Well how I designed mine which i do not use because they make a considerable amount of noise in the water we dont hear. and i believe they stress fish out.
I will guide you through it though on how i did mine, YOU HAVE TO use the mj1200 magnet though . mj 900 and 1200 have no differences besides the way the internal probe and magnet is designed . just the outside is marked different. Your prop will have a "white" wheel instead of the black.
Materials you will need according to my lay out.
mj1200
mj1200 magnet , pull the end caps off the rod (can be diffacult ) remove the shaft AHAHAH SHAFT GET IT GUYS? GIGGLE SNORT omg im funny. And throw the prop in the trash ( white wheel )
Ok here is the 1 second mspaint plans =/ im at work and dont have photoshop sorry.
Red lines are CUTS.
( the only reason yellow is in the first picture is so you know to contain the "tabs" and not cut them off when you cut the intake and out the outtake holes off. )
Now goto the picture on the bottom , the teal/gray stripe is the magnet , cut off the first little piece not the next smaller section below that . The gold line is going to be the main shaft the blue // are the end caps ( red with black rubber gromets, i suggest you use super glue gel for all of this ) This is the 3/32 shaft people are talking about , I did not have access to titanium rods locally of this size . So i just used a alum 3/32 rod ( hobby shops tend to have hollow version's if you use this cut carefully as it warps )
The brown piece is a thicker tube of carbon (hollow) I believe it is around .176. 8 dollars 3ft length. i used a few inches. But i have a remote control heli and boat i can use it for. ( The part of the magnet you cut off ( plastic piece ) there is another tab below that . I had drilled it out a little bigger so i could glue the outer shaft inside of this.
The purple obviously is the prop I tried to get as close to 3/16th as possible since that was the inside of my props dia ( the most common size of plastic props ) The carbon shaft should be close to this size also but it is measured differently so I just compared the 3/16th alum hollow rod they had next to the hollow carbon rod .
Your 3/32 ( titanium hopefully ) rod should slide through this with A VERY VERY VERY little resistance , it should be as close to a perfect fit with 0 friction as possible.
Now going to the top right.
I used a fitting of pvc i had left over , I suggest you buy this part according to size of your prop . I got the male threaded because once I cut this off it gave me more space to glue it to the mj1200 intake / out take part ( i sanded it smooth \ hence this is why gel super glue comes in handly ) ( drill holes close to the bottom , right before the "hex\wrench" part of the PVC fitting , or just put em all over its up to you, this is jus thow i did mine. )
The most important part though is that orange bar , I used a thick piece of scrap acrylic i had laying around ( any piece of THICK plastic will work also ) Make the bar and drill a hole in it but not all the way through , just enough to fit the stopper ( red with black rubbery thing that goes on the ends of the shaft ) into it , Center it perfectly and glue it , if you dont the thing will shake all around and it is impossible todo this mod without that restrainer in place.
The magnet will fit through the original maxi jet intake hole and the one through the piece of PVC this gives easy acess. Remember the piece the prop is glued to the carbon , the main shaft ( 3/32 ) is fair close to free spinning if not fully.
Now that you are done , I am sure you wish you would of just worked the few extra hours and bought a tunze.
Good luck , improvise and use whatever tubing or way to connect it you want . just remember the orange piece in some form and to have the inner shaft free and the outer glued still.
I am going to break into melev's and eat casper now.
-Brian