This is my first go at a brushless tiny whoop. My goal was to build something that flew nearly identical to my brushed tiny whoop; But with brushless motors. The reason I wanted to go brushless is because of the short life of the brushed motor. They say around 6 hours is what you can expect from a brushed motor and quite frankly I'm sick of replacing these motors. Also, with brushed motors, long before the 6 hour life is up and the motor ceases to spin, you'll notice your whoop will gradually fly worse and worse. This is obviously not ideal. So let's fix it!
The parts list
Click here to view the full build on RotorBuilds. In a nutshell I'm going with the RakonHeli Frames & the SunnySky 0705 15,000kv motors. I started with the 66mm Brushless Aluminum Whoop Kit from Rakon. I was super pumped until it came and I found out the hole pattern for these motors doesn't follow the standard 0705 motor pattern. This resulted in the motors not fitting. If you want to buy it, I'll happily sell it to you, it's very sharp!
So I ended up ordering the right frame found here. When it came in I was super stoked that the motors fit and I got it all built up. Right off the bat I noticed quite a few things that didn't seem right.. Overall I'm pretty unhappy with what I ended up with. Here are some of the issues I ran into:
- Less than ideal flight times. Flight times on a fully charged battery, running until the motors won't spin (not good to do) is just under 2 minutes.
- Unreliable self level mode. In any kind of self-leveling mode it drifts to the left. This makes flying in this mode really not very fun as you're constantly compensating. I know this could be fixed with radio trim but I'd really just be covering up the underlying problem. Reading online it appears that these motors are very noisy and cause issues w/ the gyro. I was able to swap out the loudest motor with a new one and it actually improved the drift quite a bit but still not perfect.
- Weird throttle Curve. It doesn't hover until about 75% throttle. This means you don't have a great range for throttle control. I think this is due to an undersized prop for this motor.
- Fun while it lasts. In acro mode it's quite fun for about 1.5 minutes. It's quick, it handles well, and it's great for inside flying!
What's next?
If I did it again I'd definitely go with either:
A: Smaller lighter motors
B: A bigger frame that accepts bigger props.
I plan to swap out the 3D printed battery mount so I can run bigger batteries to get better flight times. I hope the added weight of bigger batteries doesn't completely use up the extra MAHs they provide.
I plan to setup a throttle curve on my Taranis as well as properly setup the throttle mid-point describe at the bottom of this page. This should help with giving me a more balanced throttle.
I plan to replace one of the motors. I noticed it occasionally acting funny and can't help but wonder if maybe it's seriously affecting performance. If it's bent or damaged it could be causing the quad drift or the throttle issues. If 1 motor is bad, and struggles to spin up, the FC will have to compensate but not spinning up the other 3 motors fully. I'm going to try this out and circle back.
If you check out the information here on their "Brushless report" you can see why they recommend running a bigger prop on these motors. They're bigger beefier motors and can definitely swing a bigger prop. So by going with a smaller prop, I'm not getting the most out of them. This should be resolved by moving to a larger frame.
One thing I may try is ordering a larger frame and trying the motors on that. I was thinking one of these two
76mm Rakon Frame
BetaFPV 75mm Frame - This is the frame I'd really like to try but I need to figure out if I can use this same FC & ESC Stack on that frame as it looks to take a different size.
Other Thoughts
I was talking with someone on Facebook about these issues and he was able to provide some additional info. He was testing with 0703 15000kv motors, the little brother to the motors I'm using.
- With 31mm Props (same as me) and 550mah battery, he was hovering at about 75% throttle.
- When he bumped it up to a 2S battery it hover at just over 50% throttle but with very little punch over that.
- With 40mm props (the larger ducted frames mentioned) with 550mah 1S it hovers around 50% throttle but with a lot of thrust when going over that. Much better than using 2S on 31mm props.
That said, I think that these motors on 2S with this same setup is not a great way to go. 15000kv is too high for 2S and you lose all of your efficiency on the high end. In order to go 2S you'd want to go with something around a 8,000kv motor.
