What motor to use.

[Mike Brett]

The robot I am building has a rotatable wrist joint that I had intended to use a stepper motor to drive. This motor I obtained from a CD player but when I tried, it was not up to the job. The hand weighs about five Kilo with a 8mm drive shaft running in ball races.As it only has to turn a quarter and back again a motor and gearbox seems a bit of an overkill.
As you can guess I am new to this so am seeking advice .I have some powerful 90 volt solenoids or do you think I should try a more powerful stepper motor or perhaps a servo.
Cheers Mike

 

[Nigel Goodwin]

Where did you find a stepper motor in a CD player?, I don't think I've ever seen one?.

I would have though an RC servo would be ideal for the job?.

 

[Mike Brett]

my mistake

Hi Nigel
Perhaps it was not from a CD player then, it is not very big as stepper motors go. I brought a stepper driver kit to use with it, could this be used to power a servo, and would a servo have the necessary torque.
Mike

 

[Nigel Goodwin]

Hi Nigel
Perhaps it was not from a CD player then, it is not very big as stepper motors go. I brought a stepper driver kit to use with it, could this be used to power a servo, and would a servo have the necessary torque.
Mike

Stepper motors are only fairly weak, a standard RC servo is a LOT more powerful for the same size, and EXACTLY what's needed for the movement you're looking for, it's made for the job.

 

[Mike Brett]

Hi Nigel
Ok I am convinced, a servo sounds ideal, and Maplins sell one for about a tenner. But is there an easy way to power it, I assume my stepper driver is no good , so does that mean I have to use radio control circuits.
Mike

 

[Nigel Goodwin]

Hi Nigel
Ok I am convinced, a servo sounds ideal, and Maplins sell one for about a tenner. But is there an easy way to power it, I assume my stepper driver is no good , so does that mean I have to use radio control circuits.
Mike

A servo just needs a regular pulse every 20mS or so, the width of the pulse (1-2mS) sets the position of the servo, it's as easy as that.

 

[Mike Brett]

Nigel
I now understand what it takes to drive the servo and have found the circuits I need, we live and learn. Many thanks for your help.
All the best Mike.