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[chas]

Hi all, I'm trying to help a club member with his esc  problem, at least, I think it's the esc.
His set up is
Planet radio system
2 Graupner speed 600s
Tornado 50 amp esc
7.2 battery pack

The problem is that we switch on, wait for binding. Rudder works fine
Run the motors, works for a few seconds and cuts out, usualy after going from forward to reverse, then they stay dead until we switch off then on again.
 We checked the receiver by swaping chanels, no diference.
Checked the batteries, fully carged and checked on load.
Checked the shafts, 1 was very tight, aha I thought, drawing too many amps and cutting out. Disconected both motors from the shafts, tried again, same problem.
I did find some poorly solded joins to the motors, he is re doing those before we try again.
The rudder keeps working throuout, so not a radio problem.
What am I missing? All help apreciated.
Chas

[Plastic - RIP]

You're probably almost shorting the power to 0v when you suddenly reverse the motors. The current draw will be very high so the voltage will collapse (like car headlights dimming when you crank the engine). This may confuse the receiver.

You could try to reduce the resistance between battery and motors with thicker wires, separate wires to each motor (not jumpered across from one motor to the other), better quality connectors, soldered joints rather than crimps, better motor suppression caps etc. etc.

If you're a bit techy, you could put a capacitor on the line from from the ESC to the receiver to smooth out any sudden power drops.

[chas]

Hi plastic, thanks for the ideas. He is using good heavy gauge cable, so that should be ok. The motors are wired correctly. I've never used an in line capacitor for smoothing, what do you suggest that can cope with a high current?
 Wouldn't the esc be designed to cope with going directly from forward to reverse? A max of 50 amps is quoted so would guess thay a momentory peak rating is much higher.

[sparkey]

Tight shaft may be your problem,also you didn't state size of battery,I don't think it is the ESC as I have used and abused this type over the years with no problems even surviving a sinking, if the battery is too small to take current drain the voltage will drop to nil and the ESC will stop working,sort out tight shaft and try with battery of a bigger capacity try this and let know how you get on,Ray.

[Plastic - RIP]

Do not use a smoothing capacitor between ESC and motors - the currents will be too high to smooth.

As mentioned above, your battery may not be man-enough to supply the required current so a more capable battery may help.

You also might want to look at the positioning of the receiver - if it's too close to the motors (and ESC) you may be suffering from the interference from the motors confusing everything.

[HMS Invisible]

Chas,I have seen plenty of this before.
It would take one hell of a NiMH battery. Switch to Lipo as a diagnostic. It will work.
If you are curious as to how low the voltage of a NimH battery can go then try using a Hobbyking HV 7.4v bar graph monitor. Compare with a Lipo
It won't sort poor low end control needed in a tug.

A low esr electrolytic is what plastic is saying and that helps when you have a high power rudder servo or 6v bec. It is a simply try-this-first remedy I have recommended in the past. The servo draw can sometimes tip receiver voltage below a threshold the whole combo over the edge into disarm. Compact 2.4GHz receivers are sometimes deficient in this respect where 2ch bec receivers have internal 330 uF capacitors.

[inertia]

Two big amp-hungry Speed 600 motors and BEC for everything else from one little battery pack? Trouble.
I would strongly recommend using one ESC and one battery pack for each of these motors i.e. two of everything. I'd also disable the BEC in both speed controllers and run the receiver from a separate 4-cell pack. That way the risk of brown-out* is minimised.
I would only ever run two motors in parallel from the same ESC if they were low current affairs, exactly like Speed 600s aren't. If your mate wants a total cure then he'll need to spend some more money. Mike's ESCs are very good VFM, by the way!

(*Brown-out is where the receiver/ESC voltage dips momentarily a long way below its minimum operating level and the unit responds as if it's simply been turned off. This can result in the logic circuits in the receiver and ESC being left in an incorrect state when the voltage increases again).

[chas]

Thanks chaps, some good ideas there. His battery pack is rather small, previously he had tried a 6 v sla which I was suspicious of in this set up.

 To check it out I will rig the esc to 1 motor only, free running and put my 7.2 v 3.3 ah nimh on it. Does that make sense?
I'll report back next week.
 I've seen the spec on the 600s and got the impresion they draw a lot of amps.
His model is a Tyne lifeboat, around 28 inches long. If as I suspect he will have to change the motors what would anyone recomend.

Chas.

[inertia]

Two of these would be plenty on 7.2v and something like 30mm 3-blade props. http://mfacomodrills.com/motors/540-1.html
He might even get away comfortable with just one ESC, but do use a separate battery for the receiver.
DM

[HMS Invisible]

Dave, thanks for the kind remarks.

Has anyone seen an earlier example of this in a first post?
* thorough description of the installation
* told when/how the problem shows up (esc disarms on reversing the motor)
* reasoned guesses to the problem's cause.

It certainly prevented the usual wide-of-the-mark suggestions.

Chas can you replicate the disarm with the rudder servo unplugged?
...just for the hell of it.

[Netleyned]

I think Chas is an experienced hand at this.
Normally the questions come from a guy who
has bought a heap of eBay rubbish and doesn't
have a clue.
Its good to see a couple of professional technocrats
helping out
Good on you guys

Ned

[inertia]

You're welcome. Chas - please let us know the eventual outcome of all your efforts.
Dave M

[chas]

Thank's for the kind remarks. I've no electronic training but I built my first radio effected model in the 1960s when problems were the norm. I try to think a problem through but get a bit stretched sometimes.
 I will be seeing the model again next week and will check everything suggested, including unpluging the rudder servo.
 I am willing to bet he will end up changing the motors as suggested, use seperate rx batteries then things will be ok.
Chas.