View Full Version : Need help with larger e-power set-up.

09-25-2006, 03:47 PM
Iím helping my bro-in-law set up his Raidntech P-38. This will be the first plane either of us has built that has retracts, & the need to use a separate power source to power up the Rx & servos, UBEC? Question #1; Would tying 3 servos together, as in 3 landing gear retracts, into one channel so that all of the gear would be actuated with one switch cause any overloading problems? Too much current draw? Question #2; Are UBECs made with different current capacities to support fewer or more servos? This plane is looking to have 7 servos, 2 HS-55s, 1 HS-81, & 1 HS-81 MG & 3 retract servos, HS-75s I think. What size UBEC & Rx battery would be recommended for this set-up? We were thinking of using a 900mah, 2cell, 10c LiPo. TIA for any help.

10-01-2006, 02:55 PM
I would go for the standard four cell reciever battery. It would give the power to make the servos respond as they should, 900 would serve well I beleive, monitor the first flight or two. A Voltwatch on the side of the fuselage like the glo guys use would do that well with minimum weight gain.

Hobbico Voltwatch2 4.8V/6V Rx Battery Monitor



Most flights I flew when I was glo I never needed more than 900mah, but I never had that many servos.

Good luck with your project.:)

They do have UBEC in different voltages, this just seemed easier.

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10-01-2006, 03:16 PM
First of all, it would be one or the other, you wouldn't need both a UBEC AND a receiver battery.

Hobby Lobby markets a UBEC that is advertised as being good for up to 10 servos. I would think that that unit would handle your application even though you are using mini servos. I'd call Hobby Lobby and get their opinion. The UBEC's are nice. It's great not having to worry about the charge status of your reciever battery.

You're using mini's so I'm assuming your plane isn't that large. Making that assumption, if you went with a four or five cell Nimh, you'd have a large capacity battery and not a lot of extra weight.

I've never tried it but it seems to me that a 2S lipo pack would overpower the system.

10-01-2006, 08:55 PM
First of all, it would be one or the other, you wouldn't need both a UBEC AND a receiver battery

I believe that is what I said.

10-03-2006, 03:58 PM
Thanks guys,
I'm learning quite a bit with much help from these and like forums. I had originaly thought that a UBEC was basicly a voltage regulator which was used with a seperate battery pack, hence the thought of using a 2cell LiPo. I have since learned that a UBEC is a device which uses the main battery pack and basicly regulates the voltage to a level that the Rx needs along with supplying enough current capacity to operate several servos, without using the BEC in the ESC. I could also use a 4 or 5 cell Rx pack to do the same but this adds a bit of weight and like was mentioned, the need to make SURE the Rx pack is charged. If I don't have this right, please correct me. And thanks again for the information.

10-03-2006, 04:24 PM
One more small thing, if you use a UBEC, and your ESC has a BEC, then you must remove one wire from the BEC, I believe it's the red one, and I hope someone will correct me if I'm wrong. Some people say use a cheap servo connector extension between your BEC and receiver and cut the wire, or remove the pin on the connector, so you won't have to damage your ESC connector.

10-03-2006, 04:51 PM