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Old 12-06-2001, 10:32 PM   #1
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Capacitor connected to receiver? What does it benefit?

Well, lately I've seen alot of guys on magazines(mainly Japan racers) with capacitors connected to their bec terminals?What does this do or benefit? I've even seen Brian Kinwald do this on his buggy? Well, if anyone of you guys know what this does or if ya'll run this application as well please inform me...I'm just one curious person who likes to have more knowledge on my shoulder...Thanks...
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Old 12-07-2001, 03:30 AM   #2
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According to Ralf Helbing at GM it takes away servo glitching when using a strong servo.
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Old 12-07-2001, 06:07 AM   #3
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...from what i have been told, It should clean up the radio signal, reduce glitching, and clean up radio range.
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Old 12-07-2001, 06:43 AM   #4
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Anyone of you guys run this application on your car? Also, what kind of capacitor do they use example:25volts,6600uf...I've seen some japan racers use some pretty big capacitors, wouldn't it feedoff to many power to the receiver if the volt rating on the capacitor is too high since it stores the amount shown on the capacitor? Feel me up with some info here guys....If it is true that what you said TSR6 and moonman I might run this application on my car I just need know which capacitor to use and which capacitor rating would be right for this application...
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Old 12-07-2001, 07:00 AM   #5
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I use 16V 10000mF for my V12 and 10V 4700mF for the receiver.
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Old 12-07-2001, 09:16 AM   #6
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Default Caps?? Joke??!!

Just wonder why we need to install extra cap. to stable the voltage supply for the receiver. I think it is the design fault of the ESC if we need to solder an extra cap. for it. To go to the extreme, should we install a receiver battery as in the old days where mechanical speed control is used. It is a joke for this to happen while we have very advanced electronic technology today. Hey, we pay a fortune for an current up-to-date ESC.
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Old 12-07-2001, 09:27 AM   #7
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Yea but the wierd part about electronics is the really like a stable voltage, they perform better. That is what a cap is all about. It acts as a buffer between the power source and the equipment. The cap to the reciever. As a matter of fact you can almost look at it as a short term battery. I' suprised that racing legislation has not looked into this as a rules violation. or modified the rules to allow the caps.
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Old 12-07-2001, 09:30 PM   #8
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Default wierd

Yes, it is weird because of the BAD design and lack of sense of responsibility of the ESC manufacturer. The BEC circuit is not working properly. BEC circuit is suppose to output a stable voltage to receiver and servo. Obviously, in the case that required external cap., the BEC is not working. The external cap. is just a work around (quick fix) by the user. Anyway, we got to live with it or buy another one.

I think we have the right return the ESC to the manufacturer for a full refund (including shipping charges) cause the product is not working as advertised. If the ESC does come with a cap. or it state clearly in the manual that it DOES require an external cap., that is another story. BTW, where's are those ESC manufacturer, they should jump in and say something.
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Old 12-08-2001, 07:14 AM   #9
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Yokomo sells the capacitor but I don't know the numbers on it, it is pretty small though
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Old 12-08-2001, 07:46 PM   #10
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The issue of intereference cannot only be blamed at the ESCs... the motor is actually the main cause of all evils, but the motor manufacturers are not doing much about it either.... the real problem is the receiver design, it is designed to receive signals, and at the same time it must reject random signals in forms of interference. This makes the receiver design very difficult and ultimately very expensive.

The manufacturers havent much to work on either.... they dont have an effective grounding as most cars are plastic or non conductive, so they cannot rely on a good earthing for the filters to work on, which can allow the filters to "drain" the spikes to earth properly.

We need weight reduction, so the receiver battery is eliminated, we want small size too! so physically the capacitors are the main problem as their values are realted to size....and there you are, you have a receiver drawing milliamps from a source there there will be a motor and ESC supplying square waves in tens of amperes! In this situation it is almost impossible to keep the power stable, the battery internal resistance also plays a part....

With some carbon fiber chassis the situation is even worse, teh chassis is noe fully conductive and therefore there can be a potential voltage at either end, andit also becomes charged....

I am currently working on a R/C grounding system to hopefully improve something....

on the manufacturer's side, I have noticed that motors are emitting more and more due to being over tuned and thus more arcing.... the ESC quality and reliability has improved, but sadly the radio system quality has suffered in the budget price range.
So investing in a good radio system is a good starting point I believe.
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Old 12-10-2001, 12:43 AM   #11
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The reason people use the capacitor on the receiver or on the BEC output (almost the same thing) is the new hot digital servos that draw relatively high currents at pulse mode. Some ESCs are known to have problems supplying that high momentanous currents although they can supply have average current. The capacitor is used as a low pass filter to prevent the receivers voltage going up'n'down with the current the servo takes. At least the Quantum is known to have this problem and a capacitor can get you rid of some radio interference problems.
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Old 12-10-2001, 04:27 AM   #12
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Default power supply / radio ?

Yeah, the receiver manufacturer can do something to improve the noise immunity and deal with power/voltage fluctuation.

For the case that adding a cap. in the voltage supply to solve the radio problem, it is mainly the voltage fluctuation (caused by sudden high current draw) that cause the problem.

The cause is unstable voltage under heavy load. It can be solve in two direction. First, better voltage regulation on the ESC (easier). Second, better voltage regulation on the receiver (harder). My opinion bias the first one. Cause the receiver is working normally, only some ESC which claims to have BEC circuit cannot do their job good enough and cause the receiver to fail. For example, if your expensive DC battery charger fails (false peak or do not automatically stop charging) because you use a poor quality DC 12V power supply. Will you blame on the charger and request the charger manufacturer to improve it?

In the case of the new digital servo, I have no accurate info on how they operate. Reasonable guess is that the servo is digital in a sense that the position transducer (VR) or the control is digital which consume very little current. (they will provide a more accurate positioning over a longer lifetime) The actual driving motor is the same as good old non-digital servo. Please correct me if I'm wrong. It will be great if there are some web info on this.
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Old 12-10-2001, 05:31 AM   #13
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The fact is even if you provide power straight from the battery to the servos and the receiver, it won't really stop the interference issue from the motors... the poor receiver and ESC cannot have their internal filter to work correctly because at very higher current draws, even the smallest resistance between the wires and grounds will generate a potential difference and lets not forget noisy ground is as bad as a noisy supply, there is no difference when there is no real ground. In systems with high current and working at moderate to high frequencies, 90% of problems are cause from poor and insufficient grouding...

Back to the Quantum, I think they cannto fit a cap in such an enclosure and since most mod runners silders a cap to it (like the Mtronic Cube) they have jsut decided that is the way to be.
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Old 12-10-2001, 05:58 AM   #14
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I added a cap to my receiver at the point where the ESC plugs in to it. I was experiencing a lot of twitching during the turns and the cap helped clean up the mess.

The cap will not cure all your problems but most of them. I wanted to be sure that my digital servo received the best digital signal it could.
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Old 12-10-2001, 09:18 AM   #15
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Default Grounding

Ground fluctuation are mostly seen on high current switching application. Yes, they are very hard to deal with. In my point of view, running motor lower than 10 turn is pain in the $$$. I don't like to deal with cutting comm., electrical noise, heat, etc... Right now, I'm running 13 turn, 12 turn or 23 turn. No such problem what so ever.

I enjoy driving rather than maintenance, that why I like RC. If I like maintenance, I would go for 1:1 car and enjoy the complication of the mechanics, engines, etc... However, there are different people in the same planet. I would just respect them, and I would be more than happy if they do their favor to take care of my car's maintenance.
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