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  1. jbendercp

    How to design for an M8 heat-set insert in a 2mm-thickness injection molded part?

    Currently designing an ABS injection-molded part with wall thickness of 2mm. I want to use an M8 screw for mounting the part (as it is industry standard), and thinking to use a heat-set insert to keep the tooling simple (no undercuts, screw threads) and overall strength. However, manufacturer...
  2. jbendercp

    ABS molded housing snap fits--side action or bump-offs?

    Kyle--Thanks, I'm familiar with the technique you're talking about. I'll have to see if I it works in the design, as it seems to be a straightforward way to eliminate side actions. Still specifically curious about the cantilever w/ undercut (hole) and fixed hook technique that seems to be...
  3. jbendercp

    ABS molded housing snap fits--side action or bump-offs?

    Realise this is probably a poor question due to variables (part geometry, intended use). However, trying to design an ABS-plastic injection-molded part and need the two halves of the housing to snap together. As such, been pulling apart every cheap ABS injection-molded part in my house: old...
  4. jbendercp

    Multiple torsion spring problem

    Good points. Manufacturer provides details for radial constraint, max dowel diameter, and related torsional spring constant, planning on using these for analysis. While idealized, assuming (correctly, i hope) end result will be close enough for my needs. Cable stretch and friction are more my...
  5. jbendercp

    Multiple torsion spring problem

    Thanks 3DDave, this is exactly what I was looking for. In the end, just looking to size my cable and power source that generates the tension. Hoping to use some simplified model & assumptions (e.g assuming eyelets are close enough to joint centers to keep lever arm essentially constant, even...
  6. jbendercp

    Multiple torsion spring problem

    Okay, hopefully this diagram is a bit more helpful (see attached). Also drew it at a slightly tensioned state to (maybe) help with the visualization. Again, original question is regarding calculation of the amount of cable tension force (F) to generate, a given degree of rotation amongst the...
  7. jbendercp

    Multiple torsion spring problem

    I think my picture is poorly drawn to illustrate the situation. Eyelets are not right at the joints themselves, but set a bit off from the joint center. Thus, as the segments rotate (angle becomes less between segments), the eyelets from each segment are actually moving closer together (thus...
  8. jbendercp

    Multiple torsion spring problem

    Sorry, my diagram is admittedly less than helpful. The cable causes rotation in the segments because eyelets hold the cable (which is fastened at the far end) a perpendicular distance 'R' away from the joint center. Thus the tension force 'F' creates a moment about the joints due the force 'F'...
  9. jbendercp

    Multiple torsion spring problem

    Will try to do my best at explaining, you can see the less-than-helpful graphic attached as well. I have a linkage of 4 segments joined end-to-end in a straight line. Rotation at each of the three joint locations is controlled by torsion springs (all three of same spring constant). A single...
  10. jbendercp

    Plastic housing for fishing line?

    Cable will be running along the gripping surface of the hand. Worried coffee stirs won't a) hold up over large cycles and b) may compress when gripping something tightly, thus choking off the control line. Airplane control cable looks like it comes in something like $.20/ft or less, not bad...
  11. jbendercp

    Plastic housing for fishing line?

    Sorry for the delay in response, was waiting for an e-mail notification that never came. Regarding bicycle break cables: Indeed my first iteration was with brake cables I got at the local store, but this solution (the entire cable) was much too heavy. I didn't even think about removing the...
  12. jbendercp

    Plastic housing for fishing line?

    Working on a low-cost prosthetic hand design, and looking for a lightweight yet rigid material to use as a housing for the heavy fishing line that actuates fingers. Catch is that I live in rural SE Asia and need to find parts that are already used in other commonly found items (or are common...
  13. jbendercp

    Quick-release function for traveling-nut actuator?

    mcgyvr, Thanks for the thoughts. Not sure either of these would have the accuracy, and/or filtering of limb movement necessary for prosthetic use. Similar issues when people tried to use the Structure Sensor (only $500!!) and even the new Kinect Sensor. However, I just saw that one of the...
  14. jbendercp

    Quick-release function for traveling-nut actuator?

    Thanks for your insights, a thoughts regarding some of your comments: zeusfaber: no, power transmission needs will be pretty minimal ( < 5lb I would guess). The leadscrew does however give me good precision (I'm thinking digitising will be done in/around 2-4mm per slice/rotation, so probably...
  15. jbendercp

    Quick-release function for traveling-nut actuator?

    tbuelna, Good thoughts. Actually some folks have already moved this direction - the 'Structure Sensor' is a $500 3D digitizer iPad add-on that uses the camera to sense a create a 3D surface. Other companies even in traditional settings as well do exactly what you mention - develop 3d models...
  16. jbendercp

    Quick-release function for traveling-nut actuator?

    Starting to draw up plans for a affordable digitizer for use in prosthetic work in low-income settings. The primary function will be to trace the inner surfaces of plaster casts taken from client's residual limbs, converting them into a 3d-surface for computer-based model rectification and...

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