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Mabuchi FF-N20PN

3K views 21 replies 9 participants last post by  a Bill 
#1 · (Edited by Moderator)
For one of my '60s F1 proxy cars I chose to use the Mabuchi FF-N20PN motor in stock form. It's pictured on my website. After a two days of sporadic testing I have found this motor to be failure prone when run at three times its rated voltage


What I've found is that the shield mounted on the commutator base seperating the comm area from the poles/windings et al will come off at high speeds. It generally takes about 7 laps of a 65' track. I found a way around that problem by disassembling the motor and removing the shield. Not a pleasant operation but possible. Unfortunately the precious metal brushes won't survive the modification. That's the second and final problem I've encountered so far with this motor, brush failure. If you're not familiar with precious metal or don't know what the FF designation means for Mabuchi motors, it's this, no carbon brushes. Just copper fingers with silver plating. On a motor this small, that's a big problem when pushing it well above its rating.

At this point in time my schedule does not permit extended research and development of a new brush assembly but I ought to be able to do something with it eventually. Some may ask why. This is a very small motor with half decent power for its size. It allowed me to build a '64 F1 Honda with a sidewinder
It took a bit of effort but for the few laps it did run it was very smooth and controllable with excellent top speed. If this motor can be made durable then we'll all be able to build skinny F1 type cars that whoop up on full size cars running without magnets. Besides, it's different.

Unfortunately for me this puts one of my '60s proxy cars on the sideline until I can work something else out for it. The other '60s F1 proxy car will be shipped as scheduled.
 
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#3 ·
QUOTE (Phil Kalbfell @ 6 Oct 2004, 04:06)I have one of these sitting here in parts and it is the same size as the Moto GP from Scalex! Why not use the Scalex version as a replacement!

Phil
<{POST_SNAPBACK}>

Bill gave me three of the motors he is referring to last weekend. Thye are much smaller than the Moto GP motor which appears to be the same size as the TMM that I use. The Moto GP is probably a Mabuchi FK 050SH (from memory - may be off a bit) which is much narrower than an S-can but about as long.

EM
 
#5 · (Edited by Moderator)
QUOTE (compound_goose @ 22 Oct 2004, 08:25)generally running anything at 3 x reccomended voltage aint good! i ran a 3v motor in a slot car before, the com disssasembled itself!
<{POST_SNAPBACK}>

I'm running some Mabuchi FF-130SH motors that I got for about 50p ($1 US) each and they are rated at 1.5-3v, but they run great! I have 4 cars running on them now, 3 non mag and one with. They are the same size as the little Fly race motor in the M3 and seem to have similar power characteristics. I have several hundred laps on each and haven't had one fail yet, in fact they don't even get warm?!
By the way, this is with the stock 17v Scaley walwarts, one per lane!
 
#6 ·
DC motors really aren't that particular about actual voltage. In this case it is primarily a poor armature design intended for something else. When I can get more time I'll make them work. It's just one of those things I do to amuse myself.

I can usually get twice as much power out of anything before I need to do any really serious modifications. Still having trouble finding a low cost mini turbo charger for the weed whacker though
 
#8 ·
Why dont you try upping your gear ratios to reduce the amount of time the motors are at full tilt. That will be what is throwing the shield off the comm, Im surprised the copper fingers are surviving the current though
 
#9 ·
The commutator is holding up fine. The problem lies in this disk that they positioned between the comm and the windings. Not sure why it's there to begin with but when it lets go it takes a few wires with it


I rarely run a motor at full speed. I always save a little extra for 'emergencies'
That's something I learned long ago in the street scene, never show them what you've got, leave them guessing.
 
#11 · (Edited by Moderator)
aBill, can you not cover the explosion prone area with a thin layer of good epoxy? It won't help with the brush problem, but may stop the arm from grenading?


My usual method is to heat the epoxy (24 hour stuff, not the 5-minute version) until it is very runny then apply it sparingly with a toothpick or small brush, working it in as deeply as possible, and bake the arm in an electric fry-pan at about 150 degrees F (higher if the materials allow), turning frequently for the first 10-15 minutes or so. Turn the heat off after 20-30 minutes and let it cure standing vertically. Only the most radical 1/24 winds will explode after this treatment.

As I said, you'll still have the brush problem, but the arm should stay together?
Just an idea...
 
#12 ·
I'll have to see if I can get a picture of the thing. My description isn't that good. Unfortunately the armature is kind of dinky and my camera doesn't do well with small subjects. See how I casually blamed the camera for my lack of photographic ability?
 
#13 ·
This is a poor picture, as promised
but you can make out that there is a circular thingamajig between the comm and the windings. This thingamajig comes off with predictable results at high speed. The other armature is a stock size arm for comparison. Plus it gave me something to focus on, that little arm kept disappearing


 
#20 ·
Well, the epoxy held but the brushes are toast. This makes seven dead motors with no real gains in longevity. I'm rather disappointed in myself. This motor was originally intended to be used in Professor Fates '60s F1 race. I wanted a sidewinder in a skinny tired F1 car
So at this time I'll have to set this failure aside and concentrate on dumb things, like the holidays. Perhaps in late January or early February I'll be able to get my act together and make this thing work.
 
#22 ·
As you guessed, the brushes are extremely delicate so reassembling the critter is difficult. This motor uses the 'precious metal' brushes which are nothing more than thin copper arms with a silver plating that are notched so that they have three seriously thin fingers riding directly on the commutator. Any pressure placed on the fingers causes them to bend or break off. That and the higher electrical load I'm imposing on the motor heats them up too much.

What I need to do is replace the brush assembly in its entirety. I've already replaced the electrical assembly for a Mabuchi S motor with that from a Tyco X2 but getting something similar for the tiny N20 motor will be a bit more difficult. I'm considering adapting the end bell arms from an AFX Super G+ car but that's as far as I can go right now, just considering.

The armature shaft on the N20 is 1 mm in diameter. Case height is 10 mm. Not a big motor, much smaller than HO.
 
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