40 replies to this topic

[Alan Draht]

I had been thinking about building vintage dragster motors using Kemtron motor field laminations/ magnets and Ram armatures for a while.

 

I took a break from building replica vintage dragsters, gathered up what I had accumulated in the way of Kemtron motors, Ram and Pittman "padlock" motors, and figured out how to assemble the best of various vintage motor components into custom dragster motors.

 

 

 

[Lone Wolf]

The February '65 issue of Rod and Custom Cars and Models has a four page article by Bob Braverman on doing just that.

[Alan Draht]

Before I begin, my hat's off to dc-65x for his excellent posting of the "RAM and Kemtron motor mashup - the RAMtron 850" topic.

 

Link:  http://slotblog.net/...he-ramtron-850/

 

Rick's topic begins with images of Bob Braverman's February 1965 Rod & Custom magazine article, "Kemtron X-503 Hop-Up".  I had not seen this article before and it along with Rick's posts helped me figure out another way to build a Kemtron/ RAM hybrid motor.

 

 

Also, I want to acknowledge Howie Ursaner for his comment in the "Replicating Husting's 1966 Top Fuel Eliminator Magwinder" topic thread.  It's what originally got me thinking about doing this motor-building project in conjunction with building complete vintage magwinders.

 

Howie Ursaner, posted April 15, 2020:

 

"Just thought I would mention that Sandy Gross built a really fast one using a Kemtron magnet and laminations cut down with a Ram armature.  It's lighter than a DC 85 setup".

[Alan Draht]

Here is Kemtron's product bulletin for the Mustang and Bronco motors:

 

 

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[Alan Draht]

I sorted through and disassembled my stockpile of Kemtron, Ram and Pittman motors and surveyed what I had.

 

 

 

 

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[Alan Draht]

Originally, my plan was to take the field laminations/ magnet from one of a handful of Kemtron's 12 volt DC motors I had acquired for this project, and fabricate a pair of Pittman's DC-84/ 85 end plates to mount a Ram 6 volt armature between them.

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[Alan Draht]

My first attempt was "no go".

 

The armature made contact with the magnet side of the hole in the field laminations.  The arm was not positioned concentrically in the hole.

[Alan Draht]

I had put time into completely machining the end plates before doing a test fit of the components and didn't want to ditch them.  I tried some work-around's like grinding the inside of the hole in the field laminations, but soon gave up because that's an absurd way to build motors.

 

I prepared another pair of endplates, shifting the 4-hole through-bolt pattern of the 12 volt Kemtron motor's field laminations on the Pittman endplates to center the armature.  I did not machine the endplates to their final form, just drilled a new four-hole pattern.

 

The revised endplates with the re-positioned hole pattern also did not work with the Kemtron 12 volt motor's field laminations.  It was still a tight fit.

 

I took another tack, switching from the Kemtron 12 volt motor to Kemtron's Mustang motor.

 

I discovered that the Mustang motor's 8 volt armature is identical to the Ram 6 volt arm other than voltage rating.  Kemtron's product bulletin for their Mustang and Bronco motors says that the armatures in both motors are, in fact, made by Ram.

 

The armature hole diameter in the Mustang motor's field laminations appeared to be slightly larger than the Kemtron 12 volt motor's hole diameter.

[Alan Draht]

A test fit of a Ram armature in the new assembly of Pittman endplates and Kemtron field laminations/ magnet taken from a Mustang motor was successful.

 

The armature was centered in its opening within the field laminations.

 

 

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[Alan Draht]

I fabricated a set of endplates and assembled a complete motor using a Ram 6 volt armature.

 

 

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[Alan Draht]

Weight reduction is substantial.  The hybrid motor is 1.0 oz. lighter than a stock "padlock" motor.

 

 

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[Alan Draht]

I liked the results so I fabricated and assembled a bunch of these Kemtron/ Ram/ Pittman motors, six so far.

 

Five of these motors use Ram 6 volt arms; the sixth motor uses a Pittman 6 volt armature.

 

 

 

 

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[Alan Draht]

All of the motors feature ball bearings and Pittman brushes.  They all get their magnets zapped on the Carlisle re-magnetizer when they are fully assembled.

 

They spin fast on 12 volts as they are now, but should spin faster when the arms are balanced (after epoxying) and brushes are fully seated.

[Isaac S.]

Looks great, very nice. 

[don.siegel]

Great idea Alan, and an impressive assembly line. 

 

Let us know how they run on the track once you get one mounted. 

 

Don 

[Tom Katsanis]

Nice motors Alan they came out well I just did a build recently putting a 6 volt Ram arm into a stock Kemtron Mustang it is a very healthy motor.

[Alan Draht]

Thank you Isaac S., don.siegel, Tom Katsanis 

 

I don't expect that I'll be building six magwinders, one for each motor.  A few maybe.

 

The point for me with this project and a lot of my late-stage slot car building is to try to use up everything I have acquired --  vintage slot car components -- building everything that I wanted to when I was a kid, but didn't have the time or the resources to do so fifty years ago.

 

In the case of this project it's better, it seems to me, to recombine various motor components into something new that's faster, than it is to leave things stock in their boxes unused.

 

If I don't use the motors myself, they may end up on eBay some day.

[Alan Draht]

But wait, there's more.

 

I was bothered my inability to to use the 12 volt Kemtron motor's field laminations/ magnet with the Ram 7-pole or similarly-sized Kemtron 7-pole and Pittman 5-pole armatures.

 

I kept fiddling around with the Kemtron 12 volt motor/ Ram armature combination.

 

I discovered that I could fit the Ram arm into the 12 volt motor's field lam/ magnet "core" if I used the Kemtron Mustang motor's cast metal end plate at one end of the motor, Kemtron's standard stamped brush-holder endplate at the opposite end, along with four spacers, one at each bolt hole, to accommodate the Ram armature's increased length (compared with the stock Kemtron arm that came out of the 12 volt motor).

[Alan Draht]

I like everything about the Kemtron and KTM motors of the 1960's except for their brush set-ups.

 

It always seemed to me that for drag racing, the Kemtron motor's flint-sized brushes and tiny springs were a speed-limiting factor, that the Pittman-style brushes and set-up were the only way to go.

 

So, for me, the Kemtron motor's brushes have to eliminated in order to build a competitive drag racing motor, and that's quite easily done.

[Alan Draht]

But what to do about the Kemtron brush-holder endplate's orientation with respect to the motor itself?

 

It needs to be rotated 90 degrees to build a Pittman-style brush-holder.

 

The Kemtron motor uses thin stamped brass plates at both ends, under the endplates, to help keep the motor "square" and the cylindrical "core" of the field lamination/ magnet set aligned.

 

It would be easy to rotate the Kemtron motor's endplates 90 degrees if the four-hole bolt pattern was square, but it's not.  The bolt hole pattern is rectangular.

[Alan Draht]

My solution is to take the standard Kemtron brush-holder endplate, push the oilite bushing out out of its hole, ream the hole for a 1/4" diameter flanged ball bearing, and cut off each of the endplate's four corners where the motor's bolt holes are located.

 

I decided to solder the modified endplate, rotated 90 degrees, to a standard thin stamped brass plate with its 4-hole pattern.

 

This is where I borrowed a neat trick from Bob Braverman's February 1965 Rod & Custom magazine article, "Kemtron X-503 Hop-Up".

 

Refererencing that article, the key take-away for me is the the part where Braverman writes/ illustrates in Steps 6 and 7...

 

"Using a strip of typing paper, wrap EXACTLY two turns around the armature and leave about an inch hanging out for removal.  Now slip the armature into the field as shown".

[Alan Draht]

With the Ram (or Kemtron) armature inserted into the "core" of the field lamination/ magnet set, centered in the hole with the paper strip, I assembled the motor using 2-56 threaded bolts and temporary (during the soldering process only) 2-56 nylon nuts.

 

I taped everything up to protect the motor from acid fumes and flux during the soldering process.

 

I then placed the modified Kemtron endplate with a temporary 1/4" brass bushing over the armature shaft (rotated 90 degrees from its stock position), and soldered it into place on a standard thin flat brass 4-hole brass plate.

[Alan Draht]

I removed the protection tape and pulled the paper strip off of the armature and check the results.

 

The armature was centered perfectly in the field lamination "core" and it spun freely between the endplates.

 

The armature's air gap in the 12 volt motor "core" is about half of what it is in a Kemtron Mustang motor's "core".

 

More on this later...

[Alan Draht]

I still needed to create a Pittman-style brush holder.

 

A fixture for the brush holder was created using a short length of 5/32" square brass tubing.  Holes were drilled for the posts.  Then the brass tube was soldered to to endplate.  Next, brush holder posts were epoxied to the brass tube.

 

The final assembly looks like this...

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[Alan Draht]

Like my first Kemtron motor mash-up using modified Pittman cast metal endplates, weight savings is 1 oz. compared with a stock Pittman "padlock" DC-84/ 85 or similar Ram motor.

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