From: hutto@SMTC.engr.scarolina.edu (Brent Hutto)
Subject: Re: 2WD 1/10th offroad
Reply-To: hutto@smtc.engr.scarolina.edu
Organization: NIST Southeast Manufacturing Technology Center
Date: Fri, 14 Aug 92 12:14:31 GMT

In article <1992Aug13.222609.19155@beaver.cs.washington.edu>, waynew@cs.washington.edu (Wayne Wong) writes:
>
>Just some questions...
>
>(1) After about a month of racing my RC10 Team car, I noticed some
>	marks on the dogbones/universals(?) close to the outdrive hubs of
>	the transmission.  There is a perfect circle (parallel to
>	how the rear tires turn) on both the left and right.  Are these
>	markings typical?  Is it due to an incorrect setup or just part
>	of what happens when the rear a-arms are put at extreme angles?

    I don't know.  My cars have plastic sliders instead of dogbones.

>(2) I think that I want give modified racing a try.  What are typical
>	final gear ratios to use with say a 15T or 17T quad (on a 
>	relatively short and/or medium track)?  

    For a 17-turn motor with a 6-cell battery, something on the order
    of 9.0:1 is a good, safe starting point.  If you use a 7-cell pack,
    increase your 6-cell ratio by around 10%, in this case to maybe
    9.8:1 or so.  For a 15-turn motor, around 9.6:1 is safe of 6 cells
    and 10.2 or so should work with 7.  Always start on the "high" side
    (numerically) and run the motor in practice working your way "down",
    checking the run time and temperature of the motor and batteries
    after each run.

    For instance, with a 17-turn motor and a 6-cell 1400SCR packs, I
    would put a 23-tooth pinion on my car (9.40:1), if that ran for,
    say, 6 minutes I would try a 24-tooth (9.01:1), let's say that
    ran for a little over 5 minutes and the motor was warm but not
    hot, I would go to a 25-tooth (8.65:1) and see if I could still
    run for 4 1/2 minutes or so in practice.  If it worked out this
    way, I might use the 25-tooth (8.65:1) on fast, long tracks and
    be able to fall back to the 24-tooth (8.65:1) on tighter, shorter
    tracks if I needed the acceleration.

    The advantage to the method is you never run your motor, even in
    practice, with too big a pinion and bog it down, overheating the
    batteries and, especially, the motor.

>(3) Modified motor brushes... how often should one replace these?  What
>	compound do these come with?  Should I replace them with soft or 
>	hard silver brushes?  I would like to minimize comm. wear.

    I like brushes with some silver in them, but I stay away from real
    soft brushes in high-power modified motors, save the 3-run and out
    brushes for stock.  I don't remember the part number, but Reedy
    makes a good "medium-hard" brush for modified motors.

>(4) Sometimes I've noticed modified racers using 6 cells instead of 7.  Is
>	this because they want to have less "punch" out of turns,
>	save weight, etc?

    I recently switched back to 6 cells to save weight (a couple of
    ounces).  I use 1700MAH cells (both Sanyo and Panasonic) which have
    enough capacity that I can go to really low-wind modified motors
    and get plenty of power even with 6 cells and still make my time.
    For the very fastest tracks, however, I still keep a couple of
    7-cell 1400SCR packs just in case.  If I can't go fast enough with
    a 6-cell 1700SCR pack and 10-turn single, I switch to a 7-cell 1400SCR
    pack and a 12-turn single for one qualifier and, if it does better,
    for the main as well.  It good to have both options, my cars run
    better 2 ounces lighter, for sure, but they run faster longer with
    the 7-cell option.

-------------------------------
Brent Hutto
hutto@SMTC.engr.scarolina.edu
From: earl@trsvax.tandy.com
Date: 19 Aug 92 08:22 CDT
Newsgroups: rec.models.rc
Subject: Re: AM vs FM AGAIN? - Have Mercy
Message-ID: <1195667298@trsvax>