Ideas suggestions for low speed cargo crawler

[tyquestions]

Hello All-
Below is a picture of a cargo crawler I've been thinking of. Gross weight would be 2000lbs, moves between 1.5- 3mph, crawls on pavement or concrete. So far I've come up with aluminum tube welded frame with wheel motors at the rear, either motorcycle type or electric forklift type, the latter already built for heavy weight. Based on speed I've come up with aprox. 150-600 ft/lbs of torque needed, (150 for 1.5mph & 600 for 3mph).

Q1-Can i simply divide the ft/lb requirement by 2 to come up with the torque for each motor, 1 on each side in the rear?

Q2 - If a motor is rated at say 100 ft/lbs of torque on the spec. sheet, is that under no load, an industry standard load or what? How much decrease in torque could i expect as load increases? (in this case 2000lbs)

Q3 Anybody have any thoughts suggetions on either frame design, frame material, drive system?

The power system envisioned is DC with onboard battery. The crawler needs to run for 120 minutes continuously at a constant rate of speed somewhere between the 1.5-3mph.

Interested in any input.

Thanks
Tyler

 

[minger]

I'm interested to know where you came up with your numbers from; would you care to share them?

Q1-Can i simply divide the ft/lb requirement by 2 to come up with the torque for each motor, 1 on each side in the rear?

I don't see why not.

Q2 - If a motor is rated at say 100 ft/lbs of torque on the spec. sheet, is that under no load, an industry standard load or what? How much decrease in torque could i expect as load increases? (in this case 2000lbs)

That is how much torque it can put out, it is independent of the resistance it's trying to turn against. Torque is analagous to force in:
T = I \omega Where T is your net torque, I is the mass moment of inertia, and \omega is the angular acceleration.

So, you can accelerate an extremely large mass with a very small force (or in this case torque). The problem is that as you accelerate, other forces such as friction begin to increase, which puts your equation out of balance.

For your case, you're going to need to look at rolling contact. I believe we just had a thread a month or so ago regarding the same thing.

 

[Danger]

For something with such low speed and high torque requirements, I'd be inclined to go with hydraulic motors. It might be a bit too expensive, though.

 

[tyquestions]

I got the numbers from an energy calculator i found at www.1728.com/energy.htm . I can only assume it is an accurate calculator. used 2000lbs for the weight and 1.5mph for the low baseline and got 150ftlbs, and 3mph for the highend which gave me 600 ftlbs. Ijust went back to the website and reinput the figures and got the same answers, but now that i think about it, a FORD f450 has xxxhundreds of ftlbs of capacity (300, 700 I don't know but its something like that) and that thing can pull 24,000 lbs at 70 mph! Maybe that calculator is wrong?

Re: hydraulics - That was actually the first incarnation of the project, but I was overwhelmed with fluid flow, tank size, pump size in relation to how much fluid flow i would need and just absolutely could not even begin to get a handle on it. When i found wheel motors it seemed like a much simpler and straightforward setup. If you have any thoughts on the hydraulics I'm still open to it, I just could not get a handle on the whole amount of flow through the hydraulic motor thing.

I'll check the rolling contact resistance thread and see what i can pick up

Thanks
tyler