Digital servos & the Wren54??
 

I heard it mentioned by a friend that digital servos can cause some noise to the wren54's ecu?Anyone else know/heard anything about this?I am planning to put a wren in my BVM F86 & my YA F18 single.I dont want to have any concerns over this issue, I would greatly appreciate some feedback on this :D


thanks Steve

Digital servos & the Wren54??
 

I also have a BVM sabre with a wren with JR digital servos. The RPM sensor does pick up some noise when the engine is not running but that is because the ECU/ pickup is always chasing a signal and amplifies whats available (which is servo noise in this case).When the Engine is revolving it reduces the gain and all is well.There is also a thiny is available from wren the stop it as well.

jason

Digital servos & the Wren54??
 

Jason

Thanks for the info.How do you like the bvm f86/wren combo?I have seen a couple on ram500's,I would think that the f86 with a wren should be quite a bit faster than those,being that the wren is about half the weigh.What would you guess you top end speed is ? How much fuel are you running & how many minutes are you getting on an average flight?My bvm f86 has the kevlar bvm wraparound tank which I believe is 60 ozs and I am running a UAT also.

thanks Steve

Digital servos & the Wren54??
 

The Wren and RAM 500 are approximately the same weight except for the ancillary equipment which is lighter on the Wren.

I noticed the same issue when I switched to the new FADEC autostart and was told by the ECU designer.....

The problem that you say about the rpm is recently known when the power of the RX is of 4,8V and digital servos are used. This is caused by the
voltaje droping below 4V caused by the noise from the digital servos.I
have corrected it in the last batch of units, but there are a couple of
solutions that you can use:

-Use 6 volt RX power.
-Take a servo extension lead and solder a capacitor of 470microfarad
(minimum 6V) in parallel to the red (positive) and brown (negative)
leads. Install this extrension lead between the hall sensor and the
fadec.

Any of the two solutions will cure the noise. The second one is already
implemented in the current production units.

Digital servos & the Wren54??
 

Blueskies21,

MY Super Reaper has 8 Hitec digital servos and one JR digital in it and after about 15 hours of running, I haven't seen any "noise". I have used both the "220" and the "303" FADECS with no ill effects noted.

My Reaper carries 72 oz plus a small header tank. I have my timer on my Futaba 9Z set at 7 minutes, 30 seconds and it is set to only run when the throttle is above about 25%. This way, I don't have to remember to turn it on! Anyway, I typically fly at least one more maneuver after the timer goes off, do a complete circuit for landing and end up in the pits with about 12 ounces left. I've been using 8 minutes per flight as an average in my logbook. I was surprised to hear last
Sunday from an observer that it was 12 minutes from the time I disconnected the propane to the shut down. From the data downloads, I can see that I use allot of full power to haul the 18 pound airplane around. I guess that the fuel consumption is around 6 ounces per minute for my flying.

Regards,

John

Digital servos & the Wren54??
 

Further to the above.....

Hello Marc,


You should put it in the hall sensor lead, not in the fadec lead.

This isn't RFI, nothing to worry about, and the relative position of all
items inside the plane doesn't matter, because it isn't a radiated
interference. What happens is that the digital servos draw a lot of current
in very small pulses. Due at the resistence of the wires, switch,
batteries,.. this high power pulses cause that the supply voltage of the
FADEC decrease below a 4.5V in form of pulses that go directly to the
magnetic sensor circuit, and this one counts the pulses from the servos as
pulses from the engine. Installing a capacitor in the sensor line, it
filters the supply of the hall sensor and cures the problem. This problem
apppears with the rotor at rest, because automatic gain control of the
sensor is at maximum gain, when the engine turn the pulses from the magnet
are many times stronguer and the noise from the servos is ignored.

The Fadec itself can work with voltages as low as 3V, so this isn't a issue
for the microcontroller or the temperature sensor.

If you want to be sure that is a power issue, test with a 6V battery or
power the fadec with a separate battery. You will see that all is OK. If it
is radiated, the problem still will be here.

Regards,

Gaspar

Digital servos & the Wren54??
 

Ooops, 'Forgot to mention that I am using 5 cell packs with 6.0 volt Maxx Products regulators....maybe THAT'S why I haven't seen any ill effects....so far.

On another note. I have boasted here previously about my FOD screen. Well, this weekend after about the forth flight, the Reaper came back to the pits with a DENT in the screen! I don't know how much THAT would have cost me without the $3.00 screen in place....just something to think about.

John

Digital servos & the Wren54??
 

John I think I will get a fod screen right away - I guess I have been lucky so far... dont wat to press it any further! One of my big gassers actually sucked in a stone through the carb and wrecked one cylinder/piston (it was a twin reed induction, small pebble and man it was bad). I would hate to have to fix the sweet, sweet Wren because of a dumb thing like a pebble!

As for interference, I too fly with many Hitec digitals (7 in my SPAjet) and a 4 cell receiver pack. I get a bit of random rpm and temp when I am moving around the sticks but as soon as the engine starts it goes away and it workd perfect. I just upgraded to the latest FADEC unit from Gaspar and man it is a sweet thing!

AJC

Digital servos & the Wren54??
 

Thank you for all the great helpful info-its all very useful, but I need to correct & clarify my orginal question asked.I misunderstood my buddy- what he had said to me & I heard him wrong.He said that he heard that with digital servos they can cause an unusual draw off the battery with the wren ecu.Sorry for the misguided original question :)

thanks Steve