discussion Motor 'stutter'

[Guest]

Hi guys,

Can anyone help with this problem...

My motors (both) 'stutter' when on the water, i.e. they speed-up and slow down as if the trottle is being opened and closed very quickly. This does not happen when on the bench.

Motors - matched pair of 540 type with 3, 1uf (one microfarad) capacitors each, one between terminals and one from each terminal to case. Running at 12 volts and drawing 1.5 amps each at full throttle under load.

ESCs - Mtronic Viper 15 (pair)

Layout - (see picture) ESCs are behind battery (under it in photo) between motors. Receiver is to the right of the battery on the coaming. Aerial is routed (up) along coaming, across stern (top of pic) and then down on opposite side. Receiver has been replaced as I thought this was causing the problem, BEC's have been disconnected and battery pack installed. Only one servo lead runs anywhere near the aerial.

Has anyone had a similar problem? What was the solution?

Any help or suggestions would be appreciated.

TIA,

Scottie.

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[Guest]

scottie

i`ve had a similiar problem, i found it to be a loose shaft coupling, it only happened in the water when there was a load on the shaft,

just check shaft uninons, props etc for tightness.

in fact anything metal which could be touching .

any loose terminal connections as well,

let meknow how you get on bud

Adz..

 

[Guest]

Scottie, No real answers but just chucking some thoughts at you.

I too have had the slipping coupling effect but if yours speeds up and slows down as if the trottle is being opened and closed very quickly it seems more like an electrical effect.

If you can run the boat past yourself on the bank with the superstructure removed and see if it is one or both of the motors that are affected then it would help to narrow it down. Obviously if only one then you would be looking at that side only but if both then something common such as the receiver would be a possibility. Maybe put it in the bath and run it in the same way to see if you can identify which one. Another possibility would be to disconnect one side at a time and see if it persists with one or the other.

If only one side then I would suspect the speed controller but bear in mind Adz's purely mechanical suggestions. If it doesn't happen on the bench then it is load related and a slipping coupling is still a possibility.

If you are convinced it is both sides then you have to look at the receiver and its power supply. If you have already changed that and the problem persists then it is possibly only happening on one side.

Anyway, as I said just, some thoughts out loud that may be of some use. Let us know how it goes.

 

[Guest]

Yes I had that with my u-47. It then started going at half speed and making lots of noise. One of the props had fallen off!

Not enough loc-tight (I'm a dill)

 

[Guest]

Thanks for your ideas. I've checked all mechanical and electrical couplings, there's nothing loose or dirty. I'm sure the fault is electrical but I can't think what it could be....:thinking:

Since I'm only drawing about 20% of the current limit through the ESCs I don't see how they could be causing it... and why only on the water????

Yes Richard, it's both motors, I've had the top off and ran it against the bank so I can see what's happening, both motors are stuttering at the same time which is why I changed the receiver but I can't believe that two receivers are causing the same fault!

Still scatching my head,

Scottie

 

[Guest]

Well at least we are eliminating things!!

I think we need to think outside the box a bit more now and I am certain that the next step isto try a differrent transmitter. I know it seems OK on the bench but not in the water but the water itself can play a part in the signal quality.

I have only recently been playing with a very cheap foam Cessna as a trainer without much success so far. Another story. One problem was a very erratic operation of the eirlerons which I couldn't resolve. We do tend to think of the radio transmitter as a solid state device that goes on forever but, of course the electro-mechanical transducer is a potentiometer on the end of the stick and these can fail. The Cessna one responded to a squirt of WD40 into the Pot, after taking the set apart, and working the stick for 5-10 minutes.

I would try the boat next with a differrent transmitter and see what happens.

 

[Guest]

Thanks Richard but there's no problem with the transmitter. It's a Futaba 6EXA which I use for three different models including St Columba, I have no problems with any other, just the pusher tug.

In desperation I'm going to swap ESCs from St C and put them in the tug. Then if things don't improve I'll swap the 'genuine' futaba receiver from St C as well.

If it still fails there's always the lump hammer...:hammer:

Scottie

 

[Guest]

The only remaining (lonely) thought I have are that the receivers and crystals are all compatible. Don't forget that conversion one transmitters must be used with conversion one receivers and the crystals must also be conversion one etc...

If any of those are not right it will cause signal problems.

 

[wonwinglo]

Try re-routing the antennae,also make sure the rx battery is isolated as far away as possible from the other electrics,you could be getting spurious signals from the most unlikely source.

It is not unknown for harmonics to set in at certain points,it could be a freak one this,also make sure there is no 'metal to metal' linkage giving out harmonics,it could just be.

Roll out some Bluetak with a rolling pin and encase the RX battery into it,sounds daft I know but it works.

 

[Guest]

I'm following this thread with great interest as I've exactly the same problem on my Krick U25 (see avatar). The sub has only a single ESC but twin motors and it works perfectly on the bench but 'pulses' on the water - and it seems to be getting worse. My suspicion is that there may be a bent shaft that causes binding under load - or am I clutching at straws. I seem to have tried most of the other remedies unsuccesfully.

Andrew

 

[Guest]

The end may be in sight....

Following extensive testing in my bath this morning, I have isolated the cause of this problem!!!

This 'stuttering' only occurs when full power is applied forwards, reverse does not suffer at all. Also, both motors stutter at exactly the same time. 'Ah, receiver problem,' I hear you cry. But no, it happens with a genuine Futaba receiver as well as the 'cheap' one.

The problem lies in the speed controllers... believe it or not!!!

I have borrowed an older Sonic 15 from another boat and tried it alongside one of the Vipers. The Viper stutters, the Sonic runs perfectly.

I have just finished speaking to Mtronics who are as mystified as I am but, being the helpful people that they are, have asked me to send the Vipers back with a note about the problem. Now I can only hope that they will be able to duplicate the fault.

Added to that, I have a Viper 25 which exhibits similar problems. Unfotunately I can't put the boat in the bath and don't have a spare 25 amp controller to test it against.

Andrew, are you using the same ESCs i.e. Mtronic Viper? If so this may be the same problem.

I'll post any reply I get from Mtronics in this thread.

Scottie

 

[wonwinglo]

Just had a thought on this Scottie seeing as it is ESC related,you have not extended the speed controller cable by any chance ? I had one make that refused to function altogether if the cable was extended,it took me weeks to find out the cause ? can be fiddly things sometimes.

 

[Guest]

Hi Barry,

I assmue you're talking about the ESC cable that goes to the receiver, no I haven't extended that one at all. All I've done is removed the positive wire to disable the BEC function, as per instructions.

Scottie

 

[Guest]

Well done Scottie. You wouldmn't have thought thatv two ESC's would have exhibited the same problem at the same time.

Still perseverance is the only way. As I often say with these things, the fault is on the desk in front of you, all you have to do is find it!!

 

[Guest]

These ESCs have a built-in overload cut-out. When I spoke to Mtronics he asked what current my motor was drawing. Since I'm only drawing 2.2 amps max (full throttle and under load) I can't be getting anywhere near the stated max of 15 amp. My thought is that perhaps a 'batch' of controllers have got faulty components within the overload circuit. Since I bought them at the same time it would explain why they are both doing the same thing.

Scottie

 

[Guest]

Motor stutter

Hi. Having read your post I offer the following comments

You mention 1 uF capacitors for suppression, I only use 0.1 uF caps. I believe the high value is giving a smoothing effect to the speed controller output, resulting in the effect you are experiencing. Also if you are using standard electrolytic caps they will be polarised ( i.e. + to +) and will therefore be reversed connected when you change the motor direction. The voltage across the motor will also be greater than the supply voltage and this may be exceeding the capacitor max volt rating, causing the caps to break down. Mtronics may well suggest a value.

I agree with the other posts re metal to metal links causing interference and sugest you check and replace any metal to metal links.

From your picture it would appear that you may have some signal wires running near to high power wires(ie battery). It would be better to ensure that the aerial and any servo leads are routed well away from the power carrying wires, including any auxiliary circuits (eg lights, sound effects)

Hope this helps. I have several tugs with two motors and have not had your problems.

Dave

 

[Guest]

Update on my problems with ESC's...

Sorry for the long delay in updating this. Mtronics duplicated the fault I was expereincing (thank ... (insert diety of your choice)) and sent me replacements which, would you believe it, exhibited similar problems. While one of the new ones was okay the second was acting even worse than the originals. i.e. It stuttered at less than full power setting. I again spoke to Mtronics who could offer no advice as to why it was happening but said it might help if I could visit them with my model so they could see it in-situ.

I've just returned from them with the problem all but resolved.

Following lots of testing we discovered that the problem is linked to the BEC circuit!!!! I know this seems strange but it is true. As per instructions in the packet, I removed the positive lead from one ESC before plugging both into the receiver. The ESC with no positive connection to the receiver is the one causing trouble. When we put the lead back into it's shell the problem vanished.

Mtronics tech guy (a really nice lad called Paul) was as mystified as me but at least we now know what is causing the stutter if not the reason why it is happening.

The current status is that my model is working properly and Paul is going to investigate why the BEC circuit is causing the problem. He has said he will pass on relevant info to me as soon as he has any.

Scottie

 

[Guest]

...and all credit to Mtronics for following this up so positively and not fobbing you off with the usual crap we get all too often nowadays.

Thanks for sharing this with us.

 

[Guest]

Excellent news Scottie and many thanks for the update. Mtronics seem to have been very helpful. I was about to order a couple of new escs for forthcoming projects so I know where they're coming from now!

Andrew

 

[Guest]

In my opinion, Mtronics have proved themselves to be a company well worth dealing with.:bravo:

They have already replaced to blown-up ESCs without question, in this day and age that's remarkable by itself. Add to that their willingness to help with a 'strange' problem puts them right at the top of my favourite list of model equipment suppliers

Until I start building my own ESCs (something I am seriously thinking about doing) I will ALWAYS buy theirs.

Scottie