4.8 or 6V?

[andy watson]

This might be a stupid question, but...........

When I bought my Futaba 2.4GHz set it came with a receiver & battery.  The battery is a 4.8V 700mAh pack, and it seems to be working ok.  I was hoping to upgrade this though- especially as my new model will have 5 servos, so I guess it will make the battery work a bit harder.  When talking at the field someone said he had heard that 2.4GHz systems work better with a 6V supply, rather than 4.8V.

Is this correct?

If it is, and my friend didn't know, can you just plug a 6V battery straight into a receiver supplied with a 4.8V battery?  As a final question (well for now anyway) is there a way to check the power remaining in a battery?  I guess there must be, but I don't know what it is.  It doesn't need to be on board, but it would need to be cheap!!

Cheers

Andy

[andy watson]

Just found (and I did look before ) a similar question saying that as far as duration is concerned 4.8V is better- 6V will drain the batteries faster but supply more umph (technical term) to the servos.  So I will stick with the 4.8V but am still interested in finding out how to check if they are running down or not.

 Cheers

Andy

[Former Member]

[This posting has been removed]

[Frank Skilbeck]

Re the 6v for 2.4 , he was probably referring to low voltage cut off with Spektrum radios, see here for a full explanation abnd tests http://www.modelflying.co.uk/forum/forummessages/mps/dt/4/UTN/4341/V/1/SP/

You are correct about running your set up on 6v, but the servos will move much quicker but if you are doing the same work (i.e. using the same power) then with a 6v battery the current will be less. If you look at the specs for servo's they will give two torque readings, the higher is on a 6v power supply.

Your Rx battery will be OK on 5 lightly loaded servo's but I'd look at getting something bigger if you like to fly all day. 

The battery monitors that Eric mentions are very good and you can see  effect of moving the servo's on the RX battery voltage.

[Tim Mackey]

"You are correct about running your set up on 6v, but the servos will move much quicker but if you are doing the same work (i.e. using the same power) then with a 6v battery the current will be less"

Not sure I understand this explanation Frank? 

For the same "load" IE  identical servos and receiver, using a 5 cell pack will draw more current than a 4 cell, and the servos will have higher speed and torque, but the battery ( assuming the same capacities ) will drain quicker.

Andy - the most important thing is to ensure the battery ( be it 4 or 5 cell ) is capable of delivering the current required, and does not depress voltage too much. Pretty much every receiver is fine with a 6V supply, bit the odd few servos will only take 4.8v. 

[andy watson]

See...... I was clear in my understanding until you tried to make it clearer!!

As I understand it replacing a (for example) 4.8V 2400mAh battery with a 6V 2400mAh battery will result in a shorter flight capacity, but increased servo speed.  To put this into the context of my trainer and DVII, since I will not be doing any particularly stressfull flying with either, the benefits of the 4.8V pack probably outweigh the benefits of the 6V pack.  Should I adopt an aerobatic model with increased stresses and reliance of accuracy then the 6V pack might be preferable.

Eric, what you are suggesting sounds perfect- could I impose on you to provide a link so I can see what you mean exactly?

Cheers

Andy

[Former Member]

[This posting has been removed]

[Tim Mackey]

andy watson wrote (see)

As I understand it replacing a (for example) 4.8V 2400mAh battery with a 6V 2400mAh battery will result in a shorter flight capacity, but increased servo speed.  To put this into the context of my trainer and DVII, since I will not be doing any particularly stressfull flying with either, the benefits of the 4.8V pack probably outweigh the benefits of the 6V pack.  Should I adopt an aerobatic model with increased stresses and reliance of accuracy then the 6V pack might be preferable.

Andy

Yes.

[Frank Skilbeck]

Timbo - forum moderator wrote (see)

"You are correct about running your set up on 6v, but the servos will move much quicker but if you are doing the same work (i.e. using the same power) then with a 6v battery the current will be less"

Not sure I understand this explanation Frank? 

If the surface takes the same amount of force to move then the 6v one will move it quicker, the total amount of work will be the same and as work is basically power x time and power is volts x amps, you may use more or less the same amps but for a shorter period, so total current drain could be less.

On a plane I had with 7 servo's a 4 cell battery would flicker well into the red on my volt spy, but on a 6 volt battery it wouldn't budge from the green.

I also didn't notice that I was putting significantly more back into my 6v packs than my 4.8v packs. 

[andy watson]

Thanks Eric

[Bob Howard]

Firstly, before tyring to use 6v, check the servo specification. Some are specified to work only on 4.8v (6v may burn them out), some on 6v only and some on either. The Ripmax catalogue gives full voltage specs for current (no pun intended) Futaba servos, for others you may need to consult the manufactures website. 

Secondly, I always have one little niggle with 6v Rx set ups. We all know that 35 mHz PCM equipment  has a failsafe which, among other things, cuts the throttle if there is a radio link problem. Other channels can be set to hold, or to go to a default setting.

It is less well known that some, if not all, PCM equipment has a second failsafe. This monitors the Rx battery, and activates the failsave on throttle only if the battery voatage drops. On Futaba, the failsafe can be reset in the air by cycling the throttle stick to enable a powered landing to be made, however the failsafe will trip again every few seconds until the voltage drops too low to enable the radio to function.

The problem is, I cannot see how this works for a 6v system. A nearly flat 6v battery would not trigger a second failsafe, as the voltage will still be above the threshold for a 4.8v system.

I assume that a similar situation exists on 2.4gHz gear. Perhaps Ripmax, Spektrum or other manufacturers could advise.

For PPM users, with a smart failsafe fitted, the same issue will apply unless a failsafe designed for 6v is available. 

[Tim Mackey]

Frank Skilbeck wrote (see)

Timbo - forum moderator wrote (see)

"You are correct about running your set up on 6v, but the servos will move much quicker but if you are doing the same work (i.e. using the same power) then with a 6v battery the current will be less"

Not sure I understand this explanation Frank?

If the surface takes the same amount of force to move then the 6v one will move it quicker, the total amount of work will be the same and as work is basically power x time and power is volts x amps, you may use more or less the same amps but for a shorter period, so total current drain could be less.

On a plane I had with 7 servo's a 4 cell battery would flicker well into the red on my volt spy, but on a 6 volt battery it wouldn't budge from the green.

I also didn't notice that I was putting significantly more back into my 6v packs than my 4.8v packs.

I was intrigued by this scenario Frank, so did a little testing this morning ( as I am prone to do far too much ) and the results are tagged onto the latest post over in my other thread - Interestingly, although the 6V rig did consume slightly more juice overall, the static and hold consumptions were indeed about the same, in fact one parameter showed the current to be lower than on 4.8V.

Anyway...you may want to look so heres the link. ( last post ) Cheers.