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Natural Science Forum / Physics / Acoustics / December 2003Gearbox noise reduction
This is my first time to this news group, thanks in advance for your help. Has anyone had any experience or knowledge about how to quiet a DC gear motor. Our staff is stumped on how to quiet the motors to an acceptable level. Silent being the most acceptable. Any help would be greatly appreciated. Lou > Has anyone had any experience or knowledge about how to quiet a DC gear > motor. Our staff is stumped on how to quiet the motors to an > acceptable level. Silent being the most acceptable. Any help would be > greatly appreciated. That's a nasty problem. The noise is created in the meshing teeth where either the radial of the tangential force transmitted to the bearing varies with time, typically at the gear tooth meshing rate and its harmonics. The only way to stop the noise is to redesign the tooth meshing contours. The "hypoid" rear end of automobiles is aimed at this. It involves sipral contact lines; mightly complicated. Otherwise, the motor and its gearbox need to be totally enclosed in a noise reduction jacket. If the motor is bolted to a metal frame or panel, that panel can be driven as a sounding board. You may have to go to a belt/sheave drive. If the gearbox can be an independent box, it may be possible to drive the input shaft with a flexible coupling. It all can get very complex... Angelo Campanella www.campanellaacoustics.com Angelo, Many thanks for your reply. By spiral contact, do you mean helical gears? I understand that the first few gears in the chain are making all the noise because they are the ones moving very fast. So I could have these made in helical gears. Meaning the drive gear from the motor and the first spur of the box. I've tried enclosing the motors with foam, but that seams to have no effect. And the unit itself turns into a speaker when the motor is attached. So your on the right track, that I have to quiet the gearbox itself. Lou any other suggestions. > Many thanks for your reply. By spiral contact, do you mean helical > gears? I understand that the first few gears in the chain are making I think yes. The objective is to have the contact are, force and radius of contact NEVER change through all rotations. The helical gear is aimed at that. the price paid is that there is now some axial force on the gear/shaft, so the bearings have to withstnd that force as well. If you are really cleaver (or ambitious), you can mount two opposing gears on the same shaft, providing a "herringbove" appearance. That may not be necessary, but hey, anything that reduces noise is fair game. > all the noise because they are the ones moving very fast. So I could > have these made in helical gears. Meaning the drive gear from the > motor and the first spur of the box. If you have a spectral analysis done of the noise, you can pick out the actual gear via its RPM and teeth mesh rate. But the fasest one will be a good start. > I've tried enclosing the motors with foam, but that seams to have no > effect. And the unit itself turns into a speaker when the motor is > attached. So your on the right track, that I have to quiet the gearbox Good luck. And the unit itself turns into a speaker when the motor is > attached. So your on the right track, that I have to quiet the gearbox > itself. Maybe another approach. Can you isolate the gearbox from the "unit"? Can you damp the "unit"?  SignatureNoral Stewart www.sacnc.com Thanks guys for your help, I'm not sure of a couple things. One being the two opposing gears on one shaft and how to dampen the hole unit. Lou Have you considered replacing the motor/gearbox with an ungeared motor. A permanent magnet DC motor can run a very low revs due to its high torque. > This is my first time to this news group, thanks in advance for your help. > [quoted text clipped - 4 lines] > > Lou >This is my first time to this news group, thanks in advance for your help. > [quoted text clipped - 4 lines] > >Lou A- Use nylon gears - bushes etc. B- immerse it in oil. C - Slow the meshing ratio down - and then use a higher ration for the main drive. D - Bury it E -Isolate with rubber - ( you can make any shape, and density you like by vulcanizing the stuff at 350f - and pressing it into a mould. You should not be able to "feel"any play or sloppy fit. Excessive noise is also an indication of "poor"machineing, aligning choice of materials. Obviously its a camera - is it worn? |
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