AR7000 power separation mod

[moyesboy]

As discussed in another thread, I've decided to run the AR7000 rx direct from the 7.4v 2 cell lipo.

Purpose is to prevent Rx reset whatever happens with stalled servos and regulator volts drop. If the reg stays overloaded then you are still crashing but if it can drive the servos a bit then you wont be waiting 2-3 seconds for the receiver to come back on line.

The servo connections are split into two plugs per servo one with the +/-, and one with the signal.
The signal plugs all go into the rx as before.
The power plugs go into a common rail made from a 0.1" 2x10 pin boxed header cut up and all the + and all the - joined with the legs of a 4700uf cap then the back covered in hot melt glue. This common rail gets power from the 6v outlet of the 2in1 reg. The cap is probably redundant but will help the reg with start stop current peaks from the servos.
Power to the rx comes from an extra lead soldered onto the deans plug the battery connects to.

All still hanging out of the heli, but it works.
I already posted about the putting 7.4v into all the servos accidentally, so you need to take care with that and mark the plug from the deans as RX only.

One problem I see is the servo signal plugs now only have the one crimp so have not much retention force. I may secure them into the rx with hot melt or fit blank crimps (I have plugs and crimps and a crimp tool from ashtek electronics).

On an electric heli an alternative would be to power the rx with a small rx pack (250mAh?), or low current BEC.

[Ade_Law]

i did a little test on the knight which is now equipeed with nice shiney futaba bls351 brushless servos.

I pulled a Volt meter into the rx and stalled the 3 servos. the voltage dropped to 5.5v obviously only did it long enough to get the reading.

then i did the same test measuring the voltage at the regulator and it didnt change just stayed at 6v so its not the reg dropping out.

the froneco reg i have uses 2 leads into the rx to spread the load. supprisingly removing one of these leads didnt affect the voltage at the rx.

so the only explanation is that its dropping the volts on the power buss in the rx. this is bad as the whole system voltage drops.

im pondering getting 3 HD futaba extion leads and soldering the reg directly into these leads this takes the current away from the rx in a similar way to your method. soldering the reg into the extention leads also means you loose a pair of connectors from the power system.

the only current going through the rx is the tail servo but a 4th extention lead would fix this.

Ade

[Ashley Davis]

oh man, what have I started??

[LipolyGone]

Dare I say with all this complexity of wireing in your helis wouldnt it just be better to go back to basics & stuff in a 4 sub C sized RX pack of GP Nimh cells this does away with Regs totaly.
These cells are capable of delivering 30amps or more.
Sorry but I'm a firm beleiver of the KISS principle.
Martin

[LipolyGone]

Nice tidy instalation you have there Moyesboy
Martin

[moyesboy]

Nice tidy instalation you have there Moyesboy

It will be

With my 4.8 sub C 4300mAh niMH pack in cold weather the volts was dropping toward 4v under load after only 4 flights, and probably momentary dips below that. I guess I'm paranoid. NiMh are crap in the cold.

[LipolyGone]

Nah mate your right to be paranoid, alot of money at stake.
I didnt realise NMH cells were so poor in the cold, now I'm worrying as my new knight Sport has a 3600 GP matched pack & spektrum gear.
Geez more to worry about
Martin

[Ade_Law]

on my model its not the reg that is the problem its the power bus in the rx i doubt the power bus in the spektrum is any different.

moyesboys thing does 2 things. ups the votage to the rx and takes the current for the servos away from the rx too. double whammy.

on spectrum as a minimum i would be tempted to do the mod i suggested no matter what your power source.

Ade

[Chippy]

Excuse my dumbness but can someone put a link up for the thingny bob bit that you put in line to prevent the power dipping to the spektrum receiver please.
Hope this makes sense

Thanks.

[barney]

What about using a Fromeco DC-UP?

You could always use one of these. It will power the servo's/Rx for roughly 5-7 secs after a voltage dips occurs preventing dropouts.

http://www.realraptors.co.uk/zen-car...ws&news_id=190

[Leebert]

i did a little test on the knight which is now equipeed with nice shiney futaba bls351 brushless servos.
I pulled a Volt meter into the rx and stalled the 3 servos. the voltage dropped to 5.5v obviously only did it long enough to get the reading.
Then i did the same test measuring the voltage at the regulator and it didnt change just stayed at 6v so its not the reg dropping out...

Ade, did you measure the current draw with the servos stalled? I was going to measure my Knight today (with 9255s & Align 2 in 1 reg) and see what the voly drop and current draw is. It'd be interesting to see how much the difference is between brushed and B/L.

[Ade_Law]

no but the 3 fligths is did on sunday pulled an extra 150-200mah out of the pack compared to the 9252 that were in there. but thats to be expected as they were defo holding their position better that power has to come from somewhere!

i will measure it tonight.

Ade

[Sesame]

got my fromco yesterday, plugged it iin and tried all I could to get the voltage to drop stalling the servos etc. managed to get on my 4300 sub-c the voltage to drop to 4.3V lowest.

after turning it off as has been said before it will drive the servos for 3-4 seconds.

I'm going to try it in the air hopefully at the weekend, but ive also got a lipo setup somming so will probably have to ask lots of questions about the

[Leebert]

Just did a quick test on the Knight with an Align 2 in 1 (old type in heatshrink) and 9255s...

Stalled cyclic servos caused the voltage at the AR7000 rx (well, at the Revlok) to drop to 5.6 volts. The max current drawn was 3.7 amps.

This was with the heli electronics cold. It could be different is the reg was already hot.

[moyesboy]

My mod is very much belt and braces, and as I said it may well be losing as much in complexity as it gains.
There are no more crimps and connections than before, but there are more plugs. So there is more chance of a plug coming out. Also separating the 3 zip wires makes the single signal wire more vulnerable.

I jiust liked the idea of only routing what is absolutely necessary through the regulator.

When I have it all routed and stowed to my satisfaction I'll post another pic.

Probably the most reliable setup in terms of voltage and comlplexity is to use a 5 cell NiMH sub C pack and step downs for the stuff that won't take 6v. As long as on a hot day with a fully charged pack the volts don't prove too much somewhere. Then the volts should hold up well enough to prevent an rx reset.

I think my arrangement might be the way to go with an electric heli with small low cost low ampage BEC driving the RX separately with the main regulator/BEC driving the servos.

for larg models and helis I don't thing the bus power through the rx is the way to go.The tracks that join the pins in the rx are not up to it. The bigger receivers should have separate power input to the rx and servos with more than one power input to the servos. There can be a jumper to link the servo power to the rx power for less demanding applications.