05-05-2010 22:55

Edoc'sil

Re: pic: 6 inch wheel design

Any thoughts on how you would machine that? The angles look a bit tricky, almost like something you would have to mold out of plastic.

05-05-2010 23:00

548swimmer

Re: pic: 6 inch wheel design

1.3 pounds seems a little heavy. I designed some simple 6inchers without any sprocket mounts that weighed in at around .65 pounds. Also, your exterior wall looks a little thick, how thick is it?

05-05-2010 23:13

M. Mellott

Re: pic: 6 inch wheel design

Looks like you could machine the front face of the 3 closest "spokes" and the back side of the other three in one pass. Flip it over and repeat the process.

The outer wall looks like it's recessed for the tread. Does your weight include the tread material, or is it just the wheel?

I like the wider tread. Very nice, Adam!

05-05-2010 23:22

548swimmer

Re: pic: 6 inch wheel design

Just the wheel, but since it's just for a prototype CAD I extruded where the tread would be, so it should be about the same weight.

05-05-2010 23:23

Jamie Kalb

Re: pic: 6 inch wheel design

Pretty neat.

For the "free" wheel, if the hub is wider than the rim, you can attach a flat sprocket directly to the (nicely integrated) bolt pattern on the wheel without an extra spacer. I can't tell from the picture if it's already like that.

06-05-2010 08:39

Borisdamole

Re: pic: 6 inch wheel design

no way.... it would be machinable, you would just have to do 2 milling operations.... it would require flipping the wheel over to machine the back half.....

the trick with that is getting the orientation correct when you flip it, but it would not be too bad...

looks like a fun project for some students on your team to machine!

06-05-2010 10:23

Edoc'sil

Re: pic: 6 inch wheel design

It doesn't look like the spokes are flat, but it may just be distortion from the render.

06-05-2010 10:52

548swimmer

Re: pic: 6 inch wheel design

You could still machine them, you'd just need to have the z-axis be computer controlled as well.

06-05-2010 12:20

Edoc'sil

Re: pic: 6 inch wheel design

Not many schools have a 3 axis cnc with all axis computer controlled. maybe he does, but even still the part wouldn't come out like that, there would be a flat spot from where the taper on the spokes trailed off from the machining bit.

06-05-2010 14:32

A_Reed

Re: pic: 6 inch wheel design

1.3 lbs may seem a bit heavy, but with no realistic numbers to run through the ANSYS FEA I have designed it to be overly robust with a 'standard' .25x.25 square cross section for each spoke. Anyone want to help me out on getting some realistic benchmarks for moment loading, side loads and radial loads.

As for the exterior wall, it is only 3/16" thick, the extra material on the sidewalls are only 1/8" thick and are there to add side support for the treads to take some wear off of the rivets.

The machining process on the major spokes would use a Ball-Nose end mill for all of the major cuts. The first cut(s) would be a 1/4" deep pocket that creates the fillets to the outer wall and to the hub, the front face of the spokes would be flat as the material is taken out between the two fillets. The second series of cuts would use the same mill stopping at the backside of the rear spokes creating the same fillets. As the wheel is flipped and the machining process is repeated the square edges of the spokes and the fillets would be defined on the backside of the front spokes.

The smaller triangles and hub weight savings could be done with any end mill that can plunge deep enough to clear out all material left behind by the fillets on the backside of the spokes.

No the hub is planar with the rest of the wheel on both sides currently. I will take that into consideration as a way to avoid adding extra spacers.

Thank you all for the comments and question. Keep 'em coming.

06-05-2010 19:13

Edoc'sil

Re: pic: 6 inch wheel design

Ok, what high school a ball milling bit? If anyone responds yes I will apply to be a super senior at your school. To me it just seems that it would be easier to design it a bit simpler so in could be made easily inhouse.

anyhow my 2 cents

06-05-2010 20:52

A_Reed

Re: pic: 6 inch wheel design

You don't need a high end bit to cut aluminum, with the proper feed speeds and such you could use a 'cheap' bit to do the job

06-05-2010 21:30

Dan Richardson

Re: pic: 6 inch wheel design

I like the wide tread design, the offset spokes give it a nifty appeal.

Many schools do not have a 3 axis cnc mill. Many teams have at least 1 sponsors who has a 3 axis cnc mill.

06-05-2010 22:51

548swimmer

Re: pic: 6 inch wheel design

It may not be the most accurate method, but I just place a fixed constraint on the hole for the shaft and apply 300lbf to the rim.

06-05-2010 23:22

Edoc'sil

Re: pic: 6 inch wheel design

You can mill with that? Impressed, I would have thought it would dull. even still the 3 axis cnc issue remains. If you send it to a sponser to be made, you may as well just buy it.

06-05-2010 23:37

548swimmer

Re: pic: 6 inch wheel design

I have heard (though never tried) that you can mill on a router table with an all carbide bit. I don't see why something like this wouldn't work here. Obviously a router table won't help, but you can still use the bit.

08-05-2010 21:14

DonRotolo

Re: pic: 6 inch wheel design

Ball-end mills are neither expensive nor rare. We have a set.
Yes indeedy, but it's probably more dangerous that I'd be willing to let a kid do. You must use a template for the router to follow, there's little chance of really controlling it freehand. We cut the triangles into the 3/16" aluminum we used in our rookie year for our robot cart (the pattern matched the .090 'armor' on the robot). An experienced parent did that for us. Me, I thought he was crazy, but dang if he didn't do it nice and neat.


As for the wheel, I'd probably turn it on a lathe before I brought it to the mill.

08-05-2010 21:16

548swimmer

Re: pic: 6 inch wheel design

On a router table?

I'd also lathe out as much of the piece as you can initially before milling it out.