72MHz to 2.4GHz power question

dieselcrazy

Well-Known Member
Here are the details.
Lanier Yak 54 with a 3W75i
Six Hitec 645mg, four on the wing, one for each elevator
One Hitec giant scale (can not remember the model it's the larger three bearing output shaft servo)
JR 507 throttle servo
JR 945s PCM receiver 72MHz
JR HD switch harness
Voltmagic
A123 2500mah battery

I flew this set up several times. The Voltmagic never did log any peak low voltage detection.

I switched to a JR 921 2.4 receiver and now the Voltmagic logged severe low peak voltage.

I upgraded the switch to a H3C input and a three wire balance tap and dual output to the receiver.

No more low voltage detection.

So my question is why did the system work with the 72 MHz without any low voltage detection?
Does the 2.4 receiver drive the servos harder?

Thanks.
 

BRUTUS

Plank Junky
Lifetime Supporter
The rx itself draws more power, but you wouldn't think enough to drop the voltage. Its a good idea to run multiple hd servo wires, especially from the battery into the rx. Gpad you got it fixed before it made a smoking hole!
 

Classclown

Well-Known Member
2.4 was always more prone to power sappage than 72mhz. But.... The servos you are using don't use up that much power. This makes me start to wonder about your set up. The old switch you were using had a lot of resistance, and switching it out helped the 2.4 rx. Make sure none of your servos are binding on anything, check endpoints.
 

dieselcrazy

Well-Known Member
I was wondering about the receiver, I just didn't think it would draw that must more amperage. The switch harness I believe is rated at 3amp 4 max. Nothing else has changed except the receiver and the switch harness.
 

red7fifty

BadAss Member
Is that 3W a big single? It's gonna shake, and a mechanical switch is extremely prone to vibration failure. I've seen a LOT of them cause plane crashes.
If it were mine (or in this case, your airplane) I'd strongly suggest an electrical, solid state switch from Fromeco.
http://www.fromeco.org/categories/Switches
Both the Badger and Wolverine dual switch, are solid state, soft switches....(Main power does NOT flow through the switch slider......) the slider only "turns off" the power (there is however, a very small current drain when in the OFF state) so it's good practice to dis-connect the batteries for storage. In other words, if the switch were to actually fall off the board, power would continue to flow from the battery to the receiver.
Also, on a bird of that size, I'd also recommend dual batteries, dual switches, and at least (2) power feeds into the receiver. You can order the Badger or Wolverine switch for additional power inputs into the receiver, and in my opinion, 2 inputs from each battery would be a wise safety setup.
 

TManiaci

Engineer
Lifetime Supporter
I believe the difference is in the Rx response times. The 2.4GHz is faster, and that results in a greater surge load as the servos push out with more authority and hence are subject to more wind load.
 

red7fifty

BadAss Member
I believe the difference is in the Rx response times. The 2.4GHz is faster, and that results in a greater surge load as the servos push out with more authority and hence are subject to more wind load.
I agree......the receiver itself really doesn't use more power....but, because the 2.4 receiver makes the servos respond faster, the power demand goes up.
 

earlwb

Active Member
The old receivers do not log or track brownout situations. It usually just manifests itself as a glitch when you are flying on 72mhz. You may not even notice it. They use a simple PPM modulation with a frame. Thus they don't really do much to reboot and relink as there is no microprocessor or computer inside the RX.

The modern 2.4ghz receivers track brownouts more. They use a microprocessor (computer) inside the receiver and it is sensitive to brownouts. Some receivers can take longer to reboot and relink if the brownout is severe. Thus those several seconds waiting on the reboot and relink could result in a crash. Some of the latest receivers have a really fast reboot and relink in case of severe brownouts so you may only have about a half second or less for it to link back up.
 
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