Review of Requirements
Requirement | Value | Units |
---|---|---|
Permissible Mass (Motor + Gearbox) | 1.5 | kg |
Output Ideal RPM | 3-4 | RPM |
Output No Load Torque (No SF) | 44 | Nm |
Output Max Load Torque w/ (No SF) | 95 | Nm |
Backlash | < 30 | arcmin |
Budget | ~1000-1200 | USD (See note**) |
*Note: We have currently ~4000 USD budget for entire arm. Motors/gearboxes for Axis 4/5/6 are estimated to be about 1500 USD, and on axis 1 and 3 approximately 400 USD each. We also want to aim to save ~500-750 USD on arm budget for construction materials of custom parts, bearings, fasteners, etc. This leaves us with ~1000-1200 USD leftover
Review of Testing Data
- Testing was not as comprehensive as desired for axis 2 - have ran into challenges with broken components and belt skipping
- Current tests are also done on prototype arm that has a a 1.25m horizontal reach, after reanalyzing our workspace we have decided to change the maximum horizontal reach of our arm to be 1m
- With arm prototype, our measured no load torque (static + estimated dynamic torque values) at full horizontal extension (max loading scenario) was 61 Nm
- Experimental dynamic torque testing at full horizontal extension and no load showed a peak instantaneous torque of 55.5 Nm (very close to expected calculated values)
- First set of testing data was taken without gripper - installed on arm (different mass / lower moment arm) so results aren't seriously considered
- Further testing has temporarily been stopped as the belt wore out due to repeated skipping under 3kg payloads - replacement belt was installed but constant skipping still observed even under no load. To be investigated on weekend of October 1st
- Current Conclusion - Hand calculations with a generous SF (1.5x) are likely sufficient for torque requirements - performance may not be perfect but that may have to be optimized in the future