electric engine capacitors???

[pike]

I have these 2 small electric engines salvaged from a small toy. Each engine takes about 0.150 A with no load so you can guess that they are pretty small.

any way my question is about the 3 capacitors stuck to each engine.

:There is one capacitor between the terminals
:there is one capacitor between the (-) terminal and body/chassis of the engine
:there is one capacitor between the (+) terminal and body/chassis of the engine

heres the question, Why does the motor have these capacitors for???

edit: all capacitors are 0.1 uf, or marked as 104 and are of the disc ceramic type.

 

[Nigel Goodwin]

I have these 2 small electric engines salvaged from a small toy. Each engine takes about 0.150 A with no load so you can guess that they are pretty small.

any way my question is about the 3 capacitors stuck to each engine.

:There is one capacitor between the terminals
:there is one capacitor between the (-) terminal and body/chassis of the engine
:there is one capacitor between the (+) terminal and body/chassis of the engine

heres the question, Why does the motor have these capacitors for???

It's to reduce the interference generated in the motor, the action of the brushes on the commutator causes sparks - these capacitors help to reduce it. Without the capacitors fitted you will find a running motor may wipe out radio reception around it - it could also cause chaos with any electronics it's connected to!.

With a radio controlled model it's very likely to send it out of control, as the interference wipes out the radio signals.

 

[pike]

Damn your quick!! its only been half-hour. :shock:

Thanx for that Nigel, I was beggining to wonder why my PIC's were going whacko. Anyway i have hooked the motor up to a separate supply. So now my RC tank relies on 2 batteries one for the PIC and one solely for the motors. The only thing keeping them connected is the transistor sinking current from the motor.

Thanx for that

 

[Juglenaut]

go on the switch bounce problems, diodes will work as well.

If you get a big RC I would use a Diode to aid braking and brush bounce static.

Caps only absorb the static produced by the arcing effectivly stiffening the supply voltage, they will not stop brushes from arcing, but diodes will help that.

Arcing in this case causes an internal interferance (noise) as it effects the way the receiver detects the signal, caps will absorb this noise and block it from entering the ESC and into the receiver, as it acts like a low pass filter. Since most static is a high frequency it will be blocked or attentuated in a sence.

 

[pike]

juglenaut i dont know what you mean by using diodes to suppress the rippling from the motor.

So far i can get reletively nice clean reception when the motor is running at lower speeds but at full speed the recption goes crazy, completely out of control.

How would I go about this kind of problem, guys???

note- I'm using PWM methods to control the speeds. The frequency of the PWM is 19Khz

Should i try to shield the motor and reciever from interfering with each other???

 

[Juglenaut]

[/quote]juglenaut i dont know what you mean by using diodes to suppress the rippling from the motor.

Going off from switch bounce problems in Logic.

Think of it this way: The brushes contact the comutator the pads that make up the surface for the arm to receive electricity, there are slits or slots that break the contact and are timed in by endbell alignment and magnet position, however most motors have the comutator at 0 degrees to the winding most motors have fixed timing, some adjustible at the endbell. Now back to those slots in the comutator everytime the brush goes over this area, effectivly the degree amount depends on brush/comutator size for the time when both pads are making contact to the brush, the brush and the comutator make switch bounce and also a difference in potential from one winding to the next, and what is called inductive kick.

Seeing how you are running at 19kHz interferance like can cause widths in PWM to deviate more than the bandwidth receivable.

Diodes will effectivly reduce the arcing or inductive kick not so much as actually suppress it, this is what caps do, diodes in this case dissipate the ripple charge and caps will stiffen the applied voltage. Making sure that the negative side goes to negitive and this way effectivly makes reverse useless, since most RC races are forward only diodes can be used here. A circuit built this way acts like perpetual motion when it come to charge.

Series method of cap use on a motor does nothing more than double the capacitance opposition or suppression. Some places I have read this calls it polarization of the caps where as one cap goes from negative to the can, the other goes from positive to the can, using the can as a conductor it will make the can into a shield.

Motor timing can cause upper RPM interferances, Try using a .222uf and see what the result is.

You may also be getting shutter interferance at the receiver, try to wire in a cap to the BEC (battery elimination Circuit), a 1000uf cap will work nicely, or if it has no hook-up for BEC stiffen the supply into the reciever by wiring into the ESC input using red and black wires, use a electrolytic here.

 

[Nigel Goodwin]

note- I'm using PWM methods to control the speeds. The frequency of the PWM is 19Khz

19KHz sounds rather high?, I would suggest dropping to 1.9KHz might be a lot better.

You might also try connecting the metal body of the motor to your 0V supply rail - you already have two little capacitors connected to the body, but then it goes nowhere?.