# Are these Solidworks Motion simulation results wrong? How can I go about verifying them?

Question asked by R. A. on Aug 19, 2018
Latest reply on Aug 22, 2018 by R. A.

I created a planetary gear set in Solidworks, and am trying to find the output torque when there are two input torques. To the best of my knowledge, all three torques should add up to zero, but this is not the case in my motion studies. Are the results from the other studies incorrect, or is my assumption that the torques must sum to zero incorrect? If my assumption is incorrect, how can I verify the Motion results using math (preferably algebra, as I have not learned calculus yet).

Also, should I be using action/reaction torques, or are action only torques sufficient for my purposes?

If opening the files is a hassle, here is the data I am referring to:

Simulation results (all applied torques are action only):

• When a torque of -5 lbfin was applied to the sun and -10 lbfin was applied to the planet carrier, the simulation calculated the torque of the ring as +4.23 lbfin.
• When a torque of -25 lbfin was applied to the ring and -1 lbfin was applied to the planet carrier, the simulation calculated the torque of the sun as -2.53 lbfin.
• When a torque of -1 lbfin was applied to the sun and -2 lbfin was applied to the ring, the simulation calculated the torque of the planet carrier as +3.01 lbfin. Is this result close enough to be considered correct since the torques sum to +0.01 lbfin, which is very close to zero? Is it likely that this small difference between the actual and intended result is because of inaccuracies with the solver, or is this also an incorrect result?

Gear Ratios:

• Sun ÷ Planet Carrier: +.32
• Ring ÷ Sun: -2.14
• Planet Carrier ÷ Ring: +1.47

Gear Teeth:

• Sun: 56
• Planets: 32
• Ring: 120

Please ignore any interferences between gears in the attached files unless they have an effect on this issue.

Thanks