The following images are my attempt at remote controlling the 8421 Mobile Crane.

I originally saw one on youtube that had the motors stuck out the back where the knobs normally went, and i thought i could intergrate them a bit better...

The idea was to run the motor cables back through the turntable and have the recievers and battery box as the counter balance, would have been the best looking and most functional place for them.

However i ran out of M Motors and i needed extension cables, and i wasn't willing to pay S@H's insane prices just for a few cables...

The LA's worked extremely well only had to bring the top mounting point back a few places, and only lost about 1 degree at full extension of the arm by using them.

The chain for the stabilizers also worked well as when the load got to high it would slip, acting just like a clutch, which i couldn't fit in.

Posting these pictures up so if anyone else is wanting to RC the 8421 Mobile Crane they can see a different way of approaching it.

Thanks for the pics. My son and I have a Lego 8421 Mobile Crane that's just BEGGING to be motorized. If you want to finish your project, you can buy the needed 20cm Power Functions Extension Wire and PF Medium Motors NEW from Bricklink at reasonable prices:

Extension Wire: http://www.bricklink.com/search.asp?itemID...85&invNew=N .

Power Functions Medium Motor: http://www.bricklink.com/search.asp?itemID...86&invNew=N .

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peterski published 39 pictures of his motorized Lego Technic 8421 Mobile Crane on his Brickshelf gallery. It uses 3 ea. Power Functions (PF) XL motors and 3 ea. PF Medium motors. The photos show enough detail so that one could replicate his build: