1/2" diameter aluminum rod for short axles ?

I was thinking about using some 1/2" diameter aluminum rod for short axles for some robot drive units. Axle length no more than 4" or so. Bots would
weight from 15 to 35lbs. Was thinking about having a wheel on one end, through a pillow block or something similar, and a pulley or gear on the other end. Was thinking of using the alumnium rod because I can get it cheap, easily cut, etc.
But I wonder if it would be sufficient or deform under the load. Of course the best way is to build it and see how it works, but I would welcome any input before I get to that point.
Any opinions ? JCD
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pogo wrote:

1/2" aluminum rod isn't a good axle material for a 35 pound load. Mild steel should work fine, and you can work it with hacksaw, file, and drill. Just oil your cutting tools, use drill bits rated for mild steel if you need a hole, and don't let drills get hot.
Avoid tool steel or hardened steel rod; you'll struggle forever to cut the stuff.
Paint mild steel; it rusts easily.
                John Nagle                 Animats
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Thanks for the info ! JCD
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What is animats ? I went to the web site of that name (.com). Is that you ? Always curious to see what peoples' *real* jobs are ! JCD
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pogo wrote:

Yes.
I was also the team leader of Team Overbot in the DARPA Grand Challenge. We lost.
                John Nagle
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you ?

Challenge.
COOL!
What do you think of 1/4" mild steel axles for 35lb bot ? Too little ? Barely acceptable ? ( Last question on this topic - I promise! ) Thanks!
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Now you're getting close enough to marginal that the alloy and bearings matter. 3/4" is certain to work. 1/4", you need to build up a test rig and load it up.
Sawing through 3/4" mild steel rod isn't that hard. You need a vise, a hacksaw, and a pump can of cutting oil.
                John Nagle
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John Nagle wrote:

Why do you want to use the smaller diameter? If weight is the issue, then consider using a hollow tube rather than a solid rod. A tube resists bending better than a solid rod for the same weight/length.
I use a 3/8" stainless steel tube with 1/16" walls for the axle of a 20 lb robot, and it works fine. Stainless steel is harder to work with than mild steel, but it is stronger and it doesn't rust, so you don't have to paint it.

You can cut stainless steel with a hacksaw but it is hard work. Much better to use a lathe with a cutoff bar.
When building a robot, I use four materials for 99.9% of it:
1. Stainless steel for axles, joints, pivots, etc. Also for nuts, bolts, and screws. I have learned never to use cheap zinc coated screws, they don't stand up to the constant assembly and disassembly of a prototype robot.
2. Aluminum for the main structure.
3. Acetal (Delrin(tm)) plastic for precision parts that don't have to withstand too much load. Very easy to machine. Comes in white or black. I only use the black because it looks cool.
4. Acrylic for panels. Easy to cut and drill. The edges can be polished with a propane torch. I use only clear acrylic, because I like to be able to see inside for loose wires or whatever, and I like the way it looks.
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*Partly* just trying to reduce the complexity of having different size pulleys, wheels, etc. for this and that.
*Mostly* just getting a feel for what works and what doesn't --- from the pros on here !

I hadn't thought of that - good point!

All VERY good tips! They're going in my notebook! Thanks !
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Good info as always - thanks !
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