Let's Make Robots!

Servomotor torque requirement for a quadruped robot


I'm planning to build a quadruped robot soon. My design is very similar to the design in the following link.


I'm not that good at mechanics. I like to calulate the torque required for each motor. Is it ok to use the formulas/procedure in the following link to design a quadruped shown in the above link?


In the above link, it says that the torque equation obtained cannot be used for making the bot move. How do I have to modify the equation?

Reply soon.

Thanks in advance.

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@ lumi and Bajdi thanks.. :)


I think my robot won't weigh 1Kg. It is going to carry Arduino UNO, servo controller and LiPO battery, which will all together weigh round 200gm. If the servo motors weigh 45gm each, then at some point of time, 2 legs will be on air, therefore the robot will weigh (200gm + 270gm = 470gm). If I use acrylic sheet for the base and Aluminium sheets for feet, then the total weight might add up to 600gm.

So which of the following servomotor do you suggest?

HiTec HS 311?

Well, it always depends what the purpose of the robot is. My Chopstick Junior is running with very cheap (i mean really cheapy) mini servos. It was only used for running on a display, exhibition or fair, got touched by children, bended, pulled and squeezed but the servos are still working. I agree, I got to change 3 of them since the plastic gear broke but that's all. They have enough torque to pull the thing forward, no question about that. For more joy and a longer life I also recommend metal gear servos.

Thanks for the reply!

I think my bot will weigh around 1Kg. It is gonna have a microcontroller, servocontroller and batteries. I want my robot to walk on smooth surfaces and in slopes of inclination 20 degrees. Robot's legs will be approx 12cm.


I looked at servo's which gives a torque about 10Kg-cm. They seem to be cost around $30. 12 of them will cost around $360! I can't spend that much on servos.