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QUOTE Also JB WELD does a marine grade epoxy thats high temp. but it is the quick set variety, so every thing should be laid out to go. does anyone know of a retarder to thin and slow any epoxy,s setting time john
Hi John,
Use Araldite Precision (the blue and white tubes) instead of the Rapid (red and white tubes).
At room temperature this takes 24 hours to set but can be speeded significantly up by heating.
Heating it to set it is a good idea but be careful not to melt the endbell.
Cheers,
Mick.
 

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Given the preponderance of cheap crappy epoxies here, I read Loctite 380 Black Max, if Loctite have that here. It appeals to me because it can be removed.
 

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Could not find any rubberized CA glue today. Ie. 380 Black Max.

Anyone got any thoughts on Rear View Mirror glue? It must be shock resistant and can be removed with super glue remover!
 

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If you are fitting the SCX magnets into a 13UO you should be able to use a pair of retaining clips to hold them in without the use of glue, these are made out of piano wire and easy to make.
Once you flatten the tabs on the top of the can the magnets should fit straight in, be aware that you will have a tighter airgap than with the standard magnets so a badly distorted can could give you problems, either hone or use a straight one.
Good luck
[oneofwos]
 

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Thank you John. I'll check that out
 

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For guys and Ember,

Looking for a replacement for Johnson?

Rather than buying an FC130 motor and some plastic widgets I have discovered that FK-180 motors are exactly the same length as Johnson 111.

The only difference being that their bushing retaining diameter is 6mm against the Johnson 5mm so the mounting holes would need to be enlarged very slightly.

In case anyone has some old tooth brush motors!
 

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QUOTE (Abarth Mike @ 24 Jul 2012, 12:16) <{POST_SNAPBACK}>For guys and Ember,

Looking for a replacement for Johnson?

Rather than buying an FC130 motor and some plastic widgets I have discovered that FK-180 motors are exactly the same length as Johnson 111. WRONG

The only difference being that their bushing retaining diameter is 6mm against the Johnson 5mm so the mounting holes would need to be enlarged very slightly.

In case anyone has some old tooth brush motors!

What a disgrace having to quote my own post. The FK -180 is about 1.5mm shorter, it will fit and the rear "spigot" will fit just but it needs a spacer and the shaft will not reach the slot in the crown gear. SORRY for the misinformation.
 

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Bump again.

Newbie motor tweaker air gap question.

I replaced the magnets in a J111 with some mystery magnets but kept the original Johnson arm.. (The magnets were donated to me along with a Parma Home set arm.)

It all fits together. I used Loctite 480 as that is what they had. The magnets did fit and are a lot stronger.

Now I have lost 3900 RPM. 21,700 vs 17,800. I probably have more torque but... even if I change to 10/27 I get the same speed as original with 8/27.

The arm/mag clearance was tight when I reassembled. Is it simply a question of air gap? If so what magnitude of air gap makes a difference.

I know I can swap to FC-130 byt where is the added knowledge in that.
 

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Hi Mike
Both stronger magnets and less magnet gap are likely to increase torque and brakes and reduce free running revs.

With higher current motors, 0.1mm change in magnet clearance makes a difference.
I've not tried it at the current levels you are talking about, but I guess that's where to start.

You could try shimming in the weaker magnets, and see what difference that makes.
 

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300,

The magnets are quite strong a Jeweler's screwdriver sticks to the can! The arm did touch slightly so I will have to measure exactly what the air gap is. 0.1mm I'll use as a yard stick. Cheers.
 

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If your armature is only just touching the mags you could try to clean up the stack using a file!

Doesn't sound too clever but the cheap armatures of the period were not too accurate so you could have the odd lamination slightly proud, first check that you have a straight armature shaft and if you do then take a newish fine file and gently pass it over the stack while turning the armature between you fingers, only enough to take down the high spots.
Might not solve the overall problems but will at least eliminate a possibility, probably get some hate mail now for suggesting such butchery!

[oneofwos]
 

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John,

It gets worse. I read a thread once somewhere about SCX motors where one could improve Rpm by running the motor and using a small grindstone touching the arm.
 

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If the arm is touching the magnets even slightly it will reduce free running revs (and reduce torque at lower revs).
Armatures expand slightly when they heat up, this reduces magnet clearance slightly.
An easy way of checking there is some clearance is to feed a strip of thin paper though the gap. If it won't go, that will tell you where the high spots are. (If the stack is trued and magnets honed there won't be any high spots, but I assume you are not into all that)
 

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QUOTE (Abarth Mike @ 11 Sep 2012, 07:38) <{POST_SNAPBACK}>It gets worse. I read a thread once somewhere about SCX motors where one could improve Rpm by running the motor and using a small grindstone touching the arm.
Reducing the stack outside diameter is just another way of increasing the air gap (and hence increasing revs).
Also getting it round will make it run a little more smoothly.

A lathe is a good way of doing that.

For those without access to a lathe that grindstone idea will probably work as long as it's done gently enough not to blow up the motor in the process and the debris is cleaned out of the motor afterward.
John's way of filing down the high spots a file might take rather less off the life of the motor.
 
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