TenShock Motor Measurements

[LohringMiller]

I was asked about the "real" KV of the TenShock CZ11240 motor rated at 2680 KV. I took the measurements with the motors installed in two boats by spinning the drive shaft. One had a .150" shaft in a Teflon tube and the other had a .188" shaft in a brass tube. I was also interested in any difference in drag between the two shaft sizes. First I used the drill method (see namba.com/content/library/propwash/2022/april/26/). My drill turned the motors a little over 1000 rpm. I got a KV of 2523 on one motor and 2493 on the other; close to the same.

I then hooked up a 4S battery to each motor through Castle Hydra X ESC. I then ran them at full throttle for a short time until the current draw settled at a constant value. The voltage in each case was 15.1 volts. The battery was at its stored voltage. The current draws were surprisingly similar for both shaft sizes. The .150" shaft registered 12.4 amps while the .188" shaft registered 11.9 amps. The data logged rpm was 41,370 on the .150" shaft and 40,997 on the .180" shaft. That gives a KV of 2740 and 2715; again very close. Correcting for the internal resistance of 5 ohms gives 2678 and 2655. Those are very close to the manufacturers rated values; well within the accuracy of my measurements. See Brushless Motor Kv - Measure a Motor's Kv - RCexplained for details on how to calculate this.

The point is that the drill method rpm is a lot lower than the unloaded rpm. This gives values that are different. I haven't compared enough motors using both methods to see if lower rpm gives lower values of KV.

Lohring Miller

 

[RaceMechaniX]

Lohring did you test at 0 Deg of timing in the Castle?

 

[LibertyFrancis]

Lohring did you test at 0 Deg of timing in the Castle?

Exactly where my mind went.
When you leave it on default 10 deg timing castle runs dynamic self-adjusting timing.

 

[LohringMiller]

I ran 5 degree timing. What would you expect the difference to be? I got a current draw that decreased in three steps. Did this show timing changes?

Lohring Miller

 

[LibertyFrancis]

I ran 5 degree timing. What would you expect the difference to be? I got a current draw that decreased in three steps. Did this show timing changes?

Lohring Miller

From what I understand the castle timing adjustment is more based on low, mid, and high rpms. If that occurred during full throttle peak rpms then it may be something else going on.

I wish Castle included timing as one of their data points in the logs

 

[RaceMechaniX]

Lohring the timing will affect the no load RPM. 5Deg may not be too significant but something like 20 deg will be. No the current draw stepping down is just the difference in steady state versus accelerating. The loggers are not too precise in the single digit amperage draw. If you want accurate no load current it's best to use a multimeter inline being careful to spool up the motor slowly so the current draw is not excessive. Or build a 4-wire Kelvin IR meter to measure the winding resistance at a set voltage and DC current.

 

[LohringMiller]

Thanks Tyler. I was looking for a quick test of KV. It looks like the rated KV is about right. The tests were not conclusive on shaft drag. The feeling is that under load the .188" shaft is slower than a .150" shaft. I'm not convinced.

Lohring Miller

 

[RaceMechaniX]

Lohring,
I have run several tests with a single motor using a castle controller in the same boat with the same prop just switching the driveline.
In order of lowest to highest friction: .062 wire in teflon, .078 wire in Teflon, .098 in Teflon, .150 in teflon and highest was .187 in bare brass.
These were tested in a Phil Thomas P-Ltd sport hydro with a 2200kv motor and X440/3 prop. Single S-bend with 1/4 brass tubing.

I ran several long passes with each setup and went in to the data for post-processing. I clipped the data by 1 second on each end so the data set represented a steady state run with constant load. I normalized the data relative to battery voltage and calculated the under load kv. The delta to the best case showed me what the relative losses of larger wire/cable.

There is a large difference between .187 and .150 w/teflon. Unless you have a full P-motor you are definitely better using .150.

 

[LohringMiller]

That's what I heard. However, I twisted a .150" cable badly enough to stall the motor in my sport hydro. It took out the motor and ESC. I decided to go with .188" cable at least for testing. I also propped down to 40 mm props. Probably the 43 mm props will be OK with .150" cable if I'm careful with the startup.

Lohring Miller

 

[RaceMechaniX]

A lot of us are running .150 cable in the P and P-Ltd Hydro's and pushing a ton of power.
I just pulled this log file from the P-rigger running a 4060 2450kv on .150 cable.
Its showing 3300-3800W with a peak near 5700W.
Still running the same cable after 3 years.