I have a typical 1500 mah 4.8v pack.
My project is an Ultra Stick 40 with 7 standard servos. I got to thinking about the drain on the battery. I am running a Spektrum receiver.
Would I be wise to upgrade to a 6v pack with high mah capacity or would that be overkill?

I would upgrade.

A fully stalled standard servo can draw up to 2 amps of power from the batteries, far greater than battery capacity and causing a receiver reboot.

Of course this NORMALLY does not happen in a properly configured plane... but it does indicate just how much each servo can draw when there is a load placed on the servo, due to air, binding, etc.

With 4-5 servos I might stick with that pack, knowing that I should check it after 4 flights and likely recharge after 5-6 flights.

With seven servos I'll go with a higher capacity pack and opt for the higher voltage for the Spektrum/DSM2 receiver and to get faster servo response.

Depends on your flying style, linkage smoothness/effort required to move the control sufaces, charging habits, etc. A jambed and taxed servo uses up power fast. Two even faster. Also, the faster you fly the more load it takes to move a surface. Different folks will get different results with the same battery. A pilot who flies lazy 1g maneuvers at 1/2 throttle, sets up his model carefully with easy hinges and low-strain connectors and charges fully and carefully will get 3X more time than someone who has his servos buzzing at all times and slaps the sticks around every second of flight time. It's like gas mileage in cars - some get lots while others get little in the same vehicle.

If you stay at 1500mAh a 6.0v system will give you more strength to the servos but 20% less flying time between charges. So if you fly fast and need lots of oomph - go 6v.

That's me!

OK, thanks. I think I will go ahead and upgrade to the 6 volt and perhaps 1500-2000 mah should do me.
I just got to thinking about having so many servos and thought I might be better off.
I know that I will draw a little less current with the higher voltage to and that higher voltage keeps me away from that danger zone voltage wise with the receiver too.
Time to hit that local hobby store~~~again!

I have for a few years now changed everything to 6 volt whether 72 or 2.4, I no longer ever buy 4.8 packs. Sure have taken heat here on these forum for that.

I just received my 29th 2.4 Rx (mostly Hitec 7 ch and a few XPS) last week and if not quite done converting my entire fleet and will only use a pack of 6 volts on any of my 2.4 fleet (a wide range of types and venues). I only make use of a pack that is about three times the capacity of what was normally considered normal or what was included with full radio sets.

In other words in an applications that we use to use a , 5 to 700mah I would consider 1400 or so an absolute minimum with 6 volt and prefer something around the 2000 range.

I do still have and will to continue to use a couple of nostalgia airplanes on the 27Htz band.

For your stick it would be a no brainer for me to use a 6. volt pack of a minimum around 18oo but preferably just over 2000mah's. Batteries have gotten so much more affordable and small there is no reason not to.

One other consideration Don.t even consider using the old 50 to 70Ma wall worts. If you spend the money on higher capacity batterys consider the money spent on capable chargers well spent and good insurance.

John

Ken that is great and you will not regrete it. Do get up near that 2000mah figure.

Actually you got that backwards a bit. Using the higher voltage packs increses current draw and uses up your packs faster if they are of the same capacity. Where the safety net
comes from is using the packs of around three times the capacity which now with Nimh packs come out about the same weight as our old low capacity Nicd's. There also may be some safety net if you lose one cell however that kind of failure is not all that can happen and I am not a battery head or an electronics type so am not going to try to explain in detail.

John

Thanks~When I first got back into this I bought a Slow Stick to play (and got bored pretty quick)with and I just happen to have the Turnigy Accel 8 charger so I am pretty well set up for charging most anything that comes along. I may even fly electric from time to time but I have Saito 82 that is going on the Ultra Stick.

When I buy new packs these days it's always 6v too but I get the biggest mah I can locate. Doesn't cost any more.

Consider this, I fly my .60 size P-40 for three flights on average when I go the field. I run a 1100 mil amp LiFe 6.6 volt pack, 5 standard servos and a 2.4 ghz Airtronics radio. I figure thats about 20 min of flight time. It take about 100 mil amps to recharge my battery pack. If you recharge at half capicity, That means I could fly almost two hours before reaching half capacity. Just food for thought.

You are going to love that combo.

On another note, I generally fly 10 min flights and when I charge up at the end of the day I find that my planes with analog servos have used about 250 mah per flight and those with digital servos have used about 300 mah. All my planes have 5 cell, 6 volt packs, most 2000 mah capacity. I don't know what that's worth, but I thought I'd throw it out there.

If you have a few 4 cell 4.8V 1500mAhr packs and you're concerned about capacity and redundancy then connect two of those packs in parallel to your receiver via a "Y" lead.
Thats doubles your capacity and provides real redundancy; A 5 cell 6V pack does NOToffer redundancy or a safety net of any kind.

But if you feel you want/need the higher voltage, then opt for the 6.6VLiFePO4 packs that are now available. A 1800mAhr or 2100mAhr pack will provide around 2hrs of flying with that Ultra Stik if you are a relaxed pilot and let the plane do the flying and you the guiding. But you must remember to recharge when voltage drops to 6.4V. They remain at 6.7 to 6.6V for around 90% of their capacity. Once you get to 6.5V you have less than 15min flying time left.

Thanks tim,i'm putting two 1800 packs on a y lead

If you do that then dont use a Y instead use two separate switch harness one for each battery and plug the extra harness into an unused Rx port. This of course is if you powering servos through the RX power buss conventionaly.

John

Thats another option, more complex but ultimately true redundancy. Just remember to flip both sswitches to "on" to fly and to "off" after flight.
What I am concerned with is that the Rx Bus may see the two batteries in series meaning theres 9.6V on it but still only 1800mA.Hr. Hence I suggested the Y lead optin because then the Rx sees only voltage from the parallel packs. if the Rx sees the packs in series you could have a big problem on your hands...
Check with the manufacturer how they recommend this option ( 2 packs into separate Rx channels) should work.

Krash Kart and old fart, if you do opt for the Y harness route, then remember to still charge the packs separately and then reconnect to the Y when in use.

If you plug two separate batteries into two separate switch harness and to two separate Rx Ports then this is in parallel the voltage will be what every you are using 4.8/6.0 whatever and the effective capacity will be doubled if both switchs are turned on.

Also two separted charging leads/ports are avaliable for both batteries to be charged separately without removeal.

I have done exactly this numerous times for various cross country flights. Now would I do this for the average sport airplane, no of course not and folks really tend to overkill this redundancy thing.

I do use six volt packs on my entire fleet and packs that are typically three times what we once used in the past That is a good thing and will not argue that fact.

John

capacity is always a good thing thats does provide safety, sort of, but there is no safety in a 5 cell pack If you lose a cell you may be down to 4.8V for a short time but the pack loses capacity fast thanks to the resistance of the dead cell. How would youknow you'velost a cell in flight? By the time you know you have a problem its too late and the blac bag shoudl be prepared.

If you feel there is safety in 5 cell packs then that is your choice. But please do not preach it as a safety fact, its simply not true. We all need a crutch to believe in from time to time.

True safety comes from redundancy, that is a fact.

Speed- Speed - Speed - Speed IS the result of operation on volt 6 volts Period. That is a good thing and I beleve it has benefits for even learning pilots who would not neccessarily realiize the differance. That is my opinion and you will not dictate my expressing that opinion.

I am weary of you stalking me in almost every post and making irrational attempts to discredit me in any way you can with infantile arguments about word semantics.

I do follow the rules of the forum and will not respond to your harrasment any further or engage and you will not dictate what opinions I may or may not post.

Have a pleasent day

John

To which some would say, that it adds undue complexity and failure points, especially for a newbie to deal with.

Stalking you?! LOL, I think you rate yourself too highly and therefore take yourself way too seriously.

speed from 6V? well maybe? But I see you now change tack...
I don't dispute that 6v provides more TORQUE and perhaps some can feel that through the sticks, but its subjective so each to his own here. What I take exception to is continuous spreading of mythology that 5cells is a safety net, It's not. All I ask is that you refrain from spreading that.
Your feelings are your own, you own them mate, so don't try to make them my problem.

Opjose,

yeah some would say that it adds undue complexity would'nt they. After all, thats a typical arguement for "not invented here" syndrome. FACT is we participate ina highly technical hobby with equipment that is often more complex than most of us grasp. We are surrounded by complexity in Radio Control. Just open a TX. How many solder joints can fail there? A battery pack? How we survive is through managing risk and taking APPROPRIATEaction.

If an extra battery adds complexity then perhaps we should pack up and return to free flight rubber band powered stick planes.
We typically throw complexity at a system to gain redundancy, everything comes at a cost. An F-16 has4 separate flight controls systems because one has to work to keep the pilot alive. Lots of complexity there, but the redundancy is important.
So if a flyer is concerned about lock out / brown out issues and feels that battery voltage and capacity is key then it stands to reason that this power source should be redundant.
Some may say thay 6V (5cells) can still meet the voltage requirements if a cell dies but that is a very temporary supply as the rest of the cells deplete quicky due to the resistance of the dead cell. The problem becomes known when the pilot has already lost control, so wheres the safety??
So if you want true safety, then two packs in parallel is the answer. If you not concerned then one pack is sufficient to ensure long enough flying time. No ones holding a gun to anyones head.

ROTFL....

My thoughts exactly, but all to often what we are actually dealing with gets overlooked in the over-simplifications that are made.

exactly! over simplifications are rife and its one of the biggest problems in this hobby.

I almost never run two switches and packs these days but I do fail to see how it complicates things. What kind of numnum can't figure out how to install two switches and two batteries and run them into unused RX ports. 6 volt packs have been recommended by JR for all of there 2.4 systems to help with there little brown out problem for almost two years now. Yet the new radios still come with a 4.8?? With a two pack system there is no rule stating you need to turn on both switches, you can run one at a time if you desire, defeats the purpose but I have been known to forget to turn them both on a time or two.

What we need is for one of the manufacturers to develop a switch that has rudundent contacts inside one switch. Its usually not the switch that goes bad, but the contact. A switch with two parrallel contacts inside will be more reliable and serve the same purpose as using two seperate switches.