RX Battery question.

[Bridon]

I'm sure a few on here have this radio that I have just bought, so I wanted some advice if possible. It's the Futaba T6L Sport intended mainly for glider use, slope and maybe electric assist.  I understand that the TX has to be dry cell batteries to get 6v...no problem but the RX ( R3106GF) instructions states a power supply range  of  4.8v - 7.4v.

 

 I intended to use my fairly new existing airborne packs (Vapex) each of which are 4 x 2500 mAH Nimh rechargeables as I have two packs of them, I can re-charge at the field if needed with my Pro Peak Prodigy charger. 

 

However as this is the lower end of the recommended voltage range, I wanted to know, will they be OK to use with this radio or do I need to get a 6v pack?  ?

[Martin Harris - Moderator]

What they are saying is that it's designed to work on packs from 4S NiXX to 2S LiPo.  What is more important is that the capacity of the battery is suitable for the length/rate of discharge. If you do elect to use higher voltage packs check that the servos can handle the voltages safely.

[Bridon]

Thanks, Martin...so it seems I am OK to use my Nimh batteries then? They are as I said 2500mAH so a good capacity.  I meant to ak, if I decided to gu the 6v route...there is a AAA Nimh pack at 950mAH which would be a lighter payload for smaller models. Never envisage using more than 2 servos at any one time...most likely just the 2. sorry to keep asking these questions as I didn't want to make a mistake. ? 

[Martin Harris - Moderator]

I would steer clear of AAA packs unless weight is at a premium.  Voltage drop under load - especially the Vapex or other low self discharge types - may cause problems and the smaller cells don't seem to have a long life.

 

My own preference is to use 2S LiFe packs with a silicon diode as a voltage dropper.

[Don Fry]

How heavy is the glider. It will give the likes of Martin Harris a handle,  a clue.

The load on a servo, on a machine weighing 500 grams, is a lot of orders of magnitude less than the load of a  5000 gram machine. Your packs are small.
They won’t power an Amp heavy servo, trying to power an elevator, trying to pull the nose up, and at that point, you especially don’t want the receiver to stop, because it’s computer chip has stopped working. 
 

If you are route planning, and have no kit bought, I would do a route plan. Get servos that work on a LiFe battery. Any Life battery will deliver as many amps as you like. And will power the receiver. I would not route plan round a pair of AAA packs.

 

If the AAA packs fit the route map, the will serve for the moment. But they do not have much of a future, unless you just want to fly light machines. They belong to an older technology.

 

In fairness, I always reckon, you need to find a tutor. Someone who does this stuff.    Watch them fly. They will then sort you out, because the response has one mind, without a load of different opinions confusing the issue.

 

Local club, glider group.
 

[Frank Skilbeck]

To put it into perspective, my Mini Blade 1.5m span 6 servo glider initially ran on a Nimh AAA pack and was fine for a days sloping, since changed to a 2s LiFe cell but thats because they don't lose charge in storage.

 

My Wildthing sloper originally used a 600mah 4 x AA Nicd battery and that was good for a days flying too, so I doubt you'll ever need to recharge at the field.

 

 

[Bridon]

7 minutes ago, Don Fry said:

How heavy is the glider. It will give the likes of Martin Harris a handle,  a clue.

The load on a servo, on a machine weighing 500 grams, is a lot of orders of magnitude less than the load of a  5000 gram machine. Your packs are small.
They won’t power an Amp heavy servo, trying to power an elevator, trying to pull the nose up, and at that point, you especially don’t want the receiver to stop, because it’s computer chip has stopped working. 
 

If you are route planning, and have no kit bought, I would do a route plan. Get servos that work on a LiFe battery. Any Life battery will deliver as many amps as you like. And will power the receiver. I would not route plan round a pair of AAA packs.

 

If the AAA packs fit the route map, the will serve for the moment. But they do not have much of a future, unless you just want to fly light machines. They belong to an older technology.

 

In fairness, I always reckon, you need to find a tutor. Someone who does this stuff.    Watch them fly. They will then sort you out, because the response has one mind, without a load of different opinions confusing the issue.

 

Local club, glider group.
 

My models are all pretty small Don, from a Dave Hughes 'Soarcerer' to a maximum 2 mtr thermal soarer with maybe electric assist. So 2 servos and occasionally 3 at most...not heavyweights by any degree. I was hoping to be able to still use my flat 4 Nimh packs at 2500 mAH. My main concern was the voltage requirement of this RX as my packs are 4.8v and If I can use those all well and good but if I have to, then I could go up to the 6v range but I need to keep things within budget being an OAP. ?

 

[Bridon]

17 minutes ago, Frank Skilbeck said:

To put it into perspective, my Mini Blade 1.5m span 6 servo glider initially ran on a Nimh AAA pack and was fine for a days sloping, since changed to a 2s LiFe cell but thats because they don't lose charge in storage.

 

My Wildthing sloper originally used a 600mah 4 x AA Nicd battery and that was good for a days flying too, so I doubt you'll ever need to recharge at the field.

 

 

Thanks, Frank, sounds like I can use my Nimh packs still....good news, just need to decide whether 4.8v will suffice for this RX or do I play safe and go to 6v....all these replies from all on here is a great help...I am getting some good info. ?

 

Edited March 25, 2021 by Bridon

[Simon Chaddock]

Bridon

The only issue is voltage drop and using a 2500 NiMh you should be able to hold the nominal 4.8 without any problem. 

 

My own view is to use free moving hinges and mechanically efficient linkage so the majority of the servo torque actually gets to the control surface.

I always favour placing a servo right next to each control surface so it has a short direct link. Efficient linkage means only a smaller servo is required and small servos take limited amps. ?

 

It works for me.

  

 

[Frank Skilbeck]

The Rx will be fine, unless you are using several high power servos when a high current draw could cause a voltage dip that will cause the Rx to cut out. In a glider with only 2 servos the current draw will be very low and the Rx will only cut out if the voltage drops below 3.3-3.5v.

 

Quite a few modellers, myself included, use 4 cell AA Nimh packs in IC powered sports models where the current draw will be higher than in a slow flying glider. If you are going with a 1/4 scale glider then a 4/5 cell Nimh pack using sub C cells would be better, ?

Edited March 25, 2021 by Frank Skilbeck

[Bridon]

5 minutes ago, Simon Chaddock said:

Bridon

The only issue is voltage drop and using a 2500 NiMh you should be able to hold the nominal 4.8 without any problem. 

 

My own view is to use free moving hinges and mechanically efficient linkage so the majority of the servo torque actually gets to the control surface.

I always favour placing a servo right next to each control surface so it has a short direct link. Efficient linkage means only a smaller servo is required and small servos take limited amps. ?

 

It works for me.

  

 

All taken on board....thanks Simon. I will keep the Nimh packs and to be on the safe side I may precipitate any voltage drops by going for the 6 volt pack. The Sektrum gear I have uses the AR200 RX and the voltage range is wider starting at 3.5 volt so when I saw this Futaba RX started at 4.8v it did concern me that It was a bit close. 

[Bridon]

8 minutes ago, Frank Skilbeck said:

The Rx will be fine, unless you are using several high power servos when a high current draw could cause a voltage dip that will cause the Rx to cut out. In a glider with only 2 servos the current draw will be very low and the Rx will only cut out if the voltage drops below 3.3-3.5v.

 

Quite a few modellers, myself included, use 4 cell AA Nimh packs in IC powered sports models where the current draw will be higher than in a slow flying glider. If you are going with a 1/4 scale glider then a 4/5 cell Nimh pack using sub C cells would be better, ?

Thanks Frank...all much clearer to me now...to save any doubts about my 4.8v pack I think I will think about upping to the 6v packs.

 

[Eric Friend 1]

Hi Bridon,

 

As Frank says, with larger models the battery capacity needs to be upped to prevent voltage drop.

 

In my 7 metre 1:3.5 scale glider, I have two 3300maH capacity 4 cell sub-C NiMh packs and I don't suffer any voltage drops even with 10 servos in the wings. I have decent cables for the runs to the servos in the wing and to the rudder and elevator servos at the rear of the fuselage which is 2.4 metres long. I may consider upping to 5 cell packs in the future, but I have no issues with running the glider's system on nominally 4.8 volts, but the voltage at the Futaba receivers is normally around 5.1 volts during flight, as reported by telemetry. However, I am a little wary of upping to 5 cell batteries as a freshly charged battery can be significantly over 6 volts and even though the servos are rated as 6 volt, it makes me wonder how much excess voltage they can take, much like your concerns with the Futaba receiver's input voltage.

 

Enjoy yourself on the slope, it was great to be back on the North Downs today with a very successful maiden flight of one of my 'lockdown' models, a 1.5 metre fully moulded glider which interestingly had a freshly charged 4 cell NiMh AAA pack to power its two servos - it has a very small nose!!!

Edited March 25, 2021 by Eric Friend 1
Added a missing apostrophe!

[Bridon]

24 minutes ago, Eric Friend 1 said:

Hi Bridon,

 

As Frank says, with larger models the battery capacity needs to be upped to prevent voltage drop.

 

In my 7 metre 1:3.5 scale glider, I have two 3300maH capacity 4 cell sub-C NiMh packs and I don't suffer any voltage drops even with 10 servos in the wings. I have decent cables for the runs to the servos in the wing and to the rudder and elevator servos at the rear of the fuselage which is 2.4 metres long. I may consider upping to 5 cell packs in the future, but I have no issues with running the glider's system on nominally 4.8 volts, but the voltage at the Futaba receivers is normally around 5.1 volts during flight, as reported by telemetry. However, I am a little wary of upping to 5 cell batteries as a freshly charged battery can be significantly over 6 volts and even though the servos are rated as 6 volt, it makes me wonder how much excess voltage they can take, much like your concerns with the Futaba receiver's input voltage.

 

Enjoy yourself on the slope, it was great to be back on the North Downs today with a very successful maiden flight of one of my 'lockdown' models, a 1.5 metre fully moulded glider which interestingly had a freshly charged 4 cell NiMh AAA pack to power its two servos - it has a very small nose!!!

Thanks, Eric, all interesting stuff. The last part was of interest too as I have a couple of small 2 servo HLG types and the AAA lightweight packs would be an idea too....out of curiosity, what was the mAH of the 4 cell AAA NiMh pack were you using?

 

[Frank Skilbeck]

Don't get too hung up on the mah capacity, generally the more mah a Nimh battery has the higher the internal resistance, so while they will deliver a low current for longer the voltage drop under load can be higher.

 

We used to be happy going out for a days flying using standard sized servos with a 600 mah 4.8v Nicd.

 

[Bridon]

35 minutes ago, Frank Skilbeck said:

Don't get too hung up on the mah capacity, generally the more mah a Nimh battery has the higher the internal resistance, so while they will deliver a low current for longer the voltage drop under load can be higher.

 

We used to be happy going out for a days flying using standard sized servos with a 600 mah 4.8v Nicd.

 

Thanks for the info Frank....learning more each day! ? 

[Eric Robson]

It may be worth getting a rechargeable battery for the TX. I have a F6K set and Leeds model shop recommended a 4 cell Overlander eneloop  2000 battery and it seems to last for ever between charges. I also have a Spektrum TX which was originally for dry cell but they did not last very long so now that has a 7.2 lipo  that I bought from 4Max.  

[Bridon]

3 hours ago, Eric Robson said:

It may be worth getting a rechargeable battery for the TX. I have a F6K set and Leeds model shop recommended a 4 cell Overlander eneloop  2000 battery and it seems to last for ever between charges. I also have a Spektrum TX which was originally for dry cell but they did not last very long so now that has a 7.2 lipo  that I bought from 4Max.  

Sounds a good scheme Eric...always prefer rechargeable over dry cells. ?

 

[FlyinBrian]

Keep in mind that a fully charged 4 cell Nimh battery will be around 5.5v so there is plenty of headroom before the rx has any low voltage issues. IIRC Futaba rx will work ok down to about 3v. As has been said using normal servos in sports models there will be no issue.

[Bridon]

9 minutes ago, FlyinBrian said:

Keep in mind that a fully charged 4 cell Nimh battery will be around 5.5v so there is plenty of headroom before the rx has any low voltage issues. IIRC Futaba rx will work ok down to about 3v. As has been said using normal servos in sports models there will be no issue.

Much appreciated knowledge there Brian...just the info I was hoping for. i did consider going to a 6v pack but someone pointed out that most servos 'could' object to working at the higher voltage that a fully charged 6v pack would be so after reading your comment...I have decided to keep my 4.8v packs......thank you so much, mind put at ease! ? 

[Rich Griff]

Where can I get a flat pack welded tags with futaba plug 4.8 v NiMH Rx pack, and an 8 cell 9.6 v NiMH pack 4 square X 2 high type for a tx please, all at high capacity.

 

Sir, you chose the rather basic Futaba t6l tx, mode 1 ?

[Bridon]

4 minutes ago, Rich Griff said:

Where can I get a flat pack welded tags with futaba plug 4.8 v NiMH Rx pack, and an 8 cell 9.6 v NiMH pack 4 square X 2 high type for a tx please, all at high capacity.

 

Sir, you chose the rather basic Futaba t6l tx, mode 1 ?

I get mine from Vapex Batteries here in the UK...they are quick on delivery and never had any probs with them. Your other comment...I chose the Basic T6L Sport as I wanted something just basic for glider use only and it comes as Mode 2 which is ideal for me.  There are instructions in the manual for the Mode 1 conversion if required. ?

 

[Rich Griff]

Thanks for the very quick reply.

 

To convert to mode 1, does that involve down loading anything and a computer ?

 

Thanks

[Bridon]

8 minutes ago, Rich Griff said:

Thanks for the very quick reply.

 

To convert to mode 1, does that involve down loading anything and a computer ?

 

Thanks

It is just mechanical Rich...it looks quite easy and probably takes 10 minutes. I did a quick scan of the procedure from the manual. ?

[PatMc]

For batteries you could try Component Shop they have a greater range of batteries. I'd advise going for the Eneloops at least for Rx, they're more expensive but have lower internal resistance, meaning that the voltage doesn't sag as much as other types. You can get higher capacity batteries but they can cause problems when subjected to higher loads. E.g. when a glider is on landing approach using crow brake system.

PS Eneloops also discharge at a very low rate when not in use, Vapex Instants are also low discharge but in my experience don't hold their voltage as well under load.

IMO Vapex Instants are more economical & fine for a Tx but Eneloops are best choice for Rx.

 

Edited March 27, 2021 by PatMc