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Old Sep 18, 2001, 01:02 AM
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Ben74's Avatar
San Francisco, CA, USA
Joined Jun 2001
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Can I use 5 cells in an Rx pack?

hi all. i have a spare 5 cell nicad pack lying around, and i'm wondering if your average receiver (say a 555) can handle 5 cells, or if it's four cells only. i'd rather not re-solder the pack, and weight is not a major concern in this case.

thanks,
ben
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Old Sep 18, 2001, 02:11 AM
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OzMax's Avatar
Toowoomba, Queensland, Australia
Joined Jul 2001
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Re: Can I use 5 cells in an Rx pack?

Quote:
Originally posted by Ben74
hi all. i have a spare 5 cell nicad pack lying around, and i'm wondering if your average receiver (say a 555) can handle 5 cells, or if it's four cells only. i'd rather not re-solder the pack, and weight is not a major concern in this case.

thanks,
ben
I would assume that most recievers could handle a 5 cell pack. Most servos can handle it (and indeed seem to work better with them as one would expect). As for the 555, I would assume it could, but have not seen detailed input voltage specifications for this unit.

Andrew
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Old Sep 18, 2001, 02:17 AM
p471701
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works fine on 5 cells....gregg
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Old Sep 18, 2001, 04:30 AM
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The Rx is not usually the problem, it's more likely to be the servos. Most standard servos or bigger are o.k. but I doubt most micro servos will work well on 6V.

They are electric motors just like the ones we use for power. More voltage = more current = more strain on the motors and less duration from the battery.

If you really don't want to pull the pack apart you could always just solder a connector across 4 of the cells instead of all 5.

Steve
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Old Sep 18, 2001, 04:52 AM
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In larger models the use of 5 cell packs is commonplace, it helps to offset losses in long servo wiring and increases servo torque and speed. Most manufacturers now quote performance figures on both 4.8v and 6v ... even for small servos like Hitec's HS50 and 55:

http://www.hitecrcd.com/Catalog/Servos/Servo.htm
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Old Sep 18, 2001, 12:08 PM
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North Branford, CT
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FWIW,
I just lost an Escape because the Rx glitched.
Send the thing back to FMA (under warranty) they fixed it and the note enclosed said the fault was a burned out voltage regulator.

I'll not use a 5 cell pack again. Wether or not that was the cause I don't know.

YMMV

Regards,
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Old Sep 18, 2001, 12:31 PM
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Cheshire, England
Joined Mar 2001
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I hardly ever use four cell packs anymore - I enjoy the extra speed / torque you get with the five.

Never had any problems at all (even in the heli's!)

Cheers
Richard.
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Old Sep 19, 2001, 06:02 AM
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Adelaide,Australia
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I thought rx's and servos were originally designed for 4x1.5 carbon/alkaline disposable batteries (6V). 4xnicad or nimh (1.2) is only 4.8V (at best) but 5x1.2 is back up to 6V.

Could be wrong though.
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Old Sep 19, 2001, 06:12 AM
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I always use a 5 pack for the extra weight instead of lead in all of my gliders and the 5 pack gives the extra ommmph I need
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Old Sep 19, 2001, 12:05 PM
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Five cells pack will shorten the battery time by 20% than the four cells pack. Most rx uses 6.3v Capacitors and sometimes the real voltage is lower(production inconsistances). A good 5 cell pack off the quick charger will have over 7 volts, thus the smoke they packed in the capacitor at the factory will leak out. I would stay with 4 cells.

Brian
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Old Sep 19, 2001, 02:59 PM
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If you look at the specs for Cirrus servos, you'll note that their torque and speed values are based on 6.0V, not 4.8V . A little sneaky if you ask me, since the standard for rx packs is 4.8V. Hitec and others base their values on 4.8V.

You should not run 5 cells if you have selected and installed your servo's and linkages correctly, but if you just happen to have a 5 cell pack laying around, it should work. As Brian noted, increasing the cell count will reduce duration...

Pete
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Old Sep 19, 2001, 10:14 PM
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A 5 cell pack will decrease the duration but it will also speed up servo operation and increase torque. A fair trade-off for large hi-performance models. I have never heard of a servo failing due to using a 6v pack vs a 4.8.

Quirky
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Old Sep 19, 2001, 10:16 PM
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OzMax's Avatar
Toowoomba, Queensland, Australia
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Quote:
Originally posted by stephen.s1
FWIW,
I just lost an Escape because the Rx glitched.
Send the thing back to FMA (under warranty) they fixed it and the note enclosed said the fault was a burned out voltage regulator.

I'll not use a 5 cell pack again. Wether or not that was the cause I don't know.YMMV Regards,
Hmm. if the voltage reg burned out it would have been caused by too much power being dissapated by it which most likely would have been caused by too much current being drawn (caused by too many servos, a stalled servo, etc,etc. See point below.) rather than a higher than normal input voltage. Yes a reg has to dump power during the linear conversion process but the power dissipation difference between 5V input and 6V input is not a great change. (call it a tops 15% increase in power wen just powering the RF/MPU)

Also usually the servos are not connected to any regulator, they are instead directly connected to the battery, it would only have been the microprocessor (if one is in that unit) and RF circuitry which would have been connected to the regulator (and only drawing a small ammount. Probably a Pic chip drawing 1mA or so, guess at 20mA for the RF stuff, but let's just say not very much). In which case if the reg burnt out, either a bad design, or a very faulty regulator.

This is all said of course without a shread of knowledge about the schematics of your particular unit, just some of my rambling thought..

Conclusion.. always test everything before committing to the air. (or like me just fly junk planes. I never fly anything I wouldn't mind taking a sledge hammer to)

Andrew
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Old Sep 19, 2001, 10:25 PM
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Canada
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Interesting topic.. In the not too distant past (and probably currently, but I don't have recent knowledge) virtually ALL Japanses produced radio systems were designed for 1.5 dry cells (AA) in Both RX and TX, nicads being a marketing requirement for rich North Americans apparently. As a result the use of 12v(8AA alkalines) for the TX gives improved range, and 6v for the Rx gives obviously quicker servo response. Don't know about shorter Rx pack duration tho, never actually noticed (or paid attention I guess;-) in over 20 years of this use on my various Futaba's.
Not 100% sure re current Radios (haven't bought a new system in the last 3 years), but I strongly suspect that they are continuing in this tradition.
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Old Sep 19, 2001, 10:25 PM
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Toowoomba, Queensland, Australia
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Quote:
Originally posted by CaptQuirk
A 5 cell pack will decrease the duration but it will also speed up servo operation and increase torque. A fair trade-off for large hi-performance models. I have never heard of a servo failing due to using a 6v pack vs a 4.8.Quirky
Quirky,

why would it reduce the duration? I would have thought it would increase duration as you have a higer voltage to start with moving you further away from the system shutdown voltage of about 3volts or so. (maybe not see below)

ok, let's think this through (haven't had a coffee so this will be rough).

If you increase the voltage you will indeed
increase the torque of the motors which will
increase current consumption which will
decrease run time

however the run time will have increased somewhat (at previous current draw) over the 4 cell pack before the battery voltage tends to sag.

So they could almost even each other out. (noting however that the power dissapated is not a direct linear relationship to current draw)

Runtime = same, but
Servo Torque increased (and possibly to the point where servos could damage themselves...)

thoughts? (where is that coffee)

Andrew "Ramblings" Maxwell
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