My latest model project is a classic-style rocketship with a rotating ring for artificial gravity. The ring is driven by a little 9V motor and gearbox.
The last time I used one of these motor/gearbox units was in a Mechanical Mole, and when the motor’s running it’s quite a noisy little devil. Small wonder, since the plastic hull acts as a dandy soundbox.
So I need advice on reducing the motor noise. The motor is/will be mounted solidly to a bulkhead inside the hull. The hull is about the size of a coke can. I’m thinking of gluing some kind of sound absorbent/deadener to the inside of the hull.
I have 0.030" lead sheet, cotton batting, egg cartons, and celluclay (a papier-mache material) available. Which of these materials would be best to reduce sound?
A picture. The motor drives the blue central gear, which rotates the rubber-band-wrapped drum beneath it.
If you can mount it with grommets (or otherwise separating whatever part of the motor touches the structure with some rubber), that could quiet it down a bit.
How much of the noise is from the gears vs the actual motor? If it’s from the motor, maybe investing in something built to be quieter. I assume you don’t want to make the unnecessary leap to a stepper motor, but with the correct drivers, those can be just about silent.
Gear drives like that need lubricant to cut down on noise. White grease works well if it’s not a problem on the components or leaking out. Sometimes just shafts turning in tight plastic holes make a lot of noise and need lubing or the addition of an o-ring.
Don’t know if it will work for you here but a stepper motor will produce a lot less noise since you won’t need those reduction gears.
I think an integrated gear motor would be quieter. How fast do you want to rotate? If 1 RPM then a motor for a clock with a second hand would be very quiet.
It would require some rejigging but bevel cut teflon gears would be self lubricating and I imagine quite a bit quieter. Maybe a sheet of Dynamat or automotive sound deadener lining the nose cone and bottom of the motor.
The blue gears are polyethylene, I think, and seem to be pretty quiet. The gear in the gearmotor are steel, and I think I’ll give 'em a hefty coating of grease.
I have some dynamat lying around somewhere. Have to do some experimenting!
That would be my advice; the only problem is that you need both a driver and a controller (Arduino, etc.). At least I’m not aware of any that simply run when you apply a voltage, the way a standard brushed DC motor does.
If you want to get really fancy, the ultrasonic/piezo motors in SLR camera lenses are also silent. I’m sure the parts could be salvaged on eBay, but driving them would be even more difficult than the stepper.
BTW, I used this to modify a solar tracker that was originally AC powered to run from a battery (I had a nice geared stepper motor handy). The final design was smooth as silk - no motor noise or vibration at all, just like a clock should be.
IMO, your reference to a sounding board is the key point. I don’t think sound absorptive material inside the model will have much effect, because firmly mounting the motor and gears to the model is going to transmit a lot of sound directly into the body. You need, as much as possible, to isolate the motor and gears from the model with rubber or some other vibration-absorbing material. If you can do that, absorptive material inside may help deaden the remaining sound being transmitted through the air, which I think would be a small percentage of the total.
How often do you really need the gravity to be turned on? Let the ship’s complement float around most of the time; they knew what they signed up for when they accepted their berths (the crew) and bought their tickets (the passengers).
P.S. Looking forward to your pix of the final project; those are always a marvel to behold!
[quote=“kaylasdad99, post:13, topic:921180, full:true”]
How often do you really need the gravity to be turned on? Let the ship’s complement float around most of the time; they knew what they signed up for when they accepted their berths (the crew) and bought their tickets (the passengers).[/quote]
On the real ship, the ring section would be rotating for the entire trip; I think there’s enough evidence that prolonged weightlessness has serious health implications, and long-duration spacefllight really really needs artificial gravity of some sort.
On the model, it only needs to rotate for perhaps an hour or two at a time, for model shows. That’ll be limited by the 9V battery I plan to use to power it.
Thanks! Today I kinda taped the whole thing together for a sanity check:
This morning I did some experimenting, using a sound meter app on my phone. Lining the hull in the vicinity of the motor with 0.030 lead sheet gave me a decibel or two drop. But I had concerns about adding so much weight to a model that’s going to be cantilevered way out there on its stand.
So this afternoon I messed around with some 1/8" cotton batting Mrs R gave me. Two layers inside the hull reduced the sound by 4 dB, with virtually no weight increase. So cotton batting it is.
I told Mrs R that if the sound really got to bothering me, I’d just add a sound card to the base and drown out the motor with some “Hey, we’re going off to Outer Space!” music.
Board member Beowulff was kind enough to send me a lovely little gearmotor which is quite a bit quieter than my original one, so I’ve just finished reworking the motor mount to take it. I still plan to add the cotton batting, just to quiet things even more.
Record players - for vinyl records - were quiet. By design. They used quiet motors. either by direct drive (33 rpm, which is probably about what you want), or by a drive belt (which allowed the motor go a bit faster than the platter).
They typically cost only a bit more than a ‘cheap’ electric motor. Called “record player motor” or “turntable motor”.
