DATE: November 8th 2018
TIME: 4:45 - 7:00 (2.25 hours)
People Who Attended:
Alex, Seth, Tanner, Avery, Paige, Thomas
Research Meeting for Prosthetic Limb - Lemelson MIT InvenTeam
-Discussed a testing device using gears and a self made treadmill to simulate walking
-It was undecided whether our previous design or the new design would work better
-Discussed how to measure energy when running tests
-Could use force plates, piezo or anything that generates feedback when stepped on
-Mr. Foye demonstrated the use of different gear boxes and a very cheap motor attached to a lever to generate power from about a half inch of motion at the axle
-One of the gear boxes was just direct to the motor and still generated about 5 volts with practically no resistance.
-The other was more resistive but still within reason but generated upward of 80 volts
-The use of an expensive motor and gear box could result in very substantial gains in power.
-We also made a small task list to complete
Submitted by: Alex Magnuson
Today Mr. Foye shared his idea on a new testing machine using gears to create a consistent step. In addition, the machine would also use a treadmill to help simulate the motion of walking. It is disputed whether we want to pursue our previous testing idea or the new one. We learned about ways to test our devices and methods to calculate power. We can use force plates or piezo or other measurements methods and use the feedback from those devices to calculate the power that a step makes. In testing the energy production device we can use the resistance of the motor and voltage created by using the formulas and steps below to figure out power produced. The use of two gear boxes with a motor at the output and a lever at the input. The first one had very low lever resistance but a lower output at around 5 volts. The second gearbox was more resistive than the first but generated substantially more voltage at around 80 volts. A google sheet table was made to show how load effected power output based on these demonstrations (Shared with Paige and Mr. J). It was mentioned that the tools used in the demonstration were very cheap and with higher end components we could get much better numbers. We also came up a small task list for us to complete (Below).
How to test for load on lever and generator
-measure terminal to terminal resistance
-Voltage divided by internal resistance + load resistance = current total
-V/IR (Internal Resistance) +LR (Load Resistance) = I (Current Total)
-Power in watts = Current^2 * Load resistance I^2 * LR (Load Resistance)
-power*time = j
operating capacity = 13.5 Kj
Task List
1) Force deflections in various places on foot
1a) what tests
-single operation
-continual operation
1b) more ideas
-angle adjustments for ankle
Measurements
-force(piezo or force plate)
-deflection
-electrical (Voltage, Current, Power, Efficiency, Etc.)
2)Gear Motor requirements for testing machine
3) Detailing Design
4) Build Tester
5) Measurements
Mr. Foye going through some engineering calculations for testing device. |
Thomas, Alex and Seth watching as Mr. Foye illustrates the testing device options. |
Tanner uploading waiver forms on the Lemelson-MIT site. |
Tanner, Paige and Avery working on the PR Powerpoint. |
Students measuring electrical output from gearboxes with an O-scope. Notice how the voltage generated spikes on the scope into the 5 V range with this basic system. The other gear box was much higher into the 30-40 volt range.
Alex and Thomas working on a lever and generator spreadsheet (and eating pizza).
Notes from our engineering consultant, Mr. Foye:
Session number one introduced the idea of a small DC machine as a generator
this session will present two examples of gear trains connected to small DC machines to allow basic testing
the goal of the idea is to develop basic feasibility of a battery charger for the vacuum pump puck, not necessarily a production design.
One principle of feasibility development is to attempt demonstration using a configuration which suggests a direction for the production design. To aid in this the technology available to be used should be readily available, to allow a basic size and cost assessment
with a demonstrated design configuration, observations may be made about possible refinements in an optimized design. The development of the feasibility model enables the development of basic design parameters, and the demonstration and testing to validate those design parameters as practical.
The majority of the work and then becomes team development of basic ideas using readily available technology, with follow-up testing and evaluation of demonstration prototypes. This avoids some of the problems with the requirement to do a fundamental design, not taking advantage of available technology, and then requiring the fabrication of new or novel components. Using available technology, the only barrier to a testable prototype is the fabrication of the application system, rather than the basic components themselves. Using engineering principles, some extrapolation in performance of the use of optimized components can be projected.
Exploration of geartrain drive with a DC machine
in exploring the operation of a geartrain driven generator, rapid construction of test prototypes which are expected to operate near the projected required performance can be done to explore the trade-offs inherent in those system approaches. A longer geartrain with more gear elements is capable of more variation in speed and torque output, which then can be applied to a broader range of generators that may be available. It may be more feasible to generate higher voltage and lower currents, if that is desired.
On the other hand a smaller geartrain will have a much narrower range of speed and torque, restricting available machines to limited output, which then requires more extrapolation of the generator design to obtain the desired output usable by the electronics.
Using this approach they system demonstration starts to take the shape of working backwards from the load requirement to determine power electronic conversion stages. The next step is extrapolation to the generator and mechanical links to determine the generator stage required performance.
The process then becomes:
0) identify the basic range of system operating parameters that may be acceptable
1) establish basic operating characteristics of the generator
2) establish basic operating characteristics of the geartrain
3) build demonstration generator and geartrain prototypes to explore operating characteristics using data from zero, one, two
4) system and storage suggested by the data from step three
5) evaluate the results of steps three and four; iterate on steps three, four, and five is necessary to arrive at a successful result or meet a deadline
6) adapt a prototype to a demonstration tester for display of the feasible result
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