Hangar 9 B25

[Peter Ford]

Well now, I just ran the thing on a 6s pack with a 14 X 7 APC.

Wow!  got 700Watts  at 33 amps. Can't tell the RPM yet as the tach doesnt work under artificial lighting, but it was pretty draughty, I can tell you.

[Peter Ford]

Here is the port nacelle, complete with engine (motor?!) and retract. The supplied aluminium spacer mounts required cutting down. I thought they were threaded all the way through, but they were'nt, so I had to take a bit off each end. Ever tried cutting down spacers without a lathe?. Its a bitch I can tell you. Then I had to shorten the HT bolts by cutting them with a Dremel disk cutter.

Four hours later it was done. I stuck the dummy engine in with PU glue. The prop shaft on most electric motors is shorter than glow. I had to take out quite a bit of plastic as the motor frame was hitting the rear of the dummy cylinders. I ended up blacking out the frame with a large indelible felt tip pen to hide all that lovely bronze anodising

Note! No 'bits' sticking out

[Peter Ford]

ENGINE TEST!

Thought I might as well use the nacelle, as the motor was already mounted on it. The graupner discharge protection module can be seen hanging between the charge plugs. Two 5000ma batts are in the wheel well (so what do you put in yours? )

The unit was then run at @ 500watts/ 22A discharge. The ESC used for the test is a Castle Creations Phoenix 60A. It was programmed on my laptop to cut off at 6V. Of course, without the DPM that would have been Lipo Suicide. There is no point in flying a twin where one ESC could concievably cut a motor before the other.

After about 14 minutes the power curve was starting to droop a little. I moved the throttle up one click to keep it at 500watts. The battery voltage indicated by the power meter was now down to 18V!

Thats 3 V per cell! (on load)

Another few seconds and it was going to be all over- one way or the other.! At 17V indicated on the wattmeter, the green LED on the DPM changed to red (although not much use at 4004t!) and about 10 secs later the throttle blipped as a warning . If I had continued It would have blipped again, and closed the power down.

I decided to end the test and examine the batteries. I put them on the chargers and checked all the cells. None was below 3.2V and all are charging up as they should.

So the conclusion is that the graupner Discharge Protection Module does what it says. This is a good set-up for electric twins. This installation with the two Turnigy motors should give a decent 5 - 7 minute flight time on 6s 5000ma Lipo.

A simple Y lead to the two ESC's will connect via the DPM to the RX and ensure that both motors stop together. QED!

Bit too close on my camera! nearing the end of the test .475W at 21A .Voltage is @22V on load

[Tim Mackey]

Ah... but as yet, you have not then tried it with both motors and twin ESCs?

The fact that the pack dipped to below 18V is of no problem as this was whilst the pack was under quite a heavy load, I routinely drop to around 2.75V per cell in these condituions which on your 6s pack is 16.5V 

The magic 3V minimum is really only for unloaded / lightly loaded cells so you have nothing to worry about IMO.

Good stuff...I eagerly await the twin setup static tests....no reason of course that they shouldnt be fine.....just keen to see the actual versus the theory

Thanks for keeping us up to date on things...this should turn out a sweet model

[Peter Ford]

It could as easily be a 'Spruce Goose' model. The fact is its the DPM that is controlling things via the throttle, not the ESC.  I was out of Y leads!

you are quite right on the cell loading. I suppose I'm a bit jumpy, as I had a pack puff once (my fault I guess!)   

[Peter Ford]

Throttle Woes!

I've been fiddling about with the DPM (again) this week and summink aint right

There have been occasions when the Castle creations 60amp controller was'nt recieving a throttle signal via the DPM. The units have to connected up in the correct order to enable throttle control to function. I thought it was just me.

Now I have recieved the Turnigy Plush 80 ESC's from HC (Or HK!) I have been testing them out with the motors. Everything is absolutely fine there.

Trying the DPM again with the New controllers is a 'no show' Just no way, no how would anything work. In desperation I put a servo on the DPM. THAT would'nt work either.

I needed an oscilloscope to see what was going on. A blog on Watt Flyer showed a link to a free software program that is just what I needed. I can feed the servo signal from my Futaba reviever in through the sound card in my PC. As this provides two channels, and using a Y lead, I can display the Reciever signal against the signal AFTER the DPM. They should be about the same.

They're NOT. Not even close.

The red trace is the reciever pulse at mid throttle. Exactly as it should be!

The green trace output from the DPM is just two 'weedy' little 'pips' (hardly discernable) So its a dud.

I shal be sending it back to Gliders along with a print as above. I really would like to get this stuff working properly

I notice that some of the ESC,s from Turnigy are now being fitted with 'Balance Plug' cell monitoring facility.

You see I am not the only one who thinks along these lines.

[Kelly]

Hi Peter,

I am learning a lot from your blog.

It is easy to see why a lot of folks steer clear  of EP,tis a lot of techi info to master for a layman like myself..

I get the impression  that a lot of  motors, esc ,chargers etc are not up to the job, it is a electronic minefield out there. Thank goodness we have people like yourself and Timbo to guide us lesser mortals.

Looking forward to the first flight of your B-25.

Kelvin.

[Myron Beaumont]

Amen

[Former Member]

[This posting has been removed]

[Tim Mackey]

Hmmm, makes me feel somewhat justified in insisting that we see the results from the DPM when connected to twin ESCs!

That was NOT meant to sound smug....but does reinforce the importance of checking everything thoroughly in a practical and actual test...I too thought that the fact all was OK one 1 should mean it would all be OK on twins...but there ya go !

Please keep posting on progress Peter !!

I was aware of some ESCs being fitted with cell monitoring, and indeed of other stand alone units in a simialr vein...however the ability to monitor two seperate batteries AND deliver a completely linear and balanced signal to 2 x ESCs is the holy grail we are after.

[Peter Ford]

Here is the new Multicell monitor from SLK Electronics in the USA

see: www.slkelectronics.com

where you can order the unit and other bits as well. at very sensible prices. Sid has emailed me today to say a MM7 has been posted. ( I think he has been ill, hence the two week silence from me)

There is a PDF manual on the website which explains how two units can be connected for larger, or multiple pack monitoring can be arranged. As I only have 2 X 3 cells (=6) I can connect the balance plugs via a special Y adapter (available from UH) . Therefore I only require the one unit for the B25 at the moment.

With regard to the Graupner DPM, when I get a chance, I will send it back under warranty to Gliders in Newark for a replacement. I am not confident about using it though.

I have one B25 wing virtually finished, and the other one is started. Tail servos are all in and set up. There are two micro servos on the rudders and one 12kg all-metal servo with 3mm linkage to the brass elevator horn.

[Peter Ford]

A RESULT AT LAST!!!

I spoke again to Peter at Gliders Distribution. They handle Graupner products. We talked at length about the discharge module I had no luck with.

Finally the truth is dawning! The Graupner Discharge Protection module (DPM) does not pass reciever signal return to the ESC contol circuit.

So I hot wired the ESC with 4.8 volts(on the throttle cable ) and it now does actually work, but I feel it is not really a viable solution as there may be unforseen problems

BUT

Graupner now have a NEW version of their DPM It is the business! All in a neat case an sprouting no less than TWO jumpers and choice of TWO lipo cutoff levels (2.5 or3 Volts.

The jumpers allow for BEC pass through AND, the all important bit, opto power supply for ESC's that need it.

The unit will monitor up to SEVEN CELLS from TWO batteries - thats 56 VOLTS for goodness sake!

I spotted this new product on Graupner's website and called Gliders to order one. Peter called after a few days to say it was now in stock. The credit card was out faster than John Wayne could draw. A measly £20 quid and a couple more days and it was in my hands

Neat Huh!

I

[Peter Ford]

wired up a complete test rig and it works perfectly. I then went on to do a test WITH BOTH MOTORS

I set up the full, and closed, throttle endpoints. I have two 5000ma 11.2V packs wired in series to the two motors. The ESC's are programmed for Low volt cutoff (2.4Volt) and the Graupner DPM is programmed to cut at 3 volts. This way, it is the DPM that will always cut the throttle pulse to BOTH motors (via the Y lead)

I set the system up to run. The DPM signals, by LED's, the total number of cells in both batteries and now passes the throttle signal to the two Esc's The final plug on the main battery pack was plugged in.The motors went through their Audible tone responses, and gave the final 'Tada' I moved the throttle trim up and both motors fired up together almost to a beat.

As this is a bit of a 'lash-up' I am not able to do extended high power runs yet. So I had to be content with pulling just one of the Lipo balance plugs out of the Graupner DPM (that would be three cells gone seriously bad rather quickly, if you see what I mean)

Both motors immediately shut down together, despite their main battery connectors still being intact.

'RESULT!'

. This is ,of course the whole point of tmy setup. So no 'Death rolls' can occur

There is one common battery supply. Both BEC's are disabled.

below is a small part of the schematic wiring diagram supplied in the Graupner manual for the DPM

see here

you can download the full manual here also

I now need to complete the second wing on the B25 before I can do a full power run on both motors and test the DPM all the way down to a 'real' 'Low Cell' scenario

This time it will work

[Chris Rogers]

are you able to have a seperate battery to power the receiver?

[Peter Ford]

Hi Chris

The Graupner unit allows for BEC option which can be set on or off.

I would always use a separate RX battery. The Graupner unit allows the throttle signal through with no problems even with opto coupled ESC's.

It is a very flexible unit and is a 'no brainer' at the price 

[Tim Mackey]

I look forward to hearing that it will actually work as required, with both ESCs and 2 x batteries, in a real world test as it were ! Meaning, as you put it, in the scenario where the unit monitors both packs, and all individual cells, and pulses /stops BOTH motors exactly in synch several times over in testing. The graupner graphic of course only refers to a single ESC and thats where things get interesting...Y lead 2 x escs together and lets see. I know you have done a simple "pull out one balance plug" test....but, heres hoping

Good luck, and well done , please keep updating us

[Peter Ford]

 Power test BOTH motors 

I have now  bench run my set up till the LIPO's were exhausted.  This was a single pack comprising two X 3S, 5000ma delivering @22V to my two

TURNIGY 50-65A 400kv Outrunners  with two TURNIGY Plush 80A  Speed Controllers

 The setup was calibrated using the ESC programming card, selecting soft start, and the cut off set to 'LOW' (2.5V).  The throttle end points are set using the transmitter. 

I am using the Futaba 2.4GHZ equipment. The throttle trim is electronic, and you have to ensure it is closed down before attempting to start the motors. (otherwise the ESC's won't sing the 'all ready ' tones).

The trim is advanced till the idle is initiated. The close matching of the Turnigy  ESC / motor combination, means  that they start pretty well together.  NICE

The Graupner DPM was set to 'No BEC' and cut off at 3Volts.

I then spent a chilly while with two  13 X 10 props whirling away  for what seemed like ages. I also had a wattmeter in circuit. I couldn't go to quite full power for long (Too blooming freezing in the workshop!!)

The wattmeter showed I had run over 4000ma out the pack, when I detected the first signs of termination. The motors lost a little power, both together, The symptom was a bit like my old lawnmower when its nearly out of petrol!

The LED's on the Graupner DPM  flickered quite a bit as the throttle signal was cut back on both motors. This causes the pack voltage to recover a little. All the time both motors were reacting in an identical manner. Eventually they stuttered and slowed, both in complete unison. 

At this point the LIPO's were well and truly exhausted. I disconnected the pack and checked them with a CELLMETER. You could see which cell had got to 3Volts. (Pack 3, cell 2 if you want to know) 

My packs are well balanced, The other cells were very close to the minimum. I put them on the chargers and they charged back up quite happily in 75mins.

I have a very good feeling about this. In flight, I will try to land with some juice left, but its very comforting to know that I will be safe from a one motor failure situation.

Graupner have a real winner with the latest LIPO protection unit. It also has unrivalled capacity for very large setups, where individfual cells will be more at risk. I shall be fitting one of these to my TopGun Spit asap.

I have a VISIO drawn PDF of the wiring arrangement, together with notes if anyone want to see it 

[martyn sharp]

Well done Peter and yes please post the PDF

Martyn 

[Tim Mackey]

Ditto ( and the visio file please ) although I think I can visualise it all. I will PM you so you have my email addy

Ahhh, you havent entered your details for PMs on your profile page

You cold try a zip version of the file that might attach to a regular posting or convert the fie to a  jpeg?

[Peter Ford]

Hi Guys

lets see how this looks

[Peter Ford]

I just downloaded it for a looksee

Its a bit fuzzy on the text

I thought my profile gave an email address?  Cos I had a coupla PM a while back.  

[Tim Mackey]

Yes it does now

I notice on the diagram they suggest an isolator switch in the pos line of the batteries. I presume that if you wanted to use two sepaerate batteries ( one for each motor )  the  issue is that maybe the internal circuitry of the DPM would effectively connect the two batteries in parallel via the balance leads which are obviously the monitoring method ? 

[Peter Ford]

'They' dont suggest anything.

This is my preferred 'elf an safety requirement .  I do not like fiddling about with a 'live' model, especially as I have to 'flip' the model over onto its wheels after connecting up the packs.

The VOLTAGE LEVELS are what is monitored by the Graupner DPM, through the balance taps (in exactly the same way as a decent balance charger would monitor each cell in a pack)

CURRENT only flows out of the main  Lipo barrery terminals . The Graupner unit is not bothered whether you connect the main battery terminals in series or parallel.

You could also ,for example, have two 3 cell 5000ma packs connecting their balance taps by a special Y lead (they sell em at UH) to one side of GDPM and the same on the other. The battery terminals could then be configured in a series/parallel combination to provide one big 10,000ma 22Volt pack for the Mitchell.

You should only operate with one common battery pack for all motors on a multi-engine model. (Sez Castle Creations)  

Drawing available on request   

[David Ashby - Moderator]

Peter - the B-25 looked superb flying by at the Horizon event this week, (see the front page article)  we were very impressed.

Video too...

[Chris Rogers]

I just went to Graupner site to look at the Discharge Protection module and right under where they say it is in stock the have "novelty"What do they mean by "novelity"?