Conference vmszoo::rc

    On a screw thread, 48 pitch would mean 48 teeth per inch. On a gear
    it's more complicated. Off the top of my head I remember
    diametral pitch, circular pitch, axial pitch. I would guess they
    are referring to diametral pitch, so if you looked up a #48 diametral
    pitch gear in the Machinery Handbook, it would give a bunch of specs
    that would probably not be of much use to you unless you are machining
    your own gears.
    
    The 86:19 drive/pinion ratio is 4.52, so this gives you a starting
    point if you want to swap gears for different purposes. A lower
    numerical ratio, ie, 4.0, would give more top speed, while a higher
    numerical ratio (commonly referred to as a *lower* gear) ie , 5.0,
    would give more acceleration.
    
    Terry
    

    I just happened to have a machinery guide from 1946 and read all of the
    stuff about gearing and pitch.  I am also glad I'm not a mechanical
    engineer.  Your explanation about ratios was excellent and I thank you
    for that info.  Judging by the way my car can find poles and curbs
    faster than a speeding bullet, my gear ratio is probably just fine for
    now.
    
    	Thanks again,
    
    	Sal

Two other pieces of information will be helpful.  The first is the Transmission
Ratio (all the rest of the gears).  For the Losi tranny, this is 2.18.  You
multiply this number by the spur/pinion ratio to get the overall ratio.  This
number is useful at the race track when you want to compare ratios with someone
who has some other brand of truck (or car).

The second is tire size.  With the overall gear ratio and the tire size you
can compute an "inches/motor revolution".  This number allows you to compare
your truck with someone else's car.

For racing, the "proper" gear ratio is one which allows you to finish a 4
minute race without "dumping" (depleted battery).   The second measure of
"proper" gear ratio is the temperature of the motor at the end of a run.
Unless you like to buy new motors frequently, you should be able to hold
your finger on the motor without "pain".

Based on my experience with a JRX-Pro, your 86/19 is a reasonable choice
for a 350 motor (18 turn double) and car tires .  I'd guess that you need
to be closer to 86/15 with truck tires.

    Brad Morgan's advice (run 86/15) is good.  You may still have trouble
    running for four minutes, unless you have SCE batteries or *good* SCRs,
    because the 350 is not a very efficient motor.  (In my opinion you'd
    be better off investing in a more efficient motor than getting SCEs.)
    But 86/15 should not cook your motor.

    What would be a more efficient motor?   I told you I was new at this...
    and what is an 18 turn double?  What is the diff between hand wound and
    machine wound?  Thanks and thanks for the mail by the way...
    
    Sal

    I also found a local shop selling a new, sealed in the box JRx-T for
    $170.  This is cheap.  He said he got stuck with it and doesn't like
    Losi...he likes Traxxas.  Anyone interested?
    
    Sal

RE .4, .5:

I not sure I agree that the 350 is not an efficient motor...I own 4 of
them! If 86/15 doesn't make 4 minutes, something between 86/14 and 90/10
probably will and as I tell most of the "beginners": "You don't have to hit
things that hard!".  The 350 is one of the motors I recommend to people as
a good first modified motor.  If you're going to race, I'd suggest starting
out in Stock.

The performance of the electric motors we use in this sport is determined
primarily by the amount of wire on the armature.  This is because most of
the other factors like magnet material, number of poles, etc. are mandated
by the santioning bodies (R.O.A.R. in the U.S.).

Stock Motors have 27 winds of .065 (I think this is the size) wire per
pole, must be available in quantities of 5000 or more, and can cost no more
than $28.  R.O.A.R. just added another constraint of a maximum of 24 degrees
(mechanical) of timing and specifications designed to prevent tampering. 
The timing advance is similar to that of automobiles.

Modified Motors by R.O.A.R. standards must be available in quantities of
2000 units and can cost no more than $80 retail, but the rules allow
re-winding of the armature.  Up until a couple of years ago, all modified
motor armatures were wound by hand and retailed for $80.

I believe it was Trinity's Speedworks line of motors which introduced the
"machine wound" motor for about $55 retail.  This started a rash of machine
wound motors as well as a reduction in cost for some of the hand wounds.

The difference is that the machine wound motors are cheaper to produce but
are not available in as many different configurations as the hand wounds. 
The hand wound camp believes they wind a better motor.  My experience has
been that a machine wound and a hand wound of the same configuration will
have about the same performance, but the probability of the machine wound
motor suffering a premature death is a bit higher.

An 18 double is the configuration of the wire on the armature.  The 18
refers to the number of turns of wire and the double refers to how many
strands of wire are used in each turn.  The gage of the wire also
contributes to the performance of the motor but is not always specified. 
Machine wound motors are almost all doubles or singles (Speedworks has a 14
quad).  Hand wounds can be singles, doubles, triples, quads, or even
higher.  In some cases, each strand of wire is a different gage.  As the
number of turns decreases, the RPM and torque of the motor increases.  The
amp draw also increases.  As the number of strands increases the torque
decreases.

That's probably enough for now.

Brad

    There is a new generation of very efficient modified motors available,
    exemplified by the Reedy "Mr" series.  These motors have stronger
    magnets and are run with light brush springs.  They run cooler and
    slow down less during a race than previous motors.  They are perfect
    for use with 1400 SCR batteries in two-wheel drive offroad (buggies
    and trucks.)  The fragile 1700 SCE batteries are a thing of the past
    in two-wheel drive offroad.
    
    My first modified motor was a Speedworks 350.  When I switched to a
    Reedy Mr. K (17 turn quad), I found that I was a better driver than
    I thought.  The motor accelerates well, has a good top end, yet does
    not "snap" and cause uncontrollable wheelspin coming out of the turns.
    And I never come *close* to dumping in four minutes.  (Would you believe
    six minutes?)
    
    These motors are available mail order for as low as $43; a good local
    shop may have them for $50 (in spite of the $80 suggested retail price.)
    
    None of this matters much if you are just driving around in the street.
    As Brad Morgan says, when you start racing, you should start in stock.