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[pettyofficernick]

Hi there, I am trying to sort out an interference problem. The boat in question is a Graupner Weisel, it has 3 motors, the two outboard ones are the same, with an odd one in the center, all controlled by 1 bob's board, running on a 6v SLA and 27 meg radio. as soon as everything is switched on the bob's board servo goes crazy and can only be stopped by un plugging the battery. The Tx is Sanwa and the Rx is an ACOMS one, could this be the problem or is it caused by interference? I note that there are no suppressors fitted to any of the motors, will any capacitors do the job, as I have a box of assorted printed circuit type mounting ones, and I have been told by an 'expert' that any type of capacitor of any value will work.
Many thanks,
Nick

[Andyn]

bob's board

I think I found the source of your problem.

 

[dodgy geezer]

and 27 meg radio.

And I think I've found the other one...

27Mhz is very susceptible to radio frequency interference. This may come:

• through the air from a spark and into the Rx aerial
• from the motor power leads and the Bob's board via the power leads to the Rx
• through the air from unbonded metal-to-metal contact anywhere  on the boat

Easiest thing to do is go for a cheap 2.4Ghz radio system at £25. That doesn't suffer from typical motor interference.

If you want to chase interference:

1 - run with only one motor - each in turn - to see if one particular one is causing most problems
2 - fit .01mf capacitors - 1 across motor brushes and 1 from each brush to ground
3 - fit an inductor on each power line
4 - bond any metal-to-metal connection, or replace with plastic...

[Subculture]

I'd run with suggestion Number 2 first, that may be enough to cure your problems, also make sure power wiring is kept well away from the aerial.

I'm amazed you can power three motors off a single Bob's board, the things used to struggle with one motor on anything more than modest power.

[malcolmfrary]

It could be any or all of the motors, they all need suppressing.  The value of capacitor given by DG is OK, but any value between that * 10 and / 10 will be OK, the really important thing is to get the right type.  Fortunately, the cheapest type (disc ceramic) is ideal.  Connecting caps around the Bobs board terminals will probably help, as will cleaning and adjusting the wiper tensions.  Then there is the minor mater of hoping that the motors, together as a group, match the board.
Normally, with airborne interference, I would expect the rudder servo to act up most, since it is normally channel 1, which interference normally affects most.  It could be the motor/bobs board combination is creating and injecting interference into the power line powering the RX and servos.  This would upset a 2.4GHz set just as much.

[Subculture]

I'd seriously advise retiring the bob's board. A decent ESC of reasonable amperage will handle three scale motors. I use these with brushed motors-

http://www.microgyros.com

Brilliant controllers. Very wide voltage range, a true current handling capability and a decent BEC.

[Martin (Admin)]

" Fit .01mf capacitors - 1 across motor brushes and 1 from each brush to ground".... and on the Bobs board!

[TheLongBuild]

I'd run with suggestion Number 2 first, that may be enough to cure your problems, also make sure power wiring is kept well away from the aerial.

I'm amazed you can power three motors off a single Bob's board, the things used to struggle with one motor on anything more than modest power.

Interesting, I have run a speed boat on a 7.2 battery, admittedly it got warm  but worked fine

[malcolmfrary]

Interesting, I have run a speed boat on a 7.2 battery, admittedly it got warm  but worked fine

Any resistance type controller needs close matching to the motor that it is controlling to get any reasonable control.  With 3 motors of two different types any sort of matching is going to be pure luck.
Late afterthought -
As a last line of defense for a Bobs board stystem, I would consider fitting a 8.2 volt zener diode (maplin code  N45BZ ) across the bobs board power connector. to eliminate any transient spikes.  8.2 volts because it it the lowest voltage available that is more than the highest voltage that a freshly charged 6 volt SLA is likely to offer.
In retrospect, the motors do need suppressing, but the board is best retired or passed to a single motor system, and replaced by a modern ESC.