# Recommendation for bidirectional brushless DC motor torque on the cheap

#### kerege

Nov 24, 2018
1
I'm working on a DIY camera gimbal project, and I came across the issue of finding adequate brushless DC motor that:

• Has enough starting and holding torque to lift and stably hold a 5kg mass when using a 60cm-length pulley
• Is fast enough to move that mass 1.25m/s
• Preferably costs under £25 (\$32), since I have to get a lot of them for the project!
• Can be powered by an external power pack, and controlled through Arduino/RPi

I've looked all over the internet on Amazon, Ebay, AliExpress, RS Components and more, but all I've found are things that have 5 times the specs I need, for 5 times the price, or things at £12 a piece but with half the specs. If there's some place I've missed, I'd really appreciate it if someone could help.

If you have any ideas relating to doing this with multiple uni-directional motors instead, I'd be happy to hear those. See below for my current design idea, but if you have a better proposal, please do let me know.

Thanks!

#### Alec_t

Jul 7, 2015
3,241
Welcome to EP!
'On the cheap' implies a small motor. If you put a counter-balance on the opposite side of the mechanism then a small motor would have zero static weight to move if the belt is running vertically. However, the inertial mass would be double, so rapid acceleration would be out of the question.
Whatever motor you use, the torque needed would depend on the acceleration required for the camera movement

#### duke37

Jan 9, 2011
5,364
To lift 5kg (not KG) you need a force of 5G that is 5 * 9.81 = 50N roughly.
The torque will be 50 * pulley radius.
The power will be force * speed = 50 * 1.25 = 625W. This will be quite a beefy motor.

#### duke37

Jan 9, 2011
5,364
Accereration This is mass * rate of change of velocity.
If accelerate in 1sec
Acc = 1.25 m/s/s
Force is mass * acc = 5 * 1.25 = 6.25N
This is much less than the lifting force. If however you accelerate in 0.1sec then the forces are comparable.

Replies
2
Views
195
Replies
4
Views
641
Replies
3
Views
697
Replies
2
Views
2K
Replies
2
Views
747