Originally Posted by
old_dude
There are chassis dynos with load motors. I have one but it is a simple one. Bank of resistors to give three loads. Simple amp draw of test motor and load motor voltage generation to determine wheel speed. Have thought about equipping it with a accurate sensor system for true motor rpm via the sensor wire tap off.
I will add one of my theories that is backed by Tekin esc data. On tight indoor road courses or ovals, the motor is always in acceleration or deceleration. Hardly ever does one peak out unless your gearing is too low. To get the most from a motor, it must be worked as much as possible.
yea I have the minipro chassis dyno. its flywheel is aluminum. so I have an electromagnet pulsing eddycurrents on the flywheel.
an acceleration and load dyno are very good at calculating power. the accel dyno does some things batter than the load dyno and vice versa. One of the advantages of a load dyno is it can pinpoint the exact amount of peak work you can do continuously before the motor overheats. so if you add 80 watts of resistance to a 150 watt motor and it almost overheats after running it for an hour you know that the motor can dissipate 80watts/second of heat. this means 80 watts in acceleration/deceleration or constant power.
if you know that a corner that goes from 5000 rpm on entry to 10000 rpm on exit over a 1 second time fram the average rpm is 7500. the efficiency over that range goes from 40 to 60 so you have an average of 50% efficiency. if the average power at 7500 rpm is 150watts and the average efficiency is 50% 75 watts. you can run that corner indefinately. or you can run the next corner at 85 watts of dissipated heat and still stay under the thermal limit.
so if you set the motor to run 150% for 1 second the next second should be 50% so that you stay under 100%. you can look at it this way in seconds or minutes or laps or ...
furthermore you know 100% is 160f. if you like 130f you know that the average efficiency has to stay at something like 80%.
so then you realize that instead of setting the motor to take the corner at 5k in and 10k out that you get 15% more efficiency if its 7.5k in and 12.5k out. so instead of an average efficiency of 50% you have one of 65%. which means the motor can come off cooler or you can save that efficiency for the next corner.
it gets complicated if you try to follow it all in one go but if you take it step by step you will understand how to adjust power in the unique way that electric motors deliver it.
you will also see the point of over timing a motor in special situations to induce field weakening.