They don't back-drive well. The whole point of this hand design is to back-drive the contact forces into the motor, where there's force control. They're somewhat bulky, too.
Key concept: force-based motor control works quite well. Preserve that property through the gear train and force-based hand control works.
What? An ideal capstan drive can be backdriven perfectly fine. You only run into problems once it stops being ideal (e.g. built out of heavy parts, high gear ratio, etc.)
It's the high reduction ratio that's the problem. If you build a 200:1 capstan, it's not going to back drive well. And it won't be anywhere near ideal.
capstan drives help with backlash (though they are in generally less stiff than gears, so it's not without tradeoffs), but they don't really help with any of the other issues.
They don't back-drive well. The whole point of this hand design is to back-drive the contact forces into the motor, where there's force control. They're somewhat bulky, too.
Key concept: force-based motor control works quite well. Preserve that property through the gear train and force-based hand control works.
> They don't back-drive well
What? An ideal capstan drive can be backdriven perfectly fine. You only run into problems once it stops being ideal (e.g. built out of heavy parts, high gear ratio, etc.)
It's the high reduction ratio that's the problem. If you build a 200:1 capstan, it's not going to back drive well. And it won't be anywhere near ideal.
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capstan drives help with backlash (though they are in generally less stiff than gears, so it's not without tradeoffs), but they don't really help with any of the other issues.