Parma Arm ID

[Abarth Mike]

I hope this is the correct forum?

I have come into the possession of a Parma armature. The core is shinny, not green the comm has been trued and it has balance holes drilled in the core segments. One of the set of windings has a white spot of paint on it.

It has Parma HS written on the container tube. But by whom I do not know.

Anyone know what it is?

[Gone Racin]

Could be quite a few types of arm.
By the core do you mean the stack of iron plates the windings are wound round?

Are you sure it's a Parma? There are lots of makes that look quite similar.
Is there a sticker bonded on top of the windings - if so what does it say?
Is anything engraved on the stack - if so what does it say? (sometimes this can be hard to read)
How long is the stack?
What diameter is the stack? (the exact diameter can be a useful clue about what it is)

Truing the comm , balancing and truing the stack could all be done after original manufacture.
Truing the comm is routine maintenance on higher end motors, lots of the quicker guys have their own comm lathe.
There are quite a few balancing services out there. It is quite common to have arms rebalanced periodically.
Truing the stack is a straight forward lathe job.

[Abarth Mike]

I see the problem. I had not realized, it could be anything!



No etching or markings. Only what is written in a tube it came in.

The stack of iron plates is 13.05 O/D +/- .02-ish or .510 +/- .02 l Length is .505 not including the insulators on the end. .595 including insulators.

I don't have anything to accurate measure the timing but squinting through a protractor I would say a tad less than 20 maybe 8 or 17 deg but not midway ie 15.

But I see your point it could be anything. The winding wires are quite thin. It does not for instance have a low winding number.

Maybe it will have to remain a mystery?

[RichD]

It sounds like you have a 16D armature, the dimentions match and those are the only armatures that I can think of that have insulators at the ends of the stacks. Parma sells a version of this armature with a trued commutator , but when I was racing 1/24th slots balancing these armatures was not legal. Pro Slot makes their own version of the 16D armature and that is balanced. 16D arms have 70 turns of 30GA wire. Timing for stock armatures is usually around 20-25 degrees, I cranked my armatures up to 35 degrees.

[Gone Racin]

Hi Mike
Any chance of posting a photo?

The stack is a bit too short for an USRA legal 16d, and a bit long for a super 16d.
The rest of it sounds like something from the 16d family.
Some makers sold shorter stack "outlaw" arms as well as USRA legal ones.
I've measured a few standard Parma armature stacks - they are about 0.512 - 0.515 inch diameter, but would be slightly smaller if trued.

Did I understand correctly that the stack had been trued, or is it the duller coloured untrued one like the one in Rich's photo above.

[Abarth Mike]

Originally Posted by RichD

.

Visually Rich this looks exactly like the one I have. green colour, insulators on the end, etc. Mine have balancing holes drilled in the stacks but otherwise it's the same.

Only thing I have different to above, I got brave and put a caliper on the wire from the comm segment, is that I have 36-ish awg wire at .005. Could be 35 awg but... the caliper was dead on .005 not showing the subscript for 1/2 thou so I'm going with 36awg.

GR,

Visually it's the same as Rich's photo.





It was very kindly given to me in response to a Johnson resurrect question. If it helps.
Anyway I'm putting some Parma? or SCX magnets in along with this arm.
This is only for fun not for serious racing. Currently looking for Loctitie 380 but may be forced to use epoxy. Everything is available here it is just a PIA digging through the culture. What for?, why do you want it?, we have something else (usually not related) etc...

[Gone Racin]

Hi Mike
With that thickness of wire it'll be a Parma "Homeset" arm.
That fits with Parma HS written on the container tube.

These come as unbalanced arms, so it must have been balanced after purchase. Most likely just a static balance, although it is possible it was dynamically balanced. The owner could have done a static balance.

The Parma "Homeset" motor looks much like other Parma 16d, but has over twice as many turns of much thinner wire than the standard 16d spec RichD quoted. The "Homeset" takes much less current, produces much less torque and revs than other types of 16d.

The photo answers my question from an earlier post, the stack hasn't been trued.

Hope that helps

[Bill from NH]

I agree it's probably a "Homeset" arm since the normal Parma 16D uses 70T of 30 gage wire. The white paint on the end of one stack leads me to believe it's probably dynamically balanced. That appears to be someone's mark for use with a strobe light. It wouldn't be needed for static balancing.

[Gone Racin]

I agree with Bill that the most obvious reason for marking one pole like that is for dynamic balancing.

Marking one of the poles can be useful for static balancing (less chance of making a mistake about which pole was which, and drilling the wrong one!)

Curiously, some standard (unbalanced) Parma Homeset arms come with a white mark very like the one in Mike's photo. One guess as to why is preventing similar looking arms with different specs getting mixed up, not sure if that would be necessary ... anybody got any better ideas?

[Bill from NH]

If I static balance an arm, which hasn't been too frequently, I first take a Sharpie & label the poles 1, 2, 3. This has helped to prevent me from removing material from the wrong pole.

[Abarth Mike]

We that all make perfect sense. I found Home set on Roberts motor page. I was hoping to emulate Johnson but I see HS only comes out at 18,xxx. I have geared one Johnson down to 8/27 so maybe this one will have to go 10/27 if it has enough torque.

But one has to love these "user friendly" motors. If I don't like the HS arm I can simply reinsert the Johnson.

My search for Loctite 380 has got as far as me being offered 480 so now it is really confusing. Going to Home Pro on the off chance and I mean off chance that they have some Super glue Ultra!