Muller Dynamo

[gyulasun]

Crazycut,

Well,  you have consider the frequency adjust potmeter as an R1 resistor value, besides the capacitor.   Generally an RC time constant is to be considered, the smaller the R  or/and the C, the higher their (1/R*C) value i.e. the frequency. For the 555 timer there are equations to determine the output frequency or there are charts to figure out the approximate frequency. 
Here is some charts to see some R and C values: http://www.williamson-labs.com/555-tmg-charts.htm  There is a tutorial on the 555 in their pages too.

IF you really need 2MHz frequency, then you have to use the CMOS types, like LMC555C or TLC555C because the old NE555 can run up to 120-150kHz only.   Here is a data sheet for a CMOS type, LMC555 and it turns out this type can run up to 3MHz in the astable mode and the capacitor is 200pF (minimum recommended value) and the R1 or R2 resistors are some hundred Ohms only.
see Page 5, maximum frequency test circuit:   http://www.ti.com/lit/ds/symlink/lmc555.pdf   

IF you happen to have a digital multimeter which is able to measure frequency directly, you may use such instead of a scope's frequency check.

Gyula

EDIT:  here is an online circuit simulator, showing a low duty cycle 555 circuit, slightly different than what I showed above but still practical and you can check the frequency too.  And if you edit the circuit resistor or capacitor values inside the Java applet, you can see immediately their effect ( just right-click on the component you wish to adjust).
http://www.indiabix.com/electronics-circuits/555-low-duty-cycle-oscillator/

Notice:  in this latter circuit when you vary the duty cycle or the frequency, then BOTH the duty cycle and the frequency changes.

[Khwartz]

Sorry, my comment was not pertinent after well experience speaking of you, Kone 

[Khwartz]

Hi all
here are some photos of backing-magnets behind the cores in a "Romero-variant" machine I built...it had 4 magnet rotor, but added 4 more magnets for 8 magnet rotor in some of the photos....the configuration and strength of the magnets behind the cores is very hands-on in way to find what gives the best performance, and is very sensitive and touchy - as removing one magnet or adding one too many will kill the whole speed up effect...sometimes bring the motor to a stop.  Before the magnets, the motors went around 300rpm , after the magnets, it goes 1200rpm which is really dramatic difference and the draw remains the same too....you need to spend hours trying different numbers of magnets in the stacks, using an rpm meter to gauge any speed up to find the best configuration,,there is no rhyme or reason as to why the stacks look as they do for the particular motor you have to experiment with all the possibilities and find what the motor likes.
3 of the photos are of an 8 magnet-rotor version, 3 of them are for the 4 magnet rotor version...this is why some of the bottom and top plates show totally different stacks of magnets

Hi Kone!

Thanks for the pics, they give good reality about your motor and magnets configurations

[konehead]

hi Mariu
here is my pulsewidth adjsutment circuit again: (you need driver chips with it)

[mariuscivic]

Thanks Konehead! i'll save it this time on my pc.
Have you cheked if your backing magnets are influencing the hall on your dynamo?