5 replies to this topic

[Robert BG]

Hi,I've got 3 very similar Koford 15a motors and 2 of them feel very weak when you turn them over yet they were supposed to have been zapped and freshened up while the 3rd hasnt.The 2 have been gone through and there is absolutely nothing to suggest otherwise except for how they feel when I turn them over.I was quite impressed when I first saw them and dont think for a min that there was any shady stuff going on so to speak but there may have been a mistake during zapping the mags.Or I'm just missing something because its been a long time since I've built a motor.

 

Why would the mags feel weaker and have less of a indent when you turn the motor over?

To make things even more confusing the ones that feel weaker are noticeably stronger if you put something metal near the can on the backside.They literally jump off the table at a screw driver the same distance as a lighter fresh cobalt motor when the unzapped mags just sit there.

 

Am I missing something?Is there a reason why the fresh motors have less thump to them?Or is a tear down in order?

 

Thanks

[Bill from NH]

i would set up motors, put them in a car, & run them on a raceway's track. Then you'll know whether or not you have problems. i don't think running them on a power supply or rotating them by hand will tell you much of anything, other than that they are or aren't bound up. The proof of the pudding is found out on the track.

[old & gray]

When I built and raced group 12 in the late 1990's I found magnets would give different "feel"when you turned them by hand. Some had a strong center spot and would give six distinct steps, others had strong spots at the tips and had 12 steps which were so small it would seem almost seamless.

Which was best? It depends... which track, what timing on the arm, what lamination configuration.

 

I concur with Bill, a test on a track is the only way to determine performance is on the track. 

[havlicek]

What they said!  All sorts of things can make a motor feel differently when turned by hand, and the proof of a motor's condition is how it runs in a car and on the track.  **IF the motors all have the same armature laminations, same exact type and shape magnets, same gaps, same strength springs, same condition brushes, same type and condition bushings/bearings, then how they feel might be telling.  Then running them on a power supply at low voltage should produce very similar results (*although almost never EXACTLY the same results) and then too...running them in a car on the track should also produce similar performance...but again almost never exactly the same performance.  It's actually possible for the motor you *think* is going to be weak to turn out to be a honey!  

It's not impossible that whoever did the reconditioning didn't do a good job, but there's a bunch of stuff you need to do to be more certain about that conclusion.

 

-john

[Robert BG]

I'm definitely going to be running them head to head in the same setup to compare,I was just curious if anyone else has seen something similar.

[Wink Hackman]

No mistake, no confusion.  What you have experienced is normal . If you feel very little 'cog' when turning the armature by hand, that's actually an indication of a very strong magnetic field, not a weak one. If the field is saturated, it varies very little as you turn the arm.  So it sounds like the zapping has done a good job!  If you shave the tips off the magnets, or increase the air gap, the cog always increases noticeably, and you get more top-end revs but less low-end torque. Which setup is best depends on the track and your preference.