Topic: Digital Servo's newbee questions

What I would suggest is plugging a good battery checker into your RX on the ground and just giving the sticks a good waggle. On one of my models with 4 non digital 9.5kg servos and 1 11kg digital and a throttle servo I had a 5 cell 1800 mha nimh AA pack that had been peak charged and was no more than 20 cycles old, on waggling the surfaces the checker would drop into the red, but on changing to a 2000 mha NiCad all the stick waggling couldn't get the pack to move off top green light.

This I beleive is why a lot of the high power digitals clearly state on the instructions not to use nimh.

 

This I beleive is why a lot of the high power digitals clearly state on the instructions not to use nimh.

Mistakenly in my view. It may have been the case when NiMh packs were first introduced, but it's no longer necessarily true that NiMh have higher internal impedance than NiCd packs. Sadly there's no real substitute for looking up the actual specification for the cells you plan to use if low resistance is important.  The very high capacity AA NiMh cells for sale on the high street are a case in point. They may offer that capacity at low currents but seem unable to supply the high current peaks to thirsty servos without severe voltage drop.

Both my bigger models with current hungry servos have onboard checkers that are easily viewable and at a wiggle of the sticks I can easily see any power drops. Which ever type of battery you use, if the model needs power hungry servos that are expensive I think it deserves a good onboard checker at a few extra quid for peace of mind.

 

That's a very good point sizzling, however i would just point out to any users of Multiplex 12 xtal or 9 or 12 synth IPD rx who use the internal battery backer that an on-board battery monitor should not be plugged into the rx as it will give a false low reading due to the voltage lost in the battery backer.
I expect the same is true if you use something like the SM services battery backer.
You could use an on-board monitor but would have to solder on an additional lead or add in a Y lead from the switch output and plug the monitor into that, then it will not suffer the battery backer's voltage loss.

As this thread seems to have digressed slightly into the area of which battery type is best for digitals /high drain use, could I be cheeky and ask for any comment to an older thread of mine which seemed to get sort of lost :(
http://www.rcmf.co.uk/4um/index.php/topic,39653.msg424498.html#msg424498

As this thread seems to have digressed slightly into the area of which battery type is best for digitals /high drain use, could I be cheeky and ask for any comment to an older thread of mine which seemed to get sort of lost :(
http://www.rcmf.co.uk/4um/index.php/topic,39653.msg424498.html#msg424498

Errm - you want us to think of a reason NOT to use your LiPos?  Maybe the lack of reply means no-one could think of a reason not to? 

As long as your particular packs and Powerbox BEC can supply your peak servo load then I can't see any reason not to use them. Even if they are modest in discharge rate (I don't know the particular pack you have) I would still expect them to hold up fairly well for servo usage. Provided you check their state of charge between flights to be sure you have enough charge left they should be fine.

OK thanks for the input, one never knows when a thread stays dead - is it in the wrong section etc ?
one is grateful

A few posts ago we were discussing the current drawn and the need for large capacity etc.  Thought you might like to know the results of refitting my Sabre with 2 x 1100mah 5 cell nicads.  They have now been through 2 flying sessions each of 8 flights.  The first session of 8 flights was off the initial forming charge of 14 hrs at 0.1C, and the second session of 8 flights off a peak charge.  The nicads have to power 8 servos inc one JR8411 digi which is always buzzing under load due to an unbalanced all-moving tail, and 2 electronic valves which take quite a bit of current when wheels and doors are in the up position i.e most of the flight.  I didn't recharge during the sessions and at the end the SM services tester showed under load that each battery is still giving 6.2v under load, and at recharge each took 450mAh, total 900mAh.  That was for a total radio switched on time of 1hr 15 minutes.
This doesn't tell us anything about how well those particular batteries will hold up their momentary voltage under the most severe current draw the Sabre can demand, but it does show that at 5 cell currents, 2200mAh is more than enough for a long day's flying of this sort of model and flying style with lots of servos - assuming the batteries are in good condition and of good quality - these are new batteries and I won't let a battery that doesn't have a Sanyo label into my models any more.

Thanks MPX...very useful info. I am thinking my 2 x 900 m/a LiPos into my didgiswitch will be more than sufficent then. I tend to only fly this plane a couple of times each session, with an average flight time of around 15mins. I shall still just check the loaded voltage, and current drawn while all servos are twiddled