" from falling off

This should make things clear as mud.



what did i say i must have typing turrets

Is there any reason a pin such as that would be used over a keyway? Or would it just be used if you didnt have the correct broach?

Im gonna guess and say that anyone can put the wheel over the shaft and drill out the hole for the pin, if you dont use a key

those square-drill-bits are too expensive for some teams :^)

The ol’ bolt in place of the square key trick.

I like it. Even if you don’t use it in the initial build, it’s helpful to take note for quick repairs in the field. It DOES work, and works well.

Better than taping 7 hacksaw blades together and trying to cut a keyway because you didn’t have an arbor and broach. At least thats what the students told me.)

The reason we use a round pin is that a key way can’t be broached in a pocket. The broach must pass all the way through in order to cut the key way.




Do you ever strip the threads on the axles or bolts due to torsional force on the wheels?

not for first but for occra. our team has been successfully just bolted our sprockets to our wheels. and the wheels have bearings. the shaft is in those bearings, and collars hold the wheels from moving sideways. so basically our shaft is free of our wheels/sprockets. simple and works well. if you had good bearings in the wheels, you can eliminate the bearings to hold the shaft. if you really wanted it to spin under sideloads(such as turning with 4wd or plain being pushed sideways), you can actually get bearings… just cant remember the name of the bearing right now… the kind for pressing loads. GAH. cant rememebr any terms lol. like tiny turntables ish… sorry. i really cant rememebr the term right now. well anyways, if the sprocket is solid to the wheel, wheel and tire dont slip, and chain doesnt slip, wheel doesnt wobble=sprocket doesnt wobble, you’re pretty much set.
not hard to do. but this has been working for us well in OCCRA… where we dont experience as much torque and shtuff… so i unno about first.