The Relationship Between Headspeed and Kv?

[Shuttle RG]

Hello all,

My first electric conversion, a Hirobo Shuttle ZXX, has been a blast! I tried as best I could to select the right components given a fixed gear ratio of 9.625:1 and I ended up with the following based on much feedback and others setups:

Motor: Kontronik Tango 45-08 - 800kv
ESC: Castle Creations HV85
Battery: Thunder Power TP4600 6SXL

Although I am still in basic flight mode/hovering, the system works great so far. It has been suggested that you should setup so that you reach your target headspeed at ~75% throttle. However, my real world experience has been that I don't reach my target headspeed (1550rpm) until ~86% throttle.

Now, if everything remains the same and I simply change to a higher Kv motor, how much of a change in Kv would I need to reach my target headspeed at ~75%? For example, would a Tango 45-10 (920kv) do it?

Thanks for you input!
Clark

[Pinecone]

If you are running governor mode, then yes, you should be at your headspeed with a governor throttle setting of 75 - 85% to allow some head room for the governor to handle additional loads.

I would say your fine as you are, IF you are running governor mode.

[AlanMcSwain]

Motor RPM = Motor KV * Volt(3.7v) * Series Cell Count * Loading Constant (0.8)
Head Speed = Motor RPM / Gear Ratio

So work backwards...

1550 RPM (Target HeadSpeed) * 9.62 (Gear Ratio) = 14911 (Motor RPM)
14911 = Motor KV?? * (3.7*6*0.8)
OR (switching to Algebra)
Motor KV = 14911 / 17.76 = 840 Kv

This is the full throttle formula. To have these numbers at 75% throttle, multiply the KV by the inverse of the Throttle position;

840 Kv * (1 / .75) = 1120 Kv

An 1120 Kv motor will produce a headspeed of approx 2060 rpm at full throttle given your numbers.

Hope this helps.

[Shuttle RG]

Awesome guys!

Yes, that is what I came up with too Alan. This motor is 800Kv so the 920Kv (45-10) might be a better fit.

Pinecone, I am running gov mode.

Since I have a data logger with an RPM sensor, my real world numbers were somewhat different than those I initially calculated when determining my setup. So, I was just wondering if I was going about it in the right way. I am setting up another Shuttle electric and was thinking of getting a different motor since 1550rpm at 88% doesn't leave much head room. Just thought a higher Kv motor will give me more head room and be closer to 75% than 90%. :dontknow