Modifying PF Wheels for 12V Connecting Rods

[roamingstop]

Whilst I very much like the new connecting rods designed here I could not help but wonder if it would be possible to modify existing PF train wheels (with axle) to accept the old 12V style connecting rods. So I decided to sacrifice two wheels in order to find out (gasp).

First up - checking the hole tolerances on the old 12V motor wheels; they are slightly over 3mm diameter (but much less than 3.5!). So 3mm drill bit it was.

Next time to build a quick Lego jib and work out where to remove the spokes (with craft knife) so that I had a nice flat surface to drill into. It does not matter how well you plan this step; it always works out wrong, in this case narrowly catching one of the 3 reinforcing beams at the back (photo below). Better luck on round two (since this is a sacrifice I did not mind making extra holes).

PF wheel for 12V connecting rod by roamingstudio, on Flickr

PF wheel for 12V connecting rod by roamingstudio, on Flickr

First I can say that the 3mm diameter is perfect for allowing the rod to insert, but it does not 'click' tight. The reason? Behind the wheel there is an inner ridge which is thicker than the plastic through which the drill just went. (it is tagged on the flickr link). In order to get a click it is necessary to mill this extra bit out - as I tried on the right hand wheel. However it was just too easy to 'go through' and spoil the approach.

Now for the next caveat. On a PF motor; running with a 5L axle through the motor, there is just a little of the axle projecting which can foul the connecting rod as the wheel rotates underneath it. Also not quite a perfect solution.

So in summary

• An interesting experiment which shows that the old 12V connecting rods could be fitted to the modern PF locomotive wheels...
  
• But the milling would need to be done to a very high precision standard (not by hand)
  
• And there would need to be a way to ensure the rods dont foul the axles.
  

Pity as this seemed like a nice way to overhaul some of the older 12V locomotives (7760 you know your number) to PF standards. However in this case I guess it is better to use BBB medium wheels (linked in another thread).

The other alternative would be to ask a Lego part designer for a copy of the wheel 3D cad file, and add the necessary holes... and then do some 3D printing in black and red.

Edited December 28, 2012 by roamingstudio

[LEGO Train 12 Volts]

Amazing topic Roamingstudio...very usefull!

Thanks for sharing!

[1974]

Just run the old 12V motors off 9V PF/RC. I do that, speed is adequate. Rods are awesome

[roamingstop]

Good point and i will try that. Although i might tackle a dremel and wheel in a week

In the meantime this interesting post in technic forum (dual pf batteries) might be a good way to overpower the 12v motors - if anyone cares to try. Im in a hotel for a week - so no bricks for me

http://www.eurobricks.com/forum/index.php?showtopic=77490#entry1469908

Whoops here is the link

[1974]

I think 12V train motors are a good deal more fragile then PF motors and I'm not sure there's a thermo swtich inside? Also, they don't come cheap and I'm not really gonna waste a mint red one on that silly idea

And you'd need to drag around TWO batteryboxes and receivers .. I got enough hassle just trying to hide one set! (I do hack 'em though and use 9V batteries for small locos)

If there's a man/company making rods .. and another one making wheels, then they should sit down and have a coffee together