CarbonJoe

Here's a link to a nice Excel spreadsheet I made for figuring out rollout:
http://www.rctech.net/forum/4792583-post5349.html

There is no easy or exact answer for the best or correct rollout for carpet. It really depends on the motor you are using as well as the track layout. The rollouts for brushed vs brushless are drastically different for the high turn motors. For example, for a CO27, we were usually running about 1.80 inch rollout (45.72mmpr), and for 17.5 brushless, we're about 2x that (3.60 inch rollout [91.44 mmpr]). The rollout is determined by the tire diameter, pinion, and spur size. It tells you how far the car will move forward for one revolution of the motor shaft. To get the huge rollouts for brushless, most guys are running 78 tooth spurs. For brushed, 88 tooth spurs.

Oh, and I'd also true your tires down some. They will chunk more at the larger diameters. A lot of 1/12 scalers start their rear tires at 1.75 inches (~44.5mm).

Triton3d

iTrader: (17)

But how do i know that motor X gives me more or less than motor Y..ect??? any formula??

Thanks
Mike

CarbonJoe

Mike -

Unfortunately, no. Ask others that are running similar motors if you decide to race. Otherwise, that is what practice is for. Get a number of pinions and try each one to see what the net result is. And don't forget that your rollout changes as your tires wear, so to remain consistent you will need to change gearing as the tires wear.

Triton3d

iTrader: (17)

Hey Joe, how do you know that a Brushless motor has more rollout than a brushed motor?? isnt a shaft turn the same in each motor???

Mike

TraceRacing

Mike, the power curves are different between the types of motor. Brushless has heaps more torque but doesn't rev as high as a brushed.

Thin along the lines of petrol (gas) engines and diesel engines....same job, different power bands

CarbonJoe

The calculation of rollout has nothing to do with the motor type. As stated before, it is the amount that the car will roll forward given one revolution of the motor shaft. On a 1/12 scale car, the only things that matter (since a 1/12 scale car is direct drive) are the gear ratio (pinion/spur) and tire diameter. It is the power band of the motor (RPM, torque) that you need to figure out for each type of motor. This takes experimentation at the track to see what the best gearing (thus rollout) is for a given motor. Brushless motors tend to have more torque (and less RPM) than a brushed motor. So they need to be geared differently.

As a general rule of thumb, for a brushless motor, add gearing (bigger pinion, usually) until your lap times aren't getting any faster, or the motor starts to heat up above the manufacturers recommendation. Then back off one tooth on the pinion. Of course this assumes that you drive consistently each time on the track.