Recently, I wanted to give cresting demonstrations at our target range. Unfortunately, there's no power available at the site so I decided to build a battery operated machine. The main obstacle to overcome was finding a battery operated motor. After some research, I opted for a 6vdc 90:1 TT motor running at 110rpm. With a 1 inch drive wheel it maxes out at 320rpm. A VFD motor controler varies the rpms and a USB battery supply (Four AA batteries) allows me to unplug the battery box and run it off a cell phone charger when AC power is available. I discovered carbon arrow shafts fit nicely over 1/4" threaded rod and this is what I chose to build the carriage. The rollers are rubber covered bearings normally used on 3D printers and the sheet metal parts and aluminum motor chassis I fabricated myself. The drive wheel, Testors paint tray, motor mount, and controller housing I made on my 3D printer. The wood came from scraps picked up at Taylor Guitar. I believe it's Pau Ferro and Mahogany. Since most of the hardware and wood was stuff I had on hand, the build cost me less than $30.
Very nice!