High Torque Gearboxes

[Knufire]

Originally Posted by Ginger Power

Is anybody aware of a gearbox with a ratio on the order of 70:1 that is compatible with 2 cim motors and has a hex output shaft? I can't seem to find something that fits all three characteristics anywhere.

If you're good with one CIM per side with per what Aren said, Andymark has the 3-stage Toughbox (am-0977) that gets up to 51:1. The output shaft also has a long hex replacement (am-0801).

[GeeTwo]

Originally Posted by Ginger Power

Is anybody aware of a gearbox with a ratio on the order of 70:1 that is compatible with 2 cim motors and has a hex output shaft? I can't seem to find something that fits all three characteristics anywhere.

OK, a CIM has a stall torque of 343.4 in-oz. Using two and a 70:1 reduction means that you anticipate a stall torque around 48,100 in-oz, or 250+ ft-lb. On the AndyMark PG gearbox pages, they note that 39 ft-lb will shear a (round keyed) 10mm steel shaft. A bit of hind-brain physics tells me that the shear torque of a shaft is proportional to the cube of its diameter (someone please correct me if this is wrong! -- verified by equation 2b of engineering toolbox website). Assuming the same shaft material, the diameter would have to be about 18.6 mm, or essentially 3/4" diameter. I've never heard of anything with a 3/4" hex shaft. I'm not aware of anything that's "FIRST standard" with a 3/4" shaft, keyed or hex. If you need this sort of torque and power from an electric drive, my best guess for sourcing affordable motors and gears would be from the golf cart industry.

[marshall]

Originally Posted by GeeTwo

OK, a CIM has a stall torque of 343.4 in-oz. Using two and a 70:1 reduction means that you anticipate a stall torque around 48,100 in-oz, or 250+ ft-lb. On the AndyMark PG gearbox pages, they note that 39 ft-lb will shear a (round keyed) 10mm steel shaft. A bit of hind-brain physics tells me that the shear torque of a shaft is proportional to the cube of its diameter (someone please correct me if this is wrong! -- verified by equation 2b of engineering toolbox website). Assuming the same shaft material, the diameter would have to be about 18.6 mm, or essentially 3/4" diameter. I've never heard of anything with a 3/4" hex shaft. I'm not aware of anything that's "FIRST standard" with a 3/4" shaft, keyed or hex. If you need this sort of torque and power from an electric drive, my best guess for sourcing affordable motors and gears would be from the golf cart industry.

I haven't hit the search yet but does anyone know of any teams that have used golf cart gearbox parts in the past? I'm genuinely curious about what else is out there. The fact is that 900 does derpy stuff from time to time and I think the AndyMark folks might appreciate it if we quit ruining their pretty gearboxes.

EDIT: Anyone looked at RC Cart gearboxes? Any of those worthwhile?

[Michael Hill]

Originally Posted by marshall

I haven't hit the search yet but does anyone know of any teams that have used golf cart gearbox parts in the past? I'm genuinely curious about what else is out there. The fact is that 900 does derpy stuff from time to time and I think the AndyMark folks might appreciate it if we quit ruining their pretty gearboxes.

EDIT: Anyone looked at RC Cart gearboxes? Any of those worthwhile?

As long as you keep buying them, I don't think AndyMark minds.

[marshall]

Originally Posted by Michael Hill

As long as you keep buying them, I don't think AndyMark minds.

At one point they started referring to Austin and I as "loyal customers". ;-)

Once school starts back we have a bag of busted parts and some analysis to be done to them that should result in a white paper about how NOT to build a giant arm. We're learning how to fail magnificently though.

[Ginger Power]

Originally Posted by Ginger Power

Is anybody aware of a gearbox with a ratio on the order of 70:1 that is compatible with 2 cim motors and has a hex output shaft? I can't seem to find something that fits all three characteristics anywhere.

Everybody should be allowed one stupid post per month...

[Monochron]

Originally Posted by Ginger Power

Is anybody aware of a gearbox with a ratio on the order of 70:1 that is compatible with 2 cim motors and has a hex output shaft? I can't seem to find something that fits all three characteristics anywhere.

I believe the BaneBots P80's used to be able to give the kind of reduction and motor input that you want, but sadly the dual input has been discontinued.
http://www.chiefdelphi.com/media/papers/2990

Edit: Doh, I don't think they offer a hex shaft regardless.