4 ms·

I hate the phrase "zero backlash" that gets used right in the intro. Nothing has zero backlash. If it did, that would mean the material is incompressible & unst

I hate the phrase "zero backlash" that gets used right in the intro. Nothing has zero backlash. If it did, that would mean the material is incompressible & unstretchable: it would have an infinite speed of sound. You could implement FTL communication using zero-backlash actuators. Capstan drives have backlash because the rope stretches. It's very low if using a low-stretch rope, but nonzero.

fusionadvocate 7mo ago
What you are referring to is stiffness, which is different than backlash. Backlash, or play, is due to gaps.
- SAI_Peregrinus 7mo ago
  Backlash & a lack of stiffness have the same effect, but the cause happens at different scales. Just because the gaps are in between the atoms of the dyneema doesn't mean there are no gaps! There's still play due to a lack of stiffness, just less of it. The positioning errors should be lower than the feedback resolution on the servo encoders, but they won't be zero.
  - vablings 7mo ago
    I disagree; backlash is unrelated to force. If you were to graph error over force for backlash it would be a straight line but for something like dyneema it would directly scale with force applied. In a driven system the dead zone is graphable and that deadzone time or area does not change based on velocity, A lack of rigidity in couplings, gears or belts IS affected by velocity
vablings 7mo ago
Backlash is specifically the slack between directional change. The forces you describe are proportional to force. Backlash is independent of force
- hinkley 7mo ago
  Dyneema has remarkably low elongation, in addition to its very high strength to weigh ratio. Higher than Kevlar (but less heat resistant). It’s why they used it for sail cloth before rigid body sails took over most competition sailing. Aaed I believe is preloading his devices, which should eliminate most of the remaining give but also increase wear rate. Though it sounds like from the video that the biggest problem is rubbing the cord against itself, hence the channels to guide the cords.

fusionadvocate 7mo ago

What you are referring to is stiffness, which is different than backlash. Backlash, or play, is due to gaps.

SAI_Peregrinus 7mo ago
Backlash & a lack of stiffness have the same effect, but the cause happens at different scales. Just because the gaps are in between the atoms of the dyneema doesn't mean there are no gaps! There's still play due to a lack of stiffness, just less of it. The positioning errors should be lower than the feedback resolution on the servo encoders, but they won't be zero.
- vablings 7mo ago
  I disagree; backlash is unrelated to force. If you were to graph error over force for backlash it would be a straight line but for something like dyneema it would directly scale with force applied. In a driven system the dead zone is graphable and that deadzone time or area does not change based on velocity, A lack of rigidity in couplings, gears or belts IS affected by velocity

vablings 7mo ago

Backlash is specifically the slack between directional change. The forces you describe are proportional to force. Backlash is independent of force

hinkley 7mo ago
Dyneema has remarkably low elongation, in addition to its very high strength to weigh ratio. Higher than Kevlar (but less heat resistant). It’s why they used it for sail cloth before rigid body sails took over most competition sailing. Aaed I believe is preloading his devices, which should eliminate most of the remaining give but also increase wear rate. Though it sounds like from the video that the biggest problem is rubbing the cord against itself, hence the channels to guide the cords.