Using different battery types on a quad.

[JaymzShikari]

Hello, part of the reason for me building my quad was to assist with my college application for an electrical engineering course. It's "an optional pre-entry project at your(my) own cost to help the college assess your(my) current practical and theoretical knowledge." - quote from the lecturer.

I essentially had to build something that took some electrical knowledge and produce an instructional video of me building it and an instruction manual so that someone with the exact same parts and tools as me could build it to a high standard with no previous knowledge.

I submitted my completed quad (configuration listed below) and the lecturer was very happy with it. Now for the second part of the project I'm a little stuck, he has given me two common adaptations I have to make (again with instructional videos and literature). He would like me to find a way to make the whole system more efficient and find alternative power sources. I still have to use batteries I just have to make them more "user friendly" as the lecturer believes that LiPo batteries are "too dangerous" for people uneducated on the topic to use, despite the fact it's actually relatively simple to look after them.

Anyway, what I thought for making the project more efficient was to switch to a lighter frame, possibly carbon fibre, I have found some motors which are lighter and more efficient and I have found a lighter LiPo. I feel that that will be enough to create a notable increase in efficiency (If you have any other ideas or criticisms of this please tell me as I would like this to work as well as possible.)

As for the more user friendly I thought of using 1.5V Ni-Mh AA 2900 mAh rechargeable cells as I came across 16 of those lying around in my room. My thoughts were I could create 2 batteries by running 8 in series to create 2 12V Ni-Mh 2900 mAh batteries then running those two in parallel to each other to create a 12V Ni-Mh 5800 mAh battery. I've done my research on setting this up and I think it will weigh around the same as my 11.1V 2650 mAh LiPo fully set up so it would add no extra payload to the quad if I was to add just one of the batteries.

My question is: Have I overlooked something important with this idea? I feel that I have otherwise other people would have used this method to power their budget quads as it appears to be cheaper, lighter and higher capacity than a budget LiPo.

Also while I'm here I may as well post my other question, I have bought LED strip lighting for my quad so I can fly by night (as the only open field near me is also used as a footpath by a high school full of pre-adolescents that like to surround me and get in my way whilst I'm trying to fly). I would like to wire them in in the simplest way possible and I think I've devised a method of doing it without having to dismantle my quad and trying to solder over other connections I've already soldered. My ESCs aren't soldered directly to the power distribution board as I decided to solder short cables with bullet connectors onto the board and connect the ESCs in that way so I can take the set up apart and reassemble it easily. I have some spare wiring and bullet connectors, would I be able to make splitters to connect to the +ve and -ve outputs on the board meant for the ESCs and connect my lighting to those? So the LEDs on each arm of the quad are powered seperatley to each other and aren't all on one circuit? I realise that I am making this more complicated than it needs to be but I think it will be more practical for me in the long run.

Thanks for the help and sorry for boring you all to death with my life story. I'm Jaymz by the way.

EDIT: I forgot to include my setup
Frame - DJI F450
Motors - AGM 2213 935 kV
ESCs - Hobby King 15-18A
Control Board - HK KK 2.1
LiPo - Power Poly 20c 3s - 2650mAh + a low voltage alarm
Rx - OrangeRx R615
Tx - Spektrum DX4e

 

[SoCal Blur]

My understanding is that there is a reason (as you suggest) that others aren't using the battery method you propose.

You'll notice on your Lipo batteries, there is a "C" rating. This, in simplest terms, indicates the discharge rate factor that the battery can accomodate continously. For example, if you have a 1000mah Lipo battery with a 20C rating, you multiply the "C" rating (in this case 20) by the mah resulting in 20000ma or 20Amps. This means that the battery can discharge continuously at the rate of 20Amps per hour without damage. The Ni-Mh may or may not be able to accomodate that discharge rate. You'll need to do some research and experimentation to find out. You can use eCalc (google search for it) to determine what the minimum C rating you will need for your quad. I believe the general concensus is that LiPo batteries are the most efficient way to power your quad and are only dangerous if you don't take the appropriate precautions (as with all batteries).

In addition, if you are going to connect batteries in Parallel, you may want to build a buffer circuit. This circuit (basically a rectifier diode) will prevent a battery that develops an issue like a bad cell and sudden low voltage from draining the otherwise good battery(ies) it is paralleled with. I know most people don't do this, but you may want to consider it.

As far as increasing efficiency, use eCal to model different configurations. Motor size, prop size, etc. will all make a difference. eCalc will also give you an easy way to demonstrate to your lecturer the improvment in efficeincy since it provides that information in numbers and in a graph.

 

[kloner]

see if you can find anything on a technology called li-air

http://en.wikipedia.org/wiki/Lithium–air_battery

like he said the whole reason electric models have advanced so far so fast is becuase of the speed energy goes in and out of a lipo, it's something like a few ticks slower than the speed of nuclear fusion......... lightyears ahead of a lead acid or ni-cad

motor and prop change would be a decent way to improve efficiency, even just balancing the ones you got would make a difference. also motor levelness will improve it to a degree if it is not perfect now.... just setup/build stuff

 

[JaymzShikari]

Thanks for the advice, I know a guy that knows his stuff about batteries but he's away doing his PhD and wont come home until Easter. I'll ask him then.
I'll check out the Li-Air batteries too.
I've discovered that I need to work on stability before efficiency as I was having a small problem with the quad wobbling and when I just took it up to 150ft (according to my ultrasonic sensor) I fully lost control of it and had to fully let the throttle go before it crashed into a crowd of school children and I have snapped an arm.

I (naively) thought that calibrating the auto leveling on the KK2 board would do enough to keep the quad level. What should I be doing to keep it from wobbling and drifting?

A quick forum search has revealed I need to balance the props (not 100% sure what that means but I'll look into it) and to add rubber washers (O rings) to my nylon risers.

Is there anything else I can be doing?

 

[SoCal Blur]

There are a bunch of videos on youtube on how to balance a prop. Unbalanced props will cause vibration (unbalanced motors will as well) but I doubt it's the cause of your wobble. You want to check the gains in the KK2 board. Do a search for that as well. I've never used the KK2 so I can't give you any advice beyond that but I think once you get the gains sorted out, your wobble will go away.

Unless you get a FC that uses GPS/Compass, you're always going to have some amount of drift. The better you get your quad dialed in, the better it will hold position but it won't be locked in position without GPS.

One piece of advice I can give you is never fly it around people - especially before all of the bugs are fully worked out in your quad. The fact that there was a crowd of school children nearby should have stopped you from even lifting off.

 

[JaymzShikari]

They weren't nearby when I lifted off, they saw it and came to have a gawk. I didn't even notice them until I turned to see what I was going to crash into. Once I work out how to install LEDs I'm going to fly by night as there is a vast open field near me but it is only clear by night. The edge of the field is marked by streetlamps so I should be safe testing it there.

I just wish I didn't live in busy suburbia so I didn't have to fly in a public park.

I wasn't sure of the purpose of a GPS on a quad but now that I am it'll be on my list of things to purchase.

Thanks for the advice guys, I'm closing this thread now as my questions have been answered.