Rc misbehaving speed controller

[Peter VintonParticipant @petervinton69315]

I have a Hitec Lite4 radio set and a Viper Marine 15 esc in a small depron Fairey model. I can get the boat running at medium speed forwards but if I try pushing the throttle stick further forward I get a spurt of higher speed then the boat stops. Pushing the throttle further forward either gives another forward spurt before stopping or might even get it going astern. If I return the throttle lever to the medium speed setting it will run forward steadily again.

Any ideas what's wrong?

[Peter VintonParticipant @petervinton69315]

[Dave MilbournParticipant @davemilbourn48782]

Peter

Is this a new speed controller i.e. not been used previously? Vipers have a rigid set-up routine which involves flashing LEDs and much frantic stick wiggling – all is detailed both in the instructions and on the MTroniks website. Newer ones are so-called Plug and Play and don't need any of this activity. If you've done all that and got the Tee shirt then the only conclusion is a Friday afternoon ESC.

I gather that MT will exchange it for a good 'un without undue fuss.

Dave M

[Peter VintonParticipant @petervinton69315]

It's a new one claimed to be a plug and play. I'll try sending it back, thanks.

[Dave MilbournParticipant @davemilbourn48782]

Just a thought. Forgive me if I'm in the wrong territory but…

These are forward-and-reverse ESCs, which means that throttle neutral (engine stopped) is with the stick in the central position. If you try to set it up with the 'engine stopped' position at full back-stick then the symptoms might look much as you describe, with 'full throttle' giving a signal which is not recognised as valid. You should fit a spring into the transmitter to centre the throttle stick and then try the set-up again. Pulling the throttle stick backwards should, of course, reverse the motor.

Dave M

[Charles OatesParticipant @charlesoates31738]

Hi Peter, can you tell us what motor, battery and prop you are using. It might be relevent.

[ashley needhamParticipant @ashleyneedham69188]

I don't know if they have a current cutoff, which would give this. Does the motor run at full throttle with no ooad,,,ie out the water?

The throttle as far as I know should be central on startup, trimmer same/

Ashley

[Malcolm FraryParticipant @malcolmfrary95515]

As Dave first said, Vipers needed to be "taught" their environment. Later plug n pray ones might need to wake up to a valid neutral signal, then get what it "regards" as a valid forward, and then a valid reverse. Some transmitters have this logic reversed, and need to have the throttle channel switch reversed. This might result in the motor turning the wrong way, but is easily fixed by reversing the motor wires.

[Dave MilbournParticipant @davemilbourn48782]

Some geeky stuff, for those who might be interested.

A signal from the transmitter to the speed controller via the receiver is detected as a pulse of current which lasts for a variable amount of time. This time is dictated by the position of the transmitter stick and is typically somewhere in the range between 1mS and 2mS. The pulses for each channel are sent in a sequence (called a frame) followed by a longer timing pulse, and then the series is repeated. This happens about 50 times a second. The exact length of each pulse determines where the servo should be (or the ESC, which works similarly to a servo in this respect). It's logical, therefore, that the central position of the servo – or the neutral position for the speed controller – should be around 1.5mS, or halfway. This allows the same amount of travel in each direction. i.e. 0.5mS. Any signal received which is outside the limits (1-2mS) is rejected by the speed controller as invalid, and the thing usually goes into failsafe and stops the motor.

Things being what they are, the exact value of the neutral signal can vary between one transmitter and another (or one manufacturer and another). If the speed controller didn't make any allowance for this then the motor would probably run slowly in one direction or the other when you switched the set on, and it would need a small amount of trim to stop it. This is annoying and so many speed controllers require that you set them up with the neutral, full ahead and full astern values initially. So-called Plug-and-Play or Autoset speed controllers do away with this. They are programmed to "listen" to the first signal they hear when the set is switched on and, once that signal pulse has been received say 20 times without changing its value, settle on that value as neutral irrespective of what that value is. Thus you can have a set whose neutral signal is quite a long way from 1.5mS and the motor will still remain at dead stop if the transmitter stick isn't moved for a fraction of a second on switching on. OK so far?

NOW if you set the transmitter stick at fully back when you switch the radio on, the throttle signal will be at some extreme value like 1.05mS and that will be identified by the ESC as neutral. The speed controller is programmed to cope with signals 0.5mS either side of neutral because it knows those values correspond to its full speed ahead and astern. Those limits in our hypothetical case are now 1.55mS and 0.55mS. However, once you push the stick more than halfway up, the signal value exceeds the 1.55mS which the speed controller can accept as valid – so it shuts the motor down.

Push it further forward and all sorts of strange and unpredictable things can happen. Return the stick to any position below about halfway and the motor will respond again. Pulling the stick all the way back should stop the motor, but you won't be able to get the motor to reverse because you can't pull the stick back any further than all the way.

Now compare this with the behaviour of Peter's ESC and you'll see why I suspected that this is what he'd done. All we need now is for Peter to reply!

Dave M

[Peter VintonParticipant @petervinton69315]

Thanks for all the informative replies. The transmitter stick is already spring loaded to the centre so it's always switched on in the neutral position. I'm going with the duff esc theory for now so I've returned it.

[Dave MilbournParticipant @davemilbourn48782]

It was a long shot, but I hope the point was worth making for those who aren't quite so savvy as you.

DM

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