"de-amping" DC motors

[RedJanemba]

This question is actually in reference to a question I read earlier.

During the manufacturing process of a DC motor the bearings cannot be aligned perfect every time... Because of the misalignment the resultant fricition created raises the current draw (increasing noise and vibration). An increase in vibration or noise in a precision motor is unacceptable.

A "de-amping" process (which lowers the current draw) is then used. One known process involves applying a force to the top or bottom of the motor so that the bearings inside can be aligned to the shaft. The problem is that you are striking the actual motor. This is unacceptable from a design/manufacturing stance.

My question is this: Is there another known method to "de-amp" motors? Does anyone know of another process that would work?

 

[aolalde]

Misaligned bearings should be the result of defective machining of structural motor parts or wrong fits. If the rotor rubs the stator lamination, breaking forces load the motor, increasing the current drawn by the motor lines. This energy generates thermal heat and finally destroys the motor elements.

Hammering the shaft could clear or not the air gap of very small motors, as you mentioned this procedure attempts with the life of those bearings, the impacts will produce permanent damage to the rolling elements.

The best solution is accurate parts and matching fits (tolerances) between bearing, shaft, air-gap, bearing housings and frame. A motor built properly will run smooth and no external forces are required to modify interference between its elements. The current draw from the line will be to feed the magnetic circuit, the shaft load and motor losses.

 

[jbartos]

Suggestion: It depends on specified manufacturing tolerances. Obviously, the more precisely manufactured motor with smaller manufacturing tolerances is more expensive.

 

[RedJanemba]

This is true. Impacting small motors to align the bearings could decrease the life span of the motor, but is that enough to justify the cost increase in making more precise parts? From a cost analysis perspective, making more accurate parts costs more money than the potential loss of quality…

There should be a way to find the minimum necessary force required to align the bearings (which will hopefully be small enough to not cause damage). I am in the process of coming up with a mechanical design to consistently repeat this process with that minimum force, but my knowledge of electronics is limited. I was hoping this would be a “common” problem and that there were other possible solutions available.

Am I to conclude there would be no other way to de-amp a motor other than to make more precise parts?

 

[aolalde]

If you are dealing with very small motors probably pressure die-casting with steel bushings inserts for the bearing housings, accurate jigs to center processed parts and larger air gaps could give some improvement. Are you using ball bearings or bushings?

On your first post you mentioned “unacceptable for precision motors” but precision certainlly will affect the costs.

 

[RedJanemba]

The motors in question are typically 12V DC motors that will be placed in cars (seats, windows, etc...). I have almost no control over their actual casting/parts manufacture--nor do I have much information from that department.

The motors use brushes, and yes, I agree that precision will certainly affect cost--unfortunately I have no control over this part of the project. The solution to this problem must be handled either in the assemlbly phase of the motors or in the testing phase. This makes things more difficult, more difficult than I first originally thought anyway.

 

[jbartos]

Suggestion: Since cars are expected to last about 4 to 5 years, it may be assumed that the sought motors will have the life expectancy about the same. Then, the high quality motor will actually be a "jewel" in the car.