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[on:]

Hi all,

I'm making a wristband that vibrates at certain times, and found that the standard vibration motor most people use and report about (e.g. http://www.sparkfun.com/datasheets/Robotics/310-101_datasheet.pdf) does not give strong enough vibrations for my use. Does anyone know of a vibration motor that is similar in form factor (i.e. flat-cylindrical), but stronger? It could be up to an inch (25mm) in diameter. I have either 5V or 9V at my disposal in this project. I have searched quite a lot (maybe I'm using the wrong search terms), but keep getting to the same 3V, 10mm diam. motor.
Thanks!

[Reply #1 on:]

You may need to get a small DC motor that fits your size limits and add a off-center weight to the shaft to make it a vibrator.

[Reply #2 on:]

How about two contacts inside the wrist band, and a Fet that pulses a small inductor to get 100 volts or so spikes?  Probably less power than a motor.

And the more you sweat, the better it works   

[Reply #3 on:]

@John: thanks for the suggestion, but get a bit too big, it needs to fit inside a wristband. Or are there very flat motors that would do the job?

@Terry: Are you serious? If so, I'm interested, but it sounds a bit dangerous.  Would you have a link or documentation to get me started with this?

[Reply #4 on:]

Hi, RedFuse sounds a little dangerous already 

It takes about 60 volts to cause an obvious feeling on bare skin, maybe less if the contacts are, say, 2 cm apart.  I think all you need is a small inductor, such as the primary of a small audio transformer, or a small inductor from a switch mode power supply.. Hmmm.  This is a small current, traveling through skin on an extremity, not through the chest, and would not be dangerous.

The idea is simple: it's a "Boost Converter" often used in power supplies. See: http://en.wikipedia.org/wiki/Boost_converter

I think all you'd need is the inductor and a small transistor to act as the switch. If you pulsed it with Arduino for maybe 10 cycles at 50 Hz it would be an obvious signal.  You can put a resistor in series with the inductor to control the voltage to something noticeable but not uncomfortable.

How often does this signal need to be made? What is going on for the user here?? Is it something like a heart rate monitor??

[Reply #5 on:]

@John: thanks for the suggestion, but get a bit too big, it needs to fit inside a wristband. Or are there very flat motors that would do the job?

You said "up to an inch (25mm) in diameter".  Here's a nice little 5V DC motor with a 12mm diameter body (10mm across flats):
http://www.digikey.com/product-detail/en/M1N10FB11G/P14354-ND/2417078

[Reply #6 on:]

What is going on for the user here?? Is it something like a heart rate monitor??

Actually, I'm making a modern torture device. Just kidding
I'm making a feedback monitor for joggers. It gives feedback according to how well they're doing in their lapse.

The idea is simple: it's a "Boost Converter" often used in power supplies. See: http://en.wikipedia.org/wiki/Boost_converter
I think all you'd need is the inductor and a small transistor to act as the switch.

I've been reading up on inductors and boost converters and it sounds promising. But could you also accomplish this with a capacitor? Just because inductors can get quite large, and (electrolytic) capacitors are usually smaller. Also, for inductors to 'charge' you need AC power, right? How could the arduino generate that? With PWM?

[Reply #7 on:]

You said "up to an inch (25mm) in diameter".  Here's a nice little 5V DC motor with a 12mm diameter body (10mm across flats):
http://www.digikey.com/product-detail/en/M1N10FB11G/P14354-ND/2417078

Thanks, I assume if you would want to put it in a cylindrical enclosure you would put it sideways, and in that case the diameter of the enclosure would be about 30mm in diameter and 15mm in height. That would be pushing it, but still be acceptable. Then I just need to find that enclosure and a off-centre weight. Any idea where you could get either?

[Reply #8 on:]

Would this be a helpful circuit to accomplish the voltage boost: http://www.arduino.cc/playground/Main/RegulatedPositiveVoltageBooster
But if 60V is only just noticeable on the skin, I would maybe want to increase the voltage a bit more. Someone pointed out that I can use the flash mechanism of a disposable camera http://www.instructables.com/id/ElectroFried-electronic-shock-game/?ALLSTEPS. I just don't want to shock myself or anyone else...

[Reply #9 on:]

Shocking people doesn't sound very nice (or safe), but may encourage them to run faster!

To increase the strength of the vibration motor there's a couple of things you can do:

1. Use a stronger motor.
In the datasheet you linked, the term vibration amplitude is the key. The motor's speed, weight of the mass, and it's eccentricity all contribute to the vibration strength. Coin vibration motors are typically not as strong as cylindrical ERMs because their form factor limits the size of the internal eccentric mass. Some people cannibalise old toys to find them, but your datasheet names the company! https://catalog.precisionmicrodrives.com/order-parts#vibration-motor

2. Drive the motors at a higher voltage.
This increases the speed, and therefore the vibration strength. But don't exceed the motor's max voltage, it just can cause it to fail or dramatically reduce the lifetime.

3. Use two of the same motors mounted in the same direction.
It's not as efficient as suggestion 1, but it does work. The two rotating masses synchronise and it behaves as one motor with double the eccentric mass.

To control it you can use a PWM signal or GPIO through a MOSFET, but don't try to drive them direct as the current draw is likely too large for the Arduino - plus motors are noisy beasts and you should have protection in there anyway

See:
http://www.electronics-tutorials.ws/transistor/tran_7.html
http://brunningsoftware.co.uk/FET.htm
http://www.precisionmicrodrives.com/application-notes-technical-guides/application-bulletins/ab-001-discrete-driver-circuits-for-vibration-motors

[Reply #10 on:]

The "Vibration Amplitude" is only 0.8 G for the 310-101. That's not a lot.

For a diameter of 12mm, there are motors with 1.7G: http://www.precisionmicrodrives.com/vibrating-vibrator-vibration-motors/pancake-shaftless-coin-vibration-motors

You could search for "pager motor" or "coin vibration motor" or "vibrating motor", but somehow I always end up with precisionmicrodrives.com.

[Reply #11 on:]

maybe a salvaged mobile phone vibrator?

[Reply #12 on:]

Some people cannibalise old toys to find them

There are vibrating 'toys' with a small motor inside them, much admired by some females  . From what I've seen of them, the motor cannot be any larger than 1" in diameter and I believe they run off of 3 volts. I'm told they give a very noticable vibration