# How much torque can I get from a motor salvaged from a linear actuator?

#### hunted22

Joined Aug 7, 2014
3
Hello all..

I'm designing a project and I want to implement a higher torque motor. to be connected to a pulley system, to slowly pull and release a rope.

I don't have a lot of equipments in my area, but there is this 36v 24" linear actuator usually used to adjust the direction of satellite dishes. Not a lot of data about the motor, although the dish the actuator pushes is heavy.

Here is where I need someone with mechanical engineering background... assuming that the actuator can lift and release 20lb when it contracts and extend. If I remove the arm and shaft, and install a wheel in its place, so that instead of the motor assembly rotates the actuator shaft, it rotates the wheel for the pulley. Will I can still lift the same weight? if I'm going to lose power, How much % will I lose? (try to ignore gravity force).

I know that it's hard to answer without enough info on the actuator and its motor, but I just need an in-theory answer.

Also, if anyone have an idea on how much torque do motors of DC linear actuator in this range have, please share.

#### MikeML

Joined Oct 2, 2009
5,444
You need a winch.

The push-pull force of a linear actuator like you describe comes from a "lead-screw" which converts rotations of the motor shaft to linear travel. It is sort of like the scissor jack that comes with a car, you turn the shaft, and the treads on the shaft move the arms of the jack to lift the car.

If you remove the "lead screw", the motor shaft rotation will be much too fast (too little torque) to use it directly as a winch.

#### hunted22

Joined Aug 7, 2014
3

I thought that in servo/gear motors, the torque and RPM supposed to be controlled depends on the voltage, regardless of load.

#### alfacliff

Joined Dec 13, 2013
2,458
the torque and speed of lineaar actuators is determined by the gear ratios the lead screw is concidered a gear.

#### inwo

Joined Nov 7, 2013
2,419
Cheap imported ones = ~500lb lift and considered small. Saginaw ball screw lifts 2000 lb. VonWeiss 1200 lb.

One turn of acme screw lifts about 1/8" I suppose.
The main reduction is in the gearbox.

So with a 3"C pulley 1 turn will lift 3" about 24 X less torque.

500/24 = 21lb.

Plus a little gain in efficiency over acme friction.

My 1/8" lift is a guess. Check yours.

#### inwo

Joined Nov 7, 2013
2,419
I just checked a cheap broom stick actuator.

10 turns move it 1 1/4" which is 10--1/8 inch steps.

Or 1/8" per turn.

Lucky guess!

#### hunted22

Joined Aug 7, 2014
3
Any (lucky) guess on the RPM

#### inwo

Joined Nov 7, 2013
2,419
At 36 volts 45sec. / foot unloaded.

Which is ~96 turns.

~120 rpms

#### Brownout

Joined Jan 10, 2012
2,390
You need a winch.
This is a good suggestion. I've thought about this too, if I ever needed some oomph for a project. Super-cheap Chinese winches are available in the US. They come with sun gears for speed reduction and good power transfer. Course, this might be overkill for lifting 20 lbs.

Another cheap option is a boat trailer winch. The gears and spindle are built-in, and all you need to do is add a motor. Price can be as low as 15 bucks.