Sebart Miss Wind resilient power and RF install

[MattyB]

So a few months ago I picked up an absolute bargain on the BMFA Classifieds - one of my all time dream planes and my first large electric, the Sebart Miss Wind. It even came in it's own pyjamas!

On getting it home a few things were very clear...

• It's big. Like most F3A type aircraft the fuse is long as the wingspan, which of course I hadn't thought about beforehand. This led to an interesting "conversation" as I brought it in from the car...
• This particular model is in immaculate condition - other than a tiny covering tear on one wing it is absolutely perfect. Apparently the previously owner had not flown it, and he'd bought it off an inveterate builder/collector who may not have flown it either. As a result it's all in price of £400 including Hacker motor, Dualsky 80A ESC and digital Savox servos all round was a huge bargain.
• It's really nicely built. Everything is clean, straight and accurate, light but with just enough structure to be reassuring.
• The battery hatch was designed by a man who did not value his fingers. More on that later...

As it sat there on the bed rigged for the first time I decided that a) I really, really did not want to break it for any reason other than my own dumb thumbs, and b) in order to preserve those dumb thumbs from ~1100W some changes were going to be needed to ensure it could be operated with absolute safety. I therefore decided to see if I could equip it with some lightweight, affordable resilient RF and power solutions to improve things; it would also educate me on some of these systems for if and when I move on to even bigger IC models in the future.

This thread will document the install and how successful (I hope!) it is in operation.

Edited By MattyB on 10/06/2016 17:50:09

[MattyB]

First up - power, specifically RX and servo power. As purchased the model was equipped with a Dualsky 80A ESC whose onboard switching UBEC is capable of providing 3A of current. Call me a sceptic, but with 6 high torque, high speed digital servos on board and a large 6S pack as a power source I felt like that was a bit undercooked.

I therefore decided to fit a separate HV UBEC capable of delivering at least twice that current, tapped off the ESC power leads. I have had sterling performance out of the Turnigy UBECS in the past, so I decided to fit one of these which is capable of providing 7.5A peak current. It will get a long burn in too to ensure that if it suffers an early death it will be on the bench not in flight! Here it is before modification...

I didn't like the switch - an unnecessary potential failure point - so quickly removed that. I have also since added an inline XT60 between the battery tap and the UBEC to enable me to use a separate lipo when setting up the radio and completely isolate the power system when doing maintenance and setup work that requires the model to be powered:

Very importantly I have also removed the red wire from the ESC servo connector (out of shot) to prevent it providing power back to the radio gear. I have heat shrunk the connector to enable it to be replaced if I ever decide to go back to using the ESC UBEC (unlikely, but just about possible if this ESC found it's way into another model at some point in the future).

Edited By MattyB on 10/06/2016 17:55:14

[MattyB]

OK, probably the final part for today... Even separate UBECs fail occasionally, so I wanted to mitigate that possibility. I am not a fan of separate RX battery packs in electric models though - I always feel like they are the item you are most likely to forget to charge! Instead I did some digging and came up with a little jewel of a device I'd never heard of previously - the Optipower Ultra Guard 430:

"OPTIFUEL is building a highly respected reputation for developing products and accessories for the model enthusiast which now covers brands such as OPTIPOWER Ultra Guard 430, a new intelligent concept in model flight safety. ULTRA GUARD 430 is a small lightweight easy to install smart landing system designed to restore total backup control allowing you to land your model safely following a main power failure... The device is plugged into a free port on your RX or FBL system and when you power up the device waits, monitors the system set voltage, then arms at that voltage less 0.5V. The device is then armed and monitoring the system voltage and the state of the buffer pack. If the buffer pack needs topping up it will do that and balance it from the main packs or RX pack and stop when it gets to a nominal 8.1V. The device samples the system voltage every 2mS and if the system voltage drops below the armed set voltage then the buffer pack steps in if the system voltage recovers it drops out, this is seamless. The device when working can and does indicate locally that its operational and if it is charging or not but this is not able to be seen at distance. A separate external high intensity LED can be fitted that shows you are on the buffer pack, this is an option and these can be cascaded if required. The device works across 4.6V to 8V. The combo version (the board and buffer pack) are bound together by clear shrink wrap as is the super combo version (inc LED system). The total weight is <39g inc LED <35g ex the LED. All parts can be purchased separately. The device can go to storage charge if its not going to be used for some time."

At £30 and 35g it was a no brainer; I didn't go for the LED though, as I will be able to setup a telemetry alarm on my Taranis if it is ever called into action. Testing this fully will be the next stage of my install.

[Colin Carpenter]

Matt - an absolute beauty ! The Dragon Rapide of model biplanes!!! Hope you are going to fit the spats on the u/c. Jealous !!

Colin

[MattyB]

Posted by Colin Carpenter on 10/06/2016 17:49:41:

Matt - an absolute beauty ! The Dragon Rapide of model biplanes!!! Hope you are going to fit the spats on the u/c. Jealous !!

Colin

Thanks Colin - I am very pleased with it, hence all the effort I am going to on the install. Initial flights are going to be without spats because a) I don't want the drag of them on the grass for the first few takeoffs and landings, and b) the previous owner replaced the (ridiculously tiny) stock wheels with bigger ones. He still gave me the spats, but pointed out they have absolutely no chance of fitting! I will therefore try and source some larger aftermarket ones once he maiden flights are over and the final wheel size is settled.

Edited By MattyB on 10/06/2016 17:55:42

[Simon B]

I've been interested in one of these for a while. Are you removing the wings to get it in the car and, if so, how easy it it?

[MattyB]

Since it will always need to be stored wings off that's how I will put it in the car, though I think it might just fit in my Passat estate fully rigged at a squeeze. Rigging is easy though - bolts on the bottom, then 5 carbon rods simply slide into the LE at the strut points top and bottom with one more securing the top wing on the fuse centreline. With practice it could be rigged in 5-10 mins.

Video showing rigging method

Edited By MattyB on 11/06/2016 00:42:25

[MattyB]

No more progress tonight - decided to finish off my server PSU conversion instead. Big batteries need a big charger setup if you want to charge em in parallel - this one is not even breaking sweat at 24V, 20 A and just under 500W, less than half it's rated capacity. Not bad for £65 and an evenings work!

[onetenor]

For guidance on electronics/ electrics there is a very good article on the Model Boats Forum which is very well explained.Ideal for beginner and expert alike. Sorry to swear

[Steve Balaam]

Matt

Could you detail how you set up your Taranis to warn when the Optiguard is activated

Many thanks

Steve B

[MattyB]

Sure - I will post my eepe once it is done, but basically the BEC outputs 6V and the Ultra Guard will trigger at 0:5V below that, so I will just set a logical switch to be triggered at say 5.6V on the RX battery telemetry parameter, then link that to custom voice alert.

[Peter Jenkins]

Matt, you might like to know that many pilots flying 2 mtr size F3A models use something like an 800 mah 2S Lipo through a Powerbox Digiswitch that can be set for 5.5v to 6 v to power the Rx and servos. You can get 4 flights out of the LiPo quite safely as you tend to use around 80 mah per flight. The switch is software controlled but has proved very reliable. This is a very simple solution and provides a completely separate power source to the radio from the drive battery. The Optipower Ultra Guard is a very worthwhile safety measure which is on my list to get. I do have Rx battery voltage telemetry (JR XG system) and have also used a third party sensor pack that gives a range of parameters that have been useful (drive battery capacity remaining, voltage, current, power, rpm, height) but the only really important one is drive battery capacity remaining once you have completed the setup.

Just a thought.

[MattyB]

Posted by Peter Jenkins on 14/06/2016 00:28:36:

Matt, you might like to know that many pilots flying 2 mtr size F3A models use something like an 800 mah 2S Lipo through a Powerbox Digiswitch that can be set for 5.5v to 6 v to power the Rx and servos. You can get 4 flights out of the LiPo quite safely as you tend to use around 80 mah per flight. The switch is software controlled but has proved very reliable. This is a very simple solution and provides a completely separate power source to the radio from the drive battery. The Optipower Ultra Guard is a very worthwhile safety measure which is on my list to get. I do have Rx battery voltage telemetry (JR XG system) and have also used a third party sensor pack that gives a range of parameters that have been useful (drive battery capacity remaining, voltage, current, power, rpm, height) but the only really important one is drive battery capacity remaining once you have completed the setup.

Interesting. When I was doing my research I did look at the Digiswitch and separate lipo setup, but decided against it because it was another battery to remember to charge, and the max current (3A) was no better than the onboard BEC in my ESC. Are you sure they are not using HV servos and the (unregulated, 20A capable) Smartswitch rather than the Digiswitch? That would seem a better fit for a 2m F3A model, but I have no experience in this area so may well be missing something.

Posted by Peter Jenkins on 14/06/2016 00:28:36:

...The Optipower Ultra Guard is a very worthwhile safety measure which is on my list to get. I do have Rx battery voltage telemetry (JR XG system) and have also used a third party sensor pack that gives a range of parameters that have been useful (drive battery capacity remaining, voltage, current, power, rpm, height) but the only really important one is drive battery capacity remaining once you have completed the setup.

Other than RX batt voltage telemetry which comes as standard with FrSky I am going to start with just one other sensor, cell voltage telemetry. I know it will not give me a true "fuel gauge" as would a current sensor that can integrate for capacity used (that setup is available with FrSky), but the voltage sensor weighs almost nothing and should at least tell me if/when I have a dodgy cell in my pack and prevent me ever flying with a used pack! Personally I have never had any trouble using timers to manage my flight battery status, so I will just stick with what I know initially, set conservative times and see how it goes.

[MattyB]

PS - I tested my Ultra Guard and resilient RF solution last night, works like a charm - more later...

[MattyB]

OK, so on to RF resiliency… I use FrSky gear, and after 5 years of trouble free flying I remain very happy with it. My first dabble was converting a Mpx Evo with one of the old (and now unavailable) DHT-U modules, which I followed up with an A model Taranis when they were first released. Other than having to replace a couple of sub par sliders on the Taranis neither setup has ever missed a beat; the inbuilt signal strength telemetry is a model saver that has helped diagnose a couple of sub par installs without any damage, and I absolutely love the incredible capabilities that OpenTX offers (I have a pretty trick mixing setup in mind for this model which I will talk about later).

However, what Frsky haven’t offered until very recently was dual RX resiliency (they now have the Redundancy Bus, but that seems to be experiencing some issues (see bottom of page). That meant I was going to need an aftermarket option, but when I looked at the Powerbox solutions they were all rather large and expensive.

It was that point I stumbled upon the XPS X10+ channel expander from Jim Drew in the US:

The X10+ enables you to use almost any serial bus enabled RXs from the big manufacturers – it’s compatible with Futaba SBUS/SBUS2 (also used by FrSky and others), Graupner HoTT SUMD, JETI UDI, Spektrum satellite and XPS receivers. This means you can use one or two serial bus RXs with any servos you fancy, and also offers a number of useful features in addition to RX resiliency (onboard failsafe, low voltage tell tale indicator, assignable channels, synchronous servo output etc). Best of all it only weighs 7g and costs $30!

I went ahead and ordered 3, one for me and two for my Dad who will be using his in parallel to achieve 12 redundant channels in a 38cc Seagull Spitfire. We’ve now tested them on the bench and they work brilliantly – simple to configure and use, small and light so easy to install, and great functionality. The only thing they missing is servo overload protection, but for a model of this size that really should not be an issue.

Anyway, I will post a video of the full setup on the bench later if I get the chance – it is currently undergoing 3-4 hours of “soak” testing just to be sure all is well before being installed in the model.

Edited By MattyB on 14/06/2016 18:30:52

[MattyB]

A couple of videos of the X10+ and Ultra Guard on the bench - after 4hrs burn in testing tonight nothing has failed, so it's time to install all this in the model...

Overview of setup:

 

 

Testing the X10+ and Ultra Guard:

 

 

Edited By MattyB on 15/06/2016 00:22:37

[Peter Jenkins]

Matty, I can assure you that the Digiswitch is used by a great many F3A pilots. The servos most used traditionally in F3A are Futaba/JR and almost all JR servos (not the HV ones obviously) all need no more than 6 volts. I have also used the PowerBox Sensor switch with dual 800 mah LiPos. There has never been any reported problem with the servos fitted to 2 mtr F3A machines having any problems with the 3A max quoted on the Digiswitch. The advantage of a regulated voltage supply is that your servo performance remains the same despite any drop in main battery voltage - NB if main battery voltage affects the 5.9 v output then your LiPo has dropped below 3 v/cell!

I have used the Digiswitch on five 2 mtr aircraft. My current one, a biplane, uses a total of 6 mini servos (4 aileron and 2 elevator) and 1 full size rudder and the Digiswitch has not, so far(!), caused a problem.

I observe that most UK competition pilots use Futaba, JR or Jeti (gaining in popularity) brands. This might be down to established folk lore or satisfaction with proven equipment reliability and, in the case of servos, centering capability. Servo speed is generally immaterial but returning accurately to centre from either direction is essential as a wandering centre defeats the ability of the aircraft to fly accurately. I know from personal experience that some well known high end servos are guilty of this - this only came to light when I got an experienced aerobatic pilot to test fly my bird and he said "it's impossible to trim" - replace the servos with either Futaba or JR. I grant you that there are probably others that would do the job but these two are used almost universally in the F3A world.

But it's your aircraft and your call. Just thought I'd let you know what is current practice in F3A. Oh yes, some folk are now migrating to HV servos so that will allow an unregulated LiPo to be used. Whether voltage variation will cause an issue in servo performance that affects the aircraft's flight pattern I do not know.

[MattyB]

Frankly I am amazed a power supply device with a specced 3A max is used in 2m F3A models - with such large surfaces in a snap manoeuvre the instantaneous servo load must be in the 5-10A range at least  (I have measured the currents on tiny 9g digitalis and found they can draw ~1-1.5A peak each without any load applied). I guess we can only conclude that the Digiswitch is very conservatively specced and it's peak load is handling is far greater than the spec sheet states.

As to servos, well those have already been chosen and installed for me as this is a secondhand (though maybe never flown) model. They are Savox all round; I have used the brand a couple of times in gliders and found them ok. Since I have zero interest in competition and do not want to spend £50 or more per servo on a sport model they will be plenty good enough for me (I save the really good stuff for my moulded gliders!).

Edited By MattyB on 15/06/2016 02:02:16

[MattyB]

Posted by Peter Jenkins on 15/06/2016 01:12:29:

Matty, I can assure you that the Digiswitch is used by a great many F3A pilots. The servos most used traditionally in F3A are Futaba/JR and almost all JR servos (not the HV ones obviously) all need no more than 6 volts. I have also used the PowerBox Sensor switch with dual 800 mah LiPos. There has never been any reported problem with the servos fitted to 2 mtr F3A machines having any problems with the 3A max quoted on the Digiswitch.

Did some more research, and it appears we are both right - there are lots of happy F3A users, but there is also definitely some confusion about the current handling capability of the Digiswitch. However after a bit of digging it appears Powerbox are indeed underselling it's ability to handle high peak currents - extract from the online instruction manual...

"The capacity of the PowerBox DigiSwitch (1 - 3 A) is limited by the performance of the regulator when cooled efficiently, rather than by the switching capacity of the DigiSwitch. To obtain good cooling and ensure high performance, one of the heat-sinks of the DigiSwitch is attached to the outside of the unit. This part is normally installed on the model’s fuselage side, where it receives a constant flow of cooling air when the model is flying. The internal silver-coloured heat-sink is soldered to the regulator circuit board due to its greater ability to withstand high temperatures. The maximum current-handling capacity of the electronic components is 12A; this means that the unit can cope with brief peak loads up to this level without problem.

If the DigiSwitch is operated on a 5S NiCd or a 2S LiFePo battery, the maximum regulator capacity is higher because of the lower voltage level of these cells."

All very strange - why keep the 12A peak load ability off the published specs and hide it away on page 8 of the manual? I would definitely have considered the Digiswitch had I known about this, but discounted it because of the 3A limit.

Posted by Peter Jenkins on 15/06/2016 01:12:29:

...Oh yes, some folk are now migrating to HV servos so that will allow an unregulated LiPo to be used. Whether voltage variation will cause an issue in servo performance that affects the aircraft's flight pattern I do not know.

Having tested a number of BECs and seen several "wobble" under loads approaching their rated maximum I would say small voltage dips are maybe more likely with a BEC than an unregulated Lipo, especially if using a linear rather than switching BEC. Mind you, if fitting only a 800mah 2S you will still need a decent C rating - 12A is 15C, so using my entirely the unofficial rule of C ratings (most of em are completely made up, so fit a battery with at least double the C rating you expect to need at max current draw!) you are looking at a 30C pack. Maybe one of the new Turnigy Graphenes would be good - they are not the lightest, but have high cycle life and seem to be handling abuse well in recent tests.

Edited By MattyB on 15/06/2016 10:39:14

[Bob Cotsford]

Matty, I've used the XPS 10+ on a couple of models with and one without the receiver redundancy feature. No problems to date, and I like the ability to add auxiliary power supplies direct to the servo distribution where it will do the most good. It's a great pity that you can't disable the telemetry on X4R receivers as it would be a great setup with just two of these. As it is I use an X4R as primary and an X8R with telemetry disabled as backup.

I use one as an S_Bus distribution board in a wing so that I only have one S-Bus lead and one power lead to connect a wing that needs 6 channels (2 ail, 2 flap, 2 u/c).

 

ps - a word of caution - I bundled some male-male S-Bus leads with the X10+ boards from Jim Drew and on both leads the crimps failed with a gentle tug.  Very gentle!

Edited By Bob Cotsford on 15/06/2016 12:41:15

[Steve Balaam]

Hi All

I think I may give this system a try, has anybody used the Serial Link Programmer on a PC with Windows 10 ?

Steve B

[MattyB]

Posted by Steve Balaam on 15/06/2016 13:05:56:

Hi All

I think I may give this system a try, has anybody used the Serial Link Programmer on a PC with Windows 10 ?

Steve B

My dad did get the serial link programmer when we placed our order to XPS, but he does not have a Win 10 PC so I can't answer your specific question. However, what I can tell you is the X10+ (unlike most ESCs which are a nightmare!) is very easy to setup manually with the button on the board, so I wouldn't bother getting one.

Full instructions can be found here.

[MattyB]

Posted by Bob Cotsford on 15/06/2016 12:36:26:

Matty, I've used the XPS 10+ on a couple of models with and one without the receiver redundancy feature. No problems to date, and I like the ability to add auxiliary power supplies direct to the servo distribution where it will do the most good. It's a great pity that you can't disable the telemetry on X4R receivers as it would be a great setup with just two of these. As it is I use an X4R as primary and an X8R with telemetry disabled as backup.

Yes, that is a right pain - I am stuck with X6Rs for this very reason where X4Rs or even the new XSR would be perfect. The only bright spot is that after I chased them on a couple of forums including their own they have stated they are going to release new firmware "soon" to address this issue - no firm dates though.

Posted by Bob Cotsford on 15/06/2016 12:36:26:

I use one as an S_Bus distribution board in a wing so that I only have one S-Bus lead and one power lead to connect a wing that needs 6 channels (2 ail, 2 flap, 2 u/c).

I hope you used meaty wire - that is potentially a lot of current for one servo lead!

Posted by Bob Cotsford on 15/06/2016 12:36:26:

ps - a word of caution - I bundled some male-male S-Bus leads with the X10+ boards from Jim Drew and on both leads the crimps failed with a gentle tug.  Very gentle!

Thanks, I will add that to my pre install checklist (my male-male extensions were sourced elsewhere, but still worth a quick test).

Edited By MattyB on 15/06/2016 14:00:22

Edited By MattyB on 15/06/2016 14:00:40

[Bob Cotsford]

Matty, the S-Bus lead provides one source for current supply (FrSky rate their SBus decoder and hence the SBus feed at 6A), then I use a second power only lead to the X10+ board's power connection pads. Ok it's an extra connection when fitting the wings but it does give reassurance that the 4 digital servos and 2 electronic retract units are well fed.

So 2 batteries, one direct to the receiver in the fuselage, another direct to the wing mounted gubbins. Probably overkill for a 1.20 size model but it helps me sleep at night

[Frank Skilbeck]

I'd wait a while before using the new XSR rxs, there's a thread on RC Groups where there was a discussion on the exposed aerial length and they got conflicting advice from Frsky, but several people have reported range problems and gone back to X4Rs.

One other thing you may like to consider is the SM Modelbau Unisens sensor, mah, amps, volts, rpm and height all in one very small unit, I have one in my 6s Dynam Smoove (which uses the Beatles 80A SBEC ESC)