RCDT Batteries

[Dean McGinnes]

I need a source for a battery pack to power my off-the-shelf RCDT system. The requirement is for between 5 & 9 volts and 100 to 150 MAH LiPos. Anyone out there know of a source?

Thanks in advance.

[rivers]

dean,
You need a 2S1P lipo pack … 7.4 volts. There are several here:
http://www.bsdmicrorc.com/index.php?categoryID=41&offset=0
2S packs are available or you can make your own from 2 single cells.
Do you have a lipo charger that will output as low as 100 ma?

BTW, what RCDT system are you using? Is the battery for the transmitter or the receiver?

Dick

[rivers]

Here is another 2S lipo at 120 mah.
http://www.aircraft-world.com/shopexd.asp?id=6188
There are plenty of choices out there. For a RCDT you really don’t need this much output current capability. What is your weight budget?

[rivers]

The cheapest lipos are China sourced. Check the ZIPPY 100 mah single cell, 3.0 grams at $2.00 each. You need two to make your own 2-cell pack.
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7567

[Dean McGinnes]

It is a Spectrum dx5 system, I think, with a Hitec servo. I plan to use it for testing only in a very small field.

I will then remove the rc system and use my Texas MAX-IIIA for contest work.

The airframe is a 650 Sq in T-Bird with a honking Mattes-tuned OS MAX-III .29 up front.

[rivers]

Dean,
The Spektrum DX5 RC system should work well for test flying as you propose. However, it’s only the receiver that’s spec’d for 3.5 to 9.6 volts. Check it here:
http://www.horizonhobby.com/Products/Default.aspx?ProdID=SPMAR500

You will want all the onboard stuff (receiver and servo) to be powered from one battery. Most servos are rated for 4.8 volts to 6.0 volts. However, people do use them outside this range. Try your system with one, 100 to 200 mah lipo (3.7 volts nominal) powering the onboard components. The servo may slow down, but should still work. If not, you may need a 2-cell lipo with a 5 volt regulator.

[Dean McGinnes]

My plan is to use one battery for all onboard components as you suggest. I have no knowledge of electronics, but if the voltage drops below what is specified for the RX wouldn’t it shut down? Slow servos are OK as I am not doing aerobatics but a duff RX would make my day go very badly. 🙁

[rivers]

Dean,
Just to confirm… is your receiver a Spektrum AR500? Please note that this receiver was made for park flyers so it’s only good for short range.

Yes, this receiver will quit if the voltage goes below 3.5 volts, even momentarily. A single lipo has a nominal voltage of 3.7 and is 4.2 volts fully charged. You would need to always start your flying sessions with a fully charged battery. Please note that Spektrum radios can be set up to fail-safe, i.e., go to DT if the radio signal is lost.

If you are uncomfortable with this situation there are several solutions:
1. Use a 4-cell 160 mah Nimh pack. This will give 4.8 volts….perfect for both the receiver and servo. These cells are 3.7 grams each.
2. Use a 2-cell lipo with a couple of Radio Shack diodes in series with the power line to the servo. This will drop the servo voltage to about 6 volts.
3. Use a 2-cell lipo with a 5 volt BEC regulator. You will need electronics knowledge/help to do this unless you can find something off-the-shelf.

[Dean McGinnes]

I was planning on just a 2-cell lipo plugged directly into the reciever. I have no desire to get involved in a bunch of electronics with my scant building time. If that is the case, I may drop the whole thing and stick with my mechanicel timer.

[rivers]

Dean,
I hope you go ahead with the RCDT idea. I think you will be pleased with the control and safety you will get during test flying. I use a Bauer radio DT myself, and it’s very comforting to know it’s there.

I think your plan of just plugging-in a 2S lipo will work. Even though the servo will be overpowered, it’s used only briefly during flight, so most likely, it will function and survive OK. Try it on the bench to confirm.

Please disregard my suggestion of running with one lipo. Even though this idea would work, the voltage to the receiver is too low for comfort without close attention to the state of battery charge.

Whatever you choose to do, I wish you well.
Happy flying,
Dick

[Mike Richardson]

This is probably a little late but if anyone is still looking for a good source for LiPo batteries and extremly light servos and other r/c goodies. Check out this source.
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=3714
I have ordered several things from them and never had a problem. Their prices are great.
They even have several 2.5gram receivers on 2.4ghz for only $14 but I hear their range might not be what we are looking for. Some customers claim 5oo to 600 yards before they go into safe mode.

Mike R. in Indy

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