52 replies to this topic

[Steve Okeefe]

Martin,

 

Gotta agree with Don about those front wheels; they are far smaller (proportionally) than the rears, so using a body that is a replica of an actual race car (Lola T70, Cooper Ford, etc.) is not going to end up looking so good.

 

Just my opinion – yours may vary.     Better it should be a Thingie or a show car or an imaginary car (like the Avenger) – or a drag car.

 

About the gearing, those larger rear tires will make a significant difference in gearing requirements.  Instead of simple gear ratios, you might consider selecting gears (and your motor) based on the Final Drive Ratio, which takes the tire size into account

 

To calculate Final Drive Ratio, the formula is gear ratio divided by tire size.

 

So for example a vintage anglewinder with a higher RPM 26 gauge motor, 7/8” tires and 8x34 (4.25) gears would be 4.25 divided by .875, or 4.86 Final Drive Ratio.

 

A more modern Flexi-car with a higher torque, lower RPM 16D motor, .750” tires and 14x39 (2.79) gears would be 2.79 divided by .750, or 3.71 Final Drive Ratio.

 

In your car, the 12x39 gears are 3.25 ratio and the tires are 1.063.  So the Final Drive Ratio would be 3.25 divided by 1.063, or 3.06 (that's pretty low).

 

You’re going to need a relatively higher torque, lower RPM motor (something like a modern .560" diameter 16D arm and strong magnets) or a taller gear ratio (11x40 which gives you a 3.42 Final Drive Ratio) or both to power the car effectively (in other words make it go fast).

 

Side note: This is a case where I would not use 64 pitch (example: Weldun) gears.  They require a fairly close and precise mesh, and there is too much slop in the 5/32" axle tube, which means they could chew themselves up pretty quick...

 

BTW the ProSlot website (www.proslot.com) has a nifty Final Drive Ratio gear chart if you want to let it do the math for you.

 

Carry on! 

[Martin]

Thanks Steve for taking the time.

I played around with more gears and settled on this. I found a 40 that worked perfect with a 10 divide that by 1.062 and you get 3.76.  I feel that's a good start as I have  no idea what track this will run on.

 

I did find all gears are not created equal.  I found gears in my stash that were the same tooth count and the same 48 pitch but had different diameters.

So the fact that a 12/39 and a 10/40 works on the same centers show this. If you only use one brand of gears keeping the tooth count the same would work e.g. 51 combination.

 

Yes (Don and Steve) I also think the Thingie approach is best. The Avenger was my fist choice. 

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[MarcusPHagen]

Great fun watching this frame get resurrected. Nicely done, Martin!

Marcus

[Martin]

Thanks Marcus, I was letting the paint dry as I painted the can black a few days ago. Its now ready for assembly.

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[Pablo]

   

[Martin]

I am a body and chassis man, so I may need a bit if help when it comes to motor building. I am gathering parts and I will show what I have picked so far.

I want black, silver and gold to be the color pallet. So I have found an arm with silver wire and a black end bell with brass and nickle hardware. I will clean it up and post a pic. Thanks for the encouragement guys. 

[Martin]

Gathered some motor parts that meet the requirements. Black end, Silver wire balance can drive arm, New brushes and springs and the magnets that were in the can.

 

I do have a choice of end-bells, but do not know the plus,s and minuses of the brush hoods or other differences.They both fit the can. 

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[Martin]

Can someone please tell me know that this is a Clockwise timed arm.?  I forgot to check that when I was looking for arms 

[Pablo]

Can't tell for sure unless I see a photo of the comm tabs facing up.

If I had to guess I'd say it looks neutral or darn close to neutral.

 

Those springs look rather stout for that application, maybe it's just the photo.

I'd recommend zapping the mags and a re-balance and comm true on the arm.

H Man can probably do that for you; his blade static balance is plenty good for that motor.

[Bill from NH]

If those are old Mabuchi mags, you don't want to rezap them. if you do, they can end up weaker than they were before the zap. There are other old magnets you don't want to rezap too, such as the French magnets.

[Pablo]

Thanks for the correction, Bill.

I know some of the old mags aren't good candidates for zapping, just wasn't sure which.

The main thing to remember is, a high-power rewound arm needs appropriately strong magnets to run cool.

[Martin]

Thanks for your help Paul.

Hope these pics shows the timing better. It does look neutral to my eye. What say you ?

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[Martin]

Bill, there is so much I do not know about motors.

Even in the 16d size I found many variations.

 

I do have these magnets also. They are the same white and blue ends but new in package.

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[Pablo]

Your arm timing appears neutral, meaning it will perform the same in either direction.

That's good news for you.

 

If those Parma magnets fit the can and if they provide the correct size hole, sure, they will work fine.

Notice there are two "if"'s in that sentence.

 

That can has the standard Mabuchi can nubs that aligned the mags designed for it. The stock mags will fit perfectly. Once you start to use non-stock mags, those nubs will become your worst nightmare.

 

There are no standard sizes in mags. They vary in types, thickness, strengths, lengths, heights, etc.

Certain manufacturers used colors to designate north/south, but there never was an industry standard.

 

Trying to make sense of the colors and comparing one color set from 1966 to 1989 would be an exercise in futility. Welcome to vintage motors!

[havlicek]

Of the end  bells, the Mura is far far better than the Mabuchi...but may not be necessary for the arm shown. 

-The arm isn't tied or epoxied and the tabs have been soldered...all of which "might" be OK, depending on how hot the arm is, which is impossible to tell from the picture.  To know more, the arm has to be metered. 

-The arm has the standard Mabuchi com which was barely OK for even the mild stock winds.  There isn't much meat on those com plates/segments, so truing will greatly shorten it's life.  Hard running with a rewind may cause it to blow.

-Someone drill-balanced the arm, so maybe it's fine as-is, but that can easily be checked, and maybe improved if necessary.

-The magnets in the bottom picture of post #32 are stock Mabuchis, and if the arm is even "warm", they are junk.  You could shim them to close up the gap, which may work OK if the arm isn't to hot.  Zapping them is (*as Bill said) not recommended.

-The "EPX" magnets are very strong for even modern ceramic singles, but will make for a very large hole.  Your arm is probably under .510" diameter (*it's been polished), and the EPX magnets will make for a gigantic hole in that can...I think maybe as much as .570" or more.  You would also have to flatten the magnet tabs (*the slits on either side of the rectangular can holes showing in the bottom picture of post #32) to install them which would ruin your paint job.  If you decide to use the EPX magnets anyway, you'll need to either get the matching clips...OR...epoxy them in with a slug.

-Later "Hong Kong" produced Mabuchi magnets are around 10% stronger than the earlier Japanese ones, will drop right into your can and can also be shimmed.  With either the Japanese or Hong Kong Mabuchi magnets, you only need one magnet clip, but the ones shown appear to be Muras because the radius is too tight.

***If you want to use this arm and get the best results, it should be tied and epoxied, and then sent out for dynamic balancing.  It doesn't cost much, but is often worth it with rewinds.  You also *might* be able to drop in a modern 16D or Super 16D arm and one of those may fit correctly and space fine with the magnets you have.

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The chassis is really neat, but should NOT be built up into a barn-burner with an inappropriately hot motor.  It should be a fun/smooth runner.  The equivalent of a 65/30 arm with the Mabuchi magnets (*either Japanese or Hong Kong) should be more than enough to make for a good motor-to-chassis match.

[Bill from NH]

Modern 16D & S16D arms, while nice, are timed in the opposite direction to what this chassis needs. Stock Chinese 16D arms have between 15-25 degrees of advancement to run counter-clockwise at the endbell. You might get someone to wind a 16D arm advanced in the opposite direction.

[Martin]

Thanks for all the help, I have a lot to learn in this area.

 

I have some more choices, They all fit and spin in the can with the magnets that came out of the can originally with about .020" gap.

 

There is a mixture of timing from neutral to CCW and CW please can you identify rotation and give you opinion on the best candidate.

 

I will clean the com with a 1/8" wide strip of 1000 grit emery paper ( if that is acceptable ) and try and get this thing spinning. 

 

So if I have this correct. The blue wire arm and the one on the far right are CCW rotation which is not what I am looking for.

 

Would the stock arm (far left)be a milder safer choice ?

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[havlicek]

The second from the right with the grind-balance appears to be timed CW...but your original arm seemed to be neutral-timed and should be fine.  In any case, the arms would have to be metered to know which might be more or less appropriate.  Even then, installing the arm and test-running it at low voltage would be the best way to know what you have.  The stock arm would probably be fine, but might be a little anemic...or not.  Not all the stock winds are the same, with different companies having them wound to their spec.

 

 

 

I will clean the com with a 1/8" wide strip of 1000 grit emery paper ( if that is exceptable ) and try and get this thing spinning. 

 

 

That's fine, but you can also just pinch a piece of 0000 Scotchbrite around the com with one hand and twirl the arm *BY HAND* to clean it.  It will probably work faster than 1000 grit and leave a very good finish for conductivity.  A mirror finish is not necessarily the best for the com.

[Pablo]

If it was my car, I'd have H Man blade balance the stock arm, and use the stock mags.

As H Man said, over powering that lil' car would be the worst thing you can do to it.

 

You said 20 thou airgap, is that 10 thou per side, or 20 thou per side?

 

If you opt for more power, the second from the right rewound arm is timed correctly and may be a good option.

The blue one is timed wrong, so is the one on the far right.

[Martin]

Thanks guys.

Thats .020" total .010" per side. I will find a better way to measure that. What is a good air gap ?

 

Can you shim the magnets with this design can? The stamping s on the can fix one side of the magnets ( top in this case) and then it has one spring clip opposite the fixed can tabs. Is that the way you see it ?

 

I can set up 2 razor blades to static balance. I would like to have the arm spinning between 2 magnets. I have seen the balance tool somewhere.

 

I will move forward and bench test the silver wire arm and the grind balance arm. I have a way to check amps drawn and go from there.

[Pablo]

"Good" air gap depends on which arm you use and what magnets.

For both the arms I chose above, I'd stay with 10 thou per side.

 

Those Mabuchi cans are lightweight and anything tighter than that, you'll have the stacks hitting the mags if anything shifts.

 

I'm betting the silver neutral arm would run hot with the stock mags.

[havlicek]

 

 

I will move forward and bench test the silver wire arm and the grind balance arm. I have a way to check amps drawn and go from there.

 

Current draw isn't necessarily an indicator of all that much by itself.  It could mean you have a hot wind, but it also could mean something is wrong.  Example: try pinching the shaft of a motor that's running and watch what happens to the current.  Same thing can happen with misaligned bearings, poor brush-to-com contact (*arcing) caused by any number of things, something hitting inside the motor...and *just bad brushes (it happens!).

[Martin]

That all makes sense. I mainly use it to check the best direction for any giving motor. Also helps make sure I got the wheels turning the correct way to make the car move forward

[Martin]

Made a little progress and assembled  the end bell and put the red wired arm in the can (second from right) and all sounds good. 

 

It has about a .020" cap on both sides  so I may shim it if the experts recommend it ?

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[Pablo]

If it runs warm as is, yeah, I'd shim it from 20 per side down to 10 per side.

 

Looks fantastic