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prop pitch motor
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by W2LU on December 23, 2002
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My prop pitch motor recently quit after only fifty years of service. Any experience changing brushes or other suggestions as to possible problems?
Also, any suggestions for for finding 60 Hz syslens ?
73's and Seasons Greetings,
Gene, W2LU
e-mail:[email protected]
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RE: prop pitch motor
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by AC5ZO on December 25, 2002
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I have owned several prop pitch rotors over the years. I have never needed to replace brushes, but I have worked in that area of the motor before and recall that brushes are pretty typical and were available from Grainger and/or McMaster Carr industrial supply simply by measuring the brush size. You can also probably get the brushes locally from any motor repair facility. Brushes can be sanded to size if they are not a perfect fit, but wear a face mask if you need to do this.
A bigger issue might be that the commutator will be worn and will need to be turned on a lathe to make it into a cylinder again. Any motor shop can do this, and can probably put in the brushes at the same time. Some automotive stores that service generators and starter motors may be able to perform this same service. Prop pitch motors are very much like starter motors.
As far as prop pitch motors are concerned, they were designed to run on DC, although because they do not use permanent magnets, they will work on AC. I always put a bridge rectifier in the power circuit on these units. I do not filter the DC with a capacitor. As you indicated in your post, you get considerable life even running AC to the prop pitch, so I cannot guarantee that the bridge rectifier adds any life, but it is the right thing to do and costs little. Also, bypass the brushes with .001 ceramic caps if that has not already been done.
As long as you have the prop pitch apart, I also take out the oil lube and lube all the gears with lithium grease and reverse the oil seal on the top to keep water out of the gear case. The oil seal was intended to keep oil in. When the unit is used vertically, the oil never gets to that seal, so it is better to flip it over to keep the weather out. If the PP is protected from the weather, then this seal issue may not be important.
73 de AC5ZO
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RE: prop pitch motor
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by gm4aff on December 27, 2002
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Hi Gene,
I agree with all that the previous contributor says, However, my PP did fail because the brushes were worn down completely. I got some sent over by a very generous ham in California to me. These are made by Helwic Carbon Products Inc of PO Bax 24400, Milwaukee, WI 53224-0400. The re-order part number is simply 27 and the bag is marked DIA. X1/4 X11/16. Hope this helps.
Stewart GM4AFF/GM0F
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RE: prop pitch motor
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by AC5ZO on October 28, 2003
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I just rebuilt my own prop pitch and used a slightly different procedure than I posted before. As I learned to do the rebuild years ago, I was taught and accepted the concept of taking out all of the "oil" and replacing that with Lithium Grease or some similar thick grease. The reason for this change in lubricant is because of the orientation that the motors take when used to steer an antenna. Prop pitch motors are designed to be spun on an airplane motor shaft and the lubricant goes to the outside of the housing due to centrifugal force. When used vertically in a stationary position, the bearings and gears in the top part of the gearbox do not get lubricated. Greasing those bearings and gears solves the problem.
There are two sets of planitary reduction gears in a prop pitch motor. The lower set (nearer the electric motor) operates at a higher rotational speed. The lower set of gears is also below the big ring gear and gaskets where the gearcase splits. A lighter oil would be a better choice for lubricating this higher speed set of gears, so for this rebuild I used a hydraulic/gear lubricant similar to automatic transmission fluid to fill the lower half of the case. I still used heavy grease on the slower (upper) planitary reduction gears and upper bearings.
I filled the lower part of the housing while it was still open to a level just below the ring gear lower gasket. I believe that this may be a better way to lubricate the lower high speed gears since the lubricant cannot be flung off of the gears and bearings. After filling the lower part of the housing, I put the upper housing in place and bolted the unit back together. Another point is that this puts a low viscosity lubricant in the lowest torque section of the reduction drive, which will keep the motor from stiffening up in cold weather.
For those that are interested in doing this, I used New Holland 134 hydraulic/gear fluid. This is used for tractor hydraulic systems and gear transmissions. I think that any automatic transmission fluid would also work for this purpose.
I don't have a second PP motor to compare to, but I get rotation of the unit with about 200mA of current going to the electric motor. Normally I operate this motor on a variable 12 VDC and it will do about 1.25 RPM at full voltage. I normally set the rotation speed to 1.0 RPMs which is fast enough for the 40M beam.
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RE: prop pitch motor
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by AC5ZO on November 3, 2003
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In response to some email, I will add the following. The bearings in the gearbox were all replaced with sealed ball bearings where possible. There have been failures discussed where the original motor seal leaked and led to oil leaking into the motor. This type of failure is unlikely if the bearings are changed with sealed bearings. If you do not change the bearings and seals, I would not recommend the light oil modification I described above.
Most PP motors are 24VDC. I am not the original owner of this unit which appears to work well on 12VDC. The motor may have been rewound by a previous owner. This is the first one that I have ever worked on that works well on 12 VDC and will turn 1 RPM. My control unit is set up so that I can supply 24 DVC if I need to replace the current motor with another unit, someday.
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RE: prop pitch motor
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by AC5ZO on May 6, 2004
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A friend tells me that some prop pitch motors were modified for higher speed operation by a variety of mechanical changes in the gearbox. Since my motor works at about 1 RPM on 12VDC, my current PP motor apparently has one of these modifications. I have had no need to open the gearbox on this current unit, but at least the question about 12VDC/24VDC seems to have an answer.
All other PP motors I have owned in the past have not been mechanically modified and they produced a little less than 1 RPM with 24 VDC applied to the motor.
I am not familiar with this mechanical modification to speed up the PP motor, but at least one variation seems to have been published in QST June 1949. I think that there was more than one way to do this change and generally today, this modification is considered to be undesirable since these rotators are generally used for large arrays.
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