Using SBC on Hitec receivers

[TheFlyingCrust]

The guitar build is on hold due to a waterlogged shed (damp machine tools - dodgy) so I got on with the Dawn Flyer for the mass build. I'll be posting soon about that on another thread as it's getting near completion. But it's got me thinking about the power train.

There's been much discussion re. not using too much of the capacity so I wondered if there was a way of "keeping and eye" on usage during flight. Reading the manual on Hitec Specra receivers they have a Supplementary Power Connection (SPC) which can be fed with up to 35v! (When in use the servo's are powered separately).

So. 3S LiPO, Main leads powering ESC with its BEC powering the servo's. LiPO balance lead (just the 2 outer connectors used) with a lead with balance plug one end and servo plug other end. Remove jumper from receiver SBC and plug in lead. The onboard telemetry will now display the LiPO battery volts (with a bit of luck).

Rather than jump in with both feet and fry a perfectly good receiver I checked with HitecRCD and they confirmed I'm ok.

And it works! The Receiver Volts is displayed on-screen and I can set an alarm for low volts.

Has anyone else tried this and been able to monitor LiPO voltage? Do other radio systems have a similar system?

Your thoughts and observations?

Ian

[twinstar]

I was having an issue with a new E-glider: 6 digital mini servo's and reciever all powered via the BEC, I was getting brownouts from the reciever:

Using the SPC solved the issue, Im happy as I didnt have to buy anthing else to solve the problem.

[Tim Hooper]

Ian,

Now that's an idea I've not heard before - excellent!

I'm wondering if it could be used on larger models (say 10S or above), allied with a 'battery backer' device.

tim

[TheFlyingCrust]

Tim. It all depends on the max input voltage of the receiver. Hitec Optima are 35v max. I suppose you could connect across, say, 5 cells and extrapolate. Using the balance socket allows that. Just make sure the 0v terminal is used. It wouldn't do to short the LiPO out with the neg on the BEC and the Receiver not being at the same voltage!

Do you use another make of radio? What's their spec?

Ian

Edited By TheFlyingCrust on 04/03/2014 23:02:41

Edited By TheFlyingCrust on 04/03/2014 23:20:01

[TheFlyingCrust]

Correction on OP. Its Optima receiver, not Spectra (thats the tx module!). All other info given is correct.

Ian

[Chris Bott - Moderator]

Spektrum telemetry certainly allows the separate monitoring of Rx and LiPo battery voltages, with settable alarms for both.

For a while I've also been using home made mAh sensors that continually report how many mAh I've used out of the battery. This is not a sensor that Spektrum offers, but other radio manufacturers do.

I'm switching over to FrSky radio and their Taranis Tx for this reason. FrSky offer a 40A sensor and a 100A one.
this sensor it's self also reports LiPo voltage.

On top of this, FrSky also offer a 6S individual cell monitor, which can be doubled up to 12S.
This unit even has a display, so you can see all cell voltages directly on it.
At the Tx end, then, you can have alarms for low lipo volts, low individual cells, alarms based on mAh used, and a voice telling you any or all of these at the flick of a switch.

[TheFlyingCrust]

Chris, I'd guessed this could be done with a separate telemetry unit. But with the Hitec, if all you want is LiPO volts monitoring there's nothing required, except the lead described.

I'm tempted to go the full telemetry route as well, but in this case its simple.

Ian

[A.T.]

With Hitec systems, the telemetry is between the Spectra module, be it removable or internal, and Optima transceivers only, not the Minima or Maxima series which are straight receivers.

Suggest best referral is to:

Optima Transceiver (RX) - EP Models Use SPC Port for RX Power Supply (BEC only is unreliable) & correct Battery Telemetry.
Optima Transceiver (RX) - Polarity of Ports & Servo Leads - with pictures.
Optima Transceiver (RX) - PowerExpander Connections NB: also refer "After Market Accessories" above.
Optima Transceiver (RX) - SPC connection & Lead FAQ for EP & GP models - with schematics and Photos.
...Low & High Voltage setup, Current Draw/Amps - Warning: Never use Balance Taps - Video
Optima Transceiver (RX) - SPC Port Wiring Clinic - Video by 2 Brothers Hobby.

and the sub section "Telemetry" under the Hitec Forum Sticky:

Aurora A9,A9X, Spectra Pro & Optima - FAQ & Undocumented Features - Mixes, Setups, Tip

Alan Tong
Alan's Hobby, Model & RC FAQ Web Links

[Chris Bott - Moderator]

Posted by TheFlyingCrust on 05/03/2014 00:31:31:

Chris, I'd guessed this could be done with a separate telemetry unit. But with the Hitec, if all you want is LiPO volts monitoring there's nothing required, except the lead described.

I'm tempted to go the full telemetry route as well, but in this case its simple.

Ian

The Spektrum system does indeed need the extra telemetry unit in the model, I agree Ian.

Telemetry receivers from the FrSky system however, mostly report two voltages and received signal strength without any add-ons at all. Note the max volts is quite low, so a voltage divider is needed for LiPo volts. This divider is available as a £2.48 cable, and the division ratio can be selected on the Tx so that volts are reported correctly.

It seems most manufacturers have a way to do it, some more complicated than others.

[Tim Hooper]

Posted by TheFlyingCrust on 05/03/2014 00:31:31:

...... with the Hitec, if all you want is LiPO volts monitoring there's nothing required, except the lead described.

I'm tempted to go the full telemetry route as well, but in this case its simple.

Ian

I'm interested in the simplicity myself!

I use Spektrum but I really can't be bothered with all the sensors and modules. However my better half uses Hitec, and so gets to rx voltage automatically transferred to her Aurora9.

Might be the way to go for my larger models.

tim

[Chris Bott - Moderator]

I'd be very interested indeed in hearing form anyone who successfully does this. It's a simple system, whichever manufacturers gear is used. (Well Hitec or FrSky at least it seems)

My experience with using a simple voltage alarm though, is that it goes off every time I open the throttle, especially in the second half of a flight.
If I set the alarm so this doesn't happen, then it's a toss up whether I get the voltage alarm first, or I notice the power dropping off first.
In either case I've had to push past my usual timer setting to get to that situation anyway.

[Ian Jones]

On Hitec you can change the voltage that triggers the alarm, is it not the same with whatever you are using Chris?

Edited By Ian Jones on 06/03/2014 00:54:21

[Chris Bott - Moderator]

Yes of course the alarm voltage can be set Ian. I'm interested in other folks experiences, especially if they have made a success of this.

The problem that I find, is best illustrated with a typical graph.

Here, the flight started with a bit of hooliganism, then went into some smooth half throttle aeros, then a climb and glide.

It shows the difficulty of picking a particular voltage to set the alarm level at.

[Dickw]

Using a voltage alarm, I would set it at about 3.3v per cell. That would give 9.9v for your 3s Lipo, and looking at your graph a setting of 10v would be fine. That also fits in nicely with the voltages I see on my 6s aerobat. 3.3v perc cell is a reasonable minimum level for a Lipo "on load".

The trouble with voltage alarms is that the volatge varies with load, so what is a reasonable alarm level at full load might be a bit too low if stooging around at very low throttle. For that reason I prefer to use a capacity alarm (usually in addition to the voltage alarm).

Dick

[Chris Bott - Moderator]

Thanks Dick, that is exactly why I prefer a capacity alarm too.

The flight in that graph above was indeed terminated because of a capacity alarm. It never went near 10V.

When I have relied on a voltage alarm, I either get alarms every time I use full throttle, or if I set the alarm lower, I seem to "feel" the drop off in power before the alarm goes off.

[Mike Smith]

Hi Chris, I recently started using this feature on my Aurora 9 as it seemed better than relying on flight time (which doesn't taken into account throttle usage). I have my alarm set at 10v for a 3s LiPo and, as you say, it tends to alarm prematurely if you whack the throttle open during the latter part of the flight. I'd rather this than not get any warning... I guess it just needs a bit of judgement/experience to know how much more is left once the alarm starts to alert you.

Just wondering if there's a simple circuit that could be employed to smooth the voltage being seen by the Rx???

[Chris Bott - Moderator]

I guess that's the best we can hope for Mike. I guess it gives you some idea.

The thing is, we're told that we shouldn't fully empty our batteries if we want them to last, so, at the point where we want a warning, the volts may not have dropped off that much. It all seems on a hit and miss - par with just using a timer.

I think I'll stick with FrSky and mAh sensors for bigger models. As a £12 add on to a £23 8ch Rx it's not complex or expensive, and knowing exactly how many mAh I've used at all times as well as having a voltage alarm just in case, is very reassuring.

[TheFlyingCrust]

 

Just to round off this from me, I accept the dip in volts when power is demanded but as mike says, it's better than not having the indication. I'll relay my experiences with this when I get to fly the Dawn Flyer (which is just about finished - Yay!)

Here's my final electric setup that'll be used on DF. It certainly works on the bench.

Note lead from Balance Plug providing Receiver power.

The lead that needs to be made up for receiver power. The alternative is to piggyback the main connector on the ESC. That would allow only one connector to be plugged/unplugged.

 

Volts displayed on-screen. I've yet to set up the alarm. I have another model, a Bell Hop, which has the same channel settings so just using that for now.

Thanks for the feedback.

BTW the lead from LiPO to receiver cost 60p for a wired connector and about 5p for servo plug and connector.

Ian

 

Edited By TheFlyingCrust on 23/03/2014 18:13:53