Help with motor for pulling uphill

  • #1

Main Question or Discussion Point

Hello all!

I was curious how to figure out which motor to use to help pull a sled up an inclined surface of about 55 degrees. It would be pulled on snow and has a weight of about 300lbs. Would it make a difference if the motor was on the sled vs pulling from the top of the hill? How do you figure out the required power and torque for this? I haven't done physics in forever and would love any help that could be provided.

Thanks
 

Answers and Replies

  • #2
stockzahn
Homework Helper
Gold Member
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I was curious how to figure out which motor to use to help pull a sled up an inclined surface of about 55 degrees. It would be pulled on snow and has a weight of about 300lbs.
Below a schematic with the forces acting on the sled. For pulling it upwards with constant speed, the force ##F= G\,sin\alpha+R## , where

##G = mg## (##m## = mass of sled, ##g## = gravitational acceleration)
##R = N\,\mu=G\,cos\alpha\,\mu## (##\mu## = friction factor)

To find the necessary power ##P## you have to multiply the force with velocity ##v## you want to pull the sled upwards (##P=Fv##). The power also can be expressed as the torque ##T## multiplied with the rotational speed ##\omega## (##P=T\omega##). Depending on the radius ##r## of the wheel you want to use for the rope/wire to pull the sled, you find the relation between the pulling speed and the rotational speed (##v=r\omega##). This should give a good estimation for the necessary power and torque needed for the motor, but of course you have to considerate margins and losses, so the machine to use must be stronger/more powerful.

Would it make a difference if the motor was on the sled vs pulling from the top of the hill? I haven't
Both is possible, I think there are other technical considerations to make like

- is the sled pulled upwards everytime at the same location
- is it possible to attach the motor to the sled and what are the consequences (the sled gets heavier, ergo you need another motor)
- do you want the motor stay outside all the time (otherwise you have to carry it up before you want to use it)
- ...

I haven't done physics in forever and would love any help that could be provided.
That doesn't sound like to be homework, but if it is, please use the template according to the forum rules next time.
 

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  • #3
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Would it make a difference if the motor was on the sled vs pulling from the top of the hill?
You wouldn’t want to put the motor on the sled for two practical reasons: the motor is more weight that needs to be lifted, and it is much easier to get power to a motor in a fixed location. However, the choice doesn’t change the physics in any fundamental way.
 
  • #4
berkeman
Mentor
56,859
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Hello all!

I was curious how to figure out which motor to use to help pull a sled up an inclined surface of about 55 degrees. It would be pulled on snow and has a weight of about 300lbs. Would it make a difference if the motor was on the sled vs pulling from the top of the hill? How do you figure out the required power and torque for this? I haven't done physics in forever and would love any help that could be provided.

Thanks
What's at the top of the hill? What are you planning on using for a power source? Can you just use your Jeep with a winch to pull the sled up the hill?

And as @Cutter Ketch says, adding the weight of the motor and batteries to the sled is kind of counter-productive. :smile:

http://image.fourwheeler.com/f/36638142+w660+h440+q80+re0+cr1+ar0/129_1107_03+winch_anatomy+jeep_winching

129_1107_03%2Bwinch_anatomy%2Bjeep_winching.jpg
 

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