Electric propulsion system for PPG and Ultralights

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Hello community,

I would like to show you my project that i have been working for the past 6 years, it is an electric propulsion system for powered para-gliders and ultralight aircraft.

Motor is Brushless outrunner, it has a power of 20kw continuous, mass 7.7Kg. Controller is AVR8 based, it can handle 300A continuously, works on 20S (84V) li-po, it includes battery management system, it has a display with menu where all parameters of the system can be set easily. Battery is divided in 2 modules, each 10s 60Ah, total in series 20S 84V.

I would also like to thank every body on this forum who helped me when i got stuck.

If there is someone interested about more parameters, i can post a more detailed description of every thing.

I posted some pictures with the system and a link with the ground test of the system. 

https://www.youtube.com/watch?v=...

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WOW!  Nice project!

 

Any chance you can post pictures of the circuit boards?

 

What is the runtime of this setup?

 

Mihai_F wrote:
If there is someone interested about more parameters, i can post a more detailed description of every thing.

 

Of course theres interest!  Post as much information as you can.

 

I would suggest posting a schematic of your motor controller if you feel comfortable as the great minds here can point out possible issues that could show up in flight.

 

 

Great job!

 

Jim

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Are you actually going to fly it?? surprise

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Wow, very cool!

 

Would like to hear about your estimated flight time, and the weight of the battery pack.

 

Did you design both the motor and the motor controller?

 

I, not being a Mech Engr, would love to hear about how you designed the motor, and did stress testing on the design, as that is not an area in which I have much familarity.

 

I logged a flight or two in a PPC many years ago.

It was a tricycle framed unit, not a backpack unit.

 

Gotta love ultra-light aircract!

 

JC

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The runtime, or flight time i calculated to be about 40 min with 5 min reserve, these specs are if my calculation meets reality about the aircraft being able to maintain level flight with about 5,5Kw.

The pcb-s were completely home made and they are double sided, the power board is with busbars soldered on top and bottom of the pcb, minimizing inductance was a must here, 300A thru 5 cm of bus bar creates a lot of unwanted trouble, the first iteration had about 50nH on power traces (+ and -) and i had to redesign it to reduce inductance to about 16nH to keep the inductive spikes to a decent level.(the red polyester caps on power board were replaced with ceramics , this is a older photo) Command board also had 3 iterations mostly to be able to keep separate analog supply traces from digital ones. On command: board top right power supply, buck converter and linear reg-s; top left motor control, MGD-s, uC ; middle to bottom BMS  ,controller management and analog side.

 

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I actually did fly it, a lot of times, but without motor.

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As mentioned above, the estimated flight time is 40 min with 5 min reserve, if aircraft flies level on 5.5Kw. Battery weight is 28Kg, and has 4,44Kwh 60Ah, it is divided in 2 modules, each 14kg. About motor design and stress testing, i calculated the tension load on the shaft (shaft material is Cr42Mo4 steel) and on the bolts (10.9 grade) of the prop and motor, there are the most stressed parts (and bearings), the rest was done by carefully looking at how others build motors like that, and maintaining some proportions. The winding scheme was calculated (ABC pattern). There was no need to reinvent the wheel, every one that builds them, thy stick to same pattern, so i did so. All in all it came out pretty good. Aircraft on the other hand, i did a lot of load calculation and stress simulations, the aircraft is based on Goat 4  of Mike Sandlin design http://m-sandlin.info/goat/goat.htm ,and has some modifications to the wing size in order to acomadate propulsion system weight and maintain same wing loading and more important the same slow flying speed of about 43km/h. Controller i design it completely, i took some inspiration from here and there, but it did require lots of math to be done like thermal design, high current path design ect.        

Last Edited: Wed. Oct 21, 2020 - 07:38 AM
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That motor is CNC porn! A thing of beauty.

 

Unfortunately I'm not confident the electronics are up to the task. You need to consider the effects of mechanical shock and vibration. 

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WOW!

Mihai_F wrote:
The pcb-s were completely home made and they are double sided, ...
Well done especially for the PCB area.

Mihai_F wrote:
the power board is with busbars soldered on top and bottom of the pcb,
There are off-the-shelf bus bars that would ease assembly.

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Multilayer boards weren't around back then. The bus bars distributed the massive columbic flow and eliminated board flex.

...

 

"Dare to be naïve." - Buckminster Fuller

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I actually did fly it, a lot of times, but without motor.

OK then, as long as it doesn't need the motor to stay in the air.  cheeky

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Yes indeed, i have put some thought in to that, the command board is mounted semi rigid inside the unit, all the connections to it are with wires, so that there is less transmitted vibration to the board and no mechanical stress on pcb connections, the power board is mounted rigid to the unit heat sink, all the connections that go out have a snug fit thru the plates of the sides including bulk caps. There are a few things to improve, one of them is to find a way to attach those 35sq mm cables to the board by NOT soldering them, initially i wanted to use crimped lugs but they are bulky and i could not get that compact design with them. The hole unit attaches to airframe by rubber vibration isolators, that is a must to ensure that no heavy vibrations is passed to the unit. Now about mechanical shock, this system is powered by a Li-Po battery with pouch cell type, these cell types are easily deformed if subjected to mechanical stress. The cells are mounted in a aluminum box with 1,5mm thick walls, witch offers good mechanical rigidity and protection, so in case of light shock is ok, but something like crashing a PPG from 3-4 meters, will almost certainly damage the battery and possibly cause it to catch fire. So the electronics surviving mechanical shock is limited by the battery ability to survive mechanical shock. The controller unit is very rigid and tough and if dropped from 3-4 meters it has a great chance of still working, or at least greater than the battery. Pcb-s manufactured by a professional company will certainly improve mechanical safety aspect, so there is room to improve.   

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yes, the big fan is to keep the pilot cool. cheeky

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Thank you for suggestion. The bus bar that i used was kind-a of the shelf, it comes in 1meter length 11mm wide 1,5mm thick. A neat solution would be CNC or laser cut plates to match the pcb trace area, and then it can be used thinner pate, something like 1mm, witch is easier to solder and give better performance plus will look top notch.

Last Edited: Wed. Oct 21, 2020 - 09:31 PM
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I'd be looking at glueing down the inductor, crystals and the other parts that have some physical mass that are loosely attached. Vibration is death by a 1000 cuts.

 

Look at minimising the wiring - especially between the mosfets and the pcb. Maybe look at specific mosfet modules as they are designed to make things easier. 

 

Crimping the high current wiring would be preferable. Soldering thick wires creates a problem of the solder wicking up the cable and forming a stress raiser.

 

I'd also look at your pcb layout around the switching regulator - doing a star ground is not a good idea here.  What you have created is multiple inductors that will oscillate at 100MHz or so. I once had a simple mosfet circuit to switch a load. The inductance in the ground to source track caused a 70MHz oscillation.

Last Edited: Wed. Oct 21, 2020 - 09:35 PM
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Yep, thank you for advice.

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Mihai_F wrote:
this system is powered by a Li-Po battery with pouch cell type, these cell types are easily deformed if subjected to mechanical stress.
Does lithium iron phosphate have enough gravimetric energy density for this use case?

 

"Dare to be naïve." - Buckminster Fuller

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Nope, it has about half the energy density per mass. Li-po battery's are seafe, if you treat them with care. In 15 years of working with them, and i had a few smashed to the ground hard, they bent but i only had one catching fire.

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Now that it flew, and it flew verry well, it was a short 5 min flight because i was running out of daylight (sunset). It is time for upgrades, first i want to have the boards made by a pcb company, the command module i can make it with JLC pcb, but the power board i must have 30oz 1mm thick traces, i found a company that does it, but i have the feeling that might be verry expensive for a few (2 or 3) boards, so if you have any ideeas how to bond 1mm thick copper sheet to FR4 so then i can CNC mill the traces, or oather method to obtain a copper clad with 1mm thick copper on both sides. I want to increase the voltage from 20s 84v to 22s 92.4v or 24s 100.8v to be able to get the 20Kw max continous power of the motor, so i must change mosfets with ones that have higher Vdss voltage, right now i have IRFP4468, witch are 100v rated and have Rdson 2.6mohm, and i really like that low Rdson, now the next mosfet in that family is IRFP4568 witch is 150v rated but Rdson is 5,9mohm and with that, the thermal performance of the hole thing is not good enough anymore, so anoathet newer mosfet is IRF150p220 witch is also 150v but has 2.7Rdson plus the Ciss and Crss are wayyy better then the previous 2, the down side is a bit pricier but the perfornance improvement outweighs price, so i'ts ok, please have a look at that mosfet and give me some thoughts.
 

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At your power levels, you don't solder through hole mosfets. Use power devices with bolts and use copper bus bars. Or you could spot weld the mosfets to bus bars. Look at how Tesla and Toyota do their power drives - there's plenty of pictures on the interwebs.

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Cool!

Mihai_F wrote:
so if you have any ideeas how to bond 1mm thick copper sheet to FR4 so then i can CNC mill the traces, ...
Solder paste the copper sheet to PCB, reflow oven, mill, assemble, coat (tolerance to salt water fog)

Mihai_F wrote:
... or oather method ...
Some avionics and vehtronics PCBA have a milled aluminum plate bonded to the PCBA plus a conformal coat.

 


Corrosion Control For Any Surface | Anti-Corrosion Coating (NeverWet)

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"Dare to be naïve." - Buckminster Fuller

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I'm a bit worried that it will warp the bord becouse copper and fibreglas(fr4) do not expand and contract at same rate, it warped a bit the board that i already made and the bus bars were soldered with hot air one at a time.

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The upgrade process started, i got the PCB-s from manufacturer (from my town), they good quality, but no copper plated via holes, i still have to do them manually, but still far better the boards that i made. I changed the bulk caps from Nichicon to Chemicon KZN series, way better than previous, the fets are now IRF150P220 witch have much better parameters allowing faster switching and higher Vds voltage for a bit more safety margin. The power board will have copper plates cut with water jet, and then reflow-ed to board.

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I cut with water jet the copper busbars, they are awesome, i have to de-burr therm a bit, and they fit perfect.

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Wow!

Thank you for posting the update!

 

I love the flying photo!

 

OK, I like the electronics photos, too!

 

Be safe!

 

JC

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Alas, few of us have water jet cutters. Still, that is a very innovative way to improve the current carrying capacity of a circuit board. 

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Are the caps at case Gnd?---the caps tops stick out & can short to the case or elsewhere.

Also the caps insulator thin plastic will wear though & short to the case---avoid that  (why have the caps stick out?)

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Yes, the caps and case+heatsink are grounded, they fit very snug in those holes. They are out for cooling purpose, but also the case can be smaller and lighter, plus it look cool :D . 

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thank you!, i must admit i have seen it done on the internet first, but not at that scale and surface area.

Last Edited: Wed. Dec 2, 2020 - 06:47 PM
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it can handle 300A continuously, works on 20S (84V) l

That is nice, but seems a severe drawback...you might double the voltage (perhaps a safety issue?)  ...losses are prop at the square of the current, so if you double the voltage, these copper losses are 1/4th, triple volt, will be 1/9th...less heat, less copper, less strain on the PCB , an improvement in all areas, also motor heating losses from high current is reduced.  Of course lower loss is important for a battery system, especially high power.  I'd much rather deal with 150 amps or 100 amps than 300. Just some things to consider.

 

Your project overall is EXCELLENT...and certainly a lot of hard work & creativity went into it, the boards looks very very nice (though they may groan a bit)...Very clever use of the copper add-on.....one thing, I hope you are not  trying to put very high ripple current in to those electrolytics that stick out (Youi don't mention specifics of their operation).

 

Where is your circuit breaker?...(assume for flight a fuse might not be best) surprise  When dealing with such energy, this cannot be overlooked.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Wed. Dec 2, 2020 - 09:57 PM
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Yes indeed, that would be more efficient in terms of power loss, but not completely, if all components of the propulsion system are considered. So during the design of the system i took some things to consideration: I took a good look at how others do this king systems (no need to reinvent the wheel), they are separated in 3 categories, low voltage up to 63V, medium voltage 63 to 120V  and high voltage 120V up to 400V. They all go to about 300 to 500A. Up to 120V they use mosfets, but from 120 to 400V they go with igbt's and most important isolation of the traction voltage. One of the design consideration was to keep it simple (less things to go wrong), i know is not a good comparison, but i have a 15 year old and simple with no settings RC BLDC-ESC rated at 3S 30A (made by GWS China), that i abused, bashed and trashed the hek out of it and still works just fine, and that design is very basic and simple (AVR8 based also). These guys https://www.mgm-compro.com/brush...  in my opinion are the best in these field, they're stuff is the tip of the sword, but it ain't simple nor cheap (about 2000Euro for a 31Kw 63V 500A unit) but they have all the whistles and bells you can think of. So for the power that i needed max 100V and 300A were chosen. Going over 100v wood complicate the buck converter design, isolation of the traction voltage, bulk capacitor placement (because more pieces at lower capacity with higher voltage rating to get same total capacity), and a lot more. The battery side now it is easier to manage lower cell counts in series and more cells in parallel, plus more cells in parallel (12 in my case) has less chances to have a defective cell in the pack, compared to a pack that has fewer cells in parallel, and it evens out defectiveness over the hole pack making the hole pack age evenly, instead of only one cell (how annoying is when one cell puffes up in a 3 or 4s 1p pack). 

 

Caps have 17mohm ESR, 3,86A ripple rating,  23A total (6 pieces) , i did a LTSpice simulation of the ripple and it should be fine i inspired with the simulation from here: https://www.youtube.com/watch?v=... the guy talks about more in there but it contains the ripple simulation.

Last Edited: Wed. Dec 2, 2020 - 09:35 PM
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Going over 100v wood complicate the buck converter design, isolation of the traction voltage, bulk capacitor placement (because more pieces at lower capacity with higher voltage rating to get same total capacity), and a lot more. 

In electronics it is usually easier to go to higher voltage than higher current (look at your power lines), For example,  a connector can be easily 20 v or 200v , but not so easy 10 amp vs 100 amp connector.  I'd agree the performance of the higher voltage fets (such as Rds, gate drive etc), is worse  at 150V vs 60V , but remember you are fighting a squaring effect...so the battle is easily lost.

The same thing can work FOR you, since using 2 fets cuts each current in half, so each fet has approx 1/4th the heat loss & the total loss is then approx 1/2 of using a single fet.

 

By the same token we did a number of 30 kW (over 128 channels) special control systems (peak) running at 36V , so we had some big thick main "welding" cables running around & some rather heavy batteries.

 

Caps have 17mohm ESR, 3,86A ripple rating,  23A total (6 pieces) , i did a LTSpice simulation of the ripple and it should be fine i inspired with the simulation from here: https://www.youtube.com/watch?v=... the guy talks about more in there but it contains the ripple simulation.

Excellent!!--hope it is indeed fine, electrolytics can be a bit fussy. 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Wed. Dec 2, 2020 - 09:46 PM
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Yeah, fussy electrolytics, i had a few in the past   :)))    The ground test that i made in the 2 minute youtube video, is part of two 30 minute tests where the motor was run at 75% to 100% power continously, and i did not notice the caps getting hot, the ambient was 20 celsius, the controller went up to 46 celsius if i remember correctly, nothing blew up so i think is ok.

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For circuit breaker, i did not use any blush , i assumed that the battery is capable of delivering 1200A continously and 1800A in bursts and that can vaporize anything from the controller in its path, and i went in to the full power tests all or nothing. On earlier test i did blew a few mosfets NOT all 18 at once (lucky me cheeky ) , and i don't know how the hek do they fit so much smoke inside them cheeky. For flight i have a handle that disconects the positive power cable in case something goes PUF, but the thing is contained in the case so only smoke can come out, it is kinda anticlimactic cheeky.

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I hope you don't get "shot" by an electrolytic...We used to shoot little one's at each other in high school---kaboom!

 

Nice strong 550W part, errr, until you mount it on a PCB with no other major heatsink, then its's good for a whopping 4W !!   PCB mount is pretty awful for heat.crying

 

How do you get the heat from your transistors to the heatsink ?  And why are they not screwed to it in the first place? 

 

You should consider cable hold down clamps...solder connections should not be used as a load-bearing member---the heavy cable could exert quite a stress, just from twisting or their weight pulling on the connection.  Small size seems nice, but maybe secondary.  

 

For your parallelled mosfets...you should strongly consider separating the gates with small resistors  (or ferrite beads)...Do not just tie the gates together... or you have found an easy way to form a high power, undesired, oscillator!

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Thu. Dec 3, 2020 - 12:29 AM
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The mosfets are bolted directly to the heatsink (see photo, this is v1.0 but v1.3 is the same except copper plates busbars), TO247 package would be pointless without direct contact with heatsink , and they do have separate gate resistors (the white isolators in the photo), and i dit a looooot of fiddling to get rid of the ringing, there is a topic around here about that subject; https://www.avrfreaks.net/forum/... , hopefuly the new fets with better Ciss/Crss ratio wont give so much head bashing.  Cable clamps, yes still on to do list, now they are installed on the motor/controller mount/pole so the hole thing gets secured in place, a small amount flex allowed to reduce vibartion transfer, but that i might change it, i am not compleately satisfied with that arrangement, i still have to figure a way of securing those cables better, i might have a ideea to clamp them inside the case.

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You do thorough excellent work..a lot of creativity.    There is always more needed to do. Be careful with all that energy

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Thank you, will do!

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By the way, I see you use RTV on your assembly...be aware (if not already aware) most RTV has acetic acid (smell like vinegar), that will very slowly eat away any copper!!!  Bad for electronics.

 

There are special RTV that contains no acid---be sure to use it!

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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No RTV, only colophonium rosin thined with isopropylic alcohol.

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Instead of making a power PCB I would have looked into power modules either 3 phase or only single bridges like this :

It is a 295A 1200V IGBT bridge. 

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Yes, but that is overkill and is masive, it wood take to much space, for a 50kw or 100kw that wood be the solution but not at 20kw, it is way to big

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I don't suggest that module, just the way for the setup, so you don't have "real" power on the PCB,

 

Like "real" power diodes is not for solder but a nut. :) 

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I understand you, i did consider these options, but thy wew ruled out because of weight and dimensions beeing to big

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By the way, I see you use RTV on your assembly...be aware (if not already aware) most RTV has acetic acid (smell like vinegar), that will very slowly eat away any copper!!!  Bad for electronics.

There are special RTV that contains no acid---be sure to use i

 

....No RTV, only colophonium rosin thined with isopropylic alcohol.

 

eh?? No RTV???

What's this

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Hot glue, glue gun, but on v1.3 only on command module, on power module there is no need any more.

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Hot glue, glue gun, but on v1.3 only on command module, on power module there is no need any more.

Ok, NOW it sounds better & your comment makes sense.   Note that hot glue isn't super "sticky"...it tends to pop off/fall off, whereas some RTV will stretch like a strong rubber band before popping off.  Of course the surface/material type can have a large effect on the peel strength..

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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well, on command module i use it to get some rigidity to all those wires, board to wire and wire to connector, i'v noticed that it does not bond very well unless i encapsulate what i'm gluing, i'l try some "special" RTV. The  colophonium rosin thined with isopropylic alcohol, was brushed on the boards to protect copper from corrosion.

Last Edited: Mon. Dec 7, 2020 - 09:13 PM
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well, i got 2 notifications that someone wrote something on this thread, but for some reason it does not show hear, event that it say there is a #48 but is not here.... 

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it is time for a late update, V1.3 is done (it was done 2 months ago) ...

 

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Most likely some spam message was posted and then deleted by a moderator and it gave you the chance to update your thread. wink

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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That is a nice project. Did you think about starting a youtube vlog about all this stuff you make. Not everybody has such a mind to create this kind of thing. And flying it looks so much fun.

I am not this kind of person. I am always afraid not to break anything. When we had some electrical problems at our house I didn't want to resolve them by myself even if this looked so easy, so we called a professional from https://bates-electric.com/ and to be honest I was amazed how good he knew his job.

Last Edited: Tue. Apr 13, 2021 - 06:01 AM