2012.02.15, 03:09 PM
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#16
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Moderator
Join Date: Dec 2004
Location: Los Angeles (Pasadena), CA, USA
Posts: 2,809
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Ah, I see what you mean. I'm inclined to say that a bad motor is a bad motor, though -- mugler had an F1 car with a serious steering glitch even though there were caps properly soldered onto the motor. I swapped out that faulty 70t with a new 80t (no caps) and the glitching instantly went away. I imagine this could be a current drain issue so we're going to try a 50t (no caps) next outing and see if the glitching comes back. If it doesn't, then we have one control data point indicating that a crappy motor is going to cause glitching whether you put caps on it or not. And that just makes this question more difficult to answer, lol...
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2012.02.15, 03:33 PM
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#17
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Registered User
Join Date: Dec 2011
Posts: 111
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Quote:
Originally Posted by color01
Ah, I see what you mean. I'm inclined to say that a bad motor is a bad motor, though -- mugler had an F1 car with a serious steering glitch even though there were caps properly soldered onto the motor. I swapped out that faulty 70t with a new 80t (no caps) and the glitching instantly went away. I imagine this could be a current drain issue so we're going to try a 50t (no caps) next outing and see if the glitching comes back. If it doesn't, then we have one control data point indicating that a crappy motor is going to cause glitching whether you put caps on it or not. And that just makes this question more difficult to answer, lol...
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Unless the caps on that motor were faulty...
Try without any caps on that glitching motor. Then try with a new set of caps for a better theory.
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2015.03.03, 05:55 PM
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#18
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Registered User
Join Date: Feb 2015
Location: Hustisford, WI
Posts: 17
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Just wondering if any conclusions have been made in regards to NOT needing to solder caps on the motors for 2.4ghz cars.
I have a Mini Z optima and purchased a PNWC 70 Turn Stock Motor to use with it, and noticed that there were no caps included.
I do not want to order caps separately and solder them on if they are not necessary with the ASF cars.
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2015.03.03, 06:33 PM
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#19
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epic procrastinator
Join Date: Jul 2006
Location: Whistler, B.C.
Posts: 2,216
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Ive found no need for caps. All my ASF cars run the same whether thay have a motor with caps or without.
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2015.03.04, 02:12 PM
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#20
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Registered User
Join Date: Oct 2007
Posts: 336
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Hi!
I used to personnaly think the caps weren't useful anymore since the age of 2.4Ghz but two years ago I had to change my mind.
We were running kyosho stock motors in the stock category and i had a really annoying glitch problem on my chassis. The car was running perfectly fine but sometimes, all of a sudden, I had a big glitch that sent my steering all way left. Making the car pretty unpredictable to drive. I tried many things, re solder other etc until someone told me to resolder the caps on the motor. Once done, I never had the problem again.
So for me, YES, the caps are still necessary on a motor despite 2.4Ghz.
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2015.03.04, 02:29 PM
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#21
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Registered User
Join Date: Jul 2012
Location: NJ
Posts: 582
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It really depends on the motor and the situation. For me personally I have never used capacitors.
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2015.03.12, 09:42 PM
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#22
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Registered User
Join Date: Jan 2003
Posts: 514
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I would vote no. I am using two pn racing 70t motors in a 1/35th rc KV-2 tank with no caps and no interference issues. I am using spektrum radio gear, not the perfex stuff in a mini-z, but on the other hand one of the two antennas on my ar6110e is less than an inch from the brushes of one of those motors. Both motots are right next to each other, too, pretty cramped vehicle.
I would wholeheartedly say that, barring unusual circumstances or part failure, 2.4ghz radios just dont care about the interference produced by a brushed motor. If they, as a rule, did, my tank would have problems with it.
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Last edited by 379; 2015.03.12 at 09:44 PM.
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2015.03.13, 04:24 AM
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#23
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Moderator
Join Date: Dec 2003
Location: Stafford, Va
Posts: 6,064
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Without schematics I cant say positively that caps are built into the board but from the looks there is more small stuff added than what you see on the AM stuff.
The 2.4 boards are just not as susceptible as the older AM boards.
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2015.03.13, 06:46 AM
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#24
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Registered User
Join Date: Dec 2014
Posts: 215
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Quote:
Originally Posted by byebye
Without schematics I cant say positively that caps are built into the board but from the looks there is more small stuff added than what you see on the AM stuff.
The 2.4 boards are just not as susceptible as the older AM boards.
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The caps on the motor have nothing to do with the frequency of the radio. They are there to absorb some of the inductive spike that occurs when your motor switches poles on the commutator. One thing you should notice with the addition of the caps is that the blue plasma arc between the brushes and the commutator should not be as intense. The stock motor on my MR-03S went one step further and put a MOV (metal oxide varactor) between the elecs and the motor. This is to absorb even more of that energy, so that the motor is harmless to the FET's.
The hotter the motor you run, and the higher current it draws, the more dramatic the arcing is and it becomes more possible for your FET's to take damage. Especially when doing a quick forward to reverse, or vice versa. That creates the biggest arcs possible.
As far as caps on the 'board', yes there are several of them. The most obvious are the big yellow/orange ones on the top side of the board.
Those are there to help stabilize voltage on the board, so that the digital components aren't affected by noise.
There's also caps clustered around the square shaped receiver IC, for filtering the radio transmission. All three of those parts on the bottom left of the board are capacitors. All the little 'brownish' and 'greyish' looking parts are capacitors. The little black ones(two legged, not 3 legged) are resistors. There's a couple inductors in there too, which you couldn't tell they were without using a meter. Inductors are shorts to DC current. Caps will give you a varied resistance reading as they charge or discharge when you measure them, and resistors should give you a static resistance reading when you measure them.
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2015.03.13, 08:08 AM
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#25
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Registered User
Join Date: Dec 2014
Posts: 215
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The black three-legged parts are transistors (NPN bipolar junction transistors to be specific)
The large round part, semi-covered in white goo, is a relatively large inductor for stabilizing the current output of the board's power conditioning stage. Your battery voltage varies quite a bit during run-time, and this little power station assures that the voltages seen by the digital components is the same all the way up until your cells start to die out, so that your elecs stay responsive throughout all voltage variations.
The little silver cylindrical part is a crystal oscillator for the receiver IC's clock and radio receiver demodulation.
So, to answer the question as to whether or not the motor capacitors are necessary with the 2.4GHz cars...
The answer does not involve a relationship between the radio frequency and the motor capacitors. If you guys notice any differences in how robust the 'newer' elecs are compared to older models, then this difference is more than likely embedded in the FET's used, which house a protective diode in them for protecting the FET from the previously mentioned inductive voltage spikes produced by the motor.
Are the caps necessary? In my experience, so far, no... I've ran a 32T with a 14T pinion and Li-Fe's, and although the arcing is substantial, my FET's are still running like a champ. I can't speak for the long run though, however I can't think of a more harsh set-up from my FET's perspective. Of course I could simply 'stall' the motor, but this does not produce arcing(peak voltage condition), it produces a peak current condition.
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2015.03.13, 09:38 AM
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#26
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Registered User
Join Date: Dec 2014
Posts: 215
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If we look across the motor connections with a scope as we throttle from reverse to forward quickly, we can capture the phenomenon that can be a FET killer...
This was done with 4-cell eneloop pros and a 32T motor with no caps.
I set the trigger so that it would catch the exact moment that I broke a voltage threshold. I switched from reverse to forward very quickly, and you can see the change in the voltage pattern as I did. If you take into account the negative swing with respect to the abrupt positive swing, you can see that there is a 15.4V peak to peak voltage spike.
Referring to the Si4562DY data sheet...
As an absolute maximum, the FET can only handle a 20V potential between its drain and source pins, which is what your motor is across during run-time. If, in the event that these spike magnitudes exceed this maximum, the FET degrades. This does not necessarily happen immediately, but can happen over time, and then the FET fails. And keep in mind that the above analysis was done while the wheels were free spinning. Your motor experiences more load and the spikes can be even bigger when running on the ground. And as far as the motor caps are concerned, these voltage spike magnitudes are reduced because the energy is being absorbed by the cap instead of being able to peak as shown in the pic.
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2015.03.13, 02:21 PM
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#27
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VE7FM
Join Date: Oct 2010
Location: Langley, BC
Posts: 629
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Are you able to perform the scope measurements with and without capacitors across the motor and see a difference?
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2015.03.13, 03:55 PM
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#28
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Registered User
Join Date: Jan 2003
Posts: 514
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Quote:
Originally Posted by Jshwaa
Your motor experiences more load and the spikes can be even bigger when running on the ground.
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Almost makes me wish I could somehow put a scope across the terminals of both motors in my tank, then thrash the living hell out of it. Abrupt turns, abrupt stops, steep climbs, soft surfaces, the works. It seems logical that, if anything on this scale is gonna produce the biggest spikes, it'd be something heavy and hard to maneuver.
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2015.03.13, 05:12 PM
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#29
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Moderator
Join Date: Dec 2003
Location: Stafford, Va
Posts: 6,064
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The caps reduce noise traveling up and off the motor wires. This causes interference. I don't believe the 2.4 ghz boards are affected by this because of the caps in between the positive and negative contacts on the board. . I can only speculate that PN doesn't include them on their motors because they know this already seeing as they've made they're own 2.4 board...
Last edited by byebye; 2015.03.13 at 05:15 PM.
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2015.03.13, 09:56 PM
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#30
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Registered User
Join Date: Dec 2014
Posts: 215
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Quote:
Originally Posted by TheSteve
Are you able to perform the scope measurements with and without capacitors across the motor and see a difference?
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Will do that when time allows. I didn't want to mess around with soldering caps back on my motor when I may need to get back into it. When time allows, I will do up the same analysis with a motor that has the caps on it, and then take them off and do it again.
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