Help with selecting small DC motors needed!

Thread Starter

Nick Fortune

Joined Feb 9, 2016
4
I am making a spinner for a board game. I bought a small 1.5-3 VDC motor from Radio shack, but found out in doesn't glide to a stop. instead, it has a stopping spot every 10-15 degrees or so (maybe do to the magnets?). the spinner is only 2.5" wide and i need it to be more accurate as some of the slices on the spinner. i looked at the differences of other motors (ie. brush, brush-less, step, etc.), but have no idea on what will do the job i need it to do. i only expect to have voltage applied for about .5-1 second. any help would be greatly appreciated!20160209_154635.jpg
 

Johann

Joined Nov 27, 2006
190
What you need is an ac induction motor such as found in the small pump of a washing machine. Or perhaps an old fan motor? Be careful it operates at mains voltage. What you encounter is the cogging effect of the permanent magnets in the motor you bought.
 

MaxHeadRoom

Joined Jul 18, 2013
20,889
You could use a higher pole count motor, but a simpler solution may be dynamic braking, as soon as you remove power from the motor, short out the armature wires, by relay etc assuming a DC motor.
This has an instant braking effect.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
20,889
I think this is the problem. It is required to coast to a standstill. A fan motor (ac) will do this.
It sounds to me as though it is gliding past the stopping point, which braking should solve.
How is a fan motor going to stop instantly??
Max.
 

Johann

Joined Nov 27, 2006
190
You could use your existing motor if you add a flywheel of some kind to give it more inertia when power is removed.
 

Thread Starter

Nick Fortune

Joined Feb 9, 2016
4
so, if i want to use an AC motor, would i need to use a transformer or do most come with one inside? i'm new to this and thought it would be simple...
 

Johann

Joined Nov 27, 2006
190
so, if i want to use an AC motor, would i need to use a transformer or do most come with one inside? i'm new to this and thought it would be simple...
No transformer is needed under normal use. Just keep in mind that you are connecting the motor to the mains. Do so via an extension lead with a built-in circuit breaker. First make your connections with the extension lead unplugged from the mains socket. When you are done, plug in and switch on. Do not touch any exposed wiring or connection point. (There should not be any open wiring, so make certain that everything is safe).
It is as simple as the dc motor you have; just work safely and it will work.
 

Johann

Joined Nov 27, 2006
190
it cant have a power cord. it needs to be from a battery/batteries.
Then no ac motor for you, unless you use a sine wave power inverter to power the ac fan while the inverter is powered from a 12V battery. This is an overkill.
The other alternative is to fit a flywheel to your dc motor to overcome the braking effect of the magnets, but this might be difficult to do with hand tools. Is it possible to make your rotating pointer a lot heavier?
Another possibility is a dc motor with field windings in stead of permanent magnets. It will most certainly be somewhat bigger than the small dc motor you have, but it will work. No magnetic cogging after power is switched off.
 
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