Kyle L. Carithers
REU 2006
Construction
MiniRanger is built on top of a modified 1/18 scale off road R/C monster truck, the Duratrax Mini Quake. I highly recommend this R/C car for robotics, although some significant modifications are required. The modifications made for MiniRanger are listed below.
· Removed stock motor, motor mount, servo, and gears.
· Built mount for new motor.
· Cut away and sanded the ridges that supported the stock battery in the original battery location.
· Mounted new motor and mount in the original battery location.
· Changed the ratio of the gears for increased speed.
· Replaced stock servo and the servo arm. Duratrax has servo arms to fit various servos, Hitec and Futaba, for example.
· Replaced the stock springs. Initially the stiffest Duratrax springs were purchased along with the car. Ever stiffer springs were necessary though and were purchased from an industrial parts store.
· Mounted the polycarbonate platform in place of truck body.
· The universal drive shafts connecting the front wheels to the front differential were removed.
A three layer polycarbonate platform was built to mount the electronics. The bottom, middle and top layer were made from 1/4”, 3/16”, and 1/8” respectively. Polycarbonate was also used for the camera pan and swivel mount and the switch mounts. Each piece was designed using the computer-aided design software ProEngineer and cut with a jigsaw. The material was then sanded using a belt sander. The jigsaw was used because of time and access constraints. All three levels were machined in less than five hours using this method. The camera mount and the switch mounts were cut in a similar fashion, heated, and bent into shape.
Polycarbonate was chosen because it is clear, lightweight, easy to machine, and very difficult to break. LEXAN® is polycarbonate manufactured by General electric. Acrylic is similar to polycarbonate. The main benefit of acrylic over polycarbonate is that acrylic resists scratches better than polycarbonate. Polycarbonate, on the other hand, resists cracking better than acrylic. Acrylic is sold as Plexiglass, Acrylite, Lucite, and other names. Aluminum or any other metal was not used because of the risk of shorting the electrical components. Wood was not used because it is not as strong as the previously mentioned materials and is much less attractive.
Metal standoffs were used to mount the mechanical components. Nylon standoffs were used to mount the microcontroller. Extra precaution was taken to ensure that standoffs did not cause a short on the robot. Mounts designed for the SRF05 were purchased for four of the five modules. The fifth sonar module was mounted to the camera mount to find the distance of an object being tracked.