From: harald@boink.UUCP (Harald Milne)
Newsgroups: rec.models.rc
Subject: 6 volt reciever battery packs (Subject was <none>)
Summary: Futubas answer
Date: 31 Aug 92 18:06:35 GMT
Organization: Independent Software Solutions, Anaheim, CA

In article <1992Aug25.095210.486@csc.canterbury.ac.nz>, kaiser@elec.canterbury.ac.nz (Chris Kaiser) writes:
> Does anyone out there have any experience and/or comments about using 5 cell
> nicad packs (i.e. nominally 6 V) with RC gear. The system I'm looking at using
> it with comprises a Futaba R115 (I think - 5 channel FM) Rx and S143 micro
> servos. I've been told by a Futaba NZ rep that 5 cell packs are bad news and
> cause premature failure of components, however this guy had zero technical 
> knowledge (you should have heard his explaination of why PCM was better than
> FM which was better than AM :-) so I'm not sure how valid this is.
> The only problem I can see is a higher current when a servo stalls, 
> which may damage it. 

   The technical specifications for the S148 servos is at 6 volts. It may
be different for other servos. Running the S148 servos at 4.8 volts,
would be running them in a underated condition. What is interesting about
this is the servos will never run at published transit times or torque 
specifications at 4.8 volts! They will run slower and generate less torque.

   The servos will work harder under severe load at 6 volts than they would 
at a lower voltage.  Futaba doesn't publish a mean time before failure (MTBF)
specification, so the question of premature failure can not really be 
answered directly.

   In my opinion, running S148 servos at 6 volts, is running them at design
specifications. Running them at 4.8 volts is "pampering" them. At 4.8 volts
they may run longer, but you then suffer the speed and torque losses. 

   As for other servos, I don't have the specs handy. I would check and
make sure. Servos sold individually in this country have the specs right
on the package.

> Presumably the Rx has an internal voltage regulator, so it wouldn't be
> affected by the higher voltage.

   The recievers have always left a doubt in my mind, since Futuba always
mentions the supply at 4.8 volts for my R127DF and R128DF. So off I went
to Futuba of America in Irvine, CA. I asked the customer service rep
directly about 5 cell nicad packs. He said this was OK, and not to ever
exceed the 5 cells or you will fry everything including the switch harness.
Appearently somebody tried this! He had no concern about what equipment
I was using at all. Since this gentlemen sees only broken and fried 
customer equipment, I feel fairly confident about running my equipment
at 6 volts now, and plan to do so in the future. I just wish Futuba
would publish more complete specs on all their equipment, I would sleep
a lot better.

   It is interesting that your Futuba NZ rep says that 5 cell packs are 
"bad news". Futuba Corporation of America sells a 5 cell J-connector pack.
The part number is NR-5PB and is 6 volts at 450 milliamps. You might want
to ask him about that. Maybe Futuba should talk to itself 8^).

> Chris Kaiser
> 
> Postgrad, Elec. Eng. Dept.
> University of Canterbury
> Christchurch, NEW ZEALAND


-- 
Harald Milne                   RISCy Business	             ccicpg!boink!harald
Newsgroups: rec.models.rc