Preliminary Detailed Design
Team Vision for Preliminary Detailed Design Phase
Vision and Results
- Continue and complete testing of available electrical
- FSR design is complete and has been simulated.
- Finalize lower body designs
- Actuators have been abandoned and the lower body design with motors has a frame. We are working towards optimizing the design and reducing its weight.
- Begin prototyping mechanical components
- Harmonic gearboxes are in the process of being ordered, as well as raw materials for machining.
- There is a lead time on the harmonic gears so we most likely will not be able to extend 15201 prototype. We are also awaiting an account number for these to be purchased.
- Amend the test plan as necessary
- No amendments were necessary at this point in the process
- The test plan has been updated to reflect what has been completed thus far
- Finalize BOM and begin ordering parts
- Parts are being ordered and the finalized BOM is in progress
All Phase 4 Accomplishments
After our last design review we started working on designing critical sensor PCBs, finalizing the lower body design and selecting motors, ordering components to reconstruct the 15201 leg design, and creating a very high level overview of the Teensy code. Today, we have a completed FSR PCB design that has been prototyped, a finished ADC PCB design and implementation, a design to test specific parts of the breakout PCB, and a first draft flow chart for the Teensy code. Mechanically, the lower body design has been mostly finalized, actuators have been abandoned in favor of a motor only design, and the design thickness and weight has been reduced greatly. For the next review we plan to have a final design, have the remaining sensor PCBs prototyped, and begin machining our leg design.
Prototyping, Engineering Analysis, Simulation
Test Rig For EEs
- A two-joint test rig has been completed which the EEs will use for testing electrical components and walking code
- Motor mounts were modified to accommodate new motors
- The test rig is available to look at upon request
Level Shifter Test PCB
In order for the Teensy 3.2 to communicate with the various digital components (including the motors) which operate at 5 V, level shifters are necessary. A failing of the previous revision of the breakout board was that the level shifters could not supply enough current. In order to avoid that situation, the breakout this time will be fully prototyped. This requires a test PCB for connection to the level shifter. To that end, the level shifter test PCB was developed in cooperation with Benjamin Haag, of the Tigerbot V team.
Video of FSR test
(Refer to page 3 of the provided handout)
Revised Torque Analysis
(Refer to page 5 of the provided handout)
- In general, our F.O.S. approach yielded more reasonable numbers
- Some joints actually required more torque according
to our analysis
- This affects motor choice (We need stronger motors for the hip joints)
- New motors have already been chosen
Schematics and Flow Charts
Teensy Code Flowchart
(Refer to page 6 of the provided handout)
A very top-level overview of the individual Teensy code functionality.
(Refer to page 12 of the provided handout)
A preliminary overview of the electrical system for the lower body.
(Refer to page 4 of the provided handout)
The breakout will be fully prototyped before building. Changes from the previous revision of the breakout board include removing level shifter 1 V capabilities, and the change from bidirectional to unidirectional level shifters. As the motors appear to have 3 inputs and 1 output each, and no bidirectional busses, this does not appear to be an issue. The previous revision of the flowchart has two dedicated lines for the I2C bus, which do not run through the level shifter. This is kept in this revision, and will be tested.
Bill of Materials (BOM)
Test PlanLink to download revised Test Plan Document spreadsheet
Actuators hybrid design
- The actuator has to be on the outside of the leg to avoid interfering with motor.
- Obstructs human appearance, but could fit in profile with angled legs
- Retains advantage of 2 DOF in a single point
- Due to duty-cycle issues, this idea has been shelved
90% lower body design
(Refer to pages 7-10 of the provided handout)
PLEASE NOTE: THIS IS NOT THE MOST UP TO DATE MODEL. PLEASE SEE LOWER BODY DESIGN WITH ANGLED LEGS. THE TORSO FRAME HAS BEEN UPDATED TO INCLUDE AN ANGLE. BEARINGS AND SCREWS HAVE BEEN ADDED TO JOINTS. MOTORS HAVE BEEN CHANGED.
- Angled Lower Half
- Front Ankle Closeup
- Side Ankle Closeup
- Front Leg Detail
- Side Leg Detail
- Top Torso Detail
Lower body design with angled legs
(Refer to page 11 of the provided handout)
- Does not interfere with motor operation
- Provides better balance while walking by mimicking human body shape.
- Angled plates would most likely need to be welded to frame
- Less modularity
- May be able to bend to match angle instead of welding (could then use fasteners as in other designs)
Design Review Materials
Plans for next phase
- Completely Finalize and begin machining lower body
- Layout electrical system within mechanical design
- Create MSD II Project Plan