20kg/cm torque= .02 Nm

I fear you'll need a serious reduction gearing

To explain. A Speed 900 does 1.1Nm in stall@12V. A Bosch 750 does 3.3 Nm@ 40A/24V

A Hitech BS805 servo, 19kg/cm, and that's an old model.

Also, the solid foam wheels of Sewersnake ain't light, nor cheap.

Best bet you have is to copy the wheels from Saint Hammer. Cheap and light, as well makeable with normal powertools.