Small LiPo Cell

[Broz]

I'm building a very small device that will use a single LiPo cell. It needs to be small and as lightweigt as possible. I've found one made by Kokam, and I hope I'll be able to order it direct. Here's the one I found:

https://www.electro-tech-online.com/custompdfs/2009/04/SLB452128_145mAh_Grade.pdf

This one is suitable, but it would be nice to find a cell that is even smaller in dimensions and especially lighter in weight. The capacity could be less than the 145mAh offered by the Kokam cell as my device will average about 50 mA draw with peaks less than a second of about 300 mA and will only be used about 5 minutes at a time. Are there any smaller LiPo cells available?

 

[Sceadwian]

**broken link removed**

As you can see it's much smaller, and 2 grams lighter, it however also is 1/8th the available mah's and wouldn't suit your current draw. It's only rated at about 80ma's for discharge. Anything small than the 145MAh pack you're looking at is going to reduce the power/weight ratio dramatically because the basic package itself becomes most of the weight.

What is this for? Lighter than 3 grams is some pretty severe weight requirements.

 

[Broz]

It's a device going on very small RC aircraft. I could have the end user splice into the wiring harness of their aircraft and run off the battery used to power the aircraft, but I wanted this device to be easy to use with no special skills, just strap on and go. Ten grams total for the entire system was my target. It looks like I'm going to come in under that but the lighter I can make it, the better the performance. I'm very close to being done, I'm just trying to shave off as much size and weight as I can now.

 

[audioguru]

Air Hogs by Spinmaster sell indoors helicopters and airplanes that fly for 5 minutes on the charge from a tiny Li-Po battery cell. I got the Havoc Heli (look in Google) for free from Energizer Battery Company.

 

[Sceadwian]

I think those cells are the same one he's looking at, I have two from the same kind of little heli's. For the power/weight ratio, you can't do much better.

 

[Sceadwian]

Broz, exactly what does the rest of the circuit do, we might be able to help you design around your weight requirements. Keep in mind you're pretty much requiring that you work with SMD components. Considering it's micro RC it's going to be smarter to tap into the existing crafts power supply, it completely eliminates 3 grams of weight not to mention the space. Do you have photo's or links to your project or the craft it's going into? I've always been fascinated by micro RC stuff.

 

[audioguru]

Most of the tiny remote controlled helicopters and airplanes use IR, not radio waves for control. My "indoors" helicopter flies outside at dusk when the sun is down and the wind is low. It can go very high and the IR control still works.

 

[mneary]

If you're using anything like conventional servos, you could put an adapter into one of the servo lines to steal power without cutting wires.

I suppose this doesn't help much if you're trying to adapt to a variety of different aircraft.

 

[Broz]

Broz, exactly what does the rest of the circuit do, we might be able to help you design around your weight requirements. Keep in mind you're pretty much requiring that you work with SMD components. Considering it's micro RC it's going to be smarter to tap into the existing crafts power supply, it completely eliminates 3 grams of weight not to mention the space. Do you have photo's or links to your project or the craft it's going into? I've always been fascinated by micro RC stuff.

I really want to tell you guys what I'm up to because I'm excited about it, and this forum has been a big help to me. But I'm trying hard not to reveal everything before I'm done and have video of the finished product in the air. I was just looking at the battery for my Parkzone Citabria RC aircraft and it has a 70mAh LiPo. This is the smallest aircraft I'm designing my device to fly with and I'm guessing the battery, at 70mAh will have a peak discharge rate of 280mA. That's right on the edge of where I want to be. I know I could make my device so that it plugs into the onboard battery for the aircraft, but then the ease of use is diminished and requires skills to splice into the onboard battery. I could get around this by including connectors, but then I would have to supply various connectors for the different types of aircraft available. If I make it a self contained unit, then that worry is gone. That's why I'm going the route I am.

I'm almost done. I've made a physical printout of my PCB and actually placed the components on it. Good thing I did. While it looked good on the computer, when I went to place my components there were a few that got in the way of each other. It's tough designing something this small. I hope to have a flyable production quality prototype in a few weeks. You guys will be the first to see it since I've gotten so much help from here.

 

[Broz]

Most of the tiny remote controlled helicopters and airplanes use IR, not radio waves for control. My "indoors" helicopter flies outside at dusk when the sun is down and the wind is low. It can go very high and the IR control still works.

Those are the cheaper models that use IR. All of my micro RC uses radio, usually 2.4 GHz.

 

[audioguru]

The video of the Parkzone Citabria RC aircraft is only 50 seconds long. Are flights that short?
My little helicopters fly for 5 minutes to 6 minutes per charge.

 

[Broz]

The video of the Parkzone Citabria RC aircraft is only 50 seconds long. Are flights that short?
My little helicopters fly for 5 minutes to 6 minutes per charge.

Most flights are around 5 minutes. However I have taken most of the downthrust (added for stability) out of my aircraft. This means, with the throw of the throttle lever, I have a skyward bound, hard to handle, but fun aircraft to fly, or by throttling back to 1/4-1/2 throttle I can fly for 15 minutes before the aircraft shuts down to save the cell from over discharging.

 

[Sceadwian]

I'm guessing there's already a micro controller of some kind involved on the RC aircraft at some point? It would help stability if you did 'speed sensative steering'. Basically just stretch the throw of the control surface servo's depending on what the throttle was set at.

 

[Broz]

I'm guessing there's already a micro controller of some kind involved on the RC aircraft at some point? It would help stability if you did 'speed sensative steering'. Basically just stretch the throw of the control surface servo's depending on what the throttle was set at.

That's a great idea and I've given it some thought. It's not what I'm after with my current project as the added weight of my current device will tame the beast so to speak. However, it's a fact of life as it stands that down thrust is always added to these small RC aircraft at the loss of efficiency in order to gain stability. The reason is, they become so trim sensitive when they are this small. I've done everything I can playing with the throw of the servos to tame the tendency to climb at high throttle while trying to maintain efficiency and aerobatic maneuverability. Nothing short of a electronically controlled trim tied to the throttle setting will work, I'm sure of it. So yeah, that's a great idea. I've got about 10 projects after this one before I could get to such a thing, but the idea definitely has merit.

If you're interested in such things, you should PM me and we'll exchange some information. I would love to talk about the possibilities.

 

[audioguru]

About 50 years ago I made a gas powered small free-flight Piper Cub airplane sonthing like this one. The engine was 0.020 cubic inches.
i controlled its climb and dive with a pendulum. If the nose when up then the pendulum swung back and pushed the elevator down. If the nose went down in a dive then the opposite. It flew level for a long time.

 

[Broz]

About 50 years ago I made a gas powered small free-flight Piper Cub airplane sonthing like this one. The engine was 0.020 cubic inches.
i controlled its climb and dive with a pendulum. If the nose when up then the pendulum swung back and pushed the elevator down. If the nose went down in a dive then the opposite. It flew level for a long time.

That's a cool idea for a guided missile using very gradual control inputs, like the German V2. However, in the flight I'm doing, G forces far out weigh the force of gravity. Think of it as night flying. When flying at night with no instruments, one always feels "pinned" to the seat as long as one holds back pressure on the stick and the aircraft doesn't stall. Many a good men (but not good pilots) lost their lives because they thought they were upright by the force on their rear, when they were really heading into the ground inverted. The same is true for such a transducer as a pendulum.

I know from experience in flying these little buggers, that pitch trim tied to throttle setting will do the trick.

And as far as the 50 years ago part, you're as old as the Earth aren't you? No wonder you know most all of which there is to know about RF. I need to pick your brain sometime.

 

[audioguru]

I am an old geezer. Soon I will be 64.
I know a lot about audio and a little about RF.
I was an Air cadet and I flew (for a few minutes until it stalled when I tried to loop it) a twin engine Expediter.

 

[Broz]

I am an old geezer. Soon I will be 64.
I know a lot about audio and a little about RF.
I was an Air cadet and I flew (for a few minutes until it stalled when I tried to loop it) a twin engine Expediter.

That's a sweet aircraft. I've been at the helm of a twin engine once, when the Marines were recruiting me for a second time. I didn't attempt a loop, but man, I was satisfied with the flying experience. Come to think of it, that was my last flying experience. I've flown many aircraft, jumped out of a few too, but I've just realized how lame I've become. My last experience in flight period, was with me at the controls 8 years ago. I'm jumping out of an airplane next month, come hell or high water. I've never thought about how long it's been.

Years creep up on you don't they? I'm still bold, I can do it.

 

[Sceadwian]

Can I be in your will, just in case? =)

 

[Broz]

Can I be in your will, just in case? =)

LOL! Well that all depends on how you respond to my PM. But you don't want to wish for my death yet, I have a negative net worth right now. Though, I have some potential you have to admit.