Working with a group of three other students, I designed and built a robotic flowerpot. The goal of the project was to create a robot that would look like an ordinary flowerpot, but then move to a new, brighter location in a room when it sensed that there were no people around. We achieved this through building a robotic pot that could first check if there was motion around using motion sensors and then lift itself up and drive to a new location. This new location was chosen by comparing multiple photo diodes around the pot's lid.
My part in this project consisted of all of the mechanical design and most of the fabrication. The mechanical design consisted of five major subsystems:
1) The structure, including the pot.
2) The drive system, in this case an omnidirectional 3 wheeled system.
3) The "pot lift" used to lower the pot and hide the wheels when it is not driving.
4) The "head lift" used to hide the sensor's when the pot is not moving.
5) Sensor mounting and wire harness.
My part in this project consisted of all of the mechanical design and most of the fabrication. The mechanical design consisted of five major subsystems:
1) The structure, including the pot.
2) The drive system, in this case an omnidirectional 3 wheeled system.
3) The "pot lift" used to lower the pot and hide the wheels when it is not driving.
4) The "head lift" used to hide the sensor's when the pot is not moving.
5) Sensor mounting and wire harness.
Subsystem Overview
Structure:
The structure was composed of a series of laser cut acrylic plates that were held appart using standoffs. These were attached to the outer pot using L brackets. The pot was made out of a 5 gallon home depot bucket that was cut and then spray painted. This was done for several reasons. First, it satisfied our size and weight requirements. Many flowerpots of this size are very heavy, or awkwardly shaped. The bucket gave us a very light, simply shaped outer covering. It also was our cheapest option.
The picture to the left shows the structure. The pot is the transparent outer covering and the acrylic plates are shown in white.
The picture to the left shows the structure. The pot is the transparent outer covering and the acrylic plates are shown in white.
Drive System:
The drive system used in this project was a 3 wheeled, holonomic "kiwi drive." Through using three wheels that are freewheeling perpendicular to their rotational axis, any direction vector can be traveled along without rotation. This was selected because the team wanted the robot to appear to be moving magically and unexpectedly across a room. We decided that this system would best suit those goals.
The motors used are low cost servo motors, couple with Vex omni wheels. The support structure is made with laser cut delrin plastic to decrease friction and negate the need for additional bearings. These were assembled with a tab and slot system between two acrylic plates.
The motors used are low cost servo motors, couple with Vex omni wheels. The support structure is made with laser cut delrin plastic to decrease friction and negate the need for additional bearings. These were assembled with a tab and slot system between two acrylic plates.
"Pot Lift"
In order to create a flowerpot that appeared to be normal when it was not moving, we needed to have a way of concealing the wheels. We achieved this through lifting the pot up and down by a quarter of an inch. This system was a stretch goal, so it was achieve with a minimum of resources. The midsection of the robot was supported by three servo motors that had cams attached to their output shafts. When the cams turned, the robot lifted. After passing their center point, the cams hit a stop, effectively locking them in place. This made a very simple linear motion system.
"Head Lift"
The purpose of this system was to lift the upper section of the pot, both to allow sensors to view the environment and to make the pot appear to have a "face." The head was a piece of pvc pipe endcap with a plant in it that moved linearly by roughly three inches. When the pot was in "stealth mode" it would be entirely within the outer pot. When it began to move it would expand.
The head lift system was the most mechanically complex system of this robot. We did not have the budget to purchase linear motion systems, so we had to custom make linear bearings, rods and drives. The bearing system was made with a combination of machined delrin bearing blocks and extruded aluminum rods. The drive system was made with a leadscrew mounted with a custom adapter into a bearing block with both a radial bearing and a thrust bearing to support the load of the head.
The whole system is shown to the left. Several of the machined parts are shown below.
The head lift system was the most mechanically complex system of this robot. We did not have the budget to purchase linear motion systems, so we had to custom make linear bearings, rods and drives. The bearing system was made with a combination of machined delrin bearing blocks and extruded aluminum rods. The drive system was made with a leadscrew mounted with a custom adapter into a bearing block with both a radial bearing and a thrust bearing to support the load of the head.
The whole system is shown to the left. Several of the machined parts are shown below.
Sensor Mounting and Wire Harness
Due to the linear motion systems, wiring needed to be contained such that it would not break when the system moved. There was not enough space or money in our budget to use an energy chain, so I designed a miniature equivalent. A weight holds down a cable that wires are wrapped around and keeps them from coming loose and getting caught in the moving parts.