...
- Have been looking into actuator options
- Developed one set of options, with more details posted in 2022 Arm Actuator Selection Options
- Conducted arm testing
- Have not completed actuator selection for A2 - more details on that in the following sections
- Have been slow with redesigns of axis 1/2
...
- Gripper optimization, fixing slack on links
- High level overview of design choices
Jasmine - Added after the meeting
- Document current comms hardware on this confluence page
- Removed communication components from the rover
- Begun assembly on portable comms system
Experimental Results to Date
...
Expand |
---|
|
Motors- Obviously, we need to select BLDCs
- Will be selecting 24VDC BLDCs and scrapping 48VDC motors due to availability
- Integrate RLS or netzer encoders into joints, not broadcom AEATs
BACKDRIVING - A1 is backdriveable but will not experience too many loads to backdrive it when driving around
- A2 and A3 both passively backdrive
- A4 has some backdriving (not much) under 5kg load
- A5/A6 occasionally had minor backdriving under 5kg load (only witnessed this once, but other times throughout testing it did not backdriving)
- Opinion: backdriving is only a concern on joints that passively backdrive when the arm is unloaded
- Don't want to constantly consume power to hold arm position when unloaded
- When arm is loaded, we will be drawing power/current anyways and will not carry high loads under extended periods of time - thus we can probably pass over fixing backdriving on A1, A4, A5, A6
- Worm gears or breaks for A2/A3? Or just choose a transmission option with high enough internal friction to counter natural mass moment (risky, easy to get wrong)
Axis 1- Current belt tensioner loosened over time - and is somewhat difficult to readjust/tension on the fly
- Solutions:
- Apply a lead screw tightener
- Use static tensioners (like the bearings idea on A3)
- Switch to gearing (see kaydon bearing)
- Turntable bearing is not sufficent. Entire robot base tilts when larger moment loads are applied to A2
- Solutions:
- Spec a proper crossed roller bearing with high moment, axial and radial load tolerances A1 - Turntable Bearing Options (Kaydon, iGUS, chinese bearings, mcmaster)
- Currently chasing down SKF on if we can spec a turntable bearing from Kaydon through our sponsorship
- These bearings come with no teeth, or teeth on inner/outer race depending on config. If these are available, we can remove the belt and simply use the kaydon bearing as a gear/bearing at the same time - saving weight and components.
- Rated for various loads, weigh 200g-500g
- Better cable management solutions should be integrated for this pairing
Axis 2- Obviously belt drive does not work due to slipping
- Single stage reduction option availability seems initially slim (based on Electromate comms, not much external research has been completed)
- Other than that, A2's linkage and frame construction seems OK
- Simplify construction and reduce number of parts for next revision
- Better cable management solutions should be integrated for this pairing
Axis 3- Comprehensive load testing on A3 has not been completed, but from initial observations it works well.
- Reduce weight if possible / simplify number of components for next design
- Should reduce the transmission ratio on the belt. A3 is currently fine, but if anything is learned from A2 large belt ratios can occasionally be unreliable
- Closer to chris annin
- Better cable management solutions should be integrated for this pairing
Axis 4- Experimental loads are higher than initally calculated, however they are still within a similar range to A5/A6
- We can likely still spec the same motor + gearbox for all three of these axis
- Design can likely be simplified, implement off-axis encoder to reduce weird components
- I think we should continue to have the A4 motor stick out on the opposite side of the link (counter act the moment)
- Better cable management solutions should be integrated for this pairing
Axis 5/6- Differential is very rigid/stable
- Experienced loads are higher, internal tooth meshing friction may be high but also there may just be significant dynamic torque applied
- We are still within our expected calculated range (with SF), current requirements with SF are likely sufficent for upcoming design
- Reduce bulk for upcoming design
- Improve cable management
- Better cable management solutions should be integrated for this pairing
|
...
- This is BY FAR OUR MOST IMPORTANT PRIORITY TASK.
- Current Actuator Selection: 2022 Arm Actuator Selection Options
- Maxon motors are currently mostly out of stock (only this one in stock)
- From research, EC-flat motors are preferred as they have high power densities and lower weight
- Other motors are available, but simply heavier. Cheap option is nanotech plug and drive.
- We should aim to get our finalized parts selected by wednesday, and put in the order friday/next monday latest
- Need to PUSH with this - main priority for all designers
- Help select options for other peoples joints if yours are done.
- Aim to complete testing before ordering parts to validate our requirements - if testing cannot get done in time we should just increase safety factor and order
...
Key Task Delegation for This Week
Review 2022 Arm Actuator Selection Options and PROVIDE FEEDBACK/QUESTIONS/COMMENTS/CONCERNS
...