rc_fly

Hi folks. A while ago I built a Nova 40 fitted with a 46 glow 2 stroke. I also have an Arising Star that I've just learned to solo on.

My son wants to learn, but isn't interested in the noisy stuff, so I decided to convert the Nova to electric for him.

Using the 4-Max setups, I took the Precedent Hi-Boy as a baseline, as it's a similar sized trainer.

So I fitted an Overlander Thumper 3548 900kv, and a 60A ESC.

I ran some tests, using a 4S Lipo and an 11x7 glow prop. I have an Etronix power analyser.

The battery was about 80% charged.

At 70% throttle, the current was around 27A, and at 100% it was around 58A. The power on the meter was reading about 820W at 100%.

The spec sheet for the motor shows Power 710W. What is this for? Is this the max power I should be aiming for, so I'm already over it?

The spec sheet also shows the minimum prop should be 11x8 for a 4S. I'm running an 11x7, and already at limits. Going to an 11x8 would put me over the limits more. If I use an electric prop, would this help?


I'm hoping to maiden it soon, as the conversion is complete, but I don't want to turn it into a smoke generator

pmullen503

I certainly wouldn't go up in pitch or diameter, you are close to the limits of your ESC You really don't want to fry your ESC if you are using it's BEC to power your rec.. Try it with a 10x7 or 11x6 depending on what flies better; more pitch speed or more thrust. You don't have to fly at full throttle all the time!

ron_van_sommeren

That 710watt is the maximum continuous power rating, you should keep power drawn below that maximum. Otherwise the motor will overheat. See my next post about derating.
You can go lower, no problem, motor will run slightly more efficient, operating closer to point of max. efficiency.

That is merely a suggestion, e-motors are way more flexible than ic-engines.

IC engines try to keep constant torque, e-motors try to keep same rpm.
You cannot overrev an e-motor by underloading it, rpm can not get higher than rpm_noload, not even in a dive.
..
Whenever a prop- and a voltage-range are suggested, you should always combine biggest prop and lowest voltage to keep current and power drawn in bounds.
Combining the lightest prop in the list with lowest voltage poses no problem, it will give you the lowest current and power of all combinations.

Both current and power drawn are proportional to pitch and proportional to diameter⁴
Overal massively disproportional and expensive effects.

In your case current and power would want to increase by factor (8/7)=1.14.
Worst case, ignoring extra voltage losses in battery, wiring, controller and motor itself due to higher current.

Some expensive realistic and some extremely silly examples, hopefully instructive as well.

Yes, but don't use a slow-fly prop. Those are for low rpms, not strong enough.
Electric props will help, they have thinner blades, less air resistance, lower current, more effective that way.
Current and torque are proportional, in the same way that rpm and voltage are proportional.
Never use e-props on ic engines though, they cannot handle the constant hammering.

ron_van_sommeren

Power system derating
It is a good practice to have some headroom built in. Motor runs cooler, slightly more efficient too, and you have some leeway should things go south a bit.
About derating motors, controllers, batteries, electronics in general:

• Derating, starting at ... Then there is the 75% rule of thumb ...
  Questions and Answers.... - Page 928 - RCG
• About de-rating controllers and motors, starting at for everyone else:
  Questions and Answers.... - Page 290 - RCG
• Motorcurrent is proportional to voltage squared, and proportional to Kv cubed.
  A 10% change in battery voltage will give a 20% change in current, a 10% change in Kv will give a 30% increase. Not quite, because battery voltage will sag more due to higher current, but you'll get the idea.
• extra current with one or two cells added, simple table
  A.k.a. "Why did my motor and/or controller and/or battery go up in smoke ??? ¨.
  In depth discussion
  www.theampeer.org/ampeer/ampnov15/ampnov15.htm#ADD

rc_fly

Thanks for all the info. That’s plenty for me to keep in mind.

After I posted earlier, I actually found a 10x7 and an 11x5 prop and tested with those.

Both were well within limits, so I opted for the 11x5 for the thrust, and slower flying as it’s a trainer.

I maidened the Nova earlier, and it flies really well. Cruises around at 55-60-% throttle, and only needs a burst of full time get off the ground. I’ll get some electric props for the extra efficiency.

There’s a video on my Instagram of the flight.