Subsystem Build & Test
Team Vision for Subsystem Level Build & Test PhaseDuring this phase, the ComQuaT team planned to demonstrate functionality and share test results for each subsystem, including
- Leg chambers
- Tether spooling
- Drive train
We achieved these objectives except
- Leg chambers have encountered numerous technical difficulties with the Construct printers
- Tether spooling system is still in preliminary stages
- Deployment and reattachment system has been on hold while above are addressed
Opto-isolator Circuit TestTest was performed by connecting a switch between the valve and the power supply on the isolator circuit. After setup, the MOSFET was found to be unnecessary. The valve and switch were connected to the output side of the optoisolator. The switch was then toggled several times in rapid succession. This produced voltage spikes over 0.8V and up to 3V which is high enough to damage the input of the Arduino pins. The following figure shows these voltage spikes measured on the oscilloscope:
Power supply Variation TestThis test was performed in order to ensure that fluctuations on the power supply would not cause resets on the Arduino. A 25V power supply was connected to the 5V step down regulator and 12V step down regulator. The 12V step down regulator was used to power the RC motor driver. The oscilloscope was then attached to the output of the 5V regulator. Large voltage swings of 2V in amplitude were measured when the motors were started. This would cause resets on the Arduino if connected to the 5V line.
Arduino Valve Switching TestThe Arduino was connected to a prototype of the isolator circuit board. The output of the isolator circuit was then connected to 5 of the valves. The Arduino code was run to trigger the valves for 0.5 seconds every 1.5 seconds. They were programmed to have a phase difference of 0.25 seconds. It was expected that the valves could be heard triggering in this pattern. Initially, only one of the valves was heard firing. This was fixed by adding a BJT to the input of the isolator circuit and reducing the input resistance. The final circuit configuration was then given by:
After implementing these circuit changes, the Arduino code was run. When the Arduino code was run, the valves could be heard triggering in this pattern. The following video shows the Arduino powering the circuit and the clicking of the valves can be heard: Arduino Valve Switching Video
Expected Result: Hearing the valves
clicking in the pattern
Observed Results: Valves were heard clicking in the expected pattern
RC Control TestThe code for the RC was written on the Arduino. The USB host shield and motor driver shield were connected to the Arduino. The XBOX 360 controller dongle was connected to the USB host shield and connected to the controller. The code was structured to measure the displacement of the left and right controller sticks and scale them between 0 and 255.
Expected Result: Motors would move in the directions specified in the control diagrams with the specified speed
Observed Results: The motors moved in the proper directions and with reasonable angular speeds for each shaft
Pneumatic Supply System Test
Three tests were performed on the 3-way valve supply system to estimate fill rates and ensure head losses through valves wouldn't be overwhelmingly high. Test 1 connected both compressors in parallel directly into a balloon to maximize flow rate and minimize line losses. Test 2 added the 3-way valve and manifold system between the compressors and balloon. Test 3 re-configured the compressors in a series configuration to maximize delivered pressure.
When adding the 3-way valve/manifold assembly a drop in flow rate is observed. We suspect the 3-way valves have relatively high head losses due to their narrow internal channels. It appears from the tests that the series configuration inflates slightly faster than the parallel, which was not expected at first. The high pressure configuration reduces each individual pump's load and allows more air to be pushed through the 3-way valve. In a full configuration with 12 lines splitting the flow we expect line losses through individual valves to be significantly less than during these tests, and a parallel configuration may work better. Fortunately the nature of flexible tubing and barbed fittings allows for easy, repeatable re-configurations to best suit our needs.
Estimated Power Consumption
Leg Chamber Fabrication
- Heater Decoupling
- Overhang Angle Grade
- Extruder Damage/Failure
- Filament Rack Failure
- Filament Diameter Discrepancies
- and more...
Another challenge of fabricating inflatable legs is interior support. In solid objects 3D printers will fill the interior of the part with support structures, this allows the walls to remain stable and supports the top surface. Any traditional infill will block the flow of air to the leg chambers, leaving only two options: No Infill or Removable Infill. Below is an image of a print-in-progress that shows the dissolvable PVA (Polyvinyl Alcohol) support structures on the interior of the model. These support structures are intended to maintain the quality of the print's interior as well as dissolve in water after the NinjaFlex has been set.
Critical Decision Making The legs of the ComQuaT robot system are integral to the success of the project. The decision to use 3D Printing as the preferred method of fabrication for our design relied heavily on the project from University of California - San Diego, and unfortunately the levels of details included in the publication of the UCSD project, as well as the time and resources available to our team, are not sufficient for us to produce leg chambers that are similar at this time. For that reason we have begun to leverage past and present projects' research into silicone casting inflatable muscles through Dr. Lamkin-Kennard.
As an alternative method of fabrication, we have decided to cast the legs out of a flexible silicone. The Dragonskin material from Smooth On can be adjusted to achieve the desired rigidity. Two methods of casting are being explored using different molds. On recommendation from the Robotic Otter team, we are casting leg chambers in multiple steps. Each half of the leg will be cast using a vacuum chamber to ensure we minimize air bubbles in the mixture. The two halves will then be joined, again under a vacuum. Alternatively we will attempt to cast the entire leg as one piece, utilizing dissolvable 3D printed mold features for removal.
Risk and Problem Tracking
- Our Problem Tracking has been updated.
- Our Risk Assessment has been updated.
The Risk Assessment Chart has not changed since our last review.
Draft Layout for ImagineRIT Poster
Plans for next phaseBy our next demo in the last week of March, we plan to have achieved:
- Functional legs (3D printed and/or casting silicone)
- Working tether spooling system
- Working deploy/attach system
- Subsystem integration
|Project Manager||Conor McKaig|
|Lead Engineer||Zach DiLego|
|Electrical Engineer||Cameron Taylor|
|Software Engineer||Sean Bayley|
|Hardware Engineer||Zach Hayes|
|Purchasing & Materials||Marie McCartan|
|Comm. & Customer Contact||Jamie Mortensen|