17 replies to this topic

[SlowBeas]

... that make me realize how little I really know about assembling a good motor. Here's my plight:

 

Several years ago, I bought a Mura Challenger motor. I never really used it for anything, but recently pulled it out of my motor stash to see if it would run. Put it on the power supply... not bad, but the amp draw seemed to fluctuate under constant 5v. So, I thought I'd open it up and see if there's something binding inside that would cause it. That's when it happened.

 

As I opened the can, the arm fell out–- as did the magnets. Uh-oh.

 

How do I know that I've put the magnets back in their appropriate space and turned the correct way inside the can? I seem to recall that it matters which end faces the endbell. I don't see any identifying marks.

 

See what I mean? I know very little. Your insights would be appreciated.

 

jb

[Pablo]

Which ends face the endbell matters not.

 

Left to right, you have two choices:

 

1. It doesn't matter, just switch the lead wires if necessary to make it run according to the timing.

2. If the motor runs reverse of the arm timing when you have the wires the way you want them, switch sides on the magnets.

 

If I had knowledge of those motors, I could tell you which side the north and south mags go on, but I don't.

[Mbloes]

If the magnets are painted, typically the "white" magnet is the rear magnet in an anglewinder configuration.

 

Otherwise, get another one of your motors that rotates correctly. Take one of the Challenger magnets and place it on the outside of one of the magnets of the assembled motor. If it sticks, that magnet goes in the same place – if it repels, it goes on the other side of the motor.

 

Does this make sense, Jim? I would post a pic but I'm at work (where I do all of my posting).

[olescratch]

If the magnets are painted, typically the "white" magnet is the rear magnet in an anglewinder configuration.

 

Otherwise, get another one of your motors that rotates correctly. Take one of the Challenger magnets and place it on the outside of one of the magnets of the assembled motor. If it sticks, that magnet goes in the same place – if it repels, it goes on the other side of the motor.

 

Does this make sense, Jim? I would post a pic but I'm at work (where I do all of my posting).

I was taught in school, many, many, many years ago, that opposites attract and that similar polarities will repel.  Given that these magnets follow this 'rule' your suggestion may be in reverse!

[Mbloes]

Yeah, I wasn't clear.  Similar polarity magnets will "stack" - that is, the inside of one magnet will stick to the outside of another with same polarity.

 

Place your loose magnet's inside surface on the outside magnet surface of your correctly oriented motor.  If the inside surface sticks, install it in the same place in the unassembled motor.

 

If the inside of the magnet repels the outer surface of the motor's magnet, it goes on the other side.

 

Update:  Maybe this pic explains it better:

 

 

Just visualize these in a motor.

[MSwiss]

I was taught in school, many, many, many years ago, that opposites attract and that similar polarities will repel.  Given that these magnets follow this 'rule' your suggestion may be in reverse!

John,
You are right, opposites attract, but Mike was right, too.
 
The below pic shows clearly, what he was trying to convey.
 
The magnet outside the can is the same polarity as the magnet it is attracted to,inside the can, because the front of the magnet is sticking to the back of the magnet in the motor.

[olescratch]

Once again, a pic. is worth a thousand words!  Thanks for the explanation/pics to relay this info.

[SlowBeas]

Very good insights. Thanks to all. I'll give it a try to see if I can reassemble this thing correctly this time. First time I hooked it up to a power supply, I thought I was going to bring down the house --- sparking and rumbling. I could tell that the brushes were making terrible contact with the comm and the stacks were rubbing the magnets.

 

This time, I'll take a little more care in assembly.

[Mbloes]

Jim, if the magnets just "fell out", do you have magnet clips installed to hold them in place?  If things are rubbing, it doesn't sound like it.

[SlowBeas]

They were clipped -- but I obviously did a poor job of it. The end of one magnet seemed to stick out slightly and rub as the arm rotated. Will certainly do a better job rebuilding after applying the above recommendations.

[SlowBeas]

Quick update:

 

I reassembled the motor, taking care to pay attention to the above advise as I blueprinted the motor. As usual, you guys were spot-on.

 

The motor runs really well, but feels like it has an enormous amount of torque. I've geared it 11/39. I lowered the sensitivity on my controller to the very bottom, and still find that I'm still spinning the tires as I come out of the turns.

 

Amazing motor -- my first and only Mura. Now, I just need more track time to find a sweet gearing combination.

 

Thanks again for the wisdom provided.

jb

[Horsepower]

After reassembling the Challenger motor you will need to have it remagnetized.

[havlicek]

Quick update:

 

I reassembled the motor, taking care to pay attention to the above advise as I blueprinted the motor. As usual, you guys were spot-on.

 

The motor runs really well, but feels like it has an enormous amount of torque. I've geared it 11/39. I lowered the sensitivity on my controller to the very bottom, and still find that I'm still spinning the tires as I come out of the turns.

 

Amazing motor -- my first and only Mura. Now, I just need more track time to find a sweet gearing combination.

 

Thanks again for the wisdom provided.

jb

...and that's only a Challenger.  Imagine similar motor with a #25awg in the chamber.    Even *just* a 38/27 makes for a pretty deadly bank-slammer in those motors.

 

 

After reassembling the Challenger motor you will need to have it remagnetized.

Probably a good idea, but not necessarily a "must" Gary.  In this case, because the arm was hitting the magnets, that alone may have kicked them down a bit.  I'm always surprised to take a set of "average" ceramics out of similar motors, clean off all the grime and gunk, stick them back in the can and find they're "pretty much there" after all those years.  Not long ago, I had a set of magnets from an older (*but post-Green Can) Mura that actually had a perfect groove cut on the back of one side from the armature, and they only measured a very little down from where zapping them bright them to (*which was very strong).  

[SlowBeas]

Zapping the mags is probably a good idea -- especially once I determine the best gearing. I found that the 11/39 was not the right combination. I dropped the spur down to a 35, and the thing is really fast. Oddly, it's STILL spinning tires when I pull the trigger.

 

I'm going to tinker a little more with the gearing and softer tires, then look forward to taking it to a commercial track in the future. I think it could really be a killer motor. This thing feels different from anything else I've owned.

 

Thanks again for the input. It's good to have this thing running properly again.

[Eddie Fleming]

Jim I am going to suggest something that will sound wrong. Our motors have the most grunt at low rpm's and that can spin the tires. So try a smaller pinion like a 9 or 10 and get the rps's up. It may be more controllable. 

[SlowBeas]

Yeah, that definitely sounds backward to me, Eddie, but I'll give it a try.

 

My thought was to put a little strain on the motor with a smaller spur -- or a larger pinion -- to mellow the torque a little.

 

Thanks for the suggestion. I'm always interested in others' views.

[Eddie Fleming]

I don't know that motor but I would start with a 9 tooth. Someone with direct experience may want to chime in?

[MSwiss]

Jim, do you know what a choke is?

 

If you don't want to mess with one, save the motor for a commercial track.