Running vibration motors

[RyanT]

Hey all!

I'm building a vibration-driven "wake up" chair for a very good friend of mine who has a habit of falling asleep at his desk. (Ehh, that's a non-automotive desk, for you safety-conscious readers out there... ). Styled after something like this. I need some help designing the control circuitry for the vibration motors, as I almost never use motors.

Will these motors work? Datasheet. 12VDC, 4.8kRPM, 1.1A startup current, 244mA under load.

Power requirements. Am I right in thinking most any 12VDC/2A supply will be sufficient, as long as I ensure the startups are staggered? They'd be pulsed for ~1 sec, once a minute at most. I'm just using an old wall wart for now, but might switch to 18650s for the final version. Any issues there? (Duty cycle will be very low, less than a minute per day drawing 0.5A or so, excluding parasitic load.) I might even get away with a single motor, but won't know until I prototype it.

Control circuitry. I'll probably just use an Arduino nano for the brains, as I have a few resistive sensors, a piezo buzzer, and USB comm. Would I be best using something like an L298 to drive the motors, or what would you recommend? All I really need to do with the motors is turn them on for about a second every once in a while. Set-and-forget speed control to configure the vibration intensity would be a nice-to-have.

Definitely on a budget. Both my disabled friend and I are rather broke. Willing to make a few compromises.

I appreciate any insight you all can give, and my buddy will appreciate it even more.

[Manul]

Your motor datasheet link does not open. But I think you can control these motors very nicely with a simple logic level N channel mosfet in low side switch configuration. Just be sure that mosfet turns on fully from whatever logic level your MCU uses (5V or 3.3V). You probably want Rds(on) in the range of 0.1-0.5 Ohms. Don't forget gate resistor, something like 100-220 Ohms. You may also experiment how motor reacts to PWM. As I remember, Arduino has quite low PWM frequency, so there could be some problem, but maybe not. Generally PWM is really good to control motor speed. So you can adjust vibration intensity from software. Oh, and add flyback diodes.

[james_s]

The LM298 is not the right choice for this application, you would use that if you wanted to control the direction of the motor but you don't need that here. A simple transistor will work just fine, either bipolar or mosfet, it's really not critical at all. A 2A supply ought to be perfectly fine, even if you start several motors at once. 2A will be the continuous rating, it ought to be capable of supplying substantially more for a short period.

[tooki]

Hey all!

I'm building a vibration-driven "wake up" chair for a very good friend of mine who has a habit of falling asleep at his desk. (Ehh, that's a non-automotive desk, for you safety-conscious readers out there... ). Styled after something like this. I need some help designing the control circuitry for the vibration motors, as I almost never use motors.

Will these motors work? Datasheet. 12VDC, 4.8kRPM, 1.1A startup current, 244mA under load.

Power requirements. Am I right in thinking most any 12VDC/2A supply will be sufficient, as long as I ensure the startups are staggered? They'd be pulsed for ~1 sec, once a minute at most. I'm just using an old wall wart for now, but might switch to 18650s for the final version. Any issues there? (Duty cycle will be very low, less than a minute per day drawing 0.5A or so, excluding parasitic load.) I might even get away with a single motor, but won't know until I prototype it.

Is a cell phone vibrator enough to wake him? With that little motor and its very high RPM, I'd think you'd be generating a similarly high-frequency vibration. Intuitively, I'd think a slower vibration of larger amplitude might do better.

Another thing to consider entirely: a bass shaker. It's basically a coneless subwoofer intended to be attached to a seat, to create the sensation of massive bass volume without actually needing to make the walls shake. One of those, creatively attached, might work well.

Or perhaps something weirder, like a very slow geared motor turning an eccentric object, kinda like a massage chair…

hey wait a sec, why not get a cheap back massager (the kind intended for use on a chair) and hijack its control circuitry?

[james_s]

The motor he linked isn't a cell phone vibrator, it's a much larger motor, like the sort used to vibrate game controllers and those vibrating massage chair covers.

[tooki]

The motor he linked isn't a cell phone vibrator, it's a much larger motor, like the sort used to vibrate game controllers and those vibrating massage chair covers.

I know that. Re-read what I wrote:  I said that with its high RPM, it’d probably produce “similarly high-frequency vibration”.

[RyanT]

Thanks for all the replies, and sorry for not following up sooner. Got caught up in the North American heatwave with a broken AC condenser unit. Decided 40C in my office isn't good for me or my equipment. :-)

Modding a massage chair was actually an early idea of mine, but even the ultra-cheap ones on Amazon cost more than the parts I need for this (imo, better suited) design. The guy is around 125kg, and has a pretty beefy chair I'll mount to the underside of, so I went with a larger motor. I'm counting on the combination of the vibration and the noise waking him up. Obviously I'm counting on doing some prototyping.

The bass shaker is a neat idea. It'd probably work just as well, but I guess I'm just worried for the rest of his family and service dog, who are usually asleep at this point. I'm hoping the motors will be a little more discreet.

Thanks in particular to james_s and Manul for the suggestion of using a mosfet and playing with PWM from the Arduino for motor speed control. I'll switch to that, and play around with PWM.

[james_s]

Wow yeah that heat wave was brutal, not a good time to have the AC break down. The only time mine has ever failed it was the run capacitor for the compressor and fan motor. I've also seen contactors fail although I haven't personally had that issue. Older AC systems are pretty simple devices.

[Raj]

I don't know if it's a great idea, specially if the road is bumpy. Doctors say, it's bad to keep working while being sleepy. Stats say, it's better not to drive when being sleepy than to keep driving as it's as bad as driving drunk.
But an air horn can do a better job. Just tap the compressed air line and use a solenoid valve (drive it the same way you intended to drive the motor)

[RyanT]

I think you may need to give that first paragraph of the OP a more careful read.

[Raj]

I think you may need to give that first paragraph of the OP a more careful read.

Ouch...on the desk :p
Did an error of doing TLDR.