# Choosing right motors for self-balancing robot [closed]

I’m looking for right motors for my first self-balancing robot.

Design assumptions:

• robot height: around 120-200 mm
• robot weight: around 600-800 grams
• wheels: 80x10 mm or 90x10 mm
• battery voltage: not sure yet, but something between 7,2 - 12 V (depending on the motors)

So as I know, I should looking for DC motors with encoders, right? I also thought about stepper motors.

My little calculations:

Required torque = robot height * robot weight * gravity * maximum tilt angle

$$Rt_{min} = 0,12 m * 0,6 kg * 9,81 \frac{m}{s^2} * sin(40^\circ) = 0,454 Nm$$ $$Rt_{max} = 0,20 m * 0,8 kg * 9,81 \frac{m}{s^2} * sin(40^\circ) = 1 Nm$$

So, in best scenario I will need 0,454 Nm and in worst 1 Nm. So, if I have two motors then I can divide this required torque by 2, right?

Can you advise me on the right motors for my project? I’m not sure about motor speed, gear ratio and how much torque do I need to get good balancing without damaging/overloading motors.

Thank you, Adam.

• In my engineering experience, take your predicted needed torque and multiply by a little more than 2 (not divide). That’s about how much you’ll need because when a motor reverses direction, it will need to draw almost twice the current (i.e. torque). – Paul Dec 5 '19 at 22:47
• Welcome to Robotics strusmig, but I'm afraid that shopping questions really aren't a good fit for a stack exchange site. We prefer practical, answerable questions based on actual problems that you face. In general it is better ask How do I solve this problem? than What do I need to buy to solve my problem in this way? as you may preclude answers providing better solutions. Take a look at How to Ask and tour for more information on how stack exchange works. – Mark Booth Dec 6 '19 at 15:03
• @MarkBooth: I don't expect a link to a specific product. I just would like to know if a motor with specs like: - voltage: 12 V - no-load performance: 500 RPM, 300 mA - stall extrapolation: 6 kg⋅cm (85 oz⋅in = 0,6 N⋅m), will be sufficient for my project. – strusmig Dec 6 '19 at 15:30
• On stack exchange, it is better to edit your question to add information requested in comments, rather than adding more comments. Comments are for helping to improve questions and answers, and are distracting, so we try to keep them to a minimum. If all of the information needed to answer the question is contained within it, the comments can be tidied up (deleted). – Mark Booth Dec 6 '19 at 17:34
• In the past I've suggested that people ask how they can determine whether a motor is suitable, rather than ask for suggestions. If you have a look at some of the Related questions, they might give you some ideas. If the Related questions don't help, think about how you can ask a more specific question about your concerns. Why do you think buying a motor of the calculated specs wouldn't work? Do you think there's something wrong with your calculations, if so what do you suspect is wrong? etc. If you edit this question with that more information, we can re-open it for you. – Mark Booth Dec 6 '19 at 17:36