Throttle Stick not working

[Dave Cooper 6Participant @davecooper6]

Hi all

A little electronics 'teaser' problem on a 27 MHz Futaba Attack II Tx :

After fitting a throttle ratchet to the left-hand stick, the unit ceases to function with the exception of servo reverse – which works as expected…

Meter readings from the pot' are similar, but not exactly the same, as the right-hand unit. Just wondering if I should change the pot, or, try and source a complete new stick unit. As the set is now approx. 15 years old this could be tricky !!!

I'm tempted to junk it and go 2.4, but, don't like being beaten by a niggle such as this. Any ideas gratefully received,

Dave

[Dave Cooper 6Participant @davecooper6]

[Dave MilbournParticipant @davemilbourn48782]

Dave

I'm puzzled over your saying that the unit ceases to function and yet the servo reverse continues to work. These statements appear to be contradictory i.e. if the stick won't move a servo then how do you know the reverse function works?

Fitting the throttle ratchet is a purely mechanical operation so the electrical aspect of the stick shouldn't have been affected – that's unless you somehow managed to physically disconnect the spindle of the pot from the yoke or dislodge a wire somewhere.

As to junking it and going 2G4 that's more of a personal decision. Some people seem almost emotionally tied to old VHF sets whereas I wouldn't give them house-room unless I needed one for a submarine.

"Has anyone got the Green peg?" No thanks!

Dave M

[Malcolm FraryParticipant @malcolmfrary95515]

What does a servo plugged into channel 2 actually do? Both with the servo reverse operated and at normal.

It might be that the ESC plugged into that channel fails to recognise the switch-on condition with the newly ratcheted stick in an unexpected position. I have a couple of ESCs that do just that, nd need to have the stick at what they think is neutral for a few seconds before they will play, not helped by the fact that they soft start as well.

Or it could be that during conversion, a wire got snagged and fell off, but is still sitting near enough where it should be to confuse a casual observer.  Depending on which wire, strange results might appear, and it might well be that, since Futaba like to have their center timing different to everybody else, that could also make a difference to what the ESC at the other end eventually sees.

 

Edited By Malcolm Frary on 14/08/2019 11:01:42

[Dave Cooper 6Participant @davecooper6]

Hi both – thanks for the replies. The test set up is Tx /Rx /and 2 servos known to be good. (I swapped the servos over and got the same result)…

Throttle stick advanced – servo does not move. Same stick retracted – servo does not move. Servo reverse switch activated throttle servo goes to extreme position in one direction only. Yes, Dave I did not make this clear !! No ESC in the circuit at all, just conventional Futaba S3003 servos.

Thinking back over my moves to fit the ratchet, I think I may have accidentally 'tweaked' the spindle – this tends to lean toward a mechanical problem – well spotted Dave, if that's the case ! Presumably, the servo reverse is purely electrical, so, if the pot is 'parked' on zero before the switch is thrown then throwing it would give travel to the other extreme.

Now to the remedy :

1. Try and reattach spindle to pot – full strip down ?

2. Fit new pot and try and get it to mate with existing stick unit (plenty of "B5k's" available with different shaft spec's)

3. Source new stick unit complete – there must be some out there, but, they seem to have eluded me so far.

Update : one of the battery springs has just let go and is resisting solder manfully ! The set is fighting back ! I think a LiPo / NiMh uprade is also on the cards…

What 'fun'

Dave

[Dave MilbournParticipant @davemilbourn48782]

1. Undressing won't help the problem unless it activates your super-powers. "Pot-man"?

2. A new pot with a shaft which doesn't fit the yolk is a waste of time, money and effort.

3. Good luck with that!

Face it, Dave – It just doesn't love you any more and it's very, very old

There comes a time etc etc…

DM

[Dave Cooper 6Participant @davecooper6]

Hmmm, yes, you could have something there…

I think I'll give it one last go before consigning it to that big spares box in the sky !

Dave C

[Colin BishopModerator @colinbishop34627]

As Dave M says, flogging a dead horse…

Colin

[Former MemberParticipant @formermember11541]

[This posting has been removed]

[Colin BishopModerator @colinbishop34627]

Well, I suppose that's capitalism for you……

Colin

[Malcolm FraryParticipant @malcolmfrary95515]

When talking about 27MHz transmitters, it is as well to remember that they were, as complete units, very much interchangeable.as regards range, power and layout, if not internal components.

The only big difference with Futaba was their insistence that neutral was 1.25mS rather than 1.5 like the rest of the world, and they liked to reverse the servo f-r logic. So if a 27MHz transmitter in working condition that has been rendered surplus by somebody else moving to 2G4 might be an economic answer.

[Dave Cooper 6Participant @davecooper6]

Thanks for the advice Malcolm. I've just sent off for two new pot's. If it doesn't then work they won't break the bank (@ 59p each).

I'll let you know how I get on,

Dave

[Malcolm FraryParticipant @malcolmfrary95515]

While messing with the wires to the new pots, there is a good chance of finding the broken wire.

When I was apprenticing, a wise elder told me "Get as technical as you like, young Malcolm, but look for th'brokken wire first.". A few weeks later, I could have added a rider to that wisdom – "Make sure the diagram is flat enough to see all the small, but important bits like the 1 second pulse supply." In the first case, he took pity on my grovelling, in the second, my grovelling over the diagram flattened out the fold that was hiding the important bit. Eventually. Could have been dumb luck, but all part of lifes learning curve.

[Dave Cooper 6Participant @davecooper6]

As a change from preparing the hull of the little RAF launch for spraying, I unsoldered the 'faulty' pot' and took some resistance readings. Lo and behold, they were almost identical to the steering pot….

So, I carefully re-set the pot's centre (using the ohms scale on the multimeter) and matched it to the stick's angular centre position. Then re-soldered and re-fitted it to the main circuit board. Whilst I was at it, a quick reinforcement of the aerial and battery spring (negative) finished off the internal Tx work for now. Also found a circuit description of the main Futaba IC (24 pin dual in-line) – encoder /modulator and did some random continuity checks (audio low-pass filter etc)

If this does not do the trick I'll have to read my Tektronics manual and dust off my 'scope !

Dave

[Dave Cooper 6Participant @davecooper6]

Hi All

Problem solved ! I think Dave M gave the clue with my 'ham-fisted' removal of the throttle pot' to fit the ratchet…

Hull has been in masking stage up to today hence the delay in testing.

Thanks for all the other clues /advice.

Dave C

ps if anyone else has the same problem see previous post for a possible remedial action.

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