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Motor advice and counsel needed


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#1 Ecurie Martini

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Posted 04 April 2019 - 08:48 AM

I am looking for some help here in the motor choice(s).
 
Here’s the background: there is a particular Mabuchi motor series, FF-050, often called a “slimline” motor, that is particularly useful in a number of 1/32 models – particularly those with very restricted space like the 1960s Formula One cars.
 
In addition, I emphasize “choice” because (a) motor building or modification is not in my basket of tricks and (b) in many cases the rules restrict the motors to those available off the shelf.
 
At one point there were a very wide range of this of motor available ranging all the way from very mild 14K examples up to 35 and even 50K “barn burners” (in the 1/32 world). For some reason most of these higher performance variants have disappeared.
 
Looking at the universal source – eBay – there are a large number of offerings and it is possible, based on the model number, to deduce information on not only size and shape but brush and magnet material, armature wire size, and number of turns.
 
Looking at the availability, some choices can be made. Number one is the size and shape which is, of course, constant. The brush material is limited to leaf type “precious metal” brushes and there is only a general specification for the magnets although given the very low cost, $1-2 per motor, I doubt that any really exotic material is used. What can be deduced from the numbers is the wire size (diameter in millimeters) and the number of turns.
 
Now, going back to my E & M course better than a half-century ago, I do recall that the resistance of a wire is inversely proportional to the square of the radius and proportional to the length. Although the turn geometry changes as an armature pole is wound, I’m going to assume that the number of turns is roughly proportional to the length of the wire. The other thing that I recall is that the torque of a DC motor is a function of current times the number of turns. An area of uncertainty: is this torque figure also a proxy for braking effect?
 
Here are some of the choices: (and, lacking more info, assuming that the magnets are the same and all to be run at 12v)
 
Wire diameter (mm) # of turns
 
0.10                           130
0.11                           170
0.11                           190
0.13                           115
0.13                           130
0.16                             85
 
Any insight as to the probable performance in terms of speed and braking for these variants?
 
A link to the Mabuchi specs and graphs: 


Winding Specifications
 
Thanks!
 
EM


Alan Schwartz




#2 havlicek

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Posted 05 April 2019 - 07:48 AM

Hi Alan,

     While I am BY NO MEANS well-versed and certainly not "schooled" in DC motor theory, there is always the interplay between the magnets' field strength and the armature's wind.  So, while I understand and agree with the stuff about torque as it relates to the number of turns (*I was taught that "power" is a function of the number of turns), the ability of a motor to produce RPMs and torque...as well as braking is the result of the whole "system".  Going further, the shape and size (*width) of the armature's outer crown plays an important part in all this, and then there's the big aspect of "commutation".  Many/most/all of the general use DC motors produced by Mabuchi and others that I've seen use a very small diameter commutator, but one that is proportional in size to the very small brushes.  They mostly seem to use similarly shaped laminations, although there is some variability there.  So I think the magnets is one of the more important variables in this type motor.  Even though they mostly (*but not always) use ceramic magnets, some are far stronger than others, even among the same type and manufacturer, apparently having been sourced for some specific use in a particular motor.  ***By the way, the airgap in ALL DC motors is really important as to the strength of the field the armature "sees", but that also seems to be fairly consistent since they use armatures with a consistent O.D. and magnets that make for a consistent I.D.

Disclaimer:  Since the FF motors use a 1.5mm shaft AND because of the smaller can making modifying for use with a cheap/available end bell more difficult, I haven't played around with them much.


John Havlicek

#3 Ecurie Martini

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Posted 05 April 2019 - 08:48 AM

Thanks, John - I think you are spot on.  Without magnet specs, there is a lot of guessing.  I have decided to take a "brute force" approach. A $20 bill will buy a pile of these motors.  I'm going to order some and first, collect some basic bench data - no load speed, current vs voltage curves - unloaded and with a fan blade load and then pop them into a test mule chassis and see: "wottle she do" on a track.

 

Assuming I can derive some meaningful data, there are several paths: Use the data to select what appears to be the best option from the online offerings and/or contact Mabuchi and ask for info on what is available from their stock inventory that would be the best fit for the projected specs. (I'm not going into the parts business so a custom set up is not in the cards.

 

Summer project

 

EM


Alan Schwartz

#4 havlicek

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Posted 05 April 2019 - 08:53 AM

No problem Alan,  This stood out to me from your second post:

 

 

 

and/or contact Mabuchi and ask for info on what is available from their stock inventory that would be the best fit for the projected specs.

 

I'd be interested to see if Mabuchi is responsive since they've long been in (*as far as I know) strictly the industrial supply business, selling motors in REALLY large lots directly to manufacturers...but maybe (?) also to resellers to get rid of unused inventory???

BTW, someone gave me some black-painted "FF" motors years ago with two square holes and solid neo magnets that I think were produced as a test for some slot car application.  While they were "FF" size, I don't think they were Mabuchis, and because of the ridiculously strong magnets...they barely turn over.  :)


John Havlicek

#5 Ramcatlarry

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Posted 05 April 2019 - 09:32 AM

Torque is also a factor in armature diameter.  The vintage Mabuchi 13d is basically the same size as the SCX motor and (with a shorter stack) the FC and FK 130 motor series. Those motors have good baseline data as to a 'drivable' range of # of turns and wire size.  What combination of wire to fit on the smaller 050 can in not known to me.  The overall resistance per pole might be a comparison to keep in mind.

 

In bigger cans, the 16D modern standard is 70T of #30 wire.  A 13D with that armature is testable since they drop right in the can.  The old 13Ds and many current homeset motors never use bigger than #31 or #32 wire....and maybe 100 turns.

 

Support parts need to follow to make the smaller motors practical.  I can see 64 and 72 pitch pinions with the 1.5mm bore as an essential part NOW, for Eurosport F-1 and hotrod club racing.

 

The motor in the MRRC production cars is hotter than needed for many 1/32 home track racing.  RPM exceeding 30K usually makes more problems.  Our club has a limit to 22K for our group.


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#6 Ecurie Martini

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Posted 05 April 2019 - 12:45 PM

Thanks - the resistance measurement is a good idea-I'll add that to the data set.

 

I have only one car that I know is fitted with a 30K+ motor.  It is a Maserati 4CLT GP car (long wheelbase) and is fitted with a substantial brass rattle pan - not easy to drive but goes well.

 

EM


Alan Schwartz

#7 Ecurie Martini

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Posted 05 April 2019 - 12:59 PM

I've ordered 3 examples each of 5 different motors:

 

38 AWG X 130 turns

37 AWG X 170 turns

36 AWG X 130 turns

34 AWG X   85 turns

30 AWG X   22 turns (I suspect that this one will go up in smoke)

 

Off to the Bat cave

 

EM


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Alan Schwartz

#8 Geary Carrier

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Posted 05 April 2019 - 01:16 PM

Alan,

 

This is why the test pilots get the big bucks... :wink3:


Yes, to be sure, this is it...


#9 Ecurie Martini

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Posted 05 April 2019 - 01:19 PM

I have a good stock of 64 & 72 DP pinions in both 1.5 and 2mm bores as well as a lifetime  supply of 1.5 - 2.0 mm sleeves (I bought a 3' piece of 2mm OD. 1.5 MM ID SS tubing)

 

EM


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#10 MarcusPHagen

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Posted 28 August 2019 - 01:39 AM

This is an interesting project. Any interim results?

 

Marcus


Marcus P. Hagen -- see below, my five favorite quotes: applicable to slot cars & life in general.
[ "Everyone is entitled to his own opinion, but not his own facts.". . Daniel Patrick Moynihan ]
[ "Time is the best teacher. Unfortunately, it kills all its students.". . . . . . . . Hector Berlioz ]
[ "There is a very fine line between 'hobby' and 'mental illness." . . . . . . . . . . . Dave Barry ]
[ "Build what you like to build, they are all doomed." . . . . . . . . . . . . . . . . . . . . Prof. Fate ]
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