Changing the timing of a stock motor!

I heard that people were changing the timing of the stock motor. So I decided to take a motor and go through the destructive testing process..

I decided to try and do just that. I took a stock motor and got hold of a pointy type pliers and grabbed the com through the side vent holes and then twisted. Oops, this just scratched the com and bent the wire hold down tags so I presume that the guys that are doing this must be making a sort of a vice or special pliers to hold the com tight and then twist it without damaging it.

The motor I used was the new type 2 hole Johnson 540 stock motor. I put it on my Dyno and tested its no load RPM at 7.2 volts. It reached 16200 rpm. All my 2 hole stock motors run round 16000 to 17000 rpm. Very similar to each other.

stockmot.jpg (15988 bytes)

I used doctors type clamp to hold the commutator in the can. This cannot be what they are doing as the pliers are not strong enough I hear that they use Pointy pliers that are ground to fit.

stock1.jpg (30763 bytes)

 I then bent open the back tags and opened the motor completely to get more details.

stock2.jpg (36792 bytes)

I found that I had actually also damaged the running surface of the com I then also found that once you did get it moved it was much easier to move it again. So I twisted it as I wanted to and  put the armature in a com lathe and just cleaned it up.

I then put the motor back together with the timed armature. Take note of the angle created.

stockcom.jpg (33230 bytes)

I then tested the motor again. Wow, it rev'd at 19500 rpm. that was quite a difference I did not measure how many degrees I twisted it as I just twisted it enough to see that it had moved from the center  mark as indicated in the image above.

So now you know. Unfortunately for those that do or have been doing this it is easy to see if it has been done even if the com was not damaged. You just need to see if the line on the com is in the center of the armature plates. If its not it has been tampered with. The factory does not put it in wrong. If you have a motor like that and you know you have not done anything to it better you use it rather on your com lathe or something as ignorance will just embarrass you and disqualify you if caught.

Something more interesting. You do not have to cheat to get 19500 rpm! I tested my old Johnson 540 4 vent hole motors and they rev between 19000 and 21 000 rpm. Interesting! That is also with no change on the timing as it is out the box. The holes are also too small to get anything in there.

That is too big a difference in the stock motor and I believe that we should only allow one version of the Johnson motor to be fair for all.

Here is also the Tamiya spec sheet for the various "stock 540 motors"

R/C Motor Specifications RS-540SH RS-540SH RX-540VZ
Sport-Tuned Technigold
(7435044) (53068) (50290)
Rated Voltage (V) 7.2 7.2 7.2
RPM at no load (rpm) 17,200 21,500 22,000
Current at no load (A) 2.2 2.2 2.2
Max. Output (W) 96 135 183
Max. Torque (g-cm) 2,180 2,400 3,250
Rotor wire (diameter x turns) 0.65 x 27 0.8 x 23 0.8 x 21

That's it!

Hope you enjoyed the article!

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