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Finding a strong vibration motor for a watch

gregweber

New Member
Hi everyone!

I am having a hard time looking for vibration motors as an electronic part.
My goal is to find the most powerful vibration motor I can that could comfortably be worn in a watch.
The goal is to be able to wake a deep sleeper.
I would be considering a watch form factor that would be somewhat larger and heavier than normal.

My biggest problem is that most vibration motor parts I come across don't seem to actually specify the amount of vibration force produced.
I am hoping to prototype with the motors now and eventually buy in larger quantities at a low price.
I also come across custom vibration motor design companies but am hoping to find something off the shelf.

Do you have any advice for finding a good vibration motor for my use case?
 

KMoffett

Well-Known Member
For prototyping , you will probably have to purchase a bunch of different ones and try them. One-offs are pretty cheap.
 

DrG

Active Member
Thanks for those leads! None of those part descriptions actually state the force that the motor generates :(
May not be easily found for those little wearables, but a few do:

https://www.murata.com/~/media/webrenewal/products/mechatronics/actuator/pjfv/datasheet_pjfv.ashx - called "vibration quantity" but the 1.2 G makes me think it is what you are looking for.

https://media.digikey.com/pdf/Data Sheets/NMB-MAT/PNN7RB55PW.pdf - same here - see the graph

https://www.tdk-electronics.tdk.com/inf/20/10/ds/2626H023V120.pdf - this one has what you are looking for but it is a much higher voltage device.


You may just want to search through the data sheets at Digikey and the like.

Of course, you could just use one of these https://www.clevelandvibrator.com/Product/33/1015/1900-SI-Kit I'm quite certain it will awaken even the most stubborn sleeper, but it is a bear to wear on the wrist :)
 

unclejed613

Well-Known Member
Most Helpful Member
Thanks for those leads! None of those part descriptions actually state the force that the motor generates :(
that depends on the actual RPM the motor is run at. if you noticed the motor RPM numbers were "ballparked". if you can calculate the circumference of the weight's center of gravity, and know the mass of the weight, you then measure the RPM and divide by 60 (so now you have rounds per second). then multiply the RPS by the circumference to get meters per second (or millimeters or centimeters per second) then the formula E=(1/2)MV^2 giving the answer in joules. you could go to all that trouble, but in the end your goal is "can the motion be felt?"

if i were designing something in a watch, i wouldn't worry too much about the amount of force, as long as it's enough to be felt.

this reminds me of a movie called "Our Man Flint"
Flint, ( James Coburn ) had a gadget in his watch that would extend a small lever that would tap him on the wrist and "wake" him up from meditation.
 

ClydeCrashKop

Well-Known Member
Most Helpful Member

DrG

Active Member
you could go to all that trouble, but in the end your goal is "can the motion be felt?"
Yes, but....

There are now a number of wearable devices designed to awaken a sleeping driver - or actually one who is getting sleepy.


If the OP is designing such a device, the specification would be important I would think. If it is for research, the specifications are even more important.

Of course, the awakening stimulus is one thing, the detection of drowsiness/sleepiness is another. There is a good amount of research going on in this area and I would expect to see such devices integrated into the suite of enhancements in modern automobiles.

 
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gregweber

New Member
I am just trying to make a better vibrating alarm watch for normal sleeping at night. I have been frustrated with trying to buy existing products for this purpose.

An energy formula is a good idea to sanity check a published force number. But I think an enclosed vibration motor in particular would be unlikely to give the specifications needed to do the calculation.

Thanks for the links to specs that specify force. I haven't come across those particular motors yet.
The Piezo Haptic form factor looks really great, and I haven't seen this type of part before, but yeah the voltage seems like an AC outlet rather than a watch.
 

Pommie

Well-Known Member
Most Helpful Member
I would imagine that the efficiency of all vibrator motors would be pretty similar, if so, the power usage (V x A) could be a good indication of power (force).

Mike.
 

DrG

Active Member
Thanks for the links to specs that specify force. I haven't come across those particular motors yet.
Just to be clear, the data sheets came from the Digikey products sear https://www.digikey.com/products/en/motors-solenoids-driver-boards-modules/motors-ac-dc/178?FV=-8|178&quantity=0&ColumnSort=-1000011&page=1&stock=1&k=vibration+motors&pageSize=25&pkeyword=vibration+motors They have 94 different ones according to that search.

Intuitively, I would think that using two vibrators, spaced as far apart as you could manage on a wristband, and alternating their operations might provide or more salient cue, but I have no data to support that.
 

gregweber

New Member
I read that using multiple vibration motors can be tricky: they can dampen each other and alter the resonant frequency, etc. It is possible if care is taken, but the recommendation was that it is easier to get one strong motor.

Thanks for the Digikey search, I think I wasn't doing my searches right. You can probably see though how many of these don't actually state the force they generate.
 

unclejed613

Well-Known Member
Most Helpful Member
you could also use some kind of spring loaded solenoid. the solenoid actuator could be easily weighed, and you would have a known throw distance and velocity, and you could tailor the drive current amplitude and frequency to get the amount of force you want.
 

atferrari

Well-Known Member
The best I have seen:

A classic alarm clock

1571878434654.png

Sitting on a tray full of coins.

1571878515481.png
It works marvels.
 

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