8717 on 8V.......long term

[jeznewsome]

Just building up a stock of kit for a TRex700 and have got 3 8717s for the swash and a 7100R to power it all through a 2S Lipo.

But scanning the UK JR distributors site I noted the following warning

Using DS8915 Servos Without a voltage
regulator
The latest trend in 3D heli flying is to run digital
servos via receivers being powered direct from
two cell lithium packs. Fresh from charge, this
can mean voltages in excess of 8 Volts. In the
USA some of the top 3D guys are running
DS8717 servos in this manner and appear to
get away with it for a short while, although
service life is sure to be reduced.
JR have confirmed that the DS8717 is exactly the same servo as
the DS8915, re-badged for the US market. However we would
strongly recommend NOT running DS8915 servos in this manner
as they will not be covered by our warranty. This is also true of
other current JR servos, which should also not be run direct from
a 2 cell lithium pack. If you wish to use lithium batteries to power
your R/C system then please use a good quality regulator at the
recommended voltages for the JR servos and gyro being used.
JR were concerned enough about this to issue a short statement,
which is reproduced below:
“Although JR does not guarantee the DS8915 servo to work at
8.0V, this servo does seem to be workable with 8.0V. But if you
use the DS8915 with 8.0V then this will be at your own risk. JR
regret that we cannot give our approval for such use.”
Please also note that we will be unable to repair any burnt out
DS8717 servos. We will be advising service customers with such
servos that they have been sold grey imports and to return them
to their supplier for a full refund.

Now whilst I accept that buying 8717s (at a decent price) from the US means that I have no guaratee I do get worried that if one of the swash servos packs up in flight then I will crash an expensive heli! This is obviously something that I would like to avoid.

Anyone any long term views on the reliability of the 8717 on 2S Lipo power?

Otherwise shouldI be considering fitting some form of regulator (7V) to maximise the lifespan of the servos? If so any recommendations?

[andyp]

The 8717 and 8915 are the same servo. Just re-labeled for different markets (why, I dont know...).

While I can comment on 2S LiPo/LiIon longevity, how about using Li Iron Phosphate cells? These have a nominal voltage of 6.6V (compared with 7.4 for LiPo's), so are kinder on the servos.

The disadvantage is less mA per gram, but they do fast charge in 15 min.

And Fromeco (www.fromeco.com) is about to release a nice regulator for sorting out the wiring of a 'raw battery voltage' servo system.

Andrew



Subject: Unclassified - Fromeco Kiwi Regulator

Let me tell you a bit more about the Kiwi -

Perhaps the perfect regulator for modern helicopter flight systems.

You have a 2.4g Rx and high voltage usable (HV) servos (eg JR8717's):
The Kiwi regulator will provide raw battery voltage to the receiver and associated servos (typically three cyclic servos) and a regulated 5V supply for up to four other outputs (typically tail rotor and throttle). Because the receiver receives voltage directly from the battery, a low voltage brown out state is very unlikely, and no possibility of a reset due to the regulator. And it has a fail safe switch built in!
Use A123 type packs (eg the Fromeco 1200mA Iron Corps) for a 'kinder' voltage to your HV servos. Or use a LiIon or LiPo pack for even faster servo speeds and torque.

Hey, what is I am still on 72MHz (and so my receiver can only handle 6V max)?
Unlike any other product, the Kiwi can be installed to provide a 5V regulated supply to the receiver (along with tail rotor and throttle) and allow unregulated voltage to be passed to up to four other servos (typically the three cyclic servos). And yes, you can still use the built in failsafe switch!
Again, use A123 type cells for a 'kinder' voltage to the 8717's.

What if I fly on 2.4g or 72MHz and don't yet have HV servos?
The Fromeco Arizona is still the regulator of choice (giving up to 6V regulated to the receiver and servos, except tail rotor which receives a 5V regulated supply).

So, in summary, the Kiwi regulator has a built in failsafe switch and if you are running HV servos will work with 72MHZ today (5V Rx supply) and 2.4g tomorrow (unregulated battery voltage supply to the Rx).
Use A123 type cells to prolong cyclic servo life, or Li Ion/LiPo for blistering performance.

My recommendations:
1200mA A123 type cells (Iron Corps) in a 50. Use JR8717 cyclic servos. Typically 2-3 flights between charges, and charge in 15 min.
On a 90, use either the 2400mA-h IronCorps phosphate cells, or 2300mA-h IronCorps Extreme (with A123-brand phosphate cells) and charge every 3-4 flights.

IronCorps Extreme is capable of delivering big currents with little voltage drop, and can be charged in 15 minutes from flat. Their nominal voltage is 6.6V, which is much safer for the JR8717's than an unregulated LiPo pack.

[jeznewsome]

Andrew,

Well thats got me thinking! The voltage on the LiFe cells seems ideal. Just need to have a good look at the charging options (as only 1 of my 3 chargers has a LiFe setting). I like the idea of no regulator if possible and these would be just the ticket.

Will do more research, though have found some A123 cells in 2300mAH packs in the UK at Puffin Models.

Thanks Jez

[Finless]

Well my only comment based on seeing it in action. several TOP pilots have been flying the 8717's (and prior to that the 9000z) on 8V for quite some time now. I have not heard of a failure myself! I am not a top pilot and can no where near pound on a servo like they can but I look at it this way. If they can pound on them and not have a failure, do I really need to worry about longevity? Hmmmmmm.......

Bob

[dogg5306]

Bob... you did crash recently due to the fact that a servo has quit in flight...
Still the same opinion?

I'm planning to use them around 6.5v should my 6014 receiver allows it (coupled with a 2s and an Arizona regulator)

[Pinecone]

I went to the Scott Gray ReactorX. I can power the cyclic servos at eitehr 6 or6.8 volts and the Rx and the rest at 5.2 volts.

And it can put out some 15 amps for 6/6.8 volts. PLENTY for 8717s. :)

[VegasBob]

Going to power my new 700 with 7100 receiver and 8717s at 8V. What's the latest consensus, good idea, bad idea or what?