Re: motors/torque

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

Steve Edwards wrote:
> 
> Hp/lb ratios for real tanks are greater than the recommendation:
> 
>    Sherman .007 hp/lb.
>    Tiger .005 hp/lb
>    T-34 .009 hp/lb
>    M1 Abrams .011 hp/lb.
> 
> EV Warriors are rated for about .378hp -at- 12V or 1.55hp -at- 24V. Assuming a 
> model weight of 175lbs, running the motors at 12V will give you a ratio 
> of .0043, whereas running them at 24V will give you a ratio of .0177. 
> Compare these ratios to the ratios for the real tanks above; do you want 
> your model to move more like a Tiger, or an Abrams? Sticking to the 
> "real" ratios will get you scaled performance, but that's not what you 
> want when you're going up against these guys.  :-)
> 

Congratulations Steve, this is the most concise description of the 
design goals for selecting motors that I've seen, especially comparing 
the performance of real tanks with our tanks.  Models (ships or tanks) 
always require more relative power than their real counter-parts, 
because they don't operate on scaled-down water, dirt or grass.  So, 
it's nice to see that your numbers above confirm what I've always known 
experimentally.

Of course, no good deed goes unpunished ... so, for the benefit of the 
hobby and all future newbies, I hereby request that you re-format your 
most excellent message into the form of an article so that I can post it 
on the "How-To" part of the website.  Don't worry about the HTML 
formatting issues (I'll take care of that), just focus on making it a 
stand-alone article with any additional details that you think would be 
useful.  I'm sure that Prof. Sommer would be happy to assist with 
folding in some actual numbers from the spreadsheet that he maintains, 
perhaps yielding a simple scatter plot that shows desired design space 
and data points for existing tanks (real or modeled) and/or motors. 
(Here again, if you guys give me the data points, I can format the 
graphics as needed).

Bravo Zulu.

        Frank "Love When Science Is Useful" Pittelli