Determining necessary motor power to move a cart along tracks.
Determining necessary motor power to move a cart along tracks.
(OP)
I'm looking into developing the drivetrain for a cart which will be battery powered and travel at low speeds (around 0.33 m/s) along metal guide rails using v-groove wheels and weighing in around 4,000 kg. I'm trying to determine the necessary electric motor size to power the cart but my calcs just seem low. Am I missing something?
It looks like to accelerate at 0.1m/s^2 requires 12Nm of torque using a 60mm diameter wheel. (F=ma for a force of 400N times the 0.03m radius) This appears to work out to 3 hp when using an 1800 rpm electric motor. The rolling resistance appears to be 196N using a rolling resistance coefficient of 0.005. That works out to 0.09 hp using the 0.33 m/s. Summing that up comes to 3.1 hp, which even with a transmission efficiency of 80% is still only 4hp. Can I really get away with a 4 hp motor? I realize I will add on an additional fudge factor but it still seems low.
It looks like to accelerate at 0.1m/s^2 requires 12Nm of torque using a 60mm diameter wheel. (F=ma for a force of 400N times the 0.03m radius) This appears to work out to 3 hp when using an 1800 rpm electric motor. The rolling resistance appears to be 196N using a rolling resistance coefficient of 0.005. That works out to 0.09 hp using the 0.33 m/s. Summing that up comes to 3.1 hp, which even with a transmission efficiency of 80% is still only 4hp. Can I really get away with a 4 hp motor? I realize I will add on an additional fudge factor but it still seems low.





RE: Determining necessary motor power to move a cart along tracks.
For example:http:
Ted
RE: Determining necessary motor power to move a cart along tracks.
I am getting your numbers. It will take 3HP to get your cart up a 10° grade. You might want to work out the power needed to get your cart over a rock or a bolt sitting on your tracks. Your cart is moving very slow.
I visited a marine museum where they had a propeller on display. It was from a fishing boat. The propeller was about my size, around six feet. The boat's motor was capable of around 17HP. My uncle had a 200HP motor boat with a propeller I recall as being around 10" diameter, so I was a little shocked. I worked it out, and it turns out that at a believable fishing boat speed of 10mph, you have over 600lb thrust.
RE: Determining necessary motor power to move a cart along tracks.
Mike Halloran
Pembroke Pines, FL, USA
RE: Determining necessary motor power to move a cart along tracks.
RE: Determining necessary motor power to move a cart along tracks.
I'm no fan of metal/metal friction drive, either. If you can guarantee a dry rail, maybe it will work.
Mike Halloran
Pembroke Pines, FL, USA
RE: Determining necessary motor power to move a cart along tracks.
Ted
RE: Determining necessary motor power to move a cart along tracks.
1. acceleration time to achieve steady state speed
2. did you account for all of your rotational masses in the acceleration & torque calculation?
It really doesn't require much torque to keep a moving mass in motion. You must supply the peak torque to get it moving though. Peak torque is a function of translational mass, rotational mass, friction torque, efficiency loss, and on and on and on. Then the faster you want to get it moving, the higher the power required to do so.
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: Determining necessary motor power to move a cart along tracks.
What's wrapped up in the "rolling resistance coefficient"?
Do you have bearing resistance in the mix?
I agree with others that 60 mm diameter is too small. In fact, why use V-groove wheels? Something like http:
RE: Determining necessary motor power to move a cart along tracks.
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