--This one has a number of improvements including a stiffer table and a built-in speed controller. Power comes from a wall wart and anything over 9v will do. I'm using a random 12v, 200mA one and it works fine.
After parts are printed you will need to get the following parts:
--The gears have hexagonal center holes to hold hexagonal shaft collars. These collars are threaded for set screws that grip the driveshafts securely. I got these: https://www.amazon.com/gp/product/B07QNHQGZB/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
--You'll also need a pair of 6mm shafts (I got more than I needed!): https://www.amazon.com/gp/product/B072JPQX4Q/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
--And the shafts need three bearings total: 6mm id and 16mm od but I've found that size hard to find. I've included a new part: Gearbox_Frame15mm_01 which will accept the more common 6 x 15 mm bearings available here: https://www.amazon.com/uxcell-Bearing-6x15x5mm-Shielded-Bearings/dp/B07Z3F1MR5/ref=sr_1_3?dchild=1&keywords=flanged%2Bbearings%2B6x15&qid=1634408972&sr=8-3&th=1
--For a motor controller I use one of these; they're extremely cheap and easy to hook up:
RioRand RR-PWM-15V Low Voltage Dc 1.8v 3v 5v 6v 12v Motor Speed Controller, 2A PWM
--The motor I picked is the most common one I could find; it's 35.75mm diameter and has a splined shaft that's approx 1/8" diameter. I got mine from sciplus.com Amazon calls it: Weelye 2 Pcs 24V 30000RPM Children's Powered Wheel Electric Motor ,24 Volt Motor Drive Engine Accessory for Car Children Ride on Toys Replacement Parts