Preliminary Detailed Design
Team Vision for Preliminary Detailed Design PhaseOur team goal for this phase was to begin detailed design with a focus on high risk subsystems. We focused primarily on the leg and tail subsystems with a secondary focus on waterproofing, intermediate structures (spine, hips, shoulders), and RC.
We have settled on a final design for tail and have narrowed down to 2 potential leg designs. We have begun a bill of materials which we will flesh out as we continue to finalize component specifications.
Prototyping, Engineering Analysis, SimulationIterative activities to demonstrate feasibility, including assumptions you made in your analyses or simulations. Have you completed sufficient analysis to ensure that your design will satisfy requirements? Have you included all usage scenarios in your modeling?
Feasibility: Prototyping, Analysis, Simulation
Leg Motor Torque FeasibilityTo better reflect our actual designs, the leg torque calculations were revised to a 2 degree of freedom model.
We used Section 2.1 of this paper as a basis for the model.
By plugging in our rough parameters we can calculate a projected worst case torque for each joint:
|Joint||Projected Torque (kg-cm)|
The code used can be found here.
Alternate Leg Design
In order to save money on servos we looked into different mechanical designs to have a leg with a joint be moved by one servo. We found the Theo Jansen walking machine and used it as a basis for a new leg design.
It was then 3D printed and tested to make sure it would work in real life. The only issue is that the design requires a 360-degree servo in order to work and after exhaustive research, there are none available with the torque we need that are also waterproof. This means that we will need to manually waterproof the servo. We plan on trying it out with a cheap servo we already have so we do not destroy the expensive one. If this fails we will go back to the original design of moving the leg with two normal servos.
Drawings, Schematics, Flow Charts, Simulations
Bill of Materials (BOM)
Currently these are the required materials for purchasing. A budget increase request form will be eventually presented to the client, if necessary.
- Currently testing waterproof servo by running it in a bowl of water for 5 minutes once a day for 2 weeks
- Once the tail has been 3-D printed and the bearings arrive it will be assembled and tested in water with the single servo we have
- Once the waterproof servo passes our test we will order a second to be able to test the full tail motion in water with both servos
- A test setup will be created by mounting the servo that would normal be mounted on the body to a floating raft. This will allow us to see if the motion we planned will provide enough thrust in the water.
Design and Flowcharts
RC Transmit and Receive Design
To implement an RC Controller for our Robotter, we need to understand how the controllers communicate with an arduino. RC Controllers typically communicate on various channels, at 2.4GHz. Each channel corresponds to a different operation on the physical controller. For example channel 1 may be a joystick and channel 2 may be a button. That signal is transmitted from the controller to a receiver, with a matching number of channels. Many controllers fortunately come with a matching receiver. The receiver will take the signal, at 2.4GHz, and then output a converted digital signal to the arduino. The arduino can then map the receiver's signal to values that correspond to something the servos understand. The figure below outlines how the RC Trasnmit and Receive would work in the system.
Risk AssessmentWe have not yet been able to decrease the projected likelihood of any of our risks but hope to be able to do so by the end of this semester. We added an additional risk with respect to how our bearings will behave when submerged in water.
A working copy of our risk assessment can be found here.
Design Review MaterialsOur Design Review Slides can be found here
Plans for next phase
- As a team, where do you want to be in three weeks at your next review?
- As an individual on the team, what are you doing to help your team achieve these goals? (Use the individual 3-week plan template for this)