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I am building an rc car from zero and i got stuck into a little problem.My dc motor torque is 20g/cm and using gears I have achieved a ratio of 125:1 so that means i now have 20*125 = 250g/cm. My question is if i attach this geared motor to an axle that is connected to 2 wheels of 6.5cm radius each through a gear how much weight can i pull? I know that is i would've had only one 6.5cm radius wheel attached directly to the geared motor I could've pulled 250/6.5 = 40g. If i have 2 wheels attached to an axle that is spined by the gear motor I could pull 20g?

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closed as off-topic by Bob D, John Rennie, Jon Custer, Kyle Kanos, ZeroTheHero Aug 8 at 13:44

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  • $\begingroup$ if the torque will pull 40g with one wheel, it will still pull the same 40g (minus negligible amount of extra wheel weight, extra bearing friction etc.) with two wheels, it will just have better traction. $\endgroup$ – Adrian Howard Aug 3 at 20:45
  • $\begingroup$ @AdrianHoward thanks for your response! $\endgroup$ – DanVde Aug 3 at 21:25
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Your basic understanding of torque is correct: any wheel or system of wheels attached to your axle will have a combined torque of 250 g/cm. However, putting more wheels on the axle (as opposed to a single wheel) doesn't truly increase the amount of load that your vehicle can pull.

Adding additional wheels of equal size to an axle may be a better design for practical reasons such as traction and balance, but adding more wheels to an axle doesn't multiple force or torque.

As a related and rough analogy, imagine that I have two dining room tables. One has a single pedestal in the center to keep it up and the other table has the traditional four-leg design, and imagine that the tables are identical otherwise. Next, imagine that I place a 25 lbs brick on each table. The four-legged table doesn't exert a 100 lbs force on the floor as a result of the four legs. The four legs may distribute the additional weight over a larger area, and the four leg design might be less prone to failure since there are four legs to share the additional weight of the brick. But the overall additional force on the floor of each table (due to the brick) is still 25 lbs.

This response may not address every aspect of your question. I invite others to clarify.

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  • $\begingroup$ I am sure that 2 wheels won't double my torque. I want to know if those 2 wheels would divide my torque $\endgroup$ – DanVde Aug 3 at 20:50
  • $\begingroup$ Point taken. I suppose I should say that two wheels, as opposed to one, will have no overall effect on the amount of load that your car can pull, assuming perfect traction and balance. $\endgroup$ – the_photon Aug 3 at 20:56
  • $\begingroup$ thanks a lot sir! $\endgroup$ – DanVde Aug 3 at 21:25

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