Vibration Motor Strength

So I'm building a project and I need help for one part. I'm adding haptic feedback to a device that it needs to have a relatively strong response (Bigger than a cellphone and distinctively felt through a glove). However, I'm running into 2 issues:

  1. Strength. I have no clue how to compare motors. How strong is a cell phone motor, in Newtons?
  2. Where do I buy vibration motors? I've seen some on Digikey and Sparkfun, but the selections is limited. I'd be happy if one of the 2 motors was enough, but I'm afraid they may be too weak. Due to the project constraints, I need it to be readily available.

Due to the project constraints, I need it to be readily available

What does that mean? Is this a school project, or a commercial project, with plans to construct many more units?
If it is not a secret, what will this device do?

I am not sure if anyone can tell you the "Newtons" of several viberator motors. Do you even have an idea how many "Newtons" you require?

I suggest reviewing several, and buying 2 or 3 that look close to your needs. test then, to see which one gives enough power, and requires the least amps.

Vibration is usually measured in peak acceleration (m/s/s) and frequency (Hz), the
force will be related to the acceleration and the motor's rotor mass.

The vibration motors in games controllers are probably fine - they are powerful
enough and cheap and readily sourced. Buy a cheap controller and disassemble it?
I know some controllers have different motors, fast and slow/heavy to give a range
of effects. Small DC motors can have an eccentric mass attached to make your own
but you might find the bearings aren't very long lived if they aren't designed for the
off-axis loads.

So the project is for school, and is a kit for a metal detector that is being designed so it can be waterproofed for an underwater diving course. Once the design is complete we intend to publish it as open source. However, because the department requested it to be an inexpensive reproducible kit where a lot of the cost is supplied by the end user in doing the assembly themselves. Because of this, we do not want any parts to be from a weird source (Like buying and disassembling some other device).

Now, the other side of this is since it needs to work underwater while diving, the device needs to vibrate at a strength that can be distinctively felt through heavy gloves, and the device will be larger than a cellphone.

When I went browsing data sheets, and the datasheets had expressed a ‘vibration strength’ in units of force as well as a rough speed (Seemed to be +/- 20%), and while I can compare between these devices, I have no reference point to make any assessment on the part. Additionally, since this is a school project, we need to at least have a semblance of research and justification before we can buy parts, and based on the original investigation all of these motors seem really small, possibly designed for a cellphone type device or something smaller.

Underwater is a whole different ballgame - you have to vibrate the mass of all
that water too, so a more powerful device may be needed - a DC motor with custom
made eccentric mass is more promising (you get to experiment and choose a motor
powerful enough). An eccentric mass could be manufactured from an existing
standard part like a pinion gear by cutting/maching off one side...

I'm guessing that the mass of the eccentric object will need to be relatively significant as well, correct?
The idea behind it is that this will be in the handle of the device to give the user feedback, but I was wondering if the water would act as a dampener.

I don't see how you would measure the strength of a vibration device, in Newtons.

I suggest you buy some, and play with them, to see if they meet your needs.

mirith:
I'm guessing that the mass of the eccentric object will need to be relatively significant as well, correct?
The idea behind it is that this will be in the handle of the device to give the user feedback, but I was wondering if the water would act as a dampener.

I would bet that underwater you would be able to hear the motor as well.

If you're looking for a motor to play with try a cheap, electric toothbrush.

interesting project,

My guess is like above, give it a go.
Haptic feedback is just a standard motor with an out of balance mass on it,
the mass and the amount of time its on could limit the life time, bearings wearing out.

there are plenty of motors available from the big distributes.

alternatively, have we considered led indicators,

have fun, let us know how it goes.

drjiohnsmith:
interesting project,

My guess is like above, give it a go.
Haptic feedback is just a standard motor with an out of balance mass on it,
the mass and the amount of time its on could limit the life time, bearings wearing out.

there are plenty of motors available from the big distributes.

alternatively, have we considered led indicators,

have fun, let us know how it goes.

LEDs are the 'primary' indicator. The diving coach who requested the project wants us to try to incorporate a non-visual feedback as well. Waterproof audio seems really expensive and complicated to implement, especially compared to turning a motor on and off with a PWM signal and being able to seal that inside the case rather than having an extra connector that needs to usable while underwater.