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To get a general idea of the motion of this mechanism, we drew it up in Working Model and simulated it. Immediately a problem was discovered, the mechanism was found to shift not just the amplitude of the output link, but the zero amplitude. The zero amplitude being the location the link oscillates around. This is fine for a mechanism that is in a ratchetting CVT, but not so for a quadruped robot. In a ratchetting CVT
all that matters is that the amplitude change, but doing so in a walking robot can cause the walking robot to become unstable.
To get around this, the link lengths and pivot locations were tweaked in Working Model. However doing so in Working Model turned out to be an arduous and time consuming process, so a simulation of the linkage was written in Javascript. This allowed us to quickly and easily change linkage parameters and obtain values for linkage amplitude and zero amplitude in real time to optimize the linkage. We then tweaked the parameters until the desired amplitude variation of 20-30 degrees was attained and zero amplitude variation was minimized. In the end we were able to get the required amplitude variation with an input angle range of 38°-80° and with a zero amplitude variation of 1°.
Sources:
- A Variable Stroke Mechanism for Ornithopters
- Fixed Frequency, Variable Amplitude (FiFVA) Actuation Systems for Micro Air Vehicles
- Mechanisms and Mechanical Devices Sourcebook Third Edition
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