IFI Traction Wheel stationary?

Technical Technical Discussion
1

Ok, heres my question. I have an IFI Traction wheel and I want it to be stationary on the axle. So when i turn the axle the wheel turns with it. Any ideas on how to solve this? Will a pressure fit work with IFI traction wheels?

Also, does anyone know the dimensions of the protrusion of the IFI sprockets? From wheel hub to end of the hardware.

Thanks :smiley:

2

The IFI Traction Wheels are designed to be run on a “dead axle”. They’re furnished with bearings on each side of the hub for this purpose, so the hole in the sheet metal is 1.125" or so. They’re not designed for a press fit and I doubt you’d have much success with such a scheme if you were to manage it.

If you’d like for the wheel to be on a “live axle” – turned by a key in a keyway, for example – I’d recommend that you purchase either the AndyMark Key Hub or their Hex Hub. These bolt onto the IFI wheels using the same hole pattern they provide for attaching sprockets and fit through the existing bearing openings easily.

The overall width of the wheels is about .5" larger than their spec’d size – so 1" wheels are 1.5", etc. There are CAD models of all of the wheels available on their website at ifirobotics.com

3

Thank you very much. You have no idea how much that helped me.

Now where do I find a hex axle?

4

You can buy 1/2" hexagonal steel stock and machine an axle out of it. Try looking for a local metal distributor, or if you don’t mind paying a premium you can order it from McMaster-Carr (search www.mcmaster.com for “steel hex stock”).

5

I know this is random, but I just bought some steel hex stock from mcmaster… and for them, it is incredibly cheap! $10 for a 6’ is pretty good with their reputation. It also arrived the very next day.

And to backup what others have said, the AM hubs are the way to go. You really can’t beat that price and quality.

Do you have a lathe? If not, it may be difficult to get the axle in a bearing as it won’t be round. I know some teams have put the hex directly in a bearing (217?), while others made a part that is round on the outside, and has the hex on the inside to seat in bearing (195?).

IF you don’t have a lathe, you’re probably better off going with the keyed shaft.

6

I do have a lathe so it will make things easier.
Correct me if I am wrong but:
If you machine a 1/2" hex axle down so that it is completely round it will be much smaller than 1/2". So would a 3/8" inner diameter bearing be in order?

7

Actually, when you say that a hex axle is 1/2", it means that it measures 1/2" between opposite faces, not opposite corners. So you could indeed turn down a 1/2" hex shaft to fit in a 1/2" bearing.

8

if you do end up machining your axles out of 1/2" hex, machine it as little as possible. it is very difficult to cut a long, precise diameter in steel hex. One of the transmissions I did earlier required a 3" long section of 1/2" hex cut down to round, it took quite a while to get the lathe cutting it to proper tolerance the whole length. Although our tolerance was pretty tight… its still a pain. keep it simple.

9

Do any teams use aluminum hex shaft or is it always steel?

If steel is always used have teams drilled the shafts to save weight?

I hate the thought of the weight of that steel.

10

254/968 used aluminum shafts (albeit of a very strong alloy, either 7075 or 7068, I forget) in 2007 and, I believe, 2006.

11

we use 7075 for all our shafts (We had one this year out of 7068, but it had a gear hobbed onto the shaft itself). We use round stock and then mill the flats for the hex onto it, though.

We used a 2024 hex shaft for our spool to lift our elevator this year. Wouldn’t suggest it for a driveshaft or anything under a ton of load, but it worked well for the application we used it.