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Explosion proof is an unusual concept. The explosion proof box used on Groundhog got its XP rating by going through a test in which the box was filled with an explosive mixture of methane and oxygen, and then placed in an environment with the same mixture. The interior of the box was ignited, and since the surronding atmosphere did not ignite, the box was given an explosion proof rating. This feat was accomplished primarly with 400 pounds worth of steel.
In order to support that much weight, the frame of Groundhog had to structurally reinforced to prevent Groundhog from bowing under the weight. The shocks were also further compressed so as to maintain a large ground clearance under the increased load.Fine Tuning
As testing of Groundhog continued, a number of minor changes were made. In response to low mounted components getting flooded, everything was moved higher on the robot. To better accomodate the battery box, the mounting point of the explosion proof box moved twice, leaving a swiss cheese pattern of mounting holes in its wake. To fix the problem of the chain drive occasionally jumping under load, chain tensioners were added. All of these changes were in response to minor problems encountered in the field.
A few more changes occured in order to better test Groundhog. The gearing ratio between the drive motor and wheels was changed when it was found that Groundhog's slow speed was not energy efficent. Also, the data connection to Groundhog was changed from a CAT5 ethernet cable to a wireless ethernet in order to simplify testing. The incorporation of all of these changes brought Groundhog to its present state.