As an Aero Engineer, I've been mildly interested in the mUAV world, but more from a utility and design standpoint rather than the FPV racing or hobby aspect. But recently my wife and I decided to buy some land, and as a small quad can come in handy when inspecting a large area for pasture and crops, I got the great idea of dropping way more money than I wanted to design one of my own (gotta love those contrived justifications)! So got a KISS FC/ESC/motor kit on clearance from flitetest, and then immediately got sidetracked for a year. But after a crazy season, I've decided to carve out some time and finish the build, so here we are.
If you've seen the pictures, you'll know the main design aspect of this build was to utilize quality commerical batteries, specifically the M18 (5s) batteries I use for my Milwaukee tools. Since I already have the chargers for them, and that I know they're high quality lithium, my hope is the added weight can be overcome by the savagery of power that they will provide. The battery I selected is the Milwaukee M18 CP3.0, which uses Samsung INR21700-30T 21700 Li-ion Batteries, which are ~3000mAh and rated for 35A continuous max discharge (1. peak is far higher, 2. I do no reference c value, it's marketing and never reliable).
- Why this is a bad idea: It weighs 607g, which is about 260g (!) more than any equivalent 3Ah pouch battery, which is expected given each 21700 cell is 69g. Also, there's the chance that the low voltage protection kicks in and shuts the battery down in flight; I'll be testing that... If this happens, I will have to engineer a way to mimic what commercial aircraft do, and have an emergency 'reserve' 5s that can take over and execute a safe landing. See comments for additional discussion on how dumb this is
- Why someone would want to do this: As it uses the drill battery charger, I also won't need the inconvenient (and sometimes sketchy) pouch battery chargers. I also really like that I can tap the battery remaining button on the battery so I can tell if I need to charge it (great for a beginner who crashes a lot). The M18 battery is also super easy to swap out, doubles as landing gear, and provides clearance for the props, for what that's worth. At $45 a pop, the CP3.0 costs $5-10 less than an equivalent 5S RC battery. I can also use wayyyy bigger batteries (the 9Ah, 1088g version for instance) if I'm feeling unhinged.
The first thing I did was buy a 3D printed Milwaukee battery adapter on amazon, but I couldn't get the hole spacing to work, so I recreated it in solidworks and printed a modified one. I first printed a PLA prototype (or three) and am using a PETG one for the flying version; Ideally this would be Nylon, but my printer can't do that.
AND SHE VERKS! Currently, she weighs 413g empty, and 1019g with the battery. Not sure that's good for a 6in quad, but for a first build I'm ok with leaving room for improvement. That also includes a couple grams of dirt and grass from the crashes as I learn how to fly.
The only things left are:
- print a better mount for the receiver (currently the antennas are taped to the arms)
- figure out how to use the smartaudio from the video tx (not sure where to plug that pin in on the kiss FC)
- Post a vid once I learn to fly (I can only bunny hop at the moment)
I look forward to the feedback and questions - cheers!
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What kind of flight times did you get out of the 3.0 batteries?
Thanks.
So when the build was together, I was able to get 15ish min of really slow beginner flying. However my nylon printer broke, and the PLA and PETG prints of the bracket didn't hold up well, so after a few crashes and it breaking, I decided to call it. As others have discussed, the battery is better suited for a larger build with lower current draw, not FPV. Hope this helps!
you're my hero. could you just upgrade the cells now that you have the batteries? its still a good idea. could one buy a china battery and print an extension bottom. load it up with good cells and use an existing charger?
Interesting build but aside from the easy charging the battery is terrible for a few reasons.
- 35A max output is very limited especially for such a heavy quad
- You stated that the battery is a lipo but it uses lithium ion cells
- the 21700 cells inside of the battery can be bough seperately fror around 5$ each so buying 5 and adding the needed wiring would en up costing around 30$ per battery
- Their are also better cells avaiable like the samsung 21700 - 40t which have 33% more capacity then the 30t at the exact same price
- building you own would also be a lot lighter and you could even go to 6s making the 35A max output less of a problem.
- Equivelant lipo batteries would still be cheaper. (a 3000 3s battery is 20$)
Appreciate the feedback!
Yep I had throttle limited to 70% ish in the kiss FC firmware (mostly out of fear rather than any hard calculations). And as I have no reference due to lack of experience, what I think a rocket is may be a slug to the more experienced... regardless, it was quite exciting, and I had enough fun to tolerate my hands freezing off in the fridgid air!
I liken my approach as a gateway method, involving a blend between raw FPV building and DJI-like consumerism. It would also help get more people into the hobby, or enable jobsite workers who have these batteries already and they insert one in a drone to do an aerial inspection.
You're right on track with my thinking with a larger build. Based on what I learned from this build, I have plans on making an X-class drone, as well as a Y-4 VTOL fixed-wing using Pixhawk. Basically, I'm getting hooked :)
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