[originator]

Hello. I have an application that requires coupling a BLDC motor with 12.5:1 gearbox and 8mm shaft to a 12mm shaft that drives a timing pulley and belt. The application requires quite operation, and the gears are the noisiest part of the whole system. Attaching the motor/motor mount to the structure makes the noise louder due to resonance of the structure it mounts to(Aluminum I-beam and wood).

I intend to try to mount the motor/gearbox to the structure with some rubber insulators which should help reduce the vibration transfer and noise. Can any suggest a very quite method to get the gearbox energy onto the pulley shaft? A little play is ok(under 1/16" at the timing pulley OD), it is non CNC use. An aluminum or Delrin direct coulpler seems to cause too much noise, so I am considering a semi rigid rubber hose that attaches to a Delrin part that mounts to each shaft. A last resort is another shorter 1:1 belt and pulley from the gearbox to the timing belt/pulley.

Thanks for any ideas.

[Al_The_Man]

As far as couplers are concerned there are spider or sleeved couplers with various types of cushion driving material, Misumi USA sell a variety.
Depending on the Motor/gearbox weight, there are many types of stud mount rubber shock absorber type isolation mounts.
Al.

[Geof]

Also make sure the two shafts are closely aligned both concentric and parallel.

[Dropout]

Google Lovejoy connectors

[originator]

Thanks for the replies. Saturday I went to a local surplus place and picked up some rubber isolators by Lord Manufacturing. They have a plate that mounts with 4 bolts, and the center section is rubber with a steel tube in it where the bolt goes to the motor. So I added the 4 plate isolators to a piece of Delrin so that the motor is not touching anything but the rubber center, and the motor sits off the Delrin plate about an 1/8th. I rigged up two aluminum couplers, one with a 8mm hole to mount on the motor and the other side 12mm that receives a piece of rubber industrial type hose, a low pressure type. The other coupler is 12mm straight through, and mounts on the shaft to the timing pulley, the hose goes in the other side. I think the hose is about 2" long and has some flex to it which serves the application well.

The vibration transferred to the structure is now significantly reduced and much quieter. Depending on the application, the hose can be changed out to different materials to attain different tolerances, there are some rubber rods and hose that have much more rigidity that reduce the play.

[CalG]

A length of reinforced rubber tubing fixed to the shafts with hose clamps can transmit a fair amount of force, and is dead quiet.

Spider hubs on both shafts with a disc of reinforced rubber sheet bolted to each spider in an offset fashion works well also. These couplings are sometimes seen in automotive steering shafts (older vehicles, much older ;-))

[bad bearings]

If you are relying on a stepper motor or the encoder is on the motor then you may want to invest on a better coupling than just a piece of hose. Bellows couplings are a good choice as they have very high torsional rigidity and can accommodate both parallel and angular misalignment. Mounting the motor on isolators will reduce the torsional rigidity as well. I suspect that most of the vibration will be solved through the use of a good coupling. Brushed motors tend to run with less vibration.

[bad bearings]

It looks as though your motor mount--if it is shown in the photos above--is applying an axial load to the motor bearings. If you don't have a drill press you may be able to sleave the shoulder screws with some bushings from the hardware store to take up that axial load.

[CalG]

Badbearings

In the original post the comment was posted "Non CNC, 1/16th free play, etc.

A tight coupling requirement is not implied. hence the low tech would seem useful.

[bad bearings]

I apologize--I guess I hadn't seen that comment. Good luck.