Why can't things just work like they're supposed to?

[Yorkman]

Some of you may remember an earlier thread of mine re the Mossie and speed controllers and how I splammed it when one of the super-cheapo ESCs didn't start its motor as I opened the throttle after a low pass....and how I over came this problem by trimming 'forward' on the throttle channel before launch so both motors only slowed to 'tickover' rather than stopping.

Well, like this I had half a dozen or so completely successful and fun flights, tho the ESCs continued to be temperamental about starting...until one day they both refused to start at all.

So, back to GC and two Hobbywings 12ampers to solve the problem once and for all.....I thought.

After initial installation, everything seemed fine-could set full throttle and closed throttle as per the instructions, nice linear increase...but then started getting strange signals on switch-on, one ESC thinking throttle wasn't fully shut, wouldn't set full throttle like it had previously....though otherwise seemed to work fine-so, caution to the wind, let's try a test flight, thumb on throttle, about 1/3 power, launch, immediately obvious two motors aren't delivering the same thrust, despite chopping throttle imediately, Mossie arrives home in three bits....again....so, break out the superglue...again...into the wing we go....again to remove the offending article....why can't I just buy something, fit it and it works???

As for my car-that's a whole new story...

[Former Member]

[This posting has been removed]

[Andy Gates]

Pardon the dumb question coming....?

 

Have you isolated one of the BEC's on one of the speed controllers?

 

This could be part of your problem.

[Yorkman]

Posted by Andy Gates on 06/12/2009 16:08:57:

Pardon the dumb question coming....?

 

Have you isolated one of the BEC's on one of the speed controllers?

 

This could be part of your problem.

 

 Funnily enough-if you scroll down the list of recent topics, there is a thread about multiple ESCs where someone who obviously knows a helluva lot more about electrics than I do explains how isolating the BECs is not necessary!

After returning with the bits I separated the two ESCs completely (they were wired to the battery together, obviously) and the one ESC wouldn't 'program' at all,though it still worked as you'd expect, i.e start, throttle up, throttle down, stop..

Anyway, it's in an envelope ready to go back to GC tomorrow, hopefully the replacement will not give me any more grief....hmm, no 'fingers crossed' smilie....

[Tim Mackey]

Well not sure he completely endorsed the idea, and I for one, will continue to play safe and disconnect one in multiple situations, or  better still use a separate UBEC

[Andy Gates]

I am not going to argue with the other poster but my experience of twinning up ESC's without isolating the BEC's has not been very good.

 

My ESC's certainly run cooler with the BEC's isolated, even if one is powering the reciever it still is cooler than with both BEC's connected.

 

And for your information I have a pair of packs parallelled together which run both ESC's to the whole system is balanced.

 

That is just my experience.

No theories, just what I have found in practice.

 

I thought it might be worth the ask.

[Yorkman]

I'm starting to feel like giving up....

got a replacement ESC on christmas eve (well done Rob), so just took a few minutes to start installing. Decided to connect temporarily with chocolate blocks to ensure correct functioning and rotation, and to keep completely separate from the port motor set up. So, motor connected, battery connections made, port motor rx connection unplugged, throttle open fully (as per instructions to set full throttle position), connect battery...and ESC makes 'normal' connection noises, and after a couple of seconds, motor fires up . Try a couple more times, the ESC won't 'learn' the WOT Tx setting.

Disconnect the new ESC/motor completely,  connect the other, correctly functioning, motor...and...guess what? Not 'correctly functioning' at all, in fact, exactly the same behaviour as the first side.

Check Tx trim-neutral. So why, now, can I not set WOT on either ESC?

And...the original (port) motor is obviously spinning at a significantly faster speed than the new stbd set up (probably because I can't set the WOT position?).

Please help-I don't have enough hair to tear any out....

[scott cuppello]

I'm assuming here that one BEC has been disconnected? In theory you might not have to disconnect them...practice is somewhat different and more often than not, it won't work.

 

It sounds as if the ESC's have a fault to me, or maybe yo need to up-grade? although spinning at different speeds can be explained by several things, motor timing being different on each would be top of my list....as would motors with different windings [labelled the same....far more common on budget motors as people realise, you need to be careful with multi's on this one]....although we can discount that as they were originally running fine....so it's ESC, have you checked the programming on both? And what about the BEC's, they will cause exactly these kind of problems if both are left connected, and I'm assuming the are on a y-lead, not seperate RX chanels?

[Yorkman]

'motor timing being different on each would be top of my list....as would motors with different windings [labelled the same....far more common on budget motors as people realise, you need to be careful with multi's on this one].'

 

Hmmm

that's interesting....

I have in fact got the two motors to behave-went back the next day and started over, and (who knows why!) the WOT setting up etc all worked fine, and I ended up with two motors working exactly as expected, and joined the battery wires together and all seems fine.

Going back to your point though, Scott-I have also fitted two new motors, outwardly identical, same numbers and voltage ratings written on them, but bizarrely, one of them is a different diameter where it fits into the mount-

http://www.giantcod.co.uk/fc2805-1600kv-brushless-outrunner-motor-p-403764.html -and now I'm worried that it is a different spec and I'm going to get the same wingover/splat that I've had on my last two flight attempts...aaaaaaaargh.....

[scott cuppello]

Do you own or can you borrow a tacho? That will give you piece of mind, as will lot's of rudder throw......just in case.

[Yorkman]

Posted by Scott Cuppello on 31/12/2009 13:31:39:

Do you own or can you borrow a tacho? That will give you piece of mind, as will lot's of rudder throw......just in case.

 No....and no....I'm very much on my own! And it's not got a rudder ...going to head out after this coffee and see what happens...thinking about heading up to inkpen and throwing it off a hill with motors at idle-to give me some altitude to play with!

[Yorkman]

Ok, I officially give up.

Despite both motors and ESCs (supposedly) being identical, and delivering the same static thrust, on launch got another instant wingover and collection of bits.

So much for spending more money on 'better' Hobbywings ESCs.

Will go back to flying the York 4 times a year.

And to fixing my boat.

[Tim Mackey]

Oh bummer....are you absolutely sure the problem is not elsewhere?

[Yorkman]

To be honest Timbo-the problem now seems to have been the motors-I think Scott hit the nail on the head with his comment about budget motors not necessarily being the same, despite identical labelling. I've extricated the motors from the remains, and on close examination, it appears I may have been supplied with 2 different specs-here's a quote from GC motor test forum-

 

These motors are identical in appearance except the 1600Kv one had a black circlip on the back of the shaft and the other had a silver one. Whether that's a reliable way to identify which is which, I don't know. They both have a sticker saying Emax CF2805, but no indication of the Kv. The 2800Kv is noticeably stiffer to turn by hand, but that doesn't help much unless you have one of each to compare.

 

And guess what? One silver circlip, one black..

Anyway, the Mossie is history now, which is a shame, cos it was very pretty, and a hoot when it was working.

That's modelling, I guess.

[Tim Mackey]

Ah, what threw me to suggest that was that you said earlier that both motors appeared to deliver the same static thrust.

I do like a lot of what GC is doing, there is no doubt that there are some excellent bargains to be had, many of which I recommend occasionaly to peeps on here, but have to say that I too have had issues with incorrect or conflicting data for certain products.

[scott cuppello]

Sorry to hear it mate, It's essential with twins that the motors are perfectly matched, it's not un-common for the winds to be not too accurate on budget motors, not to mention very different magnets.....the end result being different perfomance from each..... I have been here before as you can imagine, I understand your frustration.

[Myron Beaumont]

Martin ( yorkman )

Too many ifs and buts eh !

Don't let it put you off --I've / we've all been there

Nothing wrong with boats mind ('er indoors tells me )

[Frank Skilbeck]

Can you measure the current being pulled by each motor, that will be a good indication of the power being cosummed, if one one is a higher Kv then on the same size prop it will draw more amps. If the amps are the same then the Kv will be about the same.

 

Also on a twin like a mossie if the motors are turning in the same direction there will be quite a torque reaction pulling the model to one side. I had read somewhere that on the full size it was common practise to open up one throttle more than the other just to correct the swing until the airspeed had built up sufficiently over the fin to provide the stability. This is what you might have seen on launch rather than mismatched thrust from the motors.

 

The other thing you could try is putting a mixer in the throttles to mix throttle with rudder to use the rudder to give differential throttle.

[Myron Beaumont]

With IC you can at least hear the "out of sync "

[Yorkman]

The thing that got me was that with the original super cheapo Escs the thing was fine (apart from motors occasionally not wanting to start, overcome by trimming throttle 'open' slightly before launch) and went straight from my hand without any dramas. So when they died, upgrading to the Hobbywings ESCs-I thought-would solve all my problems. But for whatever reason, they didn't want to work properly with the original motors (one of which had '11v' written on it, the other '7v-9v'! but which had been fine).

And the static thrust (at WOT at least) certainly seemed very close when I put two new motors in-new Escs, new motors, got to be right, surely? Not...

Anyway....24hours on, am thinking 'third time lucky'...(that was my second Mossie!)..and the Mrs is encouraging me to buy the 'Flying Styro' kit...but...160 quid...seeing that go 'splat' would really hurt...so, could be a third GAD kit...at least I'm practised at building them now...if anyone has experience of the FSK models I'd be interested to hear it.

And the boat has water in the fuel tank, in case anyone's interested-so next job is take the top off the carb and clean the float bowl, then perhaps I can play with one of my toys!!