Your Mosfet Source needs to be connected to your motor power common and the motor placed in the drain of the mosfet.
Like I posted in the link, except instead of 6v it will be whatever your motor power is.
Max.

 

sorry, can you draw on the picture what you mean? im a visual learner and im having a tough time picturing exactly what you're saying, thanks

 

The motor power common and 555 circuit common are connected.
Max.

 

well im really confused now, but I tried to draw it out.

 

Yes that is it.
You need capacitor across the motor supply, unless using an off the shelf power supply.
Max.

 

like this? and what should the cap value be? 120v would work?

 

Not the motor, across the bridge rectifier out put.
Electrolytic at least 10,000 υf
Max.

 

like this? thanks

 

wow such big caps are hard to find, I only have a 200v 1500uf on hand, ill keep looking around. on the other hand, why such a big cap?

 

I can only seem to find low voltage ones online as well, the higher voltage ones' prices go through the roof

 

can I use a bunch of low voltage ones in series instead of 1 huge cap? cant find any below few hundred dollars
or in parallel to increase capacitance?
http://www.allaboutcircuits.com/vol_1/chpt_13/4.html

 

You can parallel them to increase the capacity.
Max.

 

alright thanks, I'm going to go get the parts now

 

one solution is to use an ordinary light dimmer with a bridge rectifier across the motor, use a suitable rated Bridge Rectifier and Triac for the current,

http://www.tehnomagazin.com/images/DC-permanent-Magnet-Motor-speed-Control-schematic.gif

 

well, i tried the circuit first with a 12v motor and a different transistor and the pwm circuit worked great, but when i connected everything together with the big motor and an IRF540 (this is the only one they had and it should work too, same chip but gate is 10V) the 555 blew up, but as it was blowing up, the motor did start spinning. i have another 555 chip and the IRF540 is completely unharmed, any suggestions on the next trial?

 

May be a silly question, but are you sure you've got the right pin connections on the MOSFET? According to Max's schematic and the datasheet, the gate on the MOSFET (which should connect to the 555's pin 7) is pin 1. In your graphic schematic, there are no pin numbers on the MOSFET, but it's drawn to look like you're connecting 555 pin 7 to the middle pin. If so, there's your problem.

 

hm that may be it, although the drawing I uploaded was just freehanded at the time, I may have accidentally followed that drawing thinking I did check it; but thinking about it now, wouldn't connecting the pins wrongly on the MOSFET destroy the MOSFET itself and not the 555?

 

the mosfet has a back emf diode in, it will conduct from D to S, if you get the pins wrong way round.

D is the centre pin and tab, goes to the motor, G is the left pin, and should go to pin 3 on the timer chip.

 

Pin 3? It was connected to 7 before though

 

pin 3 is the output of a 555 timer, you can also use pin 7, but need a pull up resistor.

Also if your using a 120VDC motor, why dont you use the circuit i posed in#34, using a light dimmer and the bridge rectifier from the treadmill.