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- Regular types of toothed gears have small gaps between the teeth of mating gears
- This allows them to mesh and rotate smoothly and without damage
- A downside of this is it lets the gears “wiggle” a little bit - the small gap means that the gears can move back and forth a small amount without moving the motor
How does it work?
Main parts
- Wave generator(green)
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Examples of the flex spline’s rotation
More Technicalities
Calculating gear ratio
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- Flexspline is shaped like a top hat (like cup style, but with a “brim” on the output)
- Brim of the flexspline is the outermost diameter
- Hole for wires through the middle
Where we need it
Location | Voltage (V) | Max Current Draw [A] | Stall Torque (N-m) | Max Speed (RPM) | Reduction Ratio To Encoder | Max Speed at Encoder (RPM) | Datasheet |
Elbow | 12 | 25 | 0.669 | 4150 | 252 | 16.46825397 | |
Wrist | 24 | 5.5 | 4.8 | 67 | 1 | 67 |
Elbow
- Biggest issue
Wrist
- Second priority
- Would require significant design change
Advantages and disadvantages
Advantages
Advantage | Details | Significance |
Lightweight | ||
Precise | The robot’s claw has to perform careful tasks so high precision is very important | |
They require little maintenance -they are either working or broken and need replacing -apparently very reliable | -would not require maintenance (as much) -lasts a long time (fewer long term costs and time associated) | |
Preloaded | Def: applying pressure to fix a component in place/applying extra pressure to ensure the component can handle future strain -helps to ensure zero backlash for life of gear -top of flex spline is circular (output side) while the bottom is elliptical therefore flex spline teeth flare out slightly -this results in a conical angle that helps to preload the flex spline and circular spline -preloading removes free internal clearances (no shifting) | |
repeatability | -maintains positional accuracy when repeating a task over and over and over again |
Disadvantages
Disadvantage | Details | Significance |
EXPENSIVE | - None of the principle suppliers have prices listed (that I could find) but other sources show the price to be several hundred dollars for one unit - Would likely need to get sponsored in order to actually acquire these | |
Low speed output | - The high gear ratio means that the output speed is significantly lower than the input speed - This could be more or less important depending on the joint it’s used on |
Suppliers
Harmonic Drive ®️
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- Probably not the best accuracy which completely defeats the purpose
- Cheap though!
Usage examples
From Cone Drive website
From Harmonic Drive®️ website
From this video (technically a cycloid gearbox, not harmonic drive, but similar enough concept)
From here
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