my cursed T-28

[mrjdstewart]

ok, long story try and make short...

original owner bought the yellow T-28 trojan from banggood.com. i guess he had a heck of a time with it and mostly crashed it.

he then gave it to another member of the club which spent a lot of time and money on it, he installed a turnigy plush 40A, a separate 5A BEC, high dollar receiver, ...

he flew it and claimed the curse over, then promptly gave it to me.

i was tickled pink but also a little intimidated. i had never flown an airplane this complex. 9 servos in total and much higher speed and size than i had flown.

cut to chase. 1st maiden ended after 2 secs. spun to the left and thud. second got about 30 ft in the air then cut out, and thud.

damage wasn't bad so i took home and fixed. tried to fly again but on motor test it kept sputtering. it did not maintain full power constantly.

so after lot's of swapping, it turns out the external BEC he had wired in was the problem. when i originally tested the ESC, i had kept the BEC in the circuit. after eliminating all other options i removed the external BEC entirely i had to remove the turnigy 40a ESC due to him removing the signal wire, and replaced it with a thunderbird 54A ESC/3A BEC. and it worked.

cut to today. i have a senior member of the club who also has one of these planes to maiden and trim for me. he get's it up, trims it out no prob, and lands like a stud. he had only been up for maybe 2 mins so i immediately took back off at the stick and had a great flight. brought it in dead stick for a perfect landing

now i'm excited and go and swap batteries. i wait about 10 and hook things up. taxi out and up into the air. this time i'm gonna test the flaps and all the other things i had not played with yet. all worked perfectly and i was able to slow the plane to almost a crawl. flying inverted no issues

timer started beeping at me so i brought it in for final approach, flipped down the gear, and then lost motor.....thud.

thankfully i thinks it's repairable. needs a new prop and some glue but i think it will fly again

i have heard issues with this plane not having a large enough ESC as well as with the 9 servos, the BEC could easily be overtaxed.

i plan to reduce all possible draw. it does not need flaps so i think i will just unplug the servos. no worries about them drawing power.

we will see...



in the meantime i ordered myself one of these...

laters,

jason

 

[mrjdstewart]

well, not even the voodoo doll worked...



it's still cursed. flew it 3 times today and it tried to die twice and crashed once. thankfully it is mostly ok.

i have a 20A UBEC w/ dual outputs that will be here wednesday. i hope this will eliminate any power issues and lets me have my flaps back.

laters,

jason
\

 

[JimCR120]

I appreciate both the plane and the work you've shared, Jason. I'm sure you'll be sharing more successes due to your focus and determination.
Keep us posted.
—Jim

 

[Liam B]

Wow, sounds like quite the challenge. But that’s always good, it gives you something to do.

 

[rockyboy]

I really thought the voodoo doll copilot would have fixed things up!

How hot are the components when she comes down? Especially the ESC? If it's not getting enough venting, you could be running into problems where the ESC overheats and shuts down on you. Or if the battery is not venting and getting very hot, the internal resistance (which is exacerbated by heat) could be reducing the effective 'C' value of outbound current to a trickle.

From the description you also seem to be having the most electrical problems when drawing the most voltage (activating gear and flaps on top of everything else) at a point there isn't as much voltage (after being in the air for a bit). Without the UBEC in the mix, it makes sense that when the draw gets too much everything dies out on you as the ESC takes a nap. With the UBEC you should keep the receiver and servos happy, but could still very likely lose the motor.

Also, I wonder if you have room to haul a dedicated receiver battery so the motor can keep the main battery all to itself?

 

[mrjdstewart]

things aren't hot when i get back on the ground and there is plenty of room to add some stuff. would you power directly to the receiver with a lipo or do the glider trick with AAA's?

thanks,

jason

 

[rockyboy]

I'd hook the components together in this order:

Receiver Battery into UBEC into Receiver

Motor Battery to ESC to Receiver

Not sure about the glider AAA trick, but you have a lot of gear and servos to run so I don't think I'd trust just a couple alkaline AAA to the job.

 

[mrjdstewart]

what kind of battery you using for the UBEC?

thanks,

jason

 

[mrjdstewart]

ok. sorry now i gotcha. and yes the glider trick is a bad idea.

so i have 9 servos running a max 1.5 amp and prefer to run at 6v. i also have a 3536-KV850 motor, 1200g frame, 10x7 prop.

i want to run a 3S-2200mah battery + the 20A UBEC . do you think the extra battery is really needed with the UBEC? if so what would you do and what would you use?

ps- i power my hand built foam DLG off 3- 1.5v AAA lith/ion batteries stuffed in the battery case from a cheap LED flashlight using a salvaged bind plug with lead switched over. it powers the 2- 5g servos and receiver perfectly and weighs less than any lipo i had. what can i say, i'm cheap.



thanks,

jason

 

[rockyboy]

It should work fine with the 3s2200 and the UBEC running the receiver/servos.


But it if doesn't and you want to do separate batteries.... For powering the UBEC separately from the motor I'd suggest a 2s800 or something in that neighborhood. No need for a 3s unless you have them laying around. Somewhere between 600 and 1000 mah should be plenty of power for all the servos and gears I would think. There are people on here who can do the math and tell you the current draw per minute per component, but I'm more of an 'educated guess' flyer on this

 

[mrjdstewart]

ok, did some digging into the airplane and discovered the nose gear box had been crunched in the last crash. this was throwing the front off just enough to make the front gear servo and nose steering servo jam at the end of their throw and was pulling too many amps.

i fixed the box with some gorilla glue and took it out this morning and flew it 2 times without issues. this thing can be very docile but also very fast, especially on landing without the aid of flaps. eeeek!

i received the 20a SBEC w/ dual outputs today but was only able to get 1. i was really hoping for 2 so i could put one in my new P-40. now i have to decide if it goes in the old, crashed one, or the new, never crashed. or, i guess i could hot-swap it. hadn't thought of that.

laters,

jason