DIY self-extendable gearbox upgrade version Free 3D print model

I design this extendable gearbox for convenient daily use. It is easy to make and use using 3D printed parts and ball bearing. Since I use a self-extendable unit, it is very easy to expand to the gear ratio which you want. Hope you will like it. Subscribe to my channelhttp://youtube.com/channel/UCXJe7CK3mK-GF1Jia7-pciA