Attatching an axel to a wheel

[Zoheb N]

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?

[KenWittlief]

best way is with a slotted axel and a key.

Dont even think of using a set screw!

[Timmyd]

Originally Posted by KenWittlief

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

[sanddrag]

Originally Posted by Timmyd

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.

[Jason Kixmiller]

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.

[Rod]

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.

[KenWittlief]

Originally Posted by Rod

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.

[Rod]

Originally Posted by KenWittlief

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.

Ken,
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.

[KenWittlief]

Originally Posted by Rod

Ken,
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.

[Rod]

Originally Posted by KenWittlief

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.

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

[KenWittlief]

Originally Posted by Rod

Ken,
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?

[Doug G]

Originally Posted by sanddrag

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

Another note on shaft collars... use clamping style collars and preferably the two piece type. Shaft collars with set screws will mar the shaft which is no fun!!

Buy a simple broach set to broach 1/4" - 1/2" items. A wise investment along with several pieces 3/8" and 1/2" keyed shafting. MSC Direct has this for about $100. It's served us well for 4 years now. You may need an arbor press, although with most pieces you can press the broach through with a simple drill press (not running of course) and some cutting oil.