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arroldn wrote:

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Tested at 12 volts
Carrera 18,058-20,634 rpm 98gcm
Slot.it 22,500-23,766 rpm 170 gcm

From the test result the Slot.it on the low end is 4442 rpm's faster and 3132 rpm faster on the high end.


The average speed for the Carrera would be 19,346 rpm's and the Slot.it would be 23,133 rpm's. the Slot.it comes out with a 3,787 rpm advantage.

arroldn wrote: From Glenn's chart on motor efficency a 21,000 rpm and 170 gcm motor and a 25,000 rpm and 180 gcm motor geared 9/27 or 3:00 the 21,000 rpm motor moves a car at 22.8 fps while the 25,000 rpm motor move the car at 27.2 fps. Or you could say for each 1000 rpm the car should move 1.1 ft. Thus if we had a 3,787 rpm advantage the car in theory with the Slot.it should move at a rate of 4.16 fps faster than the Carrera.

This is a true and on a drag strip this would be most acccurate. On a track witrh turns and curves, the trick is to select a motor/gear set that will be able to reach top speed on most of the straights on a track while allowing controlability on the curves.

arroldn wrote: But this may be off since the Carrera only has 98 gcm and I'm not sure how Glenn used this factor in determining fps. But just from the RPM advantage you would think the Slot.it would be faster.

FPS is based purely on RPM (for ultimate speed), Torque (ultimite available force, limited by available power) is used to derive acceleration (How soon it gets there, countered by mass) which derives Time-to and distance-to top speeds (Based on RPM). Motors are rated is at peak performance points on their RPM/Torque curves. As a data point, the calculations I ran are based on Peak performance points, thus represent the optimal performance which few motors will ever match, due to normal variations in actual car configuration. The effective mass is used to derive acceleration from torque rating (T=Fd, F=ma). It assumes that for motor power, the magnetic downforce, more or less acts as mass. While not completely accurate, it should allow for meaningful results when dhe desire is to select from different spec motors.

arroldn wrote: Now if we look to what happens on the race track lets look to the Forums cup where I had a stock SCX and a stock Scaley in the last race on a wood track my Cars came in 1st and 5th compare to the points champions 11th place finish. The points champ also turned a faster fastest lap than both my cars. My cars were 19 and 28 grams heavier and the champ was running a Slot.it orange end bell motor rated at 21,500 rpm compare to my stock rating of 19K and 18K respectfully. So what does all this mean???

Look at this link to a description on DC motors theory

It means that the torque is a major component to real performance. The greater the torque, the quicker the acceleration which means more time spent at top speed. There are always tradeoffs. Quite frankly I find that the Orange endbell motor tends to outperform the yellow endbell from a speed/drivability perspective.

arroldn wrote: Motor speed, tires, weight, track surface all determine how a car will perform. Again in racing its not always the fastest car that wins but the one that can get optimun performance on a given track. By the way my cars with their under powered motors had their share of not qualifing for the main event. 5 DNQ's for the SCX and 4 DNQ's for the Scaley.

Forgive the rambling but does any of this make sense?

Now you got me going...