Lipo on Rx 50 size plane

[Daniel Z]

Have someone made this ? I want to use my lipos (2S) as an RX battery to save weight, I know that this can not be difficult for the experts here no?, I think that I has to have a voltage limiter to fix it at 6volts instead of 7.4 (8.5 full charged battery)

I`m on the task of building the bigger and lighter plane that my 46 fx can handle (1.54mts wingspan, little less than 5 lb)

any help will be extremely apreciated

Daniel

[FredericG]

What you need is a stand-alone BEC. Typical, low-cost BECs will transform the excessive tension in heat (voltage drop * current) and are fairly limited. There are others that are designed to handle more important currents.
Perhaps you should buy a stand-alone BEC or search for a DIY BEC.

Then you also have the issue that lipos should not be discharged below 6V. In typical configurations the ESC (often combined with the BEC) will cut-off the engine to warn you. But in your case, all a BEC could do is cut-off the power to the receiver… As an alternative you can consider the flames coming out of the plane as a sign that, well, that a crash is imminent… :D

Frederic

[vintage1]

Probaly the best thing to do SIMPLY is to use a decent 5 or 6V analog regulator - or indeed a pair of them, with one arm feeding one bank of servos and the other the reciever and critical servos - and combine it with an acurate low voltage alarm.

Splliting the load means that if one regulator overheats, the lighter loaded one will still be operational.

To be honest, the heat loss going from e.g. 7v to 5v at an amp or so - typical 4 servo max output - is only a couple of watts. Nothing a decent single chip regulator can't handle on a bit of bent alumnium.

[MAVA]

Daneil,

I almost think you can run them with out a regulator?

Why.... I have 1/3 scale Extra 300 running on 5 cell of 2600 nicads and I do not run a regulator.
When I pull the battery pack off the charger and the charger says 8.0 to 8.2v. I have no problems, I have been flying these models for at lease one year.
I run all Hitech gear.

Now I do know Hitech HS-50 servos will not work at 5 cells.

I have also been tempted to retro-fit my Great Planes UCANDO 3D to two LiPo cells. Currently I fly it on 5 Kan1000 NiMh cells un regulated.

My two cents..

Martin
Martin

[Comatose]

I've personally run standard and giant scale servos as high as 9V with no ill effects, but that was something I needed to have done quickly, was ground based and needed a bit more oomph. It was a pancake batter dispenser, so at worst if it failed there would have been a mess. Also, no idea if your reciever will be happy at 8.4.

[Daniel Z]

I have very little eperience in electronics, (only a lipo charger) so, more explicit help would be needed please, could someone make an schematic or diagram ? this should provide help for a lot of us.

Thanks in adance


Daniel Z

[FredericG]

You could use an 7805 regulator. On the datasheet you will find a diagram. All you need is the regulator and a few caps.
http://www.hanssummers.com/electronics/datasheets/

Fred

[MAVA]

Like Comatos said,

You really do not need a regulator at all!!

What kind of radio gear do(brand of receiver and brand of servos) you have?

It is a matter of wiring the lipo cells to RX connector..

Again I run some of my power models with a un-regulated battery packs?

Martin

[Daniel Z]

I`m using 3004 futaba servos 1 hitec feather and std futaba Rx I`m afraid they will fry... or not?

[Comatose]

hitec hs-50 feather? if so, then yes that will fry above 5v
the 3004s would be fine though. no idea about the rx

[Daniel Z]

the feather is for throtle, for weight saving, also thinking in Hitecs 81 MG for ailerons,

I think that this question will be arround for a while...

[Daniel Z]

how many amps can I expect the radio will pull?

[vintage1]

I ran some test on stuff.

radio alone about 50mA.
HS 55 about 10mA idle. 250mA in transit. Didn't try stalling one.

[Daniel Z]

very interseting, so, with standard servos moving I suould expect something more than an amp?

[Daniel Z]

I did some test too; with all the servos moving agresively (but with no plane) I had about 650 mA and the 7805 regulator performs very well, but I was unable to hold in hand more than 5 sec when the servos were moving bacause of heat
what do you think?

[vintage1]

I think that a TO220 will do a watt or two, and at 2v drop thats abput 1/2-1A with no extra heastink.

Too hot to hold is not that dangerous. Over 100C is.