Hi everyone, I was hoping for some recommendations on individual technic pieces to buy my son for Christmas. He loves technic and spends most of his spare time building and refining various motors, gears, etc. He has a mixed lot of technic bought on ebay including the lego landrover and the liebherr excavator. He wants the new liebherr crane but it's waaay too expensive so I would like to buy him a box of some cool pieces he might not have. His grandparents have already bought him the lego mars rover.
I was thinking:
https://www.lego.com/en-gb/product/large-angular-motor-88017 (seems to be the motor from the crane, would 2 be enough for fun building?)
https://www.lego.com/en-gb/product/color-distance-sensor-88007
Any recommendations from this community on individual pieces that they have found great to build with and/or might usefully compliment the above or his existing lego collection would be very gratefully received.
Thanks in advance!