Manual recommends a "buffer" pack?

[RotorSideUp]

i'm building a whiplash with the scorp V 130a. i have 8717 for cycle (not HV) and a torq 9188 for the tail -- was thinking of running at 6.2v, seem like the lfe pack a few replies back would be perfect, so long as dont charge it above 6.2?

thanks for the wiring diagram as well -- i'll be running a fullsize vbar with two sats, and that really clarified the wiring for me!

[Carapau]

Now don't quote me on this but with the Life you can set the BEC to 7.4. Although a LiFe has a nominal voltage of 6.6v for 2S, at its peak charge it is 7.4v thus it is fine to use it on 7.4v if you wish. You would be best served however ensuring the LiFe was fully charged before turning on otherwise it might draw a reasonable current through the BEC as it starts to charge.

If I am wrong on any of this, it will be a matter of minutes before someone points it out I am sure!

[RotorSideUp]

7.4 isn't too much for my torq 9188, but seems high for my normal voltage jr 8717s... no?

[Carapau]

Oops sorry, I thought you were asking about the BEC voltage against the buffer pack not your 8717s. I guess 7.4 V will be too much for them. I've had a loooonnnng day

[RotorSideUp]

i do have rec pack that came with my dx7 -- 1100mah 4.8 nominal nicd. its probably heavier than the life, but the voltage should be good?

[RotorSideUp]

hmm. i've found other threads where people have used 8717 (not HV) with life packs with success, so i think i'll go this route. I think it will be nice to have a buffer, and an easy way to do setup without the main batt plugged in, and add some weight to the nose of my whiplash.

[sjsamuel]

I may not be understanding you correctly, but if you are going to run the bec at 5.4v or 6v you should not use a 2s LiFe as a buffer as the voltage of the pack will be higher than the bec, and could cause damage to the ESC/bec.
You will need to run a Nimh pack in this case. From what I've heard/read for bec at 6v run a 5s Nimh pack as buffer.

[RotorSideUp]

gotcha, would have to run it at 7.4 to use the life, makes sense. perhaps the nicd is the best starting point, since i have one already that isn't being used.

[Chris_M]

This is what I use on all my heli's and can be run with bec anywhere between 5 and 6V. The pack holds 4 AAA nimh batteries and has an on/off switch right on it so its very simple and effective for buffer/emf. Just plug right into vbar/rx and no worries.

[RotorSideUp]

thats pretty nice. i've ordered a switch and eneloop 6v nicads for the job already or i'd grab this one.

[kkkklee]

I use four 6A diodes in series to lower the 2S lipo from (7.6v best store voltage ) to 4.8v and feed to the reveiver . Set up the BEC to 6.8v . Output of bec is in parallel with the output of dropped lipo output . Lipo will not be charged during bec is working since the diodes block the current . Basically , bec will take all the loading during in flight , no lipo power will be consumed . In case the bec fail , receiver voltage will be keep constant at 4.8v from the lipo .Connect one led and resistor in between the four diodes . The led will light up if bec is not working due to the 4 diodes voltage drop .Extra one diode connect the Bec output to the receiver in order to block current flow back into the bec . Total weight for the backup is about 55g. 20g for the circuit board and 30g for 35c 400mah lipo.Extra extension wire with one diode connected between bec and receiver ( 5g) .
for those pilot use hv servo you can raise the bec voltage to 8.4v and short one of the 4 diode . This will raise the backup circuit output to 5.5v (3 diode instead of 4 , 2.1 voltage drop) which can still run the hv servo .

[rchelijc]

Originally Posted by MrMel

Simple version, if you plug in a RX pack -> RX the ESC arms and is ready to run.
If you start the motor now it will pull the current through the BEC circuit

Not on mine - I plug in the LiFe first so the vbar initialises, but the Scorp V remains completely dead. I only plug in the final wire of the main packs when I'm in the middle of the field, ready to run away the moment I plug it in.

Yeah I do suffer from an unreasonable fear of losing my legs.

[MrMel]

Originally Posted by rchelijc

Not on mine - I plug in the LiFe first so the vbar initialises, but the Scorp V remains completely dead. I only plug in the final wire of the main packs when I'm in the middle of the field, ready to run away the moment I plug it in.

Yeah I do suffer from an unreasonable fear of losing my legs.

Post #17... The edit, it was only on the beta versions

[rchelijc]

Originally Posted by MrMel

To rectify my previous statement, its OK to turn on buffer first, it was only on my prototype ESC it was an issue, tested on my release version and it does not arm.

Oops sorry forget about my previous post - didn't read this before.

[rchelijc]

SBEC 7.4V to Vbar

• Has 2 power inputs to the vbar (one includes throttle signal from vbar to ESC) for redundancy

Single LiFe flight pack - I never take it off (I used to run two in parallel with no BEC)

• Has 2 power inputs to the vbar as well for redundancy
• Connects via an XT60 plug hidden in the frame

Some notes: my servos are all Futaba BLS (352 cyclics and 256HV tail)

• The max current I've managed to draw when I fully stall all cyclics is around 5A.
• I estimate max draw in flight around 6A (taking into account tail, and I don't think cyclics will stall during flight unless you have binding somewhere)
• A full flight with Tic-Tocs all the way and high-speed runs draws around 300mAh. 1100mAh is more than adequate
• No problems with auto - I had to do two purely on LiFe power when my SJ Propo/Hawk 120A OPTO esc overheated and shut itself down... twice

Disadvantages of my power system

• You carry the weight of the receiver pack (mine is 70g)
• You need to check every flight that your LiFe is healthy
• More wiring
• More complicated setup

Advantages of my power system

• LiFe is always fully charged - at least near 100% pack capacity available if BEC blacks out (with lipo, you got 20% max)
• LiFe can be stored fully charged with no problems
• 7.4V is fine for LiFe - causes zero damage
• Scorp V BEC does not take ALL the load (well, probably 95%)
• LiFe is small enough that it won't kill the BEC if accidentally connected when dead
• LiFe is super stable, tolerant to abuse, and much safer

I've been hit in the leg once from this heli that spooled up on me (I forgot to do a rebind for the vbar/JR101 to set failsafes) so my startup sequence is probably bordering on paranoia for some. Anyway, here it is:

Startup sequence

1. Mount all lipos on the heli, but don't make the final connection to the esc (leave either +ve or -ve to ESC unplugged)
2. Check LiFe voltage - should be sitting around 6.65-6.85V depending on how long you let it sit since the last flight. Anything below that, and you should do a quick top off charge to 7.4V first (should take less than 5mins at 2C charge)
3. Plug in LiFe pack and let vbar initialise
4. Do pre-flight checks, range checks, etc
5. Carry to your launch point
6. Plug in final connection to ESC and run

Post flight

1. I let the mains spool down
2. I then run in quickly and unplug the main packs (I've set mine up so I can plug and unplug at the bottom without removing canopy)
3. I carry the heli back, and maybe do some vibe analysis if I feel like it with the Rx buffer pack

Some photos

[OnTheSnap]

Rchelijc,
Is the commander protected from reverse current flow on the BEC? If not, the esc should be armed first, then the LiFE connected. At the end of the flight, disconnect the LiFE first, then unplug the packs. This also allows you to check that the BEC output is good.

[rchelijc]

Originally Posted by OnTheSnap

Rchelijc,
Is the commander protected from reverse current flow on the BEC? If not, the esc should be armed first, then the LiFE connected. At the end of the flight, disconnect the LiFE first, then unplug the packs. This also allows you to check that the BEC output is good.

I've read in another thread Georges from scorpion said that the Bec is protected against reverse current flow. This shouldn't be an issue since the life pack, even of charged to 7.4V, will drop to 6.7-6.8V over night, so it's almost impossible for a Life to cause reverse current.

At the end of flight I always disconnect the main packs first. The reason is to minimize my time next to a fully armed heli. I've seen what happens when I was accidentally in normal mode, non-gov, throttle hold, mid-Stick. No soft start.

When I let go throttle hold, it spun up so hard and fast that it wrecked the root of the blades (which was tight) and sheared the Jesus bolt clean off. Would have taken both my legs clean off had I stood nearer.