Electrifying a Wot 4

[Tim Mackey]

Perhaps something could be arranged at GMAC's next fly-in ?

Danny can bring the wot4 - you have already promised a large truckload of buns - I will do the catching.

[Chris Bott - Moderator]

already promised      - there must be a language barrier between the West Midlands and North Wales

[Tim Mackey]

Quote. "Oh and I'm trying to organise a mobile sticky bun van for the next event"

Trying just doesnt cut it Chris - I am reliably informed by my spies in the Midlands that you are Mr fixit - and all your attempts at everything always work 100%

[Former Member]

[This posting has been removed]

[Danny Fenton]

How do you get the sticky buns past Timbo and Chris to PUT IN the wot 4

I thought i was getting the ice cream? thought Mr Ashby was getting the truckload of buns, there must be a tax incentive there somewhere

[Chris Bott - Moderator]

Quote "all your attempts at everything always work 100%" 

The homebuilt GMAC PR machine must be working well!

Mind you I should have twigged that it may need a tweak when it promised calm winds, high temperatures and no darkness at night to stop flying....

[Danny Fenton]

My fault Chris, I suggested the good weather and it was the longest day of the year.....

[Chris Bott - Moderator]

Certainly was

[Tim Mackey]

yep, the nights are drawing in now lads

[Former Member]

[This posting has been removed]

[Chris Bott - Moderator]

Hi Timbo

 Any updates on your tests of the cylindrical A123's yet...?

[Tim Mackey]

Hi Chris - I confess that since making up the 6 cell battery, and doing a few bench tests, that project has been on the back burner - especially as I was in need of a charger capable of handling both the 6 X A123s and the "old" 8s LiFe pack that I have.  I have received the replacement 640Kv motor from BRC - but it came with no mounting hardware or prop driver....so thats still in the box and may be returned - again. Plus, Mrs T decided to re-kit my favourite sloper last weekend, and I have been busy re-building it, and the new slipstream wing, and reviewing the 1010b charger, and gardening, and had guests, and.......well....you get the picture.

Hopefully back to the wotty mid / end next week. My decision about motors etc is now resting on me wanting to use both the 6 X A123s AND the 8s LiFes which will otherwise be redundant, so I think I will be sticking with the 480Kv and compromising on prop size - meaning, I will prop it for reasonable duration / current with the 6 cell, and have a shorter but more spirited flight on the 8S, whilst the 6 pack re-charges

[Chris Bott - Moderator]

I know exactly where you are coming from, I'm in a ridiculously busy period right now with family and work too. Can you believe I've had the Seagul Sea Fury since Fathers Day and its still in the box!

Thank goodness Danny is fettling, (well rebuilding most of) the Cirrus Moth for me at the moment...
We're hoping to have both up together at our next funfly, with a SD Card vid camera in one and a remotely controlled vid camera in the other.   (Both on A123's of course lol)

Mind you mentioning it here might have put the kybosh on that lol

[Tim Mackey]

OK an update.

After various problems with alternative motors and ESCs etc, I ended up with ( for various reasons some of which were not my doing )  2 x 4s BRC specials which were what I term "softpak" LiFe PO4 cells with a capacity of 2000 mahr and same terminal voltage as A123s ( 3.6V ). Initial results of these in either 4s or 8s configuration were a little dissapointing with non A123 like discharge curves etc, compounded by my A8 charger not handling them properly. I now have a sexy new charger and that issue is gone. I then obtained some genuine A123s and made these into a 6s pack for the motor and prop of choice at the time. The motor then proved faulty, and was returned, and replacements no longer available. Experimenting with other motors I had, I settled on a lowish KV of 480 and 1200 watt capable KMS. However, I now had the choice of using 4s 6s or 8s packs! As 3 little bears once said.... 4s was too small, 8s was too big, and 6s was just right! However the nature of the softpak batteries was such that re-making them into a 6s pack was not possible, and besides, this would leave 2 cells redundant. Therefore I ended up changing the prefered prop down a little, living with higher revs than I ideally wanted, and going for 8s configuration. 2 further A123s were obtained, and the A123 battery was rebuilt into 8s, that way at least, I could use both batteries, without the need to keep swapping props around! Furthermore, a new ESC was obtained - one which was happy to run on 7S Lipo ( about the same as 8 Lifes ). This new A123 battery comes out at almost 30V ( 28.8 actually ) and 2Ahr with a discharge capability of some 60A+, but more importantly ( and one of  the main reasons for my using them in the initial project ) they can be charged at up to 10A. Of course, this requires a fairly meaty charger, and an even meatier PSU to power it!!

In round figures 30V x 10A = 300 watts.... and if you want your PSU to be a 12V battery, that means it needs to deliver 25A ( 300 / 12 = 25 ). Hmm, wont be using the main car battery for this one - its  along walk back home

Anyway, back on topic Mr T -  bench testing on a 12 X 6 prop showed some 1000+ watts at WOT, 43A and 1100 RPM - should go well then ! Mrs Timbo will just have to learn to throttle back

I hooked up the Eagle Tree logger for some in flight real world data and headed off down to the strip with both batteries fully charged, and my new 1010B charger, so I could test the re-charge times at the field. Both flights were conducted in VERY windy conditions - the old wotty ( at 6.7lbs now ) leapt off in no time, and climbed OOS in around 30 seconds. After this initial 30 second burst of WOT, I throttled back and let her fall alittle...entering into a more conventional flight pattern. Continued below....

[Tim Mackey]

The blustery and strong wind made evaluation difficult - however it was obvious that this was easily as fast and powerful as the old IC 52 version. Revs and consequent noise were as expected a little higher than I would like but obviously that is because I am using 8s packs, and as stated, the throttle is a proportional control

After some 9 minutes of fighting the wind, and fairly high throttle settings I brought her in for a landing. I removed the softpack, which was "warm" and put it straight on charge ( yes I know its best to let em cool a bit, but this is experimental right ) My field battery couldnt sustain the required 25A required without voltage depressing, so I ended up with around 20A @ 11.2V input, and the charger started cooking the pack at the dialled in 10A rate, but this would drop of course as the pack increased voltage. I left the pack charging, and fitted the other battery ( the genuine A123s ) and went off to the strip again. I was expecting this battery to perform better, as it was "genuine" M1s and also 2300 mahr rather than 2000 as the softpaks were. Surprisingly, although initial performance was equally as good, power dropped right off ( quite abruptly as is the norm with LiFe cells ) much sooner than I expected...in fact it nearly caught me out, as I was a fair way off, in increasingly windy and blustery conditions. I just managed to drop her back onto the edge of the strip by the time I had no juice left at all. My timer showed a disappointing 8 minutes again of actual flight.... but the battery was well flat!

Back at the pits, the charger was beeping to signal charge complete, and the data showed 1866 m/a back in, full voltage reached, and a time of 18 minutes.

Back home , I downloaded the eagle tree data but find it hard to believe the results - something is not right with this device - but thats for another report . The flights showed that obviously the model will fly very well on this setup, and in better weather conditions I reckon we are looking at 10 minute flights as the norm, the softpaks have come good, showing good duration and no noticeable power difference to the supposed better hard cell A123s. recharging in sub 20 minutes is a reality, and I can only think that the A123s need a few more flights under their belt to get on step as it were. Cells were slightly out of balance on both packs when first put on recharge, but all stabilsed fairly quickly. The LVC of the ESC did NOT do its job properly, as it was set to cut off power at 16V ( the 6s Lipo setting for this particular ESC ) which would have equated to 2V per cell for the Lifes, but eagle tree shows the A123s got down to around 1V per cell at one point...... however, as staed, I dont believe the data just yet ! However, it was obvious from the flight that they did drop to virtually nothing, yet the LVC did not kick in.

More experiments needed with the ESC I feel

IF Danny or Chris are reading this...perhaps you would like to see the FDRs and draw some conclusions. ?

[Danny Fenton]

Hi Timbo yes i would be very interested to see your results, can you mail me the FDR files??

In my experience the A123 do not need some running in, but who knows

Cheers

Danny

[Mike Johnson]

Now that's interesting, I have found that after a few cycles the A123's come up to a much better capacity and discharge rate?

Mike

[Tim Mackey]

I am afraid I am not yet in a position to say.....I have only cycled them twice since building the battery. However, as sated, I am pleasantly surprised that the softpaks seem to be performing much better than they did on the first few runs.

[Chris Bott - Moderator]

Hi Timbo

 My A123 packs have always been great straight off the blocks, never had to "run them in" at all.

I'm pleased that the soft ones have got better, that sounds promising.

Send me the FDR's and I'll have a look tomorrow night (I'm somewhere in the wilds of N Wales tonight, thank goodness for satnav, I dont think I'd ever have found this hotel without. Seems worth finding though

It sounds initially like one or two of your cylinder cells weren't full to start with? But I'm sure you would have checked? I've had packs that have needed no balancing ever, and I've had packs that go way out, needing initial balancing for hours on end and then regular balancing to keep them in check.

The last lot I had, were refused by the charger, volts too low, from new. A quick touch accross a good cell, the volts came up and the charger was happy. Those have been great ever since. Hopefullyyours will come good nice and quickly.

I can compare yours with some of my FDR's and see where theres a difference.
Dannys Eagle Tree needed a good calibrate, mine happened to be quite close. We did them against  3 separate multimeters at a steady 10A.

[Tim Mackey]

Hi Chris... have sent them to Danny. I am away now until Sundsy night late anyway, so no rush.

[Chris Bott - Moderator]

Timbo

First look at your FDR's and they are very odd.

First of all they seem to be sampling at about 4 samples a minute.  I dont even have a setting near that speed. In Tools - Choose Recorder Capture Rate. I can choose 1 Sample every 5 mins, 1 every min, 1 every second, 2/s 4/s, 8/s and 10/s. Mines set on 4 per sec.

Next - the battery volts graph starts on 0V and doesnt rise until after you've taken current. This could be a product of the very slow capture rate and having logging triggers set. Mostly I have mine set to start recording as soon as I connect it.

Full raw file shows 2 sessions, but all parameters seem to continue through from one session to the next. This doesn't seem right.

Your full bench run test looks like my graphs. When current is high volts are low etc. as you would expect.

On all your files except the bench test, the voltage graphs just look wrong, the volts dont do the "opposite" of current...

 Downloading and saving is very confusing, I've never really got my head round choosing a model before getting into the software. So always just accept whatever comes up. Maybe it saves different on screen meters with different models??
Downloading gets everything in the recorder.
I then tend to save the whole recorder file.
But it is possible to save individual sessions.
I only record voltage and current.  That gives me V,A,W,mAh against time.

[Sparks]

Timbo,

Don't know if you are still monitoring this thread. If so, could you tell me where you parked your A123's in your Wotty to get balance.

I'm building a Wot 4 and plan to use a block of 6 x A123's with a Turnigy SK4250650kv.
 I have been using this set up in a SLEC (precedent) funfly for a couple of years(see below)  and the A123's are still going strong.

Thanks, Richard

 

 

[Tim Mackey]

Hi Richard....no worries mate, I still "monitor" pretty well everything

The Wotty Leccy is no more, I robbed the cells out for anothe project, but as it was simply an experimental project anyway, I cheated somewhat and made some long aluminium stand offs which put the motor quite far ahead of the original firewall, therefore enabling a decent COG with the cells simply tucked in behind the firewall where the old liquid fuel tank was.

When I used the "softpak" LiFe battery it fitted inbetween the stand -offs - as can be seen in the pictures earlier on on this thread.

Edited By Timbo - Administrator on 07/05/2010 11:39:23