Rx volts

[Rich Griff]

I am sure I have read on here that some people are utilising batteries of more than 5 volts to power up the Rx and servos.

 

A voltage regulator has been mentioned.

 

Would that be 7805 or similar.

 

I don't know what the amps load demanded of the servos would be, as 7805 can go up to 2 amps from memory, I would need to check.

 

Or is a more advanced voltage regulator used ?

[EarlyBird]

What is your application? 

Is this regarding the ESC?

[FlyinBrian]

You can use 5 cell (6volt) NiMH batteries without a problem with most RC gear. A lot of modern receivers are happy on two Lipo cells but check the specs of your servos. There are also a lot of "HV" servos now which are happy on two Lipo cells.

 

Regulators when mentioned in connection with RC tend to be dedicated units which will regulate say two Lipo cells to give c6V.

 

There are also stand alone Battery Eliminator Circuit (BEC) units which can be used with up to 6 Lipo cells to supply c6V to the RC

 

 

Edited November 2, 2021 by FlyinBrian

[EarlyBird]

The voltage regulator is in the ESC which supplies the required 5V to drive the Rx and servos.

 

[Denis Watkins]

13 hours ago, Rich Griff said:

I am sure I have read on here that some people are utilising batteries of more than 5 volts to power up the Rx and servos.

 

Just a few points to help you decide on packs Rich.

Volts are not the whole story, and the magic 5v came about in electronics with the introduction of integrated circuits in all our gizmos.

These circuits are commonly known as microchips and are in all our gear.

 

In the past, we happily charged a 600-900mah pack to go flying for the day, and even now, we use about 300mah in a day.

We have a test regime through the day to check for pack use and cell failure.

 

Typically, AA cells nowadays, and most Lithium cells, start at 2000mah, which is far above what we need for a days flying in the Rx / servo department

[EarlyBird]

@Rich Griffis talking about i/c then??

[Frank Skilbeck]

The amps demanded by the servos would depend on how much work they are being asked to do, s small foamy with 3/4 small servos, will not need anything like the current like a larger warbird with 7+ larger servos and retracts. 

 

BTW Data sheet I found for a 7805 says 1.5amps max, so maybe fine to regulate the voltage to a single servo but not between the battery and Rx. A small servo can have a stall current above 1amp, e.g. the quoted stall current on a Hitec HS85MG is 1.2 amps.

[Nigel R]

16 hours ago, Rich Griff said:

7805

 

yeah, er, not that one! 

 

If you're using an ESC, these days, they usually have a built in switch mode BEC. Use that.

 

Bigger model, 40 or 60 size, IC, whatever - going for a separate RX pack? Just buy one that straight out works without the extra faff. 4 AA eneloops. Or a 2 cell LiFe.

 

Simple is often best.

[Rich Griff]

Yeh, think I will use NiMH Rx battery pack with similar for tx...

 

The old Futaba challenger had nicads 4.8 and 9.6 so NiMH would be ok for them also, but need to check.

 

Electric propulsion, I know the ESC supplies the Rx, but I would probably use a dedicated Rx battery pack, all up weight dependant.

 

Reading the 4max sheets that came with the heavy lipo batteries, fire was mentioned umpteen  times, as was stuff about using the battery power.

 

It's a steep learning curve this lipo stuff. Looks like I am gunna have to get a battery checker and watt meter as well. I have a temp measuring gun.

 

Lot of faff with electric propulsion...

 

I'm learning...

 

Less faff with IC I feel...but with looming problems that are only gunna get worse, electric is the way to go, sadly.

Edited November 3, 2021 by Rich Griff

[EarlyBird]

35 minutes ago, Rich Griff said:

Electric propulsion, I know the ESC supplies the Rx, but I would probably use a dedicated Rx battery pack, all up weight dependant.

Absolutely no need for a dedicated Rx battery what advantage do you see in doing so?

[Rich Griff]

Paranoia reduction, still learning about electric propulsion.

 

George did say just use the main lipo and the ESC "bec" facility.

 

The dedicated Rx battery use depends on the proposed models all up weight, which is some way off time wise...

 

The 4max sheets say stuff about duration time and 80percent battery usage etc., Which I have to suss out.

 

A bit more kit to get I think.

 

Bench test and familiarisation of the complete system ( tx and set up, binding, Rx, ESC, motor etc. ) to achieve first.

 

All new to me. 35 meg was so simple in comparison.

 

I need to relearn stuff as well as learn new stuff.

 

Relearn how to crawl, then walk, re reach A standard then practise practise practise with safety first mind set.

 

I fully appreciate electric props can start to turn unexpectedly catching out even experienced modellers. Even a paw 19 can fire up unsuspectingly  if flicked.

 

All help greatly appreciated.

[Romeo Whisky]

There are some booklets you can download, explaining various aspects of electric flight here ...

 

https://dmfc.org.uk/articles

 

[Rich Griff]

Thanks RW, will go and have a look-see, as well as threads on here, and else where.

 

Head like a sponge at the moment.

[Simon Chaddock]

Rich

Remember also that the ESC is 'intelligent' so will cut or reduce power to the main motor if the battery voltage drops below a set level. This will ensure there is enough capacity to keep the supply to the Rx and servos plenty long enough to land.

 

I am not sure its exactly 'lots of stuff' for electric. Some new kit for the correct set up but compared to what you need to operate IC it is pretty simple to actually fly electric.

Switch on the Tx, plug in the battery, do a control check and you are ready to go.

Just saying ?

 

Edited November 3, 2021 by Simon Chaddock

[Martin Harris - Moderator]

2 hours ago, EarlyBird said:

Absolutely no need for a dedicated Rx battery what advantage do you see in doing so?

It’s all so simple. All you need to do is correctly forecast the next unexpected failure and that will decide whether a separate receiver power supply will either save the model or you’re better off using the inbuilt BEC. 

?
 

Of course, in some cases it isn’t an option (e.g. opto ESCs) but we can only use experience and gut feeling to reduce the chances of a failure somewhere destroying a model. Only great fortune saved a model I was test flying for a friend. It went dead stick so I landed it but as soon as I touched down, all contact was lost. The ESC had gone into meltdown and as it landed, both supply leads from the LiPo fell off!  Had it happened 2 seconds earlier, a separate receiver battery would have been rather desirable!

[PatMc]

1 hour ago, Martin Harris - Moderator said:

It’s all so simple. All you need to do is correctly forecast the next unexpected failure and that will decide whether a separate receiver power supply will either save the model or you’re better off using the inbuilt BEC. 

?
 

Of course, in some cases it isn’t an option (e.g. opto ESCs) but we can only use experience and gut feeling to reduce the chances of a failure somewhere destroying a model. Only great fortune saved a model I was test flying for a friend. It went dead stick so I landed it but as soon as I touched down, all contact was lost. The ESC had gone into meltdown and as it landed, both supply leads from the LiPo fell off!  Had it happened 2 seconds earlier, a separate receiver battery would have been rather desirable!

I think that's a very rare occurrence, in fact I'd say even rarer than the switch of a separate battery failing. ? 

Adding the risk of forgetting to charge or overestimating the capacity left in the separate battery, IMO, makes the inbuilt BEC a better bet.  

Edited November 3, 2021 by PatMc

[Martin Harris - Moderator]

Absolutely agree Pat - the point is that there’s nothing that can protect against all eventualities. The more complex the “back up/redundancy” solution adopted, the more chance there is of something failing and we need to consider the consequences of as many failure situations as possible when deciding on our set-ups. 
 

My preference is to keep things as simple as possible but others like “black box” electronic devices. 
 

Whatever your viewpoint and chosen solution, I think we can all agree that attention to detail is the key to successful operation. 

[Allan Bennett]

If you go for a separate NiMh (or whatever) pack to power the receiver and servos, you must make sure that the BEC in the speed controller can't also supply power.  You do this simply by removing the middle, red wire, pin from the plug that connects the speed controller to the receiver.

[Rich Griff]

Thanks for that Allan, probably would not have occurred to me.

 

You live and learn...

Edited November 3, 2021 by Rich Griff

[MattyB]

21 hours ago, Martin Harris - Moderator said:

Absolutely agree Pat - the point is that there’s nothing that can protect against all eventualities. The more complex the “back up/redundancy” solution adopted, the more chance there is of something failing and we need to consider the consequences of as many failure situations as possible when deciding on our set-ups. 

 

Whilst in absolute terms this statement is correct, it ignores the fact that likelihood of "something failing" (i.e. the failure of a single redundant component within the system) is not the same as likelihood of failure of the system as a whole. If the overall setup is correctly designed* then the impact of either the primary or secondary power supply failing in any given flight will be zero - both would have to fail at the same time for an incident to occur. The likelihood of that is far lower, because total likelihood power supply failure in a given flight = % chance of failure of primary system X % chance of failure of the secondary.

 

I was advised similar to your post above as I chose the setup in my Miss Wind, but on flight 3 the telemetry enabled redundancy setup saved the model after the primary BEC failed. This and the undeniable fact that multiple layers of redundant systems are used in commercial aviation for flight critical systems (and indeed anywhere where safety is of paramount importance) shows that well designed redundancy is highly effective.

 

* - Yes, if the system were badly designed you can increase the risk by introducing a "cascade failure" type scenatio, but with the well established power redundancy units from Powerbox, Frsky, XPS, Optipower etc they have throught through those scenarios and the setup is so simple it is impossible to get wrong - just plug two known good power supplies into the redundancy unit and away you go. The only bit that was a little more complex in my setup was setting the telemetry alarms to ensure I knew when the backup had cut in.

 

Edited November 4, 2021 by MattyB

[Nigel R]

3 hours ago, MattyB said:

well designed redundancy

 

the two very important words are 'well designed'