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Heaterbot

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bellpride
Entry ID #: 185
Created: Sat, Mar 6, 2010 12:37 AM


As is inevitable on most VEX Robotics teams, Team 254 members have found themselves working on their robots late at night...often without a heater, and never with one in reach. To solve this problem, we thought of the most efficient, user-friendly way to move the heater – and came up with Heaterbot. We planned for Heaterbot to use a holonomic drive. This drive system would let the heater move freely around as well as rotate in place. We also aimed for a central spooling mechanism which could wind the extension cord connecting it to the wall. After talking with the 254A programmer, we determined that we could automate the spooling with a shaft encoder. Under normal circumstances, the spooling motor would pull slowly inwards on the extension cord. If the shaft encoder detected that the cord had stopped spooling, the motor would start to spool outward, loosening the cord. When the robot stopped moving, the motor would stop spooling, and then slowly pull inward again, taking up the slack in the cord. Because we used Autodesk Inventor, we were able to design our entire robot before picking up a single wrench. Autodesk eliminated most of the time we would otherwise waste prototyping with actual pieces – in fact, we were able to construct the entire base without a single issue; all that remained was mounting the heater on top. Some of the features we found useful were the simple orbiting tools, easy mating utilities, and lightweight user interface. But perhaps the most valuable Inventor utility was the rendering tool, which made our design look just like the real thing with ease. Although we were anticipating making a robot solely for the 2010 Digital Prototyping Challenge, we have found Heaterbot to be an incredibly useful asset in our regular build sessions. Because the robot uses so little power, we have hardly ever had to change its 7.2V battery, making it one of the most reliable, worry-free tools in our workshop.

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Comments

   bellpride on 03/15/2010

@ChrisHam: I think Tman254 might have misunderstood your question (or maybe I do!). To clarify: The inner end of the extension cord (connected to the heater) is fastened as close to the center of the spool as possible. The female prong turns pretty much in place underneath the heater and over the spool. The heater cord is in a clump in the same area, connected to the extension cord. In the "relaxed position" the extension cord is all the way in. As this cord winds out, the heater cord (not the extension cord) slowly curls because the prong rotates in place. Since the extension cord is zip-tied to the frame itself (we saw no need to zip-tie it to the heater cord), when the cord is completely stretched out, the robot simply stops moving (unless it is on some really grippy surface traveling directly away from the plug, in which case it *might* pull the cord straight out of the wall...we haven't tried to do this). The outer end of the cord (connected to the outlet) does not normally have enough force to be ripped out of the outlet (the exception is the case above). The robot is direct-driven and holonomic, and is pretty light as well. Between the minimal weight and outward spooling, there is hardly any tension in the cord at all. The onboard shaft encoder makes it fairly simple to digitally stop how far the robot can spool out - eliminating any safety hazards caused by the electrical cord.

   bellpride on 03/07/2010

@Krummel I didn't make the CAD, but I can answer your first question. The heater that we used is not ultra-powerful; it doesn't even heat up the cage in front of the dish, just the air in front of it. We've been using the heater for a year, and it doesn't heat up anything other than what is in its path. Just to be on the safe side though, we mounted the microcontroller and receiver behind it. Thanks for the comment.

   Krummel on 03/07/2010

Two things: One, has anyone formed any heat shielding, so that the high temperatures from the heater doesn't damage the robot's circuits, sensors, plastics, etc? Those heaters can make even plastic bearings melt pretty quickly. Two, why are the wheels out of alignment from left to right and front to back? In a CAD program alignment issues should be less of an issue than in real life.