How accurate is the Governor?

[cadkins]

I recently finished a Trex 500L with a Talon 90 on it. I calibrated the throttle end points and set RPM to 2400 / 2500 / 2800. I have not been impressed with the head speed in IU2 so I decided to tach it. During flight # 12-16 today, I used the helitach app and an optical tach, to check the head speed while on the ground with zero pitch. Each HS is around 50-60 RPM low. I checked the motor settings and gear ratios and they all appear normal.

I also decided to check my Blade 360CFX and all three speeds were 50-60 low as well. The 360CFX is bone stock with no changes to the Castle ESC 2600 / 2800 / 3000. In fact I don't recall ever doing a throttle calibration on it. I simply used the manual settings.

Is this an acceptable RPM governor accuracy? I always power on my heli in throttle hold mode could that be the issue? All throttle curves are 0/30/30/30/30, 70/70/70/70/70, 100/100/100/100/100.

Thanks!

[Toocool4]

I run the Talon 90 on my T-Rex550 V2 as well, mine are 50 RPM down too.

[LaDon]

Too many variables for them to be dead on all the time. Biggest being say just because you have a 540kv motor didn't mean it is exactly 540. Might be 520 in all actuality. Also depending on where the batteries are and how the esc reads it. If it is 50 rpm low then just set it all 50 rpm higher

[Gyropilot]

A +/- 2% accuracy on the headspeed seems pretty reasonable... well to me anyway.

[fastflyer20]

There are ways to measure actual Kv for a specific motor and plug that into the software.

Even easier is to tach it and adjust accordingly.

[jhamel]

Originally Posted by fastflyer20

There are ways to measure actual Kv for a specific motor...

How do you measure the motor Kv?

[fastflyer20]

Here is a pretty good thread on it:

http://www.rcgroups.com/forums/showthread.php?t=983725

[Xrayted]

Originally Posted by curmudgeon

How do you measure the motor Kv?

Its easy with a Castle ESC to determine the actual KV your motor has.

This trick is done as a motor only run while disengaged from the drive-train!

Set it in governor set RPM mode and then set the max governed RPM to some ridiculous high value like 5000rpm which will drive the ESC into 100% power out and max motor RPM trying to obtain it although it never will. You can use fixed end points as well, but you must verify that the ESC is outputting 100% power out in the logs at 100% full throttle on your TX

When in the logs, R click on the RPM button at the bottom and change the gearing ratio to 1:1 so you are seeing actual motor RPM and then simply divide the max RPM maintained by the voltage being applied, and that will be your motors exact KV

Make sure you use the voltage info from the point on the log that corresponds to the same place that you checked the RPM value from so it takes into account the exact voltage that was being applied at that max RPM. Looking at the "cursor" values on the lower left of the log will give you these matched values.

Here is my KDE 535KV motor and its almost 20Kv higher than stated

[cadkins]

Thanks for the replies. I agree 2% is fairly accurate. What I found odd was both of my helis were 50-60 RPM low. I wanted to ensure I was not doing something incorrectly. I will tweak the IU2 to 2850 on my 500L and see what I get.

[A VIKING]

Originally Posted by Xrayted

Its easy with a Castle ESC to determine the actual KV your motor has.

This trick is done as a motor only run while disengaged from the drive-train!

Set it in governor set RPM mode and then set the max governed RPM to some ridiculous high value like 5000rpm which will drive the ESC into 100% power out and max motor RPM trying to obtain it although it never will. You can use fixed end points as well, but you must verify that the ESC is outputting 100% power out in the logs at 100% full throttle on your TX

When in the logs, R click on the RPM button at the bottom and change the gearing ratio to 1:1 so you are seeing actual motor RPM and then simply divide the max RPM maintained by the voltage being applied, and that will be your motors exact KV

Make sure you use the voltage info from the point on the log that corresponds to the same place that you checked the RPM value from so it takes into account the exact voltage that was being applied at that max RPM. Looking at the "cursor" values on the lower left of the log will give you these matched values.

Here is my KDE 535KV motor and its almost 20Kv higher than stated

Dude...your knowledge base is awesome!

[Xrayted]

Nah, I stole the idea from one of the Castle guys years ago!

[RC/DC_5000]

50-60 RPM difference is incredibly close. You can blame the Helitach app as much or more than the CC software.

I'd trust the CC software more actually. But that is surprisingly close. You can buy 5 different tachometers and get 5 different measurements.

HS is not that big of a deal. As long as the battery is as fully unleashed as possible (not low throttle settings) and the gearing is optimized and you like the way it feels and its close and reasonable. Its fine.

[cadkins]

Thanks I never really thought of it only being 2% off. I'm going to adjust it slightly higher and we should be good!