This is a modification of this crossbow. 
Print parts from the original crossbow and combine them with these files.

The 3030 profile has to be shortened to 31.5cm (32cm should work too).
The needed components from the original model are:

• Case
• Cocking rope
• Footpeg
• Bolts (for this version, bolts have to be 33cm long)
• Buttstock (not needed)

Assemble them using the assembly guide in the original crossbow.
For this remix, there are some additional needed parts:

• 4 skateboard bearings
• M5 3030 profile T-nuts
• M3x25 2pcs - for back pulleys
• M3x12 3pcs - front end of the rubber shroud
• M3x8 2pcs - back end of the rubber shroud
• M5x16 3pcs - back pulley mount and rubber shroud mount
• M5x12 2pcs - rubber mount
• M5x10 4pcs - limb mount
• M3x35 2pcs - secondary pulley
• M5x45 2pcs - primary pulley
• Speargun rubber 14mm OD, two pieces of about 10cm (you need to tune the length)

The secondary pulley and back pulleys are assembled by inserting skateboard bearing into printed pulleys.