# Variable speed motor control

I have a project where I’m having difficulty finding a suitable electric drive motor for it. I need a motor that will run for 2 seconds every 6 seconds. I had in mind a geared motor but it doesn’t produce enough torque. I’m thinking a variable speed motor with enough gearing to provide the torque. If I run the variable speed at full speed and just use a simple on off function to control it. Do I still need the speed controller for it or is there a way to make it run at full speed safely with only a relay to control off and on.

Ripcrow:
I have a project where I’m having difficulty finding a suitable electric drive motor for it. I need a motor that will run for 2 seconds every 6 seconds. I had in mind a geared motor but it doesn’t produce enough torque. I’m thinking a variable speed motor with enough gearing to provide the torque. If I run the variable speed at full speed and just use a simple on off function to control it. Do I still need the speed controller for it or is there a way to make it run at full speed safely with only a relay to control off and on.

I am guessing you are looking for a DC motor. A DC motor will ONLY run at full speed with NO LOAD! Is this what you want? Seems a little strange parameter.

Paul

Finding a dc motor (12 volt ) with enough torque is difficult. I need 280 nm

A Diesel engine starter motor? :o
What kind of RPM?

It has to move a 20 kilo weight up and down in 2 seconds. Distance is 20 centimetres so it could be one revolution If needed

Ripcrow:
It has to move a 20 kilo weight up and down in 2 seconds. Distance is 20 centimetres so it could be one revolution If needed

A dribble of info at a time. NOW, tell us how often this must be done!

Paul

Ripcrow:
I need 280 nm

Really? Do you really want to lift your 20Kg load (approx 200N) 1.4m far from the pivot point? Or with a 2.8m pulley? (i assume that 280 are NEWTON-meters, Nm, and not nano-meters, nm)

Ripcrow:
Distance is 20 centimetres

So, you have to lift 20Kg, 20cm high, in 2seconds, every 6 seconds.

To lift 20Kg by 0,2m you only need 40J. If you have 2s to do that you need 20W. Double that because of reality, 40W motor.

Can you use a designed pulley and a rope?
If yes: ok, let's proceed with the discussion.
If no: for the god's sake please invest 2 min to make a draw/diagram of what you REALLY want to do, so we can have a chance to reply properly.

Oscillating a 20kg mass horizontally +/- 0.1m at a rate of 0.5Hz requires +/-6N, lifting it requires 200N,
so gravity dominates.

With a leadscrew with a pitch of 10mm it would take 0.32Nm to exert 200N linearly, assuming no loss.
Torque = force * pitch / (2 pi)

The physics gurus calculated it out at 280 Newton’s to achieve an acceleration of .2 m/s/s of a 20 kg weight. The weight has to drop 20 centimetres in 1 second and lift that weight again 20 centimetres in 1 second wait till triggered again and do it again. I need this done every 6 seconds.

I’d guess finding out what the project is might have an impact (!) here

Ripcrow:
The physics gurus calculated it out at 280 Newton’s to achieve an acceleration of .2 m/s/s of a 20 kg weight.

This is miscalculated or the problem is badly explained: with 280N you accelerate 20Kg at 14m/s/s, not 0.2.
Even if you consider 10m/s/s "lost" due to gravity we still have 4m/s/s Vs 0.2m/s/s.
The latter seems to be the most likely option, because everyone here is guessing different conditions.

Ripcrow:
The weight has to drop 20 centimetres in 1 second and lift that weight again 20 centimetres in 1 second wait till triggered again and do it again. I need this done every 6 seconds.

Do you need to have some velocity profile or the weight can just hit some endstops?

With a triangle speed profile (constant acceleration), cover 0.2m in 1s means a peak speed of 0.4m/s with an acceleration of 0.8m/s/s. In this case a whopping 16N are enough. Considering gravity is nothing more than add 200N to the bill. Can you use counterweights?

If you don't care of other stuff than to have 280N of vertical force because the guru said that, why not use an air piston?

daysleeper:
Can you use a designed pulley and a rope?