To BEC or Not to BEC?

[Nicholas Booth]

Hi all

 I am just in the final days of completion of my Top Flte DC3 build / conversion to Leccy. The two speed controllers I have both have BEC's which can be disab led by the removal of the red wire/pin from the plug. As both of these motors plug into the same Y lead, can I just remove the red wire from the Y lead effectively leaving the two reds of the ESC's still connected to each other. Or, should I remove the red from each of the ESC's.

I am not sure what the effect would be by leaving the BEC's connect to each other. I am thinking that I should remove them prior to the Y lead butg would welcome help here.

Many thanks

Nick

[Tim Mackey]

I am confused. Both motors plug into the same Y lead ??

In any case, it is generally not advisable to leave both BECs connected to the reciever ( or to each other indeed ) as they can tend to fight with each other.  I need a better description of how your whole powertrain is rigged before I can advise further... are you using the bec at all, or not ? How many servos etc are in use, and is using any type of BEC a good idea on this model etc etc.

[David Ashby - Moderator]

Pictures would be nice Nicholas, that's quite a build project, well done, hope she goes well.

[Nicholas Booth]

Appologies for being vague in my original question. I will try to clarify a little.

As it is  a twin I have two BRC 60 Profesional ESC's with BEC's, I will also be running a seperate battery for the receiver (so do no want BEC) the ESC's both will have their own 4s1p 4000Mah battery but the leads going to the receiver has to be joined together at some point. The reason I ask the question now (the build is just about complete) is that although I had an excellent project plan with everything defined as to how and where I wanted it to go, as with all good plans I completely forgot about routing the leads that go to the receiver

They are no routed through the firewall, into the rectract bays, through the middle section of the wing (past the hatched I made for the flap servos) , around a corner up two flights of stairs and about 3 hours of work to now get to the point where both the leads join the Y Lead. I forgot to disconnect the reds before connecting them to the Y lead and wondered if just taking the single red from the Y lead where it would join the receiver would be enough knowing that the two BEC's will still be effectively joined together but not to the receiver.

I think that makes sense

Nick

[Nicholas Booth]

Thanks for interest David, I have maybe been a bit selfish and kept the build to myself (My partner actually said I was obsessed with the damned thing(how very dare she!!!))

I started her back in August last year having given up waiting for summer I started my winter build a little early. I had followed a similar build on an Amercian thread and pulled all the usefull info down, changing a lot of the sheeted balsa to help lower some of the weight. I started covering her in December last year with Polyester tissue and Poly C ( I love that stuff ) giving 6 coats of Poly C with a good sand down after each, in fact the final coat was so shiney I almost left her like that.

and she looked like this

[Nicholas Booth]

Luckily I have a large shed with lots of expensive (to run) electric heaters (don't tell the wife) so have been happily spraying and spraying all Xmas.

I decided a long time a go that although it was never going to be a true scale model, I still wanted it to be based on something true, and thus spent a long time gaining picture of 'Fifi Kate' N47FK, she was based at North Weald at one point before headinginto Europe and then off to the good old U S of A. She was also a C47 when built before being converted to a DC3 many moons ago.The main thing for me was some photos that I could use. and eventually found this one.

it just hit me straight away as the one I wanted ( thats right Wifey, Fifi Kate is my new woman)

anyway, mine has eneded up looking like this

[Nicholas Booth]

It has working headlights running off a single cell 300mah lipo operated by a 3.7gram servo.

She would be ready to fly but changed my mind about which servo to use for the Rudder, I had originally planned an SD200 and have a hole just witing to fit that size servo in but as the tail wheel is also operated from that servo felt that it might take too much of a bashing so had planned a Hitec 5245MG but there doesn't seem to be any in the western Hemisphere at present, have lowere the spec slightly to a 225mg but againg none to be seen locally but have managed to source one from America of all places and no real price saving just wanted to know that a servo was ordered and paid for and was definately coming.......

I guess a first flight in the next 3-4 weeks depeneding on the arrival of said servo and of course the weather, last weekend would have been great, this weekend looks to be of the same calibre, watch the snow come in when I have her finished........

Nick

[Nicholas Booth]

[David Ashby - Moderator]

Brilliant.......

[Tim Mackey]

Ah right...so you meant originally that the two ESCs were joined with a "Y" lead NOT the two motors

OK so lets see. You are ( wisely IMO ) using a seperate battery ( dont forget to charge it ) for radio. The 2 x BECS will still be cionnected to each other and "live" as it were, but as they will be disconnected from the radio by removing the positive wire as it enters the receiver, any conflict that may have will not affect the radio. Therefore I should not worry too much about this aspect. However, much more worrying is the followig two things and I am hoping you will come back and say these are are covered - if not please address them NOW, before your lovely work is destroyed.

1) Are you using 35Mhz set? If so, what steps have you taken to prevent radio interferencefedding along that tortuos route from ESC to receiver - also any other long servo leads are a serious potential for interference.

2) What precautions are there for the dreaded "one motor's out ! " scenario? This model looks like it will be a REAL PIG if a motor dies. There is a very interesting thread going on over HERE... PLEASE STUDY!!

which I strongly advise you read, and then buy and fit the DPM in the discussion. I personally think that flying to LVC is bad practice anyway, but you just never know when that might be, especially on the all important maiden. Even with identical ESCs the chances of them having slightly different LVC points is VERY HIGH, infact an almost certainty.

Having a seperate battery for each motor system is doubling the potential ( no pun intended ) for trouble.

YOU HAVE BEEN WARNED

PS another warning..Fifi Kate has carelessly left her bra lying on the floor near the shed door, so now the wife will really have to be worried !

[Nicholas Booth]

Cheers Timbo

 I actually brought 2.4ghz just for this model so am hoping interference won't be an issue but have left the ferite rings that were attached to the esc to receiver wires attached just in case.

The idea of a DPM is something new to me, I have flown a lot of Lipo stuff for the last 3 or 4 years now and have always erred on the side of caution, completing a full power monitored run on ground (fluctuating throttle also) whilst monitoring the draw usage and also verifying this when recharging the batteries. This normally gives me a fairly good average of how long in time I get to fly and when I need to land, normally knocking off a minute for good measure.

Although I haven't performed full running tests, I had a good chat with BRC when I brought the 500watt motors and ESC's, they were quoting me that draw would be exp[ected to be around 35-40amps using a two bladed 11x7, I am using three bladed 9.9x6 (variable as they are adjustable on the ground) so I can make the most out of the setup I have. The batteries I have (two sets) are 3700 25c and 4400 25C so the draw should be less than 10c and expected figures of 5-6 minute flights safely are hoped for.

However.........am now fearing my lack of a DPM or two, I am lucky enough to fly at a large field so long run offs are possible so in the real event of a motor cut ( I went electric to remove some of this worry ) I expect to utilise a large black bag that always accompanies me to the flying field

As for the Bra....if only I could get the wife to the shed , as you can see I left a trail of her undergarments to the happiest room in my house and still no contact, I was going to speak to Bill Oddy and his nature watch series to see if I could better lure my intended bird!! (appologies if any females are reading this and find my previous comment offensive, but shouldn't you be out shopping instead of reading man's stuff???? )

Nick

I am now twicthing over my lack of

[martyn sharp]

Nick that is a really nice model by top flite and you have done it justice ,if you wife dose read this she can be prould of what you have done but please lisen to Timbo I have been following the thread he referd to and i have learnt so much from it. You must try and get someone to vidio it flying then send it to dave to add to the RCME video clips.

so well done 

Martyn  

[Tim Mackey]

Hi Nick. The size and performance etc of the LiPos ESCs and so on. is not the issue here. It is purely down to the ESCs built in "protection" circuit known as LVC ( low   voltage cutoff ) With the best components in the world, it would be nigh on impossible to gaurantee that these two circuits ( 1 x each ESC ) will be perfectly matched, and one of them will definately cut just before the other. I too do timed runs and so on, to establish a safe flight time, but as you probably know, the batteries drop off slightly in perfiormance with time, and weather and so on, and as I say, using two seperate packs compounds the potential for disaster! The Graupner DPM is only around 20 quid or so I believe, and you only need 1 - it is setup to take 2 seperate batteries such as your rig, and MUST be worth any hassle involved in fitting it retrospectively.

I certainly would NOT even think about flying such as lovely model as you have created without it.

You are now twitchinhg over your lack of.... ??...... Answers please on a postcard

1) a DPM module?

2) testicles - having allowed females to read this sexist thread? 

3) birds in general?

4) Bill oddies female accomplice?

[Nicholas Booth]

or all of the above

or maybe 5 fingers kept on typing after brain finished thinking.

I think you are right about the DPM , can you offer any suitable locations for online purchase, I guess I have a few weeks to squeeze it in before my last servo arrives and at the very least it may save one of those weekend after a horrible crash where the nearest person to you must have had something to do with it.......

Just on a side note, have also now checked number 2) and can in fact confirm a full count has been made and stock levels are correct.

Maiden flights.......have already organised two close friends to attend on a weekday so no one else will be at the field ( I don't have a problem with other people being there just if something does go wrong on the first flight I think the lack of 'What happened there' from 30 on lookers and the sharpened intake of breath of all other fliers at the field as my unscale take off is made..

One person will be there to film and watch the other to ensure the cycle clips are truly tight enough to hold any thing emitted from the trouser area and help adjust trims if she is a bit tricky to fly.

Nick

[Tim Mackey]

I dont know of suitable suppliers on line I am afraid, but email /PM Peter over in the other thread, - he has just bought one so must know the supplier I guess. Keep us posted...nice thread and build. Know what you mean about the maiden scenario ( the aeroplane that is )

[Myron Beaumont]

Wny is everybodies splelling deterioratying toodey  Evan the exphert (read this Fonetickly)

[martyn sharp]

 Well My excuse is I’m dyslectic so apologises what’s yours  

Martyn

[Myron Beaumont]

Pass

[martyn sharp]

are you sure its not the friday lunch time drinks

Martyn 

[Nicholas Booth]

if it bothers you so much maybe we can set something up with modelflying.co.uk so that all posts are sent to you priot to appearing in the forum so you can correct them for us.....or we could click on the spell checker button.....all posts to Myron for correction it is then!!!

[Myron Beaumont]

Know Proobleem

[Nicholas Booth]

Just thought I would upodate you Timbo but have failed to get hold of a DPM from a few local shops and the web site is a pain in the bottom to look though .

In the mean time, I have been running some tests on the motors and it is looking quite promising. Each motor initially pulled just over 45amps so adjusted the props and brought it down to 41amps and the watt meter registered them at about 550w at full power, the model weighing in at just under 10lbs fully loaded. I have run a series of 3 minute blasts with power fluctuations from half to full power and both bateries have recharged with 10mah of each other ( I expect a small difference as it is nearly impossible to adjust both props exactly the same) and on average the total charge going back in is aroud 1300max (3700Mah batteries) so expect that 6minute + flights are easilky possibly with 8 minutes expected with decent throttle control. I will obviously build up to that though.

Unfortunately though it looks like the weather will be rubbish over the Bank Holiday so just waiting for the good weather  to come now.

[John Wheater]

Nicholas, I am posting this reply so that I receive the updates. You will have yours flying before me but, as you can see from the photos I have a vested interest. The fuselage is now complete and I am ready to fix on the mainplanes. You may notice something odd about the nacelles. I am doing it as one of the Dart Dakotas. The Dak was world's first turboprop airliner.

[Nicholas Booth]

It has flown!! 

It was a bit windy 10-15 mph and wind was across the field instead of along the runway but it kept droping off so decided I should go for it. Whilst it was without any major incident, it was not uneventfull nether the less.

I had set all surfaces to  the neutral position and planned a long run off before actually commiting to air. In reality, this plane wants to get airborn too early for its own good. The tail lifted quite early as I had seen in many first flight takes (normally followed by a take off and tip stall) and mine decided to lift off at just over half throttle at neutral elevator. it also did so with avengance and before I could stop it, I was 2-3 foot off the ground, I throttled up and that was the mistake, after gaining another 10-15 feet it started to tip stall (all this happened in about 2 seconds) I had planned this moment in my head an awful lot but dropped the thottle back to 3/4's , pushed some down elevator, let go of ailerons and corrected with rudder. The result was almost immediate commitment to normal flight.

The rest of the flight followed without any further issues but the below points were noted for amendment / awareness.

1. half of my trim for elevator was used to point the nose downwards for normal flight, I was initially quite concerned by this as the result is the elevators at neutral are 1/4 inch below the rear most plastic trim to which they were alligned. This makes me think that as the elevator was not over sensitive, and it did not appear tail heavy the plastic part may have not been correctly alligned by me on fitting.

2. The ailerons were very effective at their initial application but had a lower ratio of affect further in their travel. I will be applying some differential before the next flight.

3. This plane tries to get airborn very quickly, I think it is very important to ensure the nose is kept down and sufficient speed is gained before getting airborn.

4. The rudder is also quite sensitive and may not need as much movement as they say in the manual. Again differential may be the way forward.

5. flaps as per the manuals settings, first stage @ 2/3rds throttle gives a 5-10 degrees nose up attitude with no other affects noticed. Second stage (landing setting) at 2/3rds throttle gave around 30-35 degrees nose up attitude and some coupling ,my be needed with the elevator. however, landing did not need them, ans from above, may cause further issues on take off if you are not carefull.

6. Landing, throttling back to 1/3rd throttle, was maybe too ambitious and severely lowere the effectivness of the elevator. The end result gave a love;y glide pattern to the runway but would not flare at all. More throttle, and maybe some flaps will help but with only one landing so far then I cannot comment fully on this.

I have used 2x3700 4s1p  batteries and have not yet charged them but had 5 mins 30 seconds complete run time includng taxi time etc. I will charge them this weekend and see what I have used in total.

Other than that, its a great plane and eveything else can be ironed out.

[Tim Mackey]

Many congrats Nicholas, it sounds like you had a fairly exciting maiden flight there, and did well to recover from the hairy take off !

You may decide to not bother with the DPM unit now that you a good idea of typical flight duration - just use the timer conservatively however I understand that Peter has received a new version of the DPM unit and is very pleased with it...check his thread for the latest update.new DPM

Again, many congrats and well done