Problems problems.....

[Simon Chaddock]

Robin

All a servo tester does is remove the radio link so if the issue still exists then the problem must lie with either the LiPo, ESC, motor or wiring, as these are the only items being used.

Without sophisticated test gear the only practical way to identify which item is causing the problem is by a process of one by one substitution with components that are known to work correctly.

[Trevor]

Thanks Simon for explaining so well what I meant! I agree that, having eliminated the radio as the source of the problem, isolating it further can be tricky. Substitution is usually the simplest approach but the OP has explained that swapping out the ESC is tricky in this model.

Just as a long shot - it's not unknown for motors to be mislabelled. If the motor has a lower kv than expected, it might explain the limp performance. Might be worth trying a larger prop ( keeping a close eye on the current draw of course) to see if the throttle then works over the full range.

Trevor

[Dave Hopkin]

Posted by Trevor on 17/05/2016 14:43:54:

Just as a long shot - it's not unknown for motors to be mislabelled. If the motor has a lower kv than expected, it might explain the limp performance. Might be worth trying a larger prop ( keeping a close eye on the current draw of course) to see if the throttle then works over the full range.

Trevor

Cant see that myself, the ESC will pulse the motor proportionately to the stick movement giving a percentage of max revs based on the stick displacement from off (assuming its calibrating) - how fast the motor spins is a function of the windings

Changing the prop will only increase the load and hence current draw/wattage but it wont make the motor rev any faster

[Peter Beeney]

With the greatest respect, of course, but taking another sideways view of all this, as always, I think the speed of the motor may depend on variously the strength of the magnetic fields, the number of poles and windings etc., but most importantly perhaps, the size of the load and the applied voltage. If the kV is 1000 then 10 volts applied = 10,000 rpm, 20 volts applied = 20,000 rpm for an unloaded motor.

The esc is an integral part of the motor, the motor drives the esc and in turn the esc drives the motor. Neither will function without the other. In my lowly opinion it’s slightly misnamed too, I’d prefer Electronic Switching Commutator, the speed control bit is only really an add-on here. The motor would certainly not function without the commutator gizmo; but it doesn’t have to have the speed controller.

If a motor is running at a steady speed with a given load and voltage and we then increase the load the motor will slow down by an exact proportional amount to that added load and the current flow will go up by an equal and exact proportional amount. These are all inexorably bound together. Add more load and the same thing happens, by an exact proportional amount again. Eventually, though, things would start to overheat due to the excessive current.

Now if our motor is back at it’s steady speed and we wish to change this by some amount then we just change the applied voltage, the motor will respond accordingly. The speed controller circuit does not control any of the drive pluses in speed or overall length, the pulse switching speed is controlled by the motor and the length of pulse, in degrees, stays the same throughout; it simply switches the current on and off a number of times during each pulse to supply an average voltage, higher or lower, and thus current, to the motor.

One of the feature that really sorts the men from the boys in terms of power trains is it’s overall resistance. The lower the better and we know model power trains do have a reasonably low resistance, so any increase can make quite a difference, percentage wise. If the resistance is say 100 milliohms and the current 50 amps then doubling to 200 milliohms will reduce the the current to 25 amps. For the same applied voltage.

Could it be then that maybe Percy’s OP is just a case of some unwanted resistance somewhere? Unlikely, I expect, but in any case I’d certainly agree with PatMc, a quick call to the supplier might the best all round solution anyway.

PB

[Norrland]

Hi Percy,

Very annoying when something that should work out of the box refuses to cooperate.

Lots of good advice already. When the first obvious ones didn’t do the trick, have you tried swapping around equipment as suggested by Simon, seems to be an obvious way to go. As I understand it you have in front of you two models of the same type (equally equipped) and both controlled by Multiplex 2.4 GHz. You have also said that it looks a bit difficult to get to get to the ESC. Have you tried the following+

1. Bind the new model to your TX. If same result probably not the fault of the Tx settings. You can also bind your model to the new Tx. If it works, supports the Tx OK.

2. Exchange the Rx’s between the models. If the new Rx works in your model, not the fault of the Rx. If the new model still doesn’t work with your Rx, supports that the Rx is OK.

3. If the new Tx and Rx seems to be OK, what remains is the ESC or motor. Is the motor connected to the ESC with bullet connectors? If that is the case, you could swap the motors between the models even if it is difficult to get the ESC out. If your motor fails to work in the new model and the new motor works in you model it looks like a faulty (or incorrectly programmed ESC).

If you can’t get it to work return it to where it was bought as proposed by PatMc. The supplier should replace it - not working on delivery.

Per

PS If you are member of a club, why don’t you ask your local electric fly expert to have look. That is the best part of a club, you can ask for help.

[Dave Hopkin]

I have to say my understand on how an Inverter controls a motor is different, especially as "current" is never switched, the duty cycle of the full voltage is pulsed, current flow is a function of voltage and resistance

[onetenor]

Remove the hot glue with a soldering iron tip Simples

[Peter Beeney]

Exactly so, Dave, surely when the voltage is switched off the current then ceases to flow? So then I’d consider that when the voltage is switched off the lack of current ceases to create a magnetic field and the motor’s speed reacts to this; therefore depending on what the on/off ratio is, the motor will just go faster or slower. That’s how I see it, anyway.

PB

[Mike Blandford]

Posted by Peter Beeney on 17/05/2016 23:08:36:

Exactly so, Dave, surely when the voltage is switched off the current then ceases to flow? So then I’d consider that when the voltage is switched off the lack of current ceases to create a magnetic field . . .

Actually the current does NOT cease to flow. The motor winding is an inductor. When you switch the voltage supply off, the inductance trys to keep the current flowing. The ESC includes a path for this current so it does continue to flow.

Mike.

[Frank Skilbeck]

From the description of the fault, it sounds like the LVC is kicking in, which means that it is either set too high (faulty ESC) or for some reason it thinks it has a 4cell lipo connected rather than a 3 cell. When you first connect it up do you get 3 beeps (3s) or 4 beeps (4s). If it's the latter the LVC is reducing power to keep the volts above the LVC setting for a 4s lipo, the default setting on the ESC is 2.85 volts per cell, so if it thinks it has a 4 cell lipo fitted then it will start to reduce power when the volts drop below 11.4v. Can you measure the voltage when you run the motor up (lipo checker in the balance port is what I usually use).

You could also try resetting the LVC setting from 2.85 v per cell (medium) to 2.6v per cell (low) and see if that gives any more power.

[Peter Beeney]

Thanks for your reply. Actually,I was considering whether to mention the fact that the switching might have other effects, but I thought it might just clog up the issue somewhat.

Yes, I believe the FETS on the esc have a diode built in which prevent the induced voltage from the winding from building up and thus preventing any unwanted voltages and currents being able to cause any mischief. I would think this is a bit like the reversed biased diode placed across a relay coil, for the same reason. When the current stops flowing the rapidly collapsing magnetic field creates a rising voltage within the windings, but because of the direction in which this is happening the diode now becomes forward biased and start to conduct. The diode is a low resistance path and it now very effectively shorts out the coil across itself. I’d have though this is of very short duration and not really enough of anything to have any reactions on anything else. The brushed motors of the past had capacitors across the windings and to ground for exactly the same reasons, to prevent the arcing and sparking at the mechanical contacts between the carbon brushes and the copper commutator segments as the armature revolved.

With many windings, a fast switch off and high DC resistance the circuit without a diode might enable the voltage to get quite high on the relay coil, but would that be the same for a motor winding?

Maybe the motor is different, but I was only trying to describe pulse width modulation as I see it, in very simple terms. That how I see everything anyway, I can’t do complicated. I’m now not even sure if we switch the voltage (and current) or the current (and voltage) or just simply ‘the electricity’ even, I’m afraid you’ll just have to bear with me on this one.

Humble apologies if this post has now gone far off topic…

PB

[Dave Hopkin]

Posted by Peter Beeney on 17/05/2016 23:08:36:

Exactly so, Dave, surely when the voltage is switched off the current then ceases to flow? So then I’d consider that when the voltage is switched off the lack of current ceases to create a magnetic field and the motor’s speed reacts to this; therefore depending on what the on/off ratio is, the motor will just go faster or slower. That’s how I see it, anyway.

PB

I dont want to hijack this thread into a long discussion of how ESC;'s function as it is quite a complex topic, for a detailed explanation this is a good place to start **LINK**

[Robin Etherton]

Percy

Any sign of a solution?

Robin

[Peter Beeney]

I think your link just takes you to a speed controller for brushed motors, Dave, but it does at least talk a bit about PWM. Some of this causes me some head scratching anyway, but it does mention the capacitors across the terminals of brushed motors etc, plus a fast acting Schottky diode across either the motor windings or the transistor, I guess for the same reason that I mentioned for the relay.

But as you say, perhaps not the time and place for this, maybe what it really needs is a general electrical thread where the subject and posts can wander about at will without causing any concern about going off topic.

PB

[Dave Hopkin]

Not sure how I goofed on the link................ this is where it should go! **LINK**

[PatMc]

Posted by Frank Skilbeck on 18/05/2016 08:50:29:

From the description of the fault, it sounds like the LVC is kicking in, which means that it is either set too high (faulty ESC) or for some reason it thinks it has a 4cell lipo connected rather than a 3 cell. When you first connect it up do you get 3 beeps (3s) or 4 beeps (4s). If it's the latter the LVC is reducing power to keep the volts above the LVC setting for a 4s lipo, the default setting on the ESC is 2.85 volts per cell, so if it thinks it has a 4 cell lipo fitted then it will start to reduce power when the volts drop below 11.4v. Can you measure the voltage when you run the motor up (lipo checker in the balance port is what I usually use).

You could also try resetting the LVC setting from 2.85 v per cell (medium) to 2.6v per cell (low) and see if that gives any more power.

Frank, ihat's what I thought might be the problem. But as I posted earlier, rather than try to look for what's wrongly programmed by counting beeps & measuring the voltage under load, IMO it would be quicker to do a reset to default.
If that doesn't cure the problem it's time to use the warranty.

[Peter Beeney]

Dave,

Taking a quick look at that new link, I’m afraid I have to say again that I’m not at all convinced. About the only thing that I’d consider that does make some sense is that fact that he says, perhaps quite remarkably under the circumstances, that the current in the stator is AC. That’s a definite fact. But I’m sure there are very convincing arguments as to why some of the other stuff is a bit questionable, to say the very least.

It would appear, then, that even his moniker, Luke Warm, is a bit generous, too…

PB

[Martin Whybrow]

Actually, Luke Warm's description is pretty much spot on. Our brushless motors are actually a form of stepper motor, or more accurately, a synchronous 3 phase AC motor. The ESC controls the speed by adjusting the frequency of the integrated waveform (the resultant waveform from averaging the PWM pulses); the actual switching is controlled by sensing the back EMF of the windings to detect where the motor is in its rotational cycle and altering the PWM signal accordingly.

What Luke Warm didn't mention, at least in the original post, is that current increases as the motor is loaded up, e.g. a bigger prop is fitted; this is because as the load slows the motor, the back EMF will drop, causing a larger 'effective' voltage to appear across the coils and driving more current through them; these is also some effect produced by the ESC which will increase the PWM duty cycle to force the motor to develop more torque, although I don't know to what extent ESCs implement this feature.

[Peter Beeney]

I would consider that a 3 phase synchronous motor is a motor supplied by a 3 phase AC supply. It simply synchronises to it’s supply frequency.

The first thing that Luke Warm says, and I quote, - ‘The ESC controls the speed of an AC motor with frequency, not voltage.’ He then goes on to state, and again quote - ‘The speed of the motor has nothing to do with voltage or amps, but instead the timing of the current fed into it.’ Nothing to do with voltage or amps, apparently, but the timing of the current… So what is the current if not amps… And finally - 'RPMs: An AC motor's ESC controls the speed (RPMs) of the motor by changing the frequency of the 3-phase trapezoidal waves; the higher the frequency, the faster the prop will turn.'

The ESC is 6 switches arranged in a half H bridge format simply to act as the commutator for the motor. Exactly as the mechanical comm. of a brushed motor. The speed controller, or throttle stick, does not change the frequency of this switching, this is controlled entirely by the speed of the motor. The speed of the motor is controlled by the applied voltage and the load; and the throttle stick does this by varying the applied voltage.

One way of perhaps indicating this is in my statement - ‘If the kV is 1000 then 10 volts applied = 10,000 rpm, 20 volts applied = 20,000 rpm for an unloaded motor.’ Of course, the comm. switching is also going twice as fast at 20,000 rpm, but it’s driven entirely by the motor, all we’ve done is to double the voltage, we’ve done nothing to the frequency. I may have got this wrong, but anyone with a tacho and a couple of batteries can very easily do this simple test to prove it for themselves, one way or the other.

Certainly an increased load will cause a larger effective voltage across the windings, but this is just Ohms Law again. Higher voltage = increased current = stronger magnetic field = more torque. Increasing the PWM duty cycle will surely only increase the voltage but also the speed, so higher voltage = etc. etc. But actually all we want to do is to control the speed, so it’s rather defeating the object. Maybe if we wanted the esc to act as a governor control to maintain a steady rpm under varying load conditions then I’m sure it’s possible there would be a need to vary the duty cycle automatically, but I’ve never seen this required by modellers; fixed wing anyway

My overall view goes something like this. When the motor is at full throttle there are no PWM pulses, just the full voltage applied in a series of pulses of fixed duration to give the motor it’s turning motion. When the throttle is operated a PWM signal is sent to these main pluses, which are still of the same fixed duration, but it breaks them up into much smaller pulses, but still each with it’s fixed time period. If within each time period the voltage is switched fully on for half the time and fully off for the other half of the time the average voltage over the whole time period will be half the full voltage. Thus it follows, surely, that if nothing changes the applied (average) voltage over the full duration pulse will simply be half the full voltage. And the motor will run at half speed. Each fully switched on period, the duty cycle, I believe, is at the full voltage and thus the full current and torque, so power is maintained to a large extent.

If the duty cycle were reduced to say 25% then it follows that the average voltage will be 25%, or one quarter. Motor will turn at one quarter speed.

I don’t really think I can say very much more, except that, as always, we will each take our different views and go our own ways. And, as always, it probably won’t make that much difference in the end anyway…

PB

[Martin Whybrow]

Why do I bother?

[Dave Hopkin]

RPMs: An AC motor's ESC controls the speed (RPMs) of the motor by changing the frequency of the 3-phase trapezoidal waves; the higher the frequency, the faster the prop will turn.

Voltage: The battery controls (provides) the voltage going to the ESC and the motor.

Amp draw: The motor's size and configuration, and the load that is placed on it, controls the amp draw.

[PatMc]

I bet the OP finds all this half baked theory on how the ESC controls the motor speed really helpful.

[gangster]

In reality the bottom line had got to be . It's a pnp model with built in motor and esc ant if it doesn't work right with either the owners TX or the TX belonging to the guy setting it up then it ain't right and needs to go back

Edited By gangster on 18/05/2016 20:34:48

[Norrland]

I don't know why but this discussion reminds me about this old cartoon.

[Martin Whybrow]

Posted by Norrland on 18/05/2016 20:58:03:

I don't know why but this discussion reminds me about this old cartoon.

I take it it's not a cartoon saying 'Page Not Found'; if it isn't, then your link's broken