Re: we seem to be gearing down ?

[Frank Pittelli <frank-at-pittelli.com>]

Steve Rosadini wrote:
> 
> Are you guys still using the KCMs? Should I 
> change course now to something else to avoid the trouble, or worse 
> disapointment? 
 >

Those are excellent questions and I'd love to answer them as soon as we 
have some more hard data, before we send everyone down a possible 
dead-end.  Since we only have a small set of data points and only one 
weekend of battles on which to base everything, it's always dangerous to 
jump to a conclusion.  As such, it remains essential that as many people 
try as many possible alternatives as possible.  Only evolution and the 
battlefield will prove the effective solution(s).

Also, it's critical to remember that the drive system and track system 
should be designed with each other in mind.  It's not clear at this time 
if a given motor/gear system will work good or bad with a given track 
system.  As Joe's spreadsheet shows, we have a number of different 
combinations, but not enough to "close the book" and pick an overall winner.

That said, here is my current position on drive systems:

1) We've seen a number of different motor/gear combos that have more 
power than KCMs, including EV Warriors, drill motors and printer motors.
Extra power definitely helps tracks turn better and makes the vehicles 
go faster.  The KCMs are designed for turning 10-12 inch diameter 
wheels, and should be the motor of choice for armored cars.  But, when 
turning tracks with 4-5" drive wheels under heavy vehicles, the KCMs 
start to bog down.

2) One 12v, 18 amp-hour battery has been sufficient for each motor/gear 
combination used during a one-hour battle.  We're not sure what the max 
draw is for some of these motors, but over the course of a one-hour 
battle, we haven't seen any vehicles that were much slower at the end of 
the hour.   Limited battery measurements and common sense indicate that 
the batteries are certainly being drawn down, so it never hurts to have 
a larger battery to withstand the abuse.  All Tri-Pact vehicles are 
standardized on a 26Ah battery, while the Tyng Regime used 18ah batteries.

3) Power and efficiency must be balanced by cost and availability.

The KCMs are clearly the low-cost/high-volume winning solution.  They 
are readily available from the Mending Shed for $15 each, which includes 
the motor and gearbox.  They are also the easiest to install, since they 
come self contained, with drive wheel adaptors.  For flexibility, we 
installed them with a v-belt to the drive wheels, using inexpensive 
v-belts and pulleys available from a number of places.  Others have used 
bicycle chains as well for the drive train, which are also inexpensive 
and readily available.  Figure about $15 each for a two-pulley v-belt 
drive train, for a total of $30 per motor installed.  (Tri-Pact started 
using KCMs specifically because of these advantages, knowing that if we 
needed more power, we could replace them without wasting too much money. 
  Besides, they can always be used in armored cars and support vehicles.)

The EV Warriors cost $25 each, which only includes the motor, and they 
are available only from surplus suppliers.  The EVs need to be "geared 
down" by about 9:1, which requires some sort of chain/sprocket or 
v-belt/pulley arrangement, plus an intermediate shaft supported by 
bearings.  Tri-Pact is currently experimenting with different mounting 
arrangements, as well as chain/belt arrangements to fit various 
vehicles.  Using a combination chain and pulley approach, it costs about 
$60 per motor for the gear system, or a total of $85 per motor installed 
(based on our preliminary configurations).

The 18v drill motors used by Joe Sommer seem to provide power/speed 
roughly equivalent to the EV warriors.  They are more expensive, but 
they include a compact gear system as well.  Joe used a 1:1 right-angle 
gear to transfer power directly to the drive shaft, but other 
arrangements are possible. I can't recall the installed cost per 
motor/drive train, but Joe can provide that, I'm sure.

4) The motors must be effectively controlled and the cost of such 
controllers (for the same reliability) increases as power goes up.  The 
KCMs have proven very reliable using 30-40amp controllers, even when 
being pushed to the limit with stuck tracks.  At the present time, we 
think that the EV warriors and the drill motors may be OK using 40amp 
control circuits, but may require 60-80amp relays for extreme 
conditions.  More field and battle testing is needed to really know for 
sure. (NOTE: The only real stress test is a battle, where battlers push 
themselves and the vehicles to the breaking point.)

So, as with everything in life, speed and power require more money and 
energy.  A number of tradeoffs are possible using the various components 
mentioned so far that allow you to optimize one or two design 
constraints, but not all of them.  The key aspect of battling is to 
decide which trade-off works best for your vehicle and expected battling 
style, and then proceed accordingly.  Only the battle itself will prove 
which approach was truly better and even then sometimes luck plays a 
bigger role than skill or planning.  And the best way to hedge your bets 
is to use a modular design, where you can easily swap things out and 
move things around over time until you get everything "just right". 
(Tiger-1 has gone through 3 major overhauls of it's drive train in the 
last 2 years and will go through at least one more over the winter.)

I hope to have some EVs installed in Tiger-1 before the end of the 
month, at which time I'll know a lot more about their advantages and 
disadvantages.  (But, I haven't thrown away my KCMs yet, just in case I 
need to retreat to known position :-)

        Frank "Got Motors All Over The Place" Pittelli