Viper Marine 15 cutting out

[Tony FentonParticipant @tonyfenton32936]

Just launched my Riverside Models narrowboat model (on the canal!) and all was going well until everything cut out – motor and rudder servo. After a few seconds it all sprang back into life again and continued this way until another cut out.

I'm using the Viper Marine 15 with BEC and Planet T5 transmitter and receiver. I saw the prop shaft was a bit loose (needs more epoxy to hold it on the support in the hull) and wondered whether this was causing the motor to sieze and stall, thereby triggering the Viper ESC to temporarily cut out? When I noticed the motor stall, I also lost any rudder control. After a few seconds everything was working again. Neither motor nor ESC were anything more than mildly warm, certainly nothing overheating. Boat and transmitter were well within range at about 5 feet maximum between them.

Has anybody got any ideas? Any help would be very much appreciated.

[Tony FentonParticipant @tonyfenton32936]

[Tony FentonParticipant @tonyfenton32936]

Forgot to add : I'm using a 6v SLA battery, MFA 719RE540/1 motor and Hitec HS-311 servo.

[Charles OatesParticipant @charlesoates31738]

First thing is to charge the battery and then check its voltage on load. What you describe are the classic symptoms of voltage drop. 6 volt SLA s are fine with the Viper, I use them myself, but 6 volts isn't far above the cut off for the electronics, and a load or poor battery can soon drop the voltage.

 And yes, fix the drive line properly, It could be stalling, and a loose set up is doing no good at all.

Let us know how you get on

Chas.

 

Edited By Charles Oates on 13/05/2016 23:50:55

[Tony FentonParticipant @tonyfenton32936]

Thanks Chas, good to know this is a common problem. First thing I'll do is fix the drive line. The battery was fully charged and it must have been after about 30 mins of running I started getting this. It would recover and I got control back again for a while then cut out after a few minutes more.

I also need to adjust the position of the servo a bit as the rudder doesn't swing equally to port and starboard.

[Charles OatesParticipant @charlesoates31738]

I hope it works out OK for you Tony. The rudder throw should be easy, a golden rule is to have the servo arm and tiller arm parallel when the rudder is straight and TX stick and trims central.

[Dave MilbournParticipant @davemilbourn48782]

Chas' advice is all good stuff. I would suggest a couple of alternatives for the future which would totally eliminate the possibility of this happening again:

1. Replace the motor with a 540LN from MFA. **LINK** Lower revving but higher torque. Also dump the SLA and fit a 7.2v NiMH pack. You may need a larger prop to compensate for the reduced motor speed but the motor will be quite happy up to about 50mm dia.

2. Leave things as they are BUT disable the BEC in the speed controller (see here **LINK** and run the receiver from a separate 4-cell AA NiMH pack.

Dave M

[Tony FentonParticipant @tonyfenton32936]

Thanks guys for the help! Just taken another look at the boat and sorted out the rudder throw, as you said Chas, getting the servo arm and tiller arm parallel when the rudder is straight did the trick – just a simple unscrew, move servo arm and rescued did the trick. I've now got equal movement to port and starboard.

I tried running the motor, checking voltage drop across the battery and discovered that the whole drive line moves too much and it it possible to press lightly down on the motor, causing the alignment to go out enough to almost stall the motor. I think I need to re-site the motor slightly to keep the universal joint as straight as possible and to eliminate as much movement as possible. The prop shaft definitely needs some fixing in place, which I'll do to achieve as near straight a line between motor and shaft as possible.

Dave – thanks for the suggestions re: motor and having a separate power pack for the receiver. I did wonder about that when I initially set everything up. But as everything was totally new to me, I ended up taking the easiest and most simple route. Now I've learnt a bit I feel that I could introduce a separate receiver battery pack quite easily – thanks for link too about how to disable the ESC's BEC. I presume having a separate receiver battery will ease the load on the main battery as well as meaning I at least have rudder control at all times?

It was quite scary seeing the model across the canal and fearing that I would lose control and not be able to get it back – the thought of wading across wasn't very appealing! Perhaps a long boat hook may be a useful emergency rescue tool to have!

Otherwise, for a first outing on my first model build I was really pleased. The boat handled very similarly to the real thing too! From steering, response to rudder, taking a little to build up speed, etc. I was also able to move the stern out from the bank by putting the tiller hard over and giving a quick forward blast on the throttle. So I'm r rally pleased with the results. Once I get these tweaks done I'll have to take it back for another trial.

[Tony FentonParticipant @tonyfenton32936]

Here she is at last night's launch and maiden voyage on the Worcester & Birmingham canal at Selly Oak.

[Malcolm FraryParticipant @malcolmfrary95515]

Looking at what specs for the motor are available I am left uncertain – some claim a gearbox on it without specifying a ratio, some don't, but the odd bit of advertising that looks believable says that MFA 719RE540/1 is a 5 pole, but high revving motor. This could have been making it work harder than it really should with resultant increased current. A narrowboat is not a high revving environment.

While the ESC is probably easily capable of handling the increased current, it will drain the battery faster and highlight any weaknesses by causing the voltage to vary downwards. If this echoes through the BEC, it might cause the receiver to cut out and have a bit of a think before responding again.

[Dave MilbournParticipant @davemilbourn48782]

The 540LN is actually a 5-pole motor which spins at half the speed of a 540/1 on the same voltage. I would not have fitted a fast-revving motor like the 540/1 into a narrow-boat model but, as Tony says, he knew no better because of his inexperience.

A separate receiver battery will only be loaded by the receiver's own circuitry ( a few milliamps) and the rudder servo motor (again, a fraction of an amp) so it will last a long time – especially if you buy a new one of about 2600maH! That means that the main battery is supplying only the motor and any drop in its voltage will have absolutely no effect on the receiver or rudder servo. Because the 540LN draws only about half the current of the 540/1 everything should last a lot longer – indeed, if you buy a 4600maH or even 5000maH main battery you'll be falling asleep before the model even slows down a little!

Just a plug for 'the old firm' – these guys can supply suitable NiMH battery packs like this one **LINK** but I think you may have to go to MFA direct for the motor. Both are easy to deal with although I'd telephone MFA if I were you.

BTW Malcolm – MFA's website describes the 540/1 as a 3-pole motor.

Dave M

Edited By Dave Milbourn on 14/05/2016 09:48:32

[Malcolm FraryParticipant @malcolmfrary95515]

Posted by Dave Milbourn on 14/05/2016 09:47:02:

BTW Malcolm – MFA's website describes the 540/1 as a 3-pole motor.

Dave M

Edited By Dave Milbourn on 14/05/2016 09:48:32

I searched for the motor mentioned in the OP, and got this – http://cpc.farnell.com/1/1/123932-mfa-719re540-1-motor-4-5-15v-450ma-5-pole.html – as the top link. I used to have a good opinion of Farnell and CPC as regards product information, but it would appear that they are just as fallible as anybody else.

Agreed a 5 pole jobbie will be much more appropriate in a narrowboat. At least the same physical configuration should make for a simple swap.

[Tony FentonParticipant @tonyfenton32936]

Looking at the 540/1 and 540ln I see from the specs that the stall current of the 540ln is just over 28A at 6V ! I'm presuming this means that if the motor stalls then it will draw this much current – too much for the Viper 15A? Is this a possibility? In which case perhaps the 540ln wouldn't be ideal?

I also wondered whether to change the 6V battery for a 12V one, but I guess this would mean more rpm from the motor, which is something I don't really need?

I like the sound of a 5 pole motor, but a little afraid that the 540ln could potentially kill the ESC?

[Dave MilbournParticipant @davemilbourn48782]

Tony

The stall current of the 540/1 will exceed the LN. The likelihood of having a fully stalled motor when sailing is very small – it's never happened to me. If it bothers you then fit a fuse between the ESC and the motor. In the case of the LN I would fit a 10A auto-blade fuse. It doesn't matter which motor wire it goes into. These are very popular for the task; they have a diode which glows green when the motor goes in one direction and red for the opposite! **LINK**

Dave M

[Malcolm FraryParticipant @malcolmfrary95515]

A 5 pole motor wound for torque rather than speed is highly unlikely to kill an ESC that has been handling a motor wound for speed and lived through it.

Apart from the motor being forced to work outside its comfort zone, I suspect that the root cause of the problem is with the power supply. If one of the cells in the battery is not just as healthy as it should be, it will discharge early and cause a sudden volt drop under load which could give the symptoms described. Having a separate RX supply will allow the radio and steering to continue working.

[Tony FentonParticipant @tonyfenton32936]

Hi guys – just got my 540ln motor from MFA, but then of course realised that I need to get a coupling insert for it! As the motor shaft is quoted as being 3mm, will a 3mm coupling insert be ok or do I need the 3.2mm one?

I had hoped to remove the coupling from the old 540/1 motor, but instead of being screwed on it seems to have been welded on and there is no screw in the little screw hole. Maybe Riverside Models who supplied the kit prepared the motor to make it easier to build the kit? There was also a capacitor and wires pre-soldered to the motor terminals.

[Dave MilbournParticipant @davemilbourn48782]

Tony

I have just been out to the Man Cave and measured the shafts of both types. They are identical @ 3.16mm diameter so you really need the 3.2mm insert.

The capacitors are RFI suppressors and not strictly necessary if you using 2G4 radio, but you will need them if you are using either 40mhZ or 27mhZ. Component Shop sell a full kit of three for a quid.

Dave M

Edited By Dave Milbourn on 21/05/2016 12:22:13

[Tony FentonParticipant @tonyfenton32936]

Hi Dave – that's great – many thanks again for your help. I'm going to get the blade fuse holder you posted a link to as well to tidy everything up, at the moment I've got an in-line fuse holder, the type with a spring and cartridge fuse, so not really ideal for higher currents.

[Tony FentonParticipant @tonyfenton32936]

Sorry – another quick question! I am thinking of replacing the 6v battery with a 12v one, just to be sure of being above the cutoff voltage and also to get a few more rpm from the new motor. If I did this, would I need to recalibrate the ESC? In fact, with the new motor should I recalibrate anyway?

[Malcolm FraryParticipant @malcolmfrary95515]

The ESC will be calibrated to the transmitter. Since this remains the same, no change. Within its limits, the ESC doesn't care about the main supply voltage. Off is still off, full on is still full on, all points in between that were proportional will still be, as should the neutral position.

Provided the motor can stand the "few extra volts" (and really, double is not a few) and the ESC can stand the increased amp draw everything will be much the same except for the motor going a lot quicker. Unless the existing batter and/or its wiring is a dud or otherwise not up to the job, there should be no worries about the cutoff voltage with 6 volts. Of course, the same weight of 12 volt battery will only have half the capacity of the 6 volt one, and will only be comfortable delivering half the current, when the demand will be potentially twice that for 6 volts.

[Dave MilbournParticipant @davemilbourn48782]

Tony

The 540LN is exactly half the speed of the 540/1 for the same voltage, but I think that the 540/1 is far too fast for the model. My suggestion was that you increase the size of the prop and use a 7.2v battery. Replacing the 6v battery with a 12v one will totally negate the installation of the new motor. Do also bear in mind that there is a much greater choice of batteries than just grey lead bricks e.g. you can purchase NiMH packs in incremental voltages of 1.2v.

DM

[Tony FentonParticipant @tonyfenton32936]

Malcolm – thanks for the advice on the ESC calibration, I had suspected this to be the case, but couldn't confirm this. It sounds like going to 12v is not sensible, especially as the idea is to replace the fast running 540/1 with the slower 540ln.

Dave, thanks again for the advice. The 7.2v NiMh pack sounds a good idea. The current prop is 40mm, so I guess I could upgrade this to 50mm.

[Dave MilbournParticipant @davemilbourn48782]

Tony

A 40mm prop is a bit too big for a 540/1 anyway – maybe that's why your battery was dropping down below 6.0v. A fine pitch plastic 45mm 3-blade prop would be a good place to start experimenting with the size. **LINK**

On reflection it might be a good idea if you were to buy a seven cell pack (8.4v) to give you what is often called "a bit in reserve". The beauty of electronic speed controllers is that you don't have to use full-throttle all the time.

Dave M

Edited By Dave Milbourn on 22/05/2016 10:36:55

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