Hello my name is Henry, i am trying to build a robot that can climb stairs. The total weight of the robot is 30 lbs. According to my torque calculation, if the robot has two 12 in arms that push 15 lbs each, the amount of torque for each arm is 180 lb-in. Someone told me that i need to use a step motor since it has a locking mechanism. So i search around and the only step motor that has that kind of torque is too heavy for my design.
Now, my question is there any alternative ways or motor that can solve my problem?
Thank you!
Hi,
A first step would be to try and determine how powerful the motor needs to be. Considering that you need 180 lb-in, depending on how fast you wish to accomplish the motion, you will be looking at something from ~50 Watts to many hundreds of Watts. In other units (for searching motor specs), you’ll need about ~21 n-m, ~215 kg-cm or ~2975 oz-in.
At this range of power, you most likely would be better off with a 24 V DC or higher motor, so as to reduce current (and heating up). Higher voltage motors may be smaller/less heavy. In that range of torque, a typical stepper motor will most likely be 8-9 kg or ~18-20 lbs, which is quite large. Therefore, you may want instead look at geared-down DC motors, such as those found here.
For example, the gearbox RB-Ban-296 supports up-to 85 lb-ft (~1019 lb-in). Combined with the appropriate motor, such as a RB-And-128 with an RPM of 5310 and stall torque of 343 oz-in (~21.4 lb-in), you’d get about 27:1 ratio and therefore roughly ~196 RPM at no load and a stall torque of ~579 lb-in, which should put your use case (180 lb-in) at just about ~31% of stall torque. That being said, such a motor has a stall torque of 130 A and will require a very powerful motor driver.
As a side note, the gearbox and motor mentioned above weight about 2 lbs and 2.83 lbs respectively, for a total combined weight of < 5 lbs per motor assembly, which is probably much better than for typical steppers of similar.
You should also be aware that if you use stepper motors in micro-stepping, you have less torque per step than in a full-step (the rated torque of the motor), so take note of that, too, when choosing your motor.
We hope this information helps!
Sincerely,
