The Robot
On our way to discovering one way to build a successful lego robot, we had the fortune of also discovering many, many ways not to build a lego robot. This is where our team name originates from - rejigging,
the careful art of taking apart individual failing sections of the overall robot and altering them to be, well, not so fail. Every single component of the robot has been built, broken, rethought, tested, failed and rejigged. Through it all however, we ended up with one functional robot ready for competition.
Following are some of the design issues we ran into.
the careful art of taking apart individual failing sections of the overall robot and altering them to be, well, not so fail. Every single component of the robot has been built, broken, rethought, tested, failed and rejigged. Through it all however, we ended up with one functional robot ready for competition.
Following are some of the design issues we ran into.
Frame
Luckily the frame was only rejigged once. The first frame to be built was test dropped and promptly burst apart in a clattery lego death. The next frame was built for the single goal of surviving The Drop Test. (it did) By virtue of lego shapes, it ended up being a very versatile frame capable of easy redesign.
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Drive, Gear Ratios
Drive was designed along with frame as one of the first features completed. It also boasts of being the only part of the robot that was never rejigged. We used a succession of 3 8:40 reductions to get us an overall gear ratio of 1:125.
The drive base was so consistent that when jostled it in order to remove the encoders, we discovered it had somehow accumulated dust. |
Caster Wheels
Our original frame design did not include caster wheels, instead it had two unpowered wheels in front. After trying to turn, without success, it was determined caster wheels were needed. Caster wheels however, are not particularly good at surviving the drop test or mounting easily where straight drive shafts were before. This was possibly the most redesigned feature of the robot with a total of 11 failed caster wheel designs. If you want help with caster wheel ideas that work, look at old robots.
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Spin Wheel
The spin wheel was the origin of some of our most major changes. Initially mounted on the left side of the robot, we tried (and failed) for about a week to pull up next to a gearbox. When we finally pinned down our numerous errors to the precision of the Vision Position System combined with wheel encoders, the side wheel had to go.
After repositioning it to the front, in true rejigger fashion it went through another 2 or 3 redesigns addressing further issues with lining up with the gearbox and amount of torque that a motor could supply to a wheel with a large radius. |
Collection Mechanism
In the spirit of K.I.S.S. (Keep It Simple Stupid) our first lever pulling mechanism was a stationary hook. We had hypothesized that by reducing the number of failing points on the robot (ie motors, sensors, servos ect) we were ensuring that it would be more reliable. Unfortunately for us the reliability of being able to parrallel park next to the wall was a lot more complicated than the reliability of wiring up another servo. Our final lever puller is a simple servo rotating a nice long arm allowing the lever to be pulled from a variety of only somewhat accurate positions.
As a side note-- being able to parallel park likely would have worked better if we had front wheel drive instead of back wheel drive, but redesigning the entire base was a lot more complicated than adding a servo. |
Hopper (Collection Bin)
This was one of the easiest features to build. While we did have to figure out how to get a bit more of a slope than the slightly backward tilt of the robot due to uneven wheel hights, a simple downward staircase was enough to give the ping pong balls combined with gravity the incentive to congregate in the back of the hopper.
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Dumping Mechanism
Also a simple mechanism. After rejoicing over the discovery that the planned height of the robot was just about as tall as the retaining wall for the city, all that was left was to put a robot width wide gate on the back. With the main goal to keep the gate as light as possible, we designed the dumping mechanism largely out of shafts.
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