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Old 03-11-2006, 03:57 PM
  #160  
John Stranahan
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Mod Motor Durability.

We made a little progress on our Mod Motor Durabiltiy at Mikes GulfCoast RC Race Track. We went up from purple springs (about 13 ounce) to silver (14 ounces). On a Trinity cobalt motor, I can get a good reading on the Trinity Spring Tension gauge. About 4.5 is good for durabilty on this track. 4.0 is ballistic but short lived. We tried the gauge on the new Aluminum Endbell Trinity Motor (Epic Shock) and it did not work as well as the spring wire arm tends to stick in the Aluminum recess. The gauge also has less leverage on the spring with this endbell so the numbers do not cross over from one motor to the other. Lin ran purple on negative and silver on positive. Usually the positive brush tends to burn more.

Results- With a new comm, I ran two heats with the silver silver combination. the comm looked good. It was copper colored and still shiny. I made only one .001 inch pass to clean it up. Lin's motor was improved, but there was still too much wear. He has to order up some more silver springs for his motors which do not have overhead springs (overhead springs have two different types of springs on positive and negative, both solder tabs are on top or overhead)

Plasma Sprayed Comm
There is a process to add metal to an object called sputtering (in a vacuum) or plasma spray (in air). This process vaporizes metal at high temperature and then the hot metal plasma deposits on the cooler object. If your comm on which you are running high silver brushes, comes out silver colored and all eaten up then you have arcing that has actually plasma sprayed the comm with a coating of silver from the brushes. Things have gotten really hot. The arcing is responsible for most of the comm damage. Heavier springs or a lower gear ratio is usually the cure.

Another problem- My motor was running well in the main and then I heard a snap at the end of one of our long straights (about 45 mph). One wire actually came loose from the comm tab, from centrifugal force, I believe, as there is no evidence of overheating. The comm and brushes looked very good. It is possible that a Hemi wind, where the wires don't cross at the comm end of the arm, is not suitable for a high speed track, unless it has an extra thread securing the wires. I found this extra wrap of high tensile thread on one of my flat wire arms. The 10 x 1, that snapped, also had larger gauge wire (15 gauge) than my previous 10 x 1 (16 gauge-same manufacturer) which was very succesful on this track. The larger wire being heavier may have caused the problem. They never tell us the gauge or type of wind. I wish they would.

This problem could also have been caused by a piece of epoxy balance material that was ejected from centrifugal force, and then collided with the comm tab. There is a bare spot on the end of the arm. Since the com tab is the one with two ends of wire, I suspect the wire broke first. I found no bits of epoxy in the frozen motor.

The photo shows a Trinity Flat wire 10 x 1 with a Hemi Wind and Thread Reinforcement. Some damage from Arcing, but only a hint of the silver plasma sprayed color.
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Last edited by John Stranahan; 03-11-2006 at 08:47 PM.
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