Perhaps it is the Li_Ion pack that is making the current draw higher through lower voltage under load. It would be interesting to re-test with a LiPo pack.
Dave,
Although the main battery voltage may have been 20v at the battery, your ESCās still may have seen fewer volts due to wire resistance. Voltage drop even on short runs 14AWG wire can be significant, so keep that in mind for the voltage that is making it to the ESCās.
Nathan
This is interesting to me. How can voltage drop across a short, multi-strand copper wire be significant? I just measured the resistance of a 2m 14 GA wire. It was 0. So if the resistance is 0 how do you get a voltage drop? What am I missing?
Iāve been wondering about the current draw in plane. Sadly, as Greg explained, I crashed mine before testing forward flight. I was hoping to see considerably less than 22 amps. The stock 1510 is a high pitch prop, which may be causing the high current draw. The aggressive pitch is required to generate lift in VTOL but excessive in plane. I am wondering if a better engine/prop combination would lead less current draw?
Nate,
What do your believers draw while in cruise? What prop/engine combination are you using?
Im using KDE 3510XF 475KV motors with 12x12 props on my Believers. At MTOM, I get between 5-7A draw at 19m/s. Truly an excellent platform.
Good to see itās less than 10 amps. Thatās more consistent with my expectations. Is that the recommended motor/prop combination?
To be honest, I cant remember what the recommendation is. Actually, it was Nate above that put us onto the wining combo. The default setup was very poor in terms of efficiency and power.
Thanks Luke. I suspect that is the case with the VTOL kit that includes everything.
Resistance of 14 gauge copper is about 2.5 milliohms/foot
At 100 amps, the voltage drop would be 100 amps * .0025 ohms/ft = 0.25 V/ft
A Sanyo 18650 3500mah cell has internal resistance of about 80 milliohms according to
What is the configuration of your custom Li-Ion pack?
kd0aij,
Thanks for the info. Is that multi strand wire?
DC resistance is the same for stranded and solid wire of equal cross-section.
@LukeWijnberg What is the configuration of your custom Li-Ion pack and which cells are you using?
It is a 6S1P pack using Sanyo 3.5A cells. We use the same packs / configs for our other Believers.
A test flight today with the CG moved back and then back some more showed very little improvement in power draw. The aircraft to me (based purely on flight characteristics and experience in flight profiles of similar airframes) seems well over weight at 8kg. Then there is a question of drag of which there is a lot of pointy things about disturbing airflow.
I think I will give it another go with a smaller Li-Ion or LiPo pack (500g and 720g lighter) before I throw in the towel and call this one a dud. Without wanting to spend much more in R&D, but the Baby Shark from Foxtech is looking far more promising.
Luke,
I would not expect a 6s1p Li-Ion pack to work well on this configuration, especially during hover modes. Something like ArxAngelās 6s6p pack made for the Crosswind would be more appropriate.
My mistake. Its actually 6S9P.
By the way, I do not have an issue at all with the hover modes. These are perfectly fine for me, even in gusty conditions.
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Luke,
Thanks for the correction. Assuming your 6s9p Li-Ion pack is now capable, I am curious as to why your hover current (80amps) is 30amps higher than Davidās (50amps)? This may relate to your seemingly higher forward flight current. Are you using a Mauch or other calibrated PM?
We are using a Mauch sensor. It is working correctly and tested at the end of each session against the recharge amount. I dont know Daveās setup, but I guess I am heavier than his.
We also upgraded the wiring all over the airframe to a mix of 8 and 10 AWG where needed. The stock is way too thin and got very hot.
Well, if nobody else posts soon, weāll have more data this summer. On my initial hover test, I had the current logging disabled by accident. I know that several others are waiting for either summer to arrive or Covid-19 to end. I can only offer my Nimbus 1800 VTOL numbers which seem reasonable. I would not expect the Believer/Freeman to triple the FF current from the Nimbus 7amps.
This is from my Nimbus fully loaded with a 2-axis gimbal and camera up front and an S100 camera below. I was using a 6s 10AH Multstar LiPo pack and SDP33 AS sensor. The average FF current seemed about 7amps in autonomous modes. The higher hover currents were due to ascending on take-off. Perhaps this is a difference between your hover current and Davidās.
Hi Luke, your current during Cruising is very efficient. What is your total weight (AUW) in that case? Is the configuration of your Vtol as 4+1 Quadplane or Y3 Tri with dual front Tilt rotor??
I understand that Nathan also had similar result using 12x12 Apc propeller. But his configuration was not Vtol (correct me if I am wrong Nathan).
Regards
Tony
Hey Ton999,
Why do you think his current draw at cruising is efficient? Seems quite high to me. Itās more than 4 x what he is getting on a Believer. Yes there will be a current penalty due to the extra drag associated with the VTOL setup but I wouldnāt expect it be 4x. Swinging a bigger prop will also cost a few more amps. I canāt find the exact engine, but with a sunnysky 3520 (520kv) eCalc says he should be drawing 8.4 amps at 17 m/s,
Dave