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Mel's software uses pulse width modulation to achieve the smooth motor motion needed for fine tracking accuracy. The downside is this also produces a "ringing" type sound that can get amplified through the mount's structure. The solution to this has been discussed on the "scope-drive" listserver, but the bottom line always seems to return to providing a "soft" mount for the motors as the most effective solution.

The problem I had with using a "soft" mounting was that I was using the bearings in the motors to help stabilize the worms so that Periodic error would be both repeatable and minimized. So, changing to a "soft" mount required replacing the motor bearings with a different bearing set, and then mounting the motor to a rubber mounting, using nylon machine screws, and using a rubber coupling between the motor shaft and the new shaft/bearings that turn the worm.

I also took advantage of the modification to add a slotted disk and LED/Photodiode detector to each axis drive to be able to use Mel's AutoPEC Sync capability. The dimensions of the modification will also eventually allow adding small flywheels in hopes of speeding up my rather stately 0.5 deg/sec slew rates.

	This is the original "Hard" mount for the azimuth motor
	This is the updated "Soft" mounting for the azimuth motor

Two sections of 2" square aluminum extrusion were used. The first one (closest to the worm gear) carries two small flanged bearings that carry a 1/4" dia shaft that replaces the motor shaft/bearings for providing support to the worm. If the worm I was using has shafts extending out both ends, or if I had a "good" bushing for it to run in, I would not need the additional support to the worm. The first section also provides an open section of that new 1/4" shafting to carry the slotted disk and LED/Photodiode detector for the AutoPECSync system, and will eventually also have a flywheel on that section of the shafting.

The second section provides space for a rubber coupling (a 1.5" section of fuel line and two tiny hose clamps) between the motor shaft and the new shafting going to the worm. It also has the motor end of the 2" square extrusion cut away and replaced with a 1/4" thick rubber pad that the motor flange then screws to. Nylon machine screws/nuts are used for mounting both of these. The rubber pad and the fuel line both provide the actual "soft" mounting.

I was concerned about "windup" that might get introduced with a fuel line coupling, so I had the ends of the two shafts come to within about 1/8" of each other, and placed the clamps close to the ends of the shafts. I cannot see any windup in the eyepiece, even at high magnification.

The proof is in the sounds though. I was astounded at the improvement!!!! I recorded the sounds of the Az motor both before and after the modification and have them posted as a 10 second long .wav file named "Motor.wav". You can download the 144kb zipped file "Motor.zip" file by clicking here. Then unzip it to motor.wav and click on it to play it. The first 5 seconds are before the modification, and the last 5 seconds are after the mod. You will need the volume turned up on your system to hear much from the last 5 seconds of the recording!!! Sorry for the poor sound quality, my ELQ camcorder was used for the recording device and the gain seems to make the soft mount portion sound louder than it really was. (ELQ= Extremely Low Quality). The ringing sound is still there (of course) but the volume is only about 20% as much as before the soft mount mod.

I intend to try potting the winding of the motor to see if that further improves the sound deadening. The plan for potting is to "soak" the field windings themselves with SuperGlue (CA) and then fill in all the rest of the volume around the windings with RTV (silicone rubber). I will post the results from that experiment when completed.....