# Gearbox torque?

bauboya
gearbox torque?!?

Hi, I don't know much about mechanics and I'm trying to build a mechanism to drive a set of syringes, and I need to buy a gearbox motor to drive the syringe shaft forward and back. the syringe needs to be driven 70mm, and I'm going to attach a rack and gear to the motor to get this motion. however, because of the hydraulics, it actually requires quite a bit of force, and i don't know what gearbox motor will be strong enough to drive it. i didn't know how to measure how much force i need so i put weights on the shaft and it needs 2.5kg to drive forward at a good speed. (it doesn't have to be incredibly fast but i don't want it to be terribly slow either).

could anyone recommend a motor that will be strong enough to drive it at a good pace??
or tell me what information and numbers to look for in the data sheet??

thanks so much!

## Answers and Replies

bauboya

the speed i want to drive it at is 10mm/sec

jags

U need to buy high torque and low rpm motor to drive the shaft

jags

Buy the brushless motor under the specification
Power: 200 Watts
*.RPM/Volt (KV): 1000
*.Continuous Current: 6-15A
*.Burst Current: 19A*

Bob S

A 70 mm stroke at 10 mm/sec sounds straight forward. The required power is
P = F dx/dt = 2.5 Kg x 9.81 m/sec2 x 10 mm/sec x 1 m/1000 mm = 0.25 Newton-meters/sec = 0.25 joules/sec = 0.25 watts
So probably a 1 or 2 watt motor will suffice. A stepping motor turning a lead screw is one approach. 70 mm will be 55 turns on a 1/4-20 pitch screw. You can either count digital motor steps or use limit switches at the ends. 10 mm/sec will be about 8 turns/sec. A direct drive 480 RPM stepper motor on a 1/4-20 lead screw will work. The control electronics will be less if you use a DC gear motor geared down to 480 RPM with limit switches.

Gold Member

I don't know anything about steppers, but I definitely agree with Bob about the lead screws. You just can't beat those suckers for power and smooth movement. I use them for all sorts of stuff. They're incredibly easy to make, as well. Just take some threaded rod (or a bolt for short strokes) with a matching nut, and connect the nut to the thing that you want to move.