Anyone Heard of Pitch Pump Test on VBar??

[TheBigE]

Okay,

I was out out the field yesterday flying, and had a talk with a fellow flyer.    He saw that I was running 8717 servos on my heli, with a Jive 120A ESC using the Jive BEC.   

He said that these servos will draw too much voltage and cause a reset (Spektrum or V Bar) if you do the Pitch Pump Test in V Bar.   

So of course I asked about the details of this test.    Basically, in V Bar advance settings you can set you pitch to be VERY VERY Aggressive around Center stick.   Think of it as extreme positive EXPO (In Spektrum Talk, Negative I beleve in Futaba)   Then if you cycle the stick quickly the servos will react and essentially the BEC in the Jive cannot maintain the Voltage, at 4.5 Volts for 10s V Bar Resets and 3.8 V (?? maybe less) Spektrum Resets. 

Okay, this happens, but then my questions is when would this ever happen in flight.  I have asked him if he has seen this but he could not say.    Apparently this is the test that the V Bar programmer recommends to be doubly safe.

Now for full disclosure I am running HeliCommand on my E5 and V Bar on my E7, soon they will both be HC.   I am not sure this is an issue.   

Has anyone else tried or heard of this test?  It seems a bit extreme to me.   Like back in the Pre FBL days, when you would check binding in the head, some people would check for binding in extreme corners of the cyclic (hence the cyclic ring) but I never did, I figured if I am at those extremes I have other things to worry about.   I would never see that in normal flight envelope. 

I have had 60 great flights on my Setup, do not see the need to add an additional BEC.   I know I am not getting the top performance out of the servos, but I am happy with the performance and have learned to fly the machine, if that makes sense.

Thoughts?

Erik

[Chris Sexton]

I have heard of this, and Rob Cherry and I have had this happen on Savox SB2271 HV cyclics.  I have never heard of it on 8717s though.

If you have had 60 good flights, and you dont run a TON of pitch pump in vbar, then I wouldn't sweat it.

[TheBigE]

So this happened in flight?   What was the pitch pump setting?  What were the flight characteristics.

I am switching over to HC (in E7, E5 had been HC from day one)  need to do some research on minimum voltage for that system. 

[curmudgeon]

I imagine that brown-outs would be more of a concern when running the BEC on 12S.   On 6S, there would be substantially more current available to run the electronics.

I have not seen the JIVE BEC specs, but I assume that it uses the same input voltage as the ESC itself.

[Chris Sexton]

So this happened in flight?   What was the pitch pump setting?  What were the flight characteristics.

I am switching over to HC (in E7, E5 had been HC from day one)  need to do some research on minimum voltage for that system.

Rob has had them fail in flight, but on the bench he and I got them to brown out just bouncing the collective. Rob tried everything and even tried different BECs, 6s and 12s.

A fellow HeliFreak member did some scope testing with the Savox SB2271 and found they could spike 30A easy. Again, this is the Savox SB2271.  They work GREAT on 2S lipos. I haven't heard of troubles with the JR 8717s. I have ran them on my E7 for a while, no issues at all on a Castle BEC Pro on 12s. I run Pitch pump at 30.

[Tommy Wagner]

One other way to test this is to put the cyclic stick on the corner and let it go this causes high spike in the amps and will cause brown outs of there is a issue.

I think is also safe to say that most of us do not take as much good care of our receiver pack as we do our flight packs as they are cheaper to replace
 

I have always used 2s lipos for all my helis and regulators to step down if needed.

I do not push them as far as a lot of people do 3 flights and they get charged or replaced with a fresh pack. It's a matter of is that one extra flight worth the money and time to repair a heli and not knowing if that was the problem or some other gremlin in the system.

I have 8717 on 2s on the E7 and N5c with no issues to date ( knock on wood).


Tommy

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[bmclaurin]

OP, if you're really worried about it, you can always just run a small buffer pack.

[TheBigE]

Thanks,  I may start looking in to Buffer Packs   I have not had any issues to this point, so I think I am safe. 

For those that run a 2S Lipo, are you running a separate RX from the FBL Unit (Vbar, Helicommand, etc)?

[Chris Sexton]

I have ran it both ways. Sats on a VBAR and now SBUS RX on VBar. Just put the power leads into the FBL, SBUS delivers the power to the RX. If you are running a separate RX, I would recommend you have two power leads, one going into the FBL and one into the RX.

Even on my 2S lipo setups, I run two power leads into my VBars. To share the load.

[Tommy Wagner]

All s-bus Running one power lead to the receiver and one power to the FBL unit except my N5c which is running just the power to receiver the S-bus cable powers the 750. That is running 8717 with no problems


Tommy

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[aclysma]

So I'm a bit late to the discussion, but RC Today show very recently put up a fantastic podcast episode you may be interested in. It explains the rationale of the V-bar pitch-pump test and how to perform it. Alex (a.k.a OnTheSnap) discusses why this is becoming a bigger problem these days with newer servos. (8717s are certainly not new, but they are coreless servos, and coreless servos tend to have higher transient current demands than brushless servos)
http://rctodayshow.com/2013/04/rc-today-show-074-power-play/

I personally would not want to fly a machine that cannot pass the pitch pump test but you may be able to find enough people having success with 8717s with the jive internal BEC to feel comfortable with it.

In any case I would strongly recommend listening to that episode so that you can make an informed decision for yourself!

[TheBigE]

Thanks, I will check out the episode.   I just switched over to HC FBL unit from VBar, and it has a much more sensitve Voltage/Current requirements.    This was in my E7, and it really brings to life the demand these servos have on the electronics. 

In short, I ended up running both the master and slave wire from the Jive BEC and adding a buffer pack.    I would say running both master and slave wires, seems to do the trick and the buffer pack is just an added safety margin.   This was just long enough until my WR BEC arrived.   

I will be updating my E5 to run both master and slave wires to the FBL unit, but do not think I need a buffer pack.  I have over 60 flights and no issues, but I was some insurance.