Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: lozvik on July 24, 2009, 10:11:33 am

Title: Do I need capacitors on motor?
Post by: lozvik on July 24, 2009, 10:11:33 am
I have twin 540 motors running on 6v using a single mtroniks viper marine 25 esc, so far I have not used caps on the motors, however it does mention there use in the esc instructions, so what are they for, and do I actually need them?
Title: Re: Do I need capacitors on motor?
Post by: DickyD on July 24, 2009, 10:53:08 am
Yes you do need them.

Non technically they cut out interference from the motor affecting your radio gear.
Title: Re: Do I need capacitors on motor?
Post by: barriew on July 24, 2009, 11:01:47 am
I have twin 540 motors running on 6v using a single mtroniks viper marine 25 esc, so far I have not used caps on the motors, however it does mention there use in the esc instructions, so what are they for, and do I actually need them?


If you are on 27 or 40Mhz you definitely need them. If you are on 2.4 Ghz, then they are advised but not essential as the radio is less susceptible to interference from motor "noise".

Barrie
Title: Re: Do I need capacitors on motor?
Post by: lozvik on July 24, 2009, 11:07:02 am
cheers guys ill get some, I wondered why my boat stuttered after only 40yds
Title: Re: Do I need capacitors on motor?
Post by: andrewh on July 24, 2009, 11:45:11 am
Lozvik

Yes, that would be it :}

The commutator of the motor is a rotating, sparky switch and that is a huge and horrible broad-band spark transmitter.  The capacitors absorb and damp most of the radio-frequency rubbish

The full fit of capacitors is 3 - one from each brush to the motor case, and one between the brushes.

You said a 540 motor - which means NOT a Graupner "speed" motor. 
Most (if not all) of the "Speed" motors have a capacitor between the brushes when you buy them, and this does a pretty good job.

andrew
Title: Re: Do I need capacitors on motor?
Post by: lozvik on July 24, 2009, 12:21:55 pm
hi mate, my motors are just the bog standard 6.99 jobs and dont have any capacitors fitted at all.  At present im having to have every inch of reciever antenna out of the boat to avoid interference, once ive fitted the caps will it mean ill be able to use the nomal spring loaded aerial that connects from inside boat or is that not the case?
Title: Re: Do I need capacitors on motor?
Post by: andrewh on July 24, 2009, 12:34:19 pm
More than likley, Lozvik

The symptoms you describe are exactly what you would expect from an unsurpressed motor - fit the caps an see the improvement

It's not relevant since you have the motors, but one motor supplier is very lyrical about his motors with a complete metal case - no ventilation holes - and he maintains that the case acts as a faraday cage and keeps the mess inside.  Physics suggests that he should be right.  Physics would also suggest that his motors would rely on a smooth golden case for cooling -  so you might lose on the roundabouts what you gain on the swings :}
andrew
Title: Re: Do I need capacitors on motor?
Post by: kiwimodeller on July 25, 2009, 12:33:08 pm
Sometimes it helps to have a small resistor in series with each capacitor. For a very good article on R F suppression have a look at the website of Model Solutions of Canada (listed in the Mayhem Traders Directory)
Found their website for you, it is http://www.modelsolutions.ca/. Their tech article explains why we get interference and all sorts of tips for preventing it. Hope this helps, Ian.
Title: Re: Do I need capacitors on motor?
Post by: lozvik on July 25, 2009, 01:08:36 pm
thanks Ian and for all yr help guys, what a great forum for information  :-))
Title: Re: Do I need capacitors on motor?
Post by: Ghost in the shell on July 25, 2009, 01:28:53 pm
ever driven down the road, listenning to a Long wave or Medium wave radio station, and gone under power lines that cross the road and picked up nothing but crackling.  or heard crackles on the radio during a thunderstorm.  That is what is happnin to the radio in the boat.  the rx is like your car radio, sparking of the motor, well thats the lightning.

same basic hapenning, only on a smaller scale
Title: Re: Do I need capacitors on motor?
Post by: lozvik on July 25, 2009, 02:28:44 pm
ever driven down the road, listenning to a Long wave or Medium wave radio station, and gone under power lines that cross the road and picked up nothing but crackling.  or heard crackles on the radio during a thunderstorm.  That is what is happnin to the radio in the boat.  the rx is like your car radio, sparking of the motor, well thats the lightning.

same basic hapenning, only on a smaller scale

Thanks I understand now, cheers
Title: Re: Do I need capacitors on motor?
Post by: Peter Fitness on July 25, 2009, 11:24:46 pm
If you are on 27 or 40Mhz you definitely need them.

We use 29 and 36 Mhz in Australia, and they're needed for those frequencies, too.

Peter.
Title: Re: Do I need capacitors on motor?
Post by: barriew on July 26, 2009, 09:46:02 am
Peter,

I should have said anything other than 2.4Ghz - but I fit them on boats using that anyway {-)

Barrie
Title: Re: Do I need capacitors on motor?
Post by: Bunkerbarge on August 19, 2009, 08:20:28 am
Does anyone know where the relevent capacitors can be purchased from?
Title: Re: Do I need capacitors on motor?
Post by: Peterm on August 19, 2009, 08:36:09 am
I buy mine in sets from Westbourne Models.   Pete
Title: Re: Do I need capacitors on motor?
Post by: rsm on August 19, 2009, 08:44:02 am
I buy mine from Maplin electronics, they only cost a few pence but you need to know what you want.

Roger.
Title: Re: Do I need capacitors on motor?
Post by: DickyD on August 19, 2009, 08:53:43 am
ACTion sell them. cost 1.00
Title: Re: Do I need capacitors on motor?
Post by: Bunkerbarge on August 19, 2009, 08:56:15 am
Thanks Guys.
Title: Re: Do I need capacitors on motor?
Post by: portside II on August 19, 2009, 09:32:21 am
do different motors require cap's of different values , if so is there a scale/chart that would give us an idea.
daz
Title: Re: Do I need capacitors on motor?
Post by: Martin [Admin] on August 19, 2009, 10:19:57 am

I know I'll be shot down in flames for this but -
I usually use actions kits as they are such good value (damm, I forgot to by some at Llanberis!)
but last time I ran out, I just took 3 disk capacitors of an old circuit board / computer power supply
I had lying around and fitted those without problem....

http://modelsolutions.ca/articles/DavidsOriginalArticles/RFIArticleMarch2006.pdf
http://modelsolutions.ca/articles/RadioControlModelerSummer2006/RCBoatModelerSummer2006.pdf
http://modelsolutions.ca/articles/SCRDecember2007/SCRDecember2007.pdf
Title: Re: Do I need capacitors on motor?
Post by: DickyD on August 19, 2009, 11:29:32 am
Sorry I agree with you Martin the ACTion ones work for me.  :-))
Title: Re: Do I need capacitors on motor?
Post by: Ghost in the shell on August 19, 2009, 11:33:04 am
portside. i don't think so.
Title: Re: Do I need capacitors on motor?
Post by: portside II on August 19, 2009, 11:33:18 pm
ok it was just a thought as one motor i have was causing interference with the radio rx ,i have now fitted 1 cap across the terminals and 2 , from the can to each terminal. now with the tx ant down the radio is ok at range.
a happy daz