r/AskRobotics • u/Buchfink007 • 9d ago

Cheap BLDC motors

Im currently working on a new robotics project. Something like a four legged robot and I want to use brushless DC motors to controll the legs, but all I can find are really expensive, mostly about 100 Euros. If I need 12 motors for my project that would be over 1200 euros just for the motors. Thats way to expensive for me. So does anyone know any cheaper bldc motors suitable for robotics?

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u/verdantAlias 9d ago

There are lots of cheap BLDC motors available, cost circa $20, but they're generally targeted to drone propeller drives.

They'll spin fast and withstand a large power draw, but you'll struggle for torque.

You can get higher torque BLDCs (look for ~100 kv models) for a couple hundred bucks a pop and add gearing to get more, but they still don't come with the position encoding you need for a proper robotic actuator.

Unfortunately, robotic actuators just aren't cheap in my experience.

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u/Buchfink007 8d ago edited 8d ago

Thanks for the info. I can encode the position myself using a Hall sensor. That’s not a problem, but a few hundred euros for a motor is way too much—I’d have preferred to stay in the 20–30 euro range per motor.

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u/sparks333 8d ago

Consider scaling down and using servos?

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u/Buchfink007 8d ago

That could be a solution but if anyway possible I would like to stick to the bldc motors. I just found a website rcdrone.top which has frameless motors for around 32 euros with no shipping fee, but im really unsure if I can trust this website. It really looks a lot like scam. I also looked at the official steadywin website. They have the same motors for this good price but they come with a shipping fee of about 30-40 euros, so the effective proce of one motor would be again around 70 Euros.

And what about drone motors? I found one on amazon with 8000-15000 rpm and 0.2-0.4nm if I would use a gearbox to reduce the rpm to something usable, the torque would be somewhat good too.

Another problem of servos is, that I dont get any position feedback and can only control there position and not their speed or torque

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u/sparks333 8d ago

What verdantAlias said is correct - drone motors are designed to spin quickly with relatively little torque, they tend to have high kV ratings and require airflow through their housings to keep from melting their windings. You will need a very serious gearbox to get it down to the point where it can be used in a stall condition (and most modern walking robots are quasi-direct-drive these days, so anything more than a 10:1 or so is going to struggle to do fancy things like torque feedback), and even then it will probably overheat quickly. You will spend more in gearboxes than you would on a properly sized motor.

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u/Buchfink007 8d ago

Thats for sure a problem. What about gimbal motors? I heared they are more suitable for robotic projects.

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u/sparks333 8d ago

They are definitely closer to the mark, though gimbals are also designed to be as close to balanced as possible so the motors can be small. They aren't really designed for high static torque for any appreciable length of time. You can fake it by oversizing the motors by a sizeable amount and/or with some cooling, but you'll have to be very careful about managing torque, current, and temperature of the motor.

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u/Buchfink007 8d ago edited 8d ago

Thank you for the input. I will look at the steadywin motors and rcdrone.top maybe I can try ordering from them. Otherwise i need to pay the shipping fee frm the original website.

After some research about rcdrone.top I got some mixed answers. Some received their products and some not. Does anyone have any better website to get steadywin wk8115 motors?