Trouble in't engineroom

[GreeboTheCat]

Hi PDs,
My Glasgow is beginning to look like a boat now with all the gubbins installed and the decks in place but I've struck a real problem with the propulsion system. I'm getting a massive amount of sparking from the motor brushes. I've attached a simple diagram of the setup and as you will see I'm running 2 x MFA 919D (100:1) motors from a pair of identical Mtronics ESCs (15 amp), fed from an Action Electronics Distribution Board powered by a 12V 7 Amp/Hr Gel Cell. The distribution board powers the Rx directly so I don't need BEC from the ESCs. (both red wires disconnected).

If I only switch one ESC on, everything works ok at low revs (forwards and reverse) but as I open the throttle the motor brushes start sparking and the motor is very intermittent. With two ESC running the problem is much worse.

I have tried running the motors direct from the battery (no ESC) and both motors run perfectly then which means they are OK so the problem is with RX/ESC/Dist board. I have tried running the ESC direct from the battery (eliminating the dist board with BEC connected via the ESC) Problem still there. I've tried routing the servo cables well away from the motor power lines but to no avail.

Ideas? 

[Tug--Kenny]

I would suggest that your ESC's are damaged , or Underrated. I had a stuttering motor once when the throttle was opened up, and changed the ESC   to a larger amperage one. Mind you, the original one went to bottom of the lake at full speed.

You could run a more analytical test to isolate the problem.

1  Run a different motor on on ESC (not an MFA type)
2. Run original motor on 20 amp ESC
3..Fit capacitors across motor terminals

Try this and see how you get on.

Ken

[Eddy Matthews]

Motors create RF (radio frequency) noise that can interfere with your radio signal. The best way to keep RF problems at a minimum is to solder a .01uF (micro-farad) capacitor onto each motor lead then onto the casing of the motor. To further dampen RF noise, solder a .047uF capacitor across the two motor leads. The best way to get the capacitor leads to adhere to the motor casing is to rough up the casing a little with some wet and dry and put some flux on it before soldering.

Most decent electrical component stores keep capacitors, Maplins, Tandy etc etc.... And they are ony about 10p-12p (UK) each.

Just make sure the voltage rating is at least 250% higher than the voltage you'll be using. I generally use 500v myself, but anything ABOVE that is fine...

Eddy

[GreeboTheCat]

The motors do have caps soldered across the terminals (as supplied) but I  didn't bother to check what value they were, just assumed they would be the right ones.
While I was pondering the problem today, it did occur to me that during all my testing, I did not have the TX aerial extended so RF would be a bit low or am I clutching at straws now?Having just paid 40 quid for a pair of ESCs, I'm dreading the thought of having to fork out more than that for a couple of 20 amp ones. Can't send the old ones back as I replaced all the bullet connectors with proper gold-plated ones.

[oldie]

Ken has the right idea, test by substitution, one component unit at a time.   Oldie

[Eddy Matthews]

Remember to keep the Rx and aerial lead AWAY from any power leads and the motors/speed controllers!

I generally try to run power leads down one side of the model, and the aerial down the other side....

Keep the Tx 5 or 6 feet away from the model when testing, having it too close can swamp the Rx and it gets confused causing glitching as described.

I've used the MFA motors many times and haven't come across too many problems with them.

Regards
Eddy