Calculating needed gear ratios for r/c vehicles

[loic2003]

So, I'm looking to build my own transmission for a customised radio controlled vehicle. Creating the gears isn't a problem, but calculating the actual ratios is. How is this done by engineers usually? Do they do tests and figure what's a decent balance of torque and speed, then base everything off of that, or what?

Essentially, I'm building a buggy that'll be powered by two .21 engines. So, are there some calculations I can do using predicted HP, wheel diameter, etc... or do I calculate the ratio of a commercial r/c truck that's powered by a single .21, then make the primary drive maybe 25% higher?

It's a long shot posting in here, but I have been suprised in the past!

Thanks in advance.

 

[iamwiz82]

How are you powering using two engines? One powering the front and one in the back?

 

[swtethan]

http://www.et-studios.com/motorsports/gears/gears.html

gear ratio calculator

 

[swtethan]

http://www.4lo.com/calc/gearratio.htm

this?

 

[loic2003]

Originally posted by: iamwiz82
How are you powering using two engines? One powering the front and one in the back?

Removing the flywheels and replacing them with a larger toothed gear. There will be a central shaft that has a gear connecting the two engines and a flywheel to keep it moving.
This shaft is also what'll be used to start them, most likely using an electric drill with a one-way bearing.

Of course it's completely an experiment, I think tuning the two carbs to be the same is going to be a freaking nightmare, but having twin engines (180 degrees out of sync so there's always a power stroke) would be nothing short of awesome.

I'm currently building up CAD plans, so I'll post them up as and when...