mattnin

I think there is some error, we'll see how my other tests go. I am worried that the Sentry's resolution isn't high enough. For instance, check out the voltage readings. It shows 7.742V and the next step it registers is 7.837. So I imagine it only has 256 bits of resolution or less. I don't know. So I assume it would have that same lower resolution for all its readings, RPM, Current, etc....

Plus, the Hacker 13.5t motor revved up so quick, so it would be very hard to show lower RPMs. Literally after the first .1s, the flywheel was already at over 7000RPM! It appears to almost nearly have reached its max RPM in nearly 2 seconds. So this means only 20 inputs will be of value. The Sentry only takes a reading every .1s, but so does the Fantom Dyno. I might get better information if I lowered the voltage actually. The Fantom Dyno has a 5V output for testing, and so I may run the Tekin RS Pro off of that, and a 6V receiver pack.

Or.... I may just figure out how to collect the data myself using a PLC or some other discrete device hooked up to the sensor harness and using the motors hall sensors to record RPMs, and take voltage and current readings. I would like to take a reading every 0.01s and have a resolution of 3 decimal places for current and voltage and be able to take a more precise RPM reading as well.

I really do feel my math is correct. I have spent several days with my physics book, sample 19t brushed dyno data from the fantom, measuring the flywheel and so on and so forth, and I feel I have a correct methodology. I received a PM on rctech that I should consider the moment of inertia for the rotor, and I agree that is important to add as well. So soon enough, I will include that. That also means that the power ratings I show below will improve. I also plan on calculating the 'friction factor' and adding that to further increase the power. I can determine that by spinning up the motor to max rpm, and having drag brake turned off, and taking readings while the motor decelerates. That deceleration that I measure will become the friction factor, and will be added to the total power of the motor.

I may have discovered something from all this however. The fantom dyno has been rumored to show incorrect power ratings for its motors, and showing poor efficiency data. When I tried calculating everything, my data was close, but well above the fantoms. So I figured maybe fantom uses a different moment of inertia, so I tried solving for that using the RPM and torque they gave and I got a number. Then I tried using that number to calculate torque for different RPMs, and it never added up. So I have no clue how they calculated torque. There could be an argument made that maybe fantom has a deceleration figure for friction and air resistance, but that would only increase the value of power I am getting. Below is an example of fantoms data, and the data I calculated:

fantom #'s
time .1s rpm 3713 torque 1107 gm*cm watts 42.24 amps 73.1 effcy 11.6%
time .2s rpm 6113 torque 998 gm*cm watts 62.67 amps 64.2 effcy 19.5%

my #'s
time .1s rpm 3713 torque 1886.162gm*cm watts 71.95 amps 73.1 effcy 19.59%
time .2s rpm 6113 torque 1219.649gm*cm watts 76.57 amps 64.2 effcy 23.85%

I have a theory that maybe fantom didn't correctly convert torque from N*M to gm*cm the proper way, or something, because I just cannot come up with their torque numbers for some reason.