Torque / HP to move a disc with 20,000 lbs on it

  • Level: Undergrad 
  • Thread starter Thread starter josh0916
  • Start date Start date
  • Tags Tags
    Disc Torque
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
Sign up Log in
2 replies · 1K views
josh0916
Messages
1
Reaction score
0
I am trying to spec out a motor to move a disc on a bearing, the disc has a mass on it weighing 20,000lbs. The diameter of the disc is 3.33ft. Angular acceleration of 0.1047 rad/s^2 to 3RPM. I am assuming coefficient of friction of 0.5.

1. Can I use the assumption that the mass on the disc doesn't matter much for my calculation and use that weight (20,000lbs) for my I=(1/2)*m*r^2?
2. Is the 0.5 coefficient pretty conservative in general for a disc on a bearing?

If so, I am getting I=55778
T=I*a*(coefficient of friction) = 2920
HP = 1.668

This sound about right? Thanks for any help.
 
Physics news on Phys.org

Discussion

josh0916 said:
I am trying to spec out a motor to move a disc on a bearing, the disc has a mass on it weighing 20,000lbs. The diameter of the disc is 3.33ft. Angular acceleration of 0.1047 rad/s^2 to 3RPM. I am assuming coefficient of friction of 0.5.

1. Can I use the assumption that the mass on the disc doesn't matter much for my calculation and use that weight (20,000lbs) for my I=(1/2)*m*r^2?
2. Is the 0.5 coefficient pretty conservative in general for a disc on a bearing?

If so, I am getting I=55778
T=I*a*(coefficient of friction) = 2920
HP = 1.668

This sound about right? Thanks for any help.
You don't use units, so it's hard to tell what you have calculated.

The equation for the mass moment of inertia, I = mr2 is probably OK for calculating the MMOI of the disk, but you haven't described the shape or distribution of the 20,000-lb weight on the disk, so who knows what to use for the MMOI.

Another problem is, in the MMOI formula, m stands for the mass of the object, not its weight, which is W = mg, where g is the acceleration due to gravity, or g = 32.2 ft/s2. Physics is pretty picky about these things.

Where did you obtain a coefficient of friction of 0.5? What kind of friction? To me, this seems a bit high, especially if a bearing is involved.
 
  • Like
Likes   Reactions: Subhash
josh0916 said:
1. Can I use the assumption that the mass on the disc doesn't matter much for my calculation and use that weight (20,000lbs) for my I=(1/2)*m*r^2?

The mass of the disc might not matter if it's small in relation to the load.

What Steamking said... The shape of the load might matter a lot.