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[RobinStobbs]

My equipment is:
Viper Marine 25 driving a MFA (Como Drills) 919D motor from a 12 volt 'gel' battery. Radio gear is Hitec Ranger II on 26.995 MHz and linear distance from controller to receiver is about 180mm.

My problem is:
At full ahead the motor momentarily and intermittently cuts out for brief moments but at half ahead it does not do this.  On full astern there is also no problem.

Attempted cures:
The 919D motor comes with a capacitor (of no indicated capacitance) between + and - leads.  I tried adding a 100 uf capacitor to this - in parallel - with no success.  I then tried a 10 uf capacitor between + and casing and another between - and casing and then this again with the 100 uf capacitor between leads.  None of these combinations worked.  I have also tried shielding the receiver with aluminium foil.

Any suggestions on a cure?  Would braid screening/shielding around the servo leads help?  The antenna goes directly from receiver up through the aerial tube. Might there be an internal problem with the Marine 25 controller (This is brand new and not previously used on any other model)? 

I have Viper controllers in three other boats, one of which is a large tugboat with twin motor setup and two controllers which are only about 80-100mm from the radio receiver.  This is the first time I am using the 919D motor and initially suspecting there might be a problem with the motor changed my setup with an identical unit - both had this cutout problem on full ahead setting.

Can somebody please come up with a suggestion before I turn said model into an artificial reef.  

Rob

[FullLeatherJacket]

Rob
The MFA motors are notoriously "noisy", both mechanically and electrically. Light oil usually fixes the former while I haven't handled one yet that couldn't be tamed electrically with the 3-capacitor trick. I very much doubt if the motor is putting out enough power to trigger either the thermal or current overload in the ESC, and even a flattened 12v supply should continue to operate the regulator inside the ESC, so there's every probability that there is a problem with the ESC's internals.
I have to say that I have handled a 25A MTroniks ESC and, unlike the 15A Viper (which is actually quite a nice little piece of kit), it was an absolute pig. The motor "hunted" at full revs and there was very little top-end speed control. This happened on several different types of motor, including the geared Torpedo/919D.The customer ended up selling all three such units and re-equipping.
It may be that the one I tested and the one you have came from a faulty batch; usually when a post criticising Product XYZ appears on here there are howls of protest from happy users! However, Milbourn's Maxim #12 says "If at first you don't succeed then try something else - no need to be a damned fool".
Suit yourself.
FLJ

[sheerline]

Hi Rob, I suggest you ditch the electrolytics and do the following:
Fit a 0.1 mFd disc ceramic capacitor directly across the motor terminals, then two more, one from each motor terminal to the motor casing. You could also take a wire from the motor casing back to the battery negative terminal to earth this item. This should cure it but if not, the motor itself may be dirty and require a good clean with a non oily de-greasing electrical cleaning solvent. Ensure it is the non flammable type and spray it directly onto the commutator whilst running the motor flat out. You will probably find a load of black carbon gunge runs from the motor whilst at the same time, the motor rpm should increase considerably. Dirty motors are a cause of a lot of radio interference especially at 27mHz.
You could also check for metal to metal electrical noise from control rods, prop shaft or any other metal to metal joints which are not electrically bonded together. When they rattle or move around together they create static which is picked up by the receiver and the 27mHz which you are using is more susceptible to this kind of interference than the higher frequency 40mHz gear which is generally in use . Try soldering a wire between the metal components to electriclly short them together.
Chris

[RobinStobbs]

Thank you FLJ and Chris.   

Mtroniks response was "It sounds very much like the motor is pulling too much current for your battery at full forwards speed.  The way to cure this is to fit a large capacitor across the battery input wires to the speed controller.  You will need to purchase a 10,000uF 16V capacitor and solder it across the battery wires on the speed controller (as close the controller as you can) you will need to remove some of the wire insulation to allow soldering to the wires."

I can sure try this but I can't see that a 919D motor could pull so much from a fully-charged 7.5AH battery that there is a significant voltage drop to the ESC which, in any case is powered from the Rx battery pack and not the motor battery! (Rx batteries are freshly-charged Uniross 20000mAH pencells).  I have checked for radio noise between motor and prop shaft - coupling is the fibre-filled variety so motor and shaft are insulated from each other. 

As for the 919 motor being noisy - sure is - wish I could find more of these vintage models of which I have three and they continue to purr sweetly after 30 years of intermittent use!

Ciao, Rob

[FullLeatherJacket]

Eyewash!
That's supposed to be a 25A ESC. I use a 919D regularly as a test motor for our own stuff and there's no way they draw that amount of current. I reckon about 1.3A no-load, rising to maybe 5A with a pretty hefty prop in the 'oggin. If the voltage across the battery drops by as much as 0.5v with the motor running full-chat then I'd be surprised.
If Chris's values don't work (and they should....) then up the centre cap to 0.22uF ceramic. If you still get problems then don't spend any more time on it. I'd recommend you stick the offending ESC on E-Bay and buy a proper one. Modesty forbids me suggesting any particular type...... 
FLJ

[RobinStobbs]

My feeling precisely FLJ.  I have run windscreen wiper motors off batteries like that without any problem - in fact I have run an experimental  62" ASRL  off two similar batteries (in parallel) with an outboard starter motor - the performance was exciting but in those days we never had sophisticated electronic speed controllers and it was run with a Schumacher type switch - on and off!    Just as soon as I can get down to Port Elizabeth and purchase those capacitors (we don't have the efficient online purchasing setup you do!) I'll give it a shot.  Thanks again. Rob

[787Eng]

(Rx batteries are freshly-charged Uniross 20000mAH pencells). 

You have removed the Red wire from the ESC receiver plug?
As I see you are supplying external receiver power and the Speed controler you are using has a built in BEC .

Mark

[RobinStobbs]

Oh yes, Mark!  One of the first things I do with all the Mtroniks ESCs I have!!
R

[malcolmfrary]

If the red is disconnected, the RX and servos are running on the RX supply, the internals of the ESC are running on its internal BEC. 
I have had the odd mtronics respond badly to "full throttle plus a bit", when the trim tab has been nudged.  The symptom was a full stop, probably because the program logic didn't like an over-length pulse.  Thats just an empirical observation, and it wasn't a 25 amp version.

[victorian]

I have a very similar problem with a couple of Viper 15's running car heater motors. The motors cut momentarily which originally I put down to the tooth belt drives skipping or the pulleys slipping. It was only after a lot of head scratching that i realised that it's not mechanical at all, but the motor current tripping out.

I've never completely cured it but I found by trial and error that connecting both BEC's to the receiver  (I know, only connect one!) the problem is minimised. I've tried a seperate rx battery but that actually makes it worse. Radio is 2.4 Ghz Turborix, there are plenty of caps and the problem is nothing to do with RF interference.

Mtroniks were very non-commital about it and I'm convinced it's a design problem in the ESC - why else would use / non use of the BEC make a difference? (I've tried all the obvious ground wires, earthing motor frames, etc., with no effect). The ESC simply trips momentarily at different power settings despite motor currents being less than 1.5A. It's much more prone to do it in one direction than the other. True, impulsive currents from the (brand new) motors due to commutator design or something might be the actual cause, but why does connecting the BEC make a difference?