Washbot Phase 2: Optimization
The second phase of the project by this product design firm in Miami involved optimizing the design for production. It included:
The entire system was controlled by AC/DC and pneumatic components. Features of the AC system included:
- Transformer cable converting AC to DC to supply 14A to 45A,
- Sever PCBs designed for communication, component control and power control
- Main/Power PCB to supply power to external controllers and on-board devices
- RF module to communicate with a wireless remote controller
- Motor Controller PCB developed by us to control motor direction, but not speed rated for a 90 V 3A max DC motor
- Valve controllers
- Brake controllers
- Main Control Unit
The pneumatic system, whose most crucial components were:
- Rotary actuators to control and stabilize the structure
- Valves to control the flow of air, allowing for the change in direction of the motors
- Electrical brakes and valves used with code to manipulate and control the rise and decrements of the structure
This solution was optimized from concept phase and split into 3 parts
This development was challenging because we had to come up with a simple, easy to build modular solution that was effective in its purpose. We developed a telescopic solution that uses pulleys and steel wires.
One motor is rotating 2 steel wire spools via a set of timing belts kept tight on timing pulley, thus transferring the entire rotation of the motor shaft to the spools, which has steel wire wrapped around. They rotate in opposite directions and when the rotary switches from CCW to CW, then the telescopic segment also switches the direction of movement, thus achieving the in and out movement.
One segment houses the nozzle, camera housing and sensors at the tip and it is aligned on axis via a set of adjustable wheels and ball bearings. It can slide in and out on 4 rails that are welded on the outer structure. The hose and cable that powers the tip nozzle and camera, are secured to the upper segment of the Washbot arm, by a set of rollers.
The Truss geometry which is the same for all segments. The only difference being the pipe dimensions used.
These are universal throughout the entire design and had to be designed to be secure, light, compact and strong. We developed a joint made out of two halves (one motorized and the other offers structural support) rotating along a common axis/shaft. The motorized joint is powered by a pneumatic motor and secured by a magnetic safety brake which locks when no current passes through it.
The encoded motor is powered by a set of 2 pneumatic hoses that enter the joint, coming from the segments below it. As you go up towards the uppermost joint, the number of hoses secured into the segments lowers by a factor of 2 for each joint that passes.
This was the last phase of engineering services by our product design firm in Miami was where we performed Finite Element Analysis (FEA) to ensure that the mechanical system would not fail due to gravity, heavy loads, or power loss. After several Analysis iterations we the following were determined:
- Washbot segments can be kept light and product energy efficient by using AL6063-T6 as the structural material. This gave acceptable stress concentrations limits and a safety factor of 1.5.
- Stronger washers and larger bolts for the main connection points between Truss and Joint should be used, based on the analysis performed by the engineers at Letsky Innovations a product design firm in Miami.