If you're measuring things on a multimeter all you're getting is the RMS voltage, and that's in a very narrow frequency range, if you're measuring above the frequency your meter is good for you're going to get a distorted reading. Even the best RMS multimeters are usually only good into the low KHZ range, mine is only good up to a couple hundred hertz. If your meter isn't a true RMS meter then the readings you get can be pretty much discarded as useless as the internal circuitry will affect it's reading more than the signal itself.

Depending on how the 555 circuit is built changing the duty cycle will affect the frequency a bit, not much you can do about it on a 555, it's an analog device, if you want a more precise drive frequency and duty cycle you can get micro controllers that have glitch free PWM outputs that will give you very high precision frequency and duty cycle.

If you use a capacitor across the motor leads in series with a diode to prevent it from discharging to ground during the off cycle it will provide hold up power and smooth out the abrupt changes in voltages from a PWM source. When a discharged capacitor is connected it will suck a LOT of power as it's a low impedance load to a square wave so it will slow the sharpness of the power rise to the motor as it's own impedance will draw less power, then when the PWM is turned off the capacitor will be isolated by the diode and discharge it's available power to the motor smooth it's shutdown voltage by drawing power from the capacitor. Making the curves less sharp will decrease the noise the motor can generator, as a hard square wave will generator many odd harmonics well above it's natural frequency into the audible range. This would probably most benefit from a low PWM frequency, in the hundreds of hertz range. But the capacitor and diode will introduce some loss which need to be taken into account.

__________________

 

Well i've seen the wave forms already. Now I've an idea.

We'll, I'm gonna take advantage from this post to ask you guys if it is possible you to give me ideas to my R/C car transmitter. I'd like to use a PIC or simple analog or digital methods.

I'm open to sugestions.

Best regards

 

Which part of the transmitter do you want to build? The RF module inputs (i.e., the modulator) are pretty well defined...see various PC-based trainer systems. Some transmitters have outputs for trainer cords. You can use that output to see what you will need to do for your own modulator.

If you want to build the RF section, that is quite another matter and raises licensing issues. John

 

The modulator I intend to buy it. Those PCB very small TX and RX working at 433Mhz..

My question is related with the way to put the information on the modulator. Wich could be the best way to say go fwd and the information is created and then go to the modulator. Can you understand? I can't explain it in english, it's quite wierd to explain x) but I hope made myself explained!

btw, can you tell where are selling on the internet those kinds of potentiometer used in R/C car trasmitters, looking like a pistol..

Best regards

 

They are called joysticks.

The cheapest source is probably from an old, discarded transmitter. We don't know where you are. In the US most modeling clubs either have some to give away or sell at rummage sales, or the members will give them to interested new members.

John