This tutorial is intended to complement RobotShop’s Drive Motor Sizing Tool by providing you with a step by step explanation as to the calculations behind the dynamic tool. In the image below, half a mobile robot is shown. Although in this scenario only two out of the four wheels…

@Cameron It’s really up to you - it’s part of the equation so it needs to be considered. Looking into the moment of inertia may be a bit much (but certainly not out of the question if you want to be precise). Just think of the distance you want it to cover in order to reach a cer…

Yeah that’s what I have done. Looked into inertia calculations but can get a bit nightmare trying to find CG of individual components and such like. Glad you’re still around though, noticed this was originally posted in 2012!

Why do we multiply by100/efficiency. What efficiency are we talking about. The torque produced by motor . I am having some problems understanding this part, can u please explain?

@crawler The efficiency is the overall efficiency of the system, most notably the batteries -> motor controller -> DC motors -> Gearbox. If you have data as to the efficiency of each section, multiply them all to get a total efficiency. If not, you will need to estimate the value…

Should add dynamics so that Torque T = T = fR + Inertiaa/r^2 instead of T = f*R, which is only for statics ?

is that the inertia of wheel since it is the only rotational part?

If in case a robot needs to ‘pull’ a weight of 2000Kgs. Is that similar to ‘carrying’ a weight of 2000Kgs when it comes to calculating motor’s power. If that is correct, can I simply substitute 2000Kgs in place for mass in your calculations ??

@Harshesh Gokani Yes and no; if the load is being dragged as opposed to rolling (i.e minimal friction), there will be significant resistance which needs to be factored into the equation. You also need to take into account the fact that the robot itself will need to weight enough …

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cbenson June 16, 2015, 10:34am 11

@kelvin If you know the inertia of the system (not easy to do especially if you’re still in the process of choosing the parts), then you can certainly refine the equations.