Servo Voltage Question and a Bit of Set up Advice

[C8RLS]

I am currently running a Spektrum AR7100R receiver on a Trex 700n, this fed through to an Align 3G unit which fed through to 3 * DS620 and a JR DS8900G on the tail.

I have had a few problems with the Align unit so swapping it to a Beastx unit.

The question I have is that the AR7100R will regulate the voltage to the Rudder, Aux 2, Throttle and gear to 5.2 volts

All other channels are not regulated and hence would be the 2 cell lipo voltage at 7.4v

The servos are all rated well below the 7.4v but there has not been any issue with the servos so far. I am concerned as I read the JRDS8900 will only accept a maximum of 4.8v and the DS620 servos are rated at 4.8v to 6.0v

So here goes the question - If I connect the Beastx to the AR7100R what voltage will it be sending to the servos, the unregulated 7.4v or the regulated 5.2 volts?

The option I see is to use an Align Voltage Regulator that will drop the Lipo voltage to 5.8volts and feed that into the AR7100 and also use a step down on the servo wire from the Beast X to the JR tail servo.

I could just do the above but forget using the Align Voltage Regulator and accept the higher voltage to the DS620’s at 2 cell lipo voltage and just use a step down to the JR tail servo.

I purchased this 700 second hand a long while ago, it was flybarred then and I changed it to flybarless using an Align 3G unit when they were first available, the heli has not had much use at all. My concern is what voltage will the Align 3G unit have been sending through to the servos as well?

The heli hasn’t had that much hammer at all but I am concerned that the high voltage has been fed to the servos way above their rated power. I have yet to check to see if the voltage to the JR servo has been stepped down with an inline voltage step down or not by the previous owner.

Your suggestions, comments, ideas etc would be greatly appreciated so I can get this project completed and have confidence that I wont be burning the servos out!

[GIXERMAN]

if you connect beastx unregulated will take 2s lipo upto 8.5v, so this will be given straight to your servos and they will go pop at some point. the align drop down is 5.2v which the 8900g will take, or futaba or western robotics do a better one/more reliable

[Mark_T]

... the align drop down is 5.2v which the 8900g will take ...

It won't be 5.2V if you start with a 2S Lipo though, it is only good for about a 0.7V reduction from memory as it is designed to work with the Align 2-in-1 which kicks out around 5.8V

[LaurenceGough]

It won't be 5.2V if you start with a 2S Lipo though, it is only good for about a 0.7V reduction from memory as it is designed to work with the Align 2-in-1 which kicks out around 5.8V

You beat me to it .

Expensive mistake, you do not want to run the 8900G at much more than 5.2V IMO.

I think even running DS620's on 2S lipo is again very risky, apparently a few have been getting away with DS610s which are geared for more torque less speed, so should be in theory better but again in my opinion this is a big risk as they are not rated even close, if any cyclic or tail servo fails on your model you are not going to have a nice day.

I would recommend running this regulator for the tail servo:

VR5203 Dual Output Regulator (SPMVR5203): Spektrum - The Leader in Spread Spectrum Technology

You would need to have a regulator for all your servos to be truly running within the specs, or to buy HV servos like I ended up doing .

I think you could run the Align Voltage Regulator and then a ~0.7V drop down for the tail servo, but you have to watch the amp rating of this regulator as by memory it is not that high. You would have to run bench tests to make sure that the voltage does not drop too much causing a loss of control or reg failure.

[coolice]

Hey.

As Mark says above the Align drop down will only drop voltage by about 0.7/0.8 volts, so the voltage going to the 8900G will still be too high. You can make up step downs with more of a voltage drop, but what value resistors you'd need I do not know.

The Align servos have been known to run on straight 2s LiPo power, but they've also been known to fail pretty quickly on it to, so I would not suggest running them on this voltage to safe guard the model and your own safety while its flying.

You could connect a LiFe pack straight to the spektrum receiver, these packs output 6.6 volts rather than 8.4 from a LiPo. Then you could look at a tail servo drop down of about 1 volts to make the JR tail servo happier.
This would remove the need for a regulator or BEC unit, so be tidier and more cost effective.
.

[GIXERMAN]

I have been running a 8900g for 2years @5.1v never had a problem.

[LaurenceGough]

I have been running a 8900g for 2years @5.1v never had a problem.

5.1 or 5.2 possibly a little more will be just fine and is what I run mine on, but the Align tail reg will still end up being 7.7V going straight to the 8900G if running off a Lipo direct

[bulnose]

could he use a gryphon regulater? , or does that reciever HAVE to be powered by a lipo

[C8RLS]

Thanks everyone for your comments, simply by changing to the Beast X on this model it has opened up a real can of worms!

When I bought this model everything was running throught the AR7100 at straight voltage apart from the tail servo which was using the regulated output channel in the receiver at 5.2 volts, but when the outputs are taken from this reciever, cyclic unregulated and tail regulated to 5.2 volts what does the BeastX do with it, does it keep the tail at 5.2 volts and the cyclic unregulated or does it make the voltage for all outputs from the BeastX unregulated?

I cannot find the answer anywhere!

It seem that more than likely the answer for this model is get a decent regulator and a different receiver, step down to the tail servo oh and a new governor! Almost a complete new setup then LOL.

[DaveMac]

The power from the goes through the elevator and aileron cables I'm sure so you will get the full voltage on the beast x.

You could split the rudder servo output to take the power from the ar7100 thus being regulated and the control signal from the beast x. There is a diagram on how this works but I can't find it at the moment.

[yuppyflyer]

I would assume that the Beast x has a single power bus rail and whatever the highest input voltage will be the output to all the servos attached.

On my T-rex 700N I use AR7100 and Beast X. On the cyclic servos (JR8915) I run high voltage so separated the signal wires and power wires on these three servo leads. The signal wires go direct to the Beast X, and the power wires to the AR7100. The other servo wires, rudder etc. go from the 5.2v side of the AR7200 to the Beast x as normal. So Beast X running 5.2v, cyclic running 8.4v. Using a 2S lipo to power it all and has worked well for a long time.

[Mark_T]

I run high voltage so separated the signal wires and power wires on these three servo leads. The signal wires go direct to the Beast X, and the power wires to the AR7100. The other servo wires, rudder etc. go from the 5.2v side of the AR7200 to the Beast x as normal. So Beast X running 5.2v, cyclic running 8.4v. Using a 2S lipo to power it all and has worked well for a long time.

If you are going to stay with the AR7100R then that us the 'easiest' way to do it as it will keep the voltages separate.

Personally though I wouldn't be considering running DS620's direct from a 2S lipo ...

[C8RLS]

Thanks everyone, in the end I have changed the receiver to an AR 9020 that I had which came with my DX18, used an Align G600 Governer that I also had spare and purchased a Gryphon regulator, an in line voltage step down for the tail servo and that all combined seems to have done the trick, just got to tidy all the wiring up now!