Another way to join shafts together is using the 2x2 Center Offset Round Lock Beam 228-2500-1925. From a prior post:
The good news is that we included 6x of this part in the new 2nd generation 228-8899 IQ Education Kit, and another 4x in the 228-7597 2nd generation IQ Competition Spare Parts Kit. Any new VIQC teams that buy the complete 2nd generation IQ Competition Kit would get 10x of this part.