Torque Req'd to Start Movement
Torque Req'd to Start Movement
(OP)
My apologies in advance...I may not supply all the necessary info. on the first try. I need to build a material cart (on casters of some 8" to 12" dia.) that will carry a #2,500 load (total weight: cart + load = approx. #3,500). Cart is approx. 4'-0" x 8'-0" x 3'-0" tall. The cart will be manuevered by a human. The environment is hazardous (fumes from process) so the device should be non-sparking, explosion-proof, etc. The idea, so far, is to look into using an air gear-motor to drive the cart. I don't know if this will work as one of the first things I need to know is "How much torque will I need to overcome the "at rest" position, break friction, start to move, whatever the term is". Also, I will probably be interested in horsepower requirements and I don't know that formula either. Is HP simply the value by which the cart remains in motion? My need is probably for slow movement, low rpms i.e., "Granny Gear". So I'm thinking that the important factor is the torque. (?)
Another thought (if the air motor can't produce enough torque) is to have a sort of "power assist" thing where the cart does not move because of the air motor but with a (little) effort by the operator the cart can be manipulated and possibly stopped sooner / easier. So, is there any formulae for calculating "power-assist" forces? I would greatly appreciate any help, ideas or thoughts regarding this. In fact, there may be a better way and if someone has an idea, please let me know! Thank you.
By the way, does anyone know if this is even remotely possible without the need for power? Given the right size wheels, proper bearings, etc., is it possible that a human could move this much weight without unreasonable effort & stress?
Another thought (if the air motor can't produce enough torque) is to have a sort of "power assist" thing where the cart does not move because of the air motor but with a (little) effort by the operator the cart can be manipulated and possibly stopped sooner / easier. So, is there any formulae for calculating "power-assist" forces? I would greatly appreciate any help, ideas or thoughts regarding this. In fact, there may be a better way and if someone has an idea, please let me know! Thank you.
By the way, does anyone know if this is even remotely possible without the need for power? Given the right size wheels, proper bearings, etc., is it possible that a human could move this much weight without unreasonable effort & stress?





RE: Torque Req'd to Start Movement
There will be slopes, irregularities, dirt, other stuff on the rolling surface that will affect this.
Wild guess is that you will need a force of 5-10% of the weight to start motion. Convert this force to torque.
RE: Torque Req'd to Start Movement
RE: Torque Req'd to Start Movement
Also there are many reasons why this would be unlikely to be achieved in practice, including the obvious point that warehouse floors have slight gradients, which might be very exciting.
Cheers
Greg Locock
RE: Torque Req'd to Start Movement
RE: Torque Req'd to Start Movement
RE: Torque Req'd to Start Movement
power required = torque (N-m) x angular speed (in rad/s not rpm)
power will be in watts.746 watts = 1 HP
the formulas are all there, good luck!
RE: Torque Req'd to Start Movement
For a 1.5 ton load this would be about 36 pounds.
In practice you would need more
than that, you'd probably want at least 0.05* the weight of the truck.
Cheers
Greg Locock
RE: Torque Req'd to Start Movement
Use the largest size of wheels possible. Use steel wheels and roller (needle) bearings. Rubber will flaten and require a lot more initial force. On a level floor a "good" man can move 4000 pounds without too much trouble. We do it all the time in our shop, (concrete floor with cracks) but on a heavy load only the steel wheeled carts are used.
Good luck
Ralph
RE: Torque Req'd to Start Movement