Hey guys,
Thought I'd share the latest Pixhawk build. This little guy is a work in progress but so far the results are great. It's surprisingly stable and the battery lasts about 6minutes will full gear.
Even with the enclosed prop frame, FPV gear, Pixhawk + GPS + Telemetry, 2600mah 3S battery, Tmotors, and 12a OPTO this only weights 790grams. I'll share more details, video and the build photos if anyone is interested.
Happy droning, Tedro
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PIxhawk and Danaus - You inspired me:
3DR TelemRadio temporarily wedged.
All the blue tape retards airflow through the open ports to the Baro inside. Better AltHold, supposedly.
Wide open flow for the organized air blowing down.
But I wanted to fly longer and carry more weight.
That's a 5200mah 4S lipo in the middle.
20 50cm standoffs were used instead of the 35cm provided. That makes room for all sorts of bigger batteries.
I built it upside down to maximize the organized airflow down.
That put the rotor plane right in the middle of the battery mass, so it's nicely balanced.
KDE 2350 motors handle the 4S.
T-Motor 20A ESCs were tricky to get under the Lumenier PDB.
No holes were in the top-plate for landing gear, So I used squares of foam rubber for feet on all sides to catch my landing attempts.
No GPS or cameras yet. I wanted to be sure that eCalc was telling the truth about getting 14 minutes flight time before I went all in. FPV cam, Mobius, and NEO M8N are going on next. Then I'll do an endurance test.
I still need to route the power module along the side instead of underneath. It's making contact with the ground and will abrade on concrete.
Maiden flew for 13 minutes and had 15.4 left. AltHold was rock solid using the default Quad parameters. I may never tune this beastie.
For the observant, the tips of Prop #1 are chipped. That's what happens when the antenna of the TelemRadio comes unscrewed and gets sucked through the motor.
That's a good question!... There are a few people doing endurance quads like EndofDays 2hr+ beast.. but generally people shy away from low C high capacity battery packs that they have to build themselves.
There are quite big differences between cells. I know that the Panasonic NCR18650 series are known to be very high quality. Tesla use them (afaik NCR18650B series). There is a write up on the IMR 18650 3100mAh here. Note that you won't get the rated capacity out of a cell at high discharge currents... they come down to something like 2000mAh at high discharge for a 3100mAh cell... ymmv :)
Thanks Felixrising, this is very helpful. I think a 1P may be possible using these batteries that are rated for 20am each! Even better they are rated at 3100mah. At a 150 grams (3 batteries in series) I'd be close to 2900mah with 20amps.
Question is... why aren't a lot more people doing this?
The 2900mAh value is "Max Discharge" 4.2v->2.5v. Usable is more like 2700 or 2750mAh. I estimated 2700/cell and because you'd need at least a 2P pack you get 2700x2=5400mAh. A 3S2P pack is minimum to meet the current draw of those motors. Once you have measured hover and climb current, you can get an idea what battery set up you'd need.... if your hover is close to 20A, that wouldn't be enough to handle current draw in climb, and you'd be forced to go to a 3S3P pack instead... which probably doesn't work out weight wise. Ideally your current during normal climb would be less than 20A and therefore a 2P pack will be sufficient, if it's a bit borderline you might be able to limit your climb rate further to limit your current draw but that is really becoming a limiting factor. Motor/Prop combo and limiting the weight you're carrying is really important when you're working with limited battery C ratings... good luck with it! :)
One other thing, what do you think about just this?
Yes, the MN1806 T-Motors. I'm very impressed with this motor so far.
How do you get the 5500mah number on this config?
I picture the below kind of set-up, 6 of these 2900mah lions in series? Each individual battery weights 46g that's 276g total, that works. It's 60 more grams than my current lipo battery but the flight time gain is worth exploring.
What's the deal with building these? Have you used this setup on a quad? Can I buy this type of battery setup pre bundled?
This quad is meant for cruising. Not planning any more than 75% throttle with slow and steady pitch and yaw. This will be one of the best ideas if it works!
My assumptions are you'd be drawing less than 20Amps continuous which should be correct given the motors you are using are T-Motor MN1806 2300kv (?) although your peak at 100% throttle might exceed the peak threshold of 36A. For this a 3S2P pack of Panasonic NCR18650PD 2900mAh would be suitable. These can individually deliver 10A continuous and 18A short term (5-6s), or 20A constant/36A peak for the 3S2P pack...
I had to move the Telemetry module to the front since it was interfering with the VTX. Not much, but enough "crackling" to make it annoying. The antenna cannot be seen from the FPV cam nor the GoPro. Also changed the GPS mount to 1. get it further away from the GoPro and 2. this mount weights 4 grams less.
Felixrising, I really like that idea. I've ordered a power meter just so I can determine the amp draw. I'll have those details by end of this week. I've searched around for more information on how to use those type of batteries but there's not much for quads. Do you have any good links to share? I'd like to learn more about the configuration of the batteries and any disadvantages over using lipo. Getting 5500mah out of 276g would be great. Right now I'm using 2600mah at 216g.
Mark, right now I'm using 44 machine screws. Each weights .27gram. So in total I have 11.88 grams of screws. I can't shave 15-20g from the total, but if I can drop .15 to .20g from each that will help! Nice idea I have to look further into.
Mini, as Gary mentions the FC is powered by the Power Module. No need for BEC ECSs or special wiring. For this build I'm using ZWT Spider 12a OPTO that I found cheap on Amazon. They work fine so far. I'm going to swap them out for KISS for weight savings. Good luck with your build, don't rush it.
Hi Mini,
I am using DJI Opto ESCs with both a Pixhawk and a PX4 and they are no problem and do not require (nor can you perform) calibration, because they are digital they cannot be calibrated.
They do not have a built in BEC, but other than that they work just fine and since you are probably using the "Power Module" with the Pixhawk, the BEC is not missed.
If you do need an additional UBEC it is no problem to add one, I am using an external UBEC on my PX4 based copter..
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