# Changing an ERM (eccentric rotating mass) motor

1. Aug 9, 2015

### BillIsTheDill

I'm not well versed in electrical engineering, but I was looking at this. http://www.precisionmicrodrives.com/vibrating-vibrator-vibration-motors/pager-motors-erm-motors
It suits my needs for a project, but I need to modify some aspects of it.
In layman's terms, can someone explain to me how I can make it vibrate at certain frequencies?
Also, from my understanding, it runs when a current is run through it. Can it be run on a rechargeable battery, if so, how would I make the necessary modifications?

2. Aug 9, 2015

### Staff: Mentor

3. Aug 10, 2015

### BillIsTheDill

Thanks. When I look at the specs it shows a wide range of frequencies at various voltages. How/can I control this? Also, am I right about the other part. If so, how can I modify it?

4. Aug 10, 2015

### Staff: Mentor

It is used in cell phones. They use rechargagle batteries, don't they?

You vary the speed by varying the voltage. Are you asking how to design a circuit to do that?

5. Aug 10, 2015

### Merlin3189

As far as I can see from the link you provide, these are just permanent magnet brushed DC motors with an eccentric mass attached to the spindle.

As said earlier, the vibration frequency will be the motor speed and for PMDC motors that is more or less proportional to the voltage applied to the motor. So you would just need to find the voltage which gave the required frequency, then use a constant voltage source. (If this "more or less" is not accurate enough, there are more complex DC motor control circuits which can control the speed more accurately. Otherwise you'd need to monitor the frequency and apply feedback to stabilise it. The "mol" variation is due to friction varying with temperature and, in the long term, wear.)

The electricity used can come from any source capable of supplying the required current at the necessary voltage. The link suggests just about any sort of battery including rechargeables: "... ideal for battery power supplies. The combination of voltages makes these motors suitable for single / double cell power buses of Alkaline, Zinc, Silver Oxide and single cell Lithium primary sources, NiCd, NimH, Li-ion secondary rechargeable batteries."
A mains power supply could obviously provide whatever you want.