Nori Francesco

Genova 28th January 2008

TOOLS TO BE USED

coated steel wire (Cod U7194561 Carl Stahl)

set of small screwdrivers

cyanoacrylic glue

steel wire cutter

set of hexagonal screw drivers

power grippers

tensioners (open cable version: CAD code ??????????)

iCub wrist cabling

In this document we describe how to cable the wrist. The wrist movements (roll, pitch and yaw) are achieved with three motors located in the forearm. The wrist roll (or pronosupination) is achieved directly, i.e. without any cable driven joint.

The wrist pitch and yaw are instead cable driven. The actuation is achieved with two motors which jointly collaborate to the pitch and yaw degrees of freedom. The actuation is differential with the following relationship:

wrist_pitch = M1

wrist_yaw = M1 + M2

where M1 and M2 are the angular positions of the the two motors contributing to the movements. We have:

RIGHT_ARM

M1: angular position of 2B2M1

M2: angular position of 2B2M2

LEFT_ARM

M1: angular position of 1B2M1

M2: angular position of 1B2M2

M1 (wrist_pitch and wrist_yaw): SxWrPy and DxWrPy

WrPy
Motor / 1B2M1 (SxWrPy) and 2B2M1 (DxWrPy)
Cable / Carl Stahl CG077063

Pictures:

Joint pulley (with holes visible).

  1. Take a piece of uncoated cable (more or less 20 cm). Let its extremities be E1 and E2.
  2. Pass the cable trough the hole (H) in the pulley.
  3. Block the cable on the hole H with some cyanoacrylic glue.
  1. Twine the cable on the pulley. The number of turns around the pulley has to be decided on the basis of the entrance and exit pulleys (P1 and P2): the cable should be tangential to the pulleys.
  2. Block the cable on the motor with some tape. This will allow you to maintain the cable positioned on the pulley.
  3. Take a piece of cable. Tie in a knot at one extremity. Take the other extremity (E3) and pass it trough the hole H1 on the pulley P3. Exit the pulley trough the hole H2.
  4. Take a tensioner and remove the left-hand (LHS1) and the right-hand screws (RHS1).
  5. Remove E1 from the tape that blocks it on the motor.
  6. Pass E3 trough the hole in LHS1. Pass E1 through the hole in RHS1.
  7. Tie in a knot (KN1) on E1. This knot should be positioned so as to have the tensioner in the middle of the admissible range of movements.
  8. Tie in a knot (KN3) on E3. This knot should be positioned taking into account the length of the tensioner.
  9. Twine the cable E3 on the pulley P3 (see the picture). Screw LHS1 and RHS1 on the tensioner.
  10. Take a piece of cable. Tie in a knot at one extremity. Take the other extremity (E4) and pass it trough the hole H3 on the pulley P3. Exit the pulley trough the hole H4.
  11. Take a tensioner and remove the left-hand (LHS2) and the right-hand screws (RHS2).
  12. Remove E2 from the tape that blocks it on the motor.
  13. Pass E4 trough the hole in LHS1. Pass E2 through the hole in RHS1.
  14. Tie in a knot (KN2) on E2. This knot should be positioned so as to have the tensioner in the middle of the admissible range of movements.
  15. Tie in a knot (KN4) on E4. This knot should be positioned taking into account the length of the tensioner.
  16. Twine the cable E4 on the pulley P3 (see the picture). Screw LHS2 and RHS2 on the tensioner.

TIPS AND TRICKS:

In order to increase the cable tension it is useful to unscrew the screws S1 and S2. After having completed all the described operations the cable tension can be increased by tightening the

screws S1 and S2.

M2 (wrist_yaw): SxWrYw and DxWrYw

WrYw
Motor / 1B2M2 (SxWrYw) and 2B2M2 (DxWrYw)
Cable / Carl Stahl CG077063
  1. Take a piece of uncoated cable (more or less 20 cm). Let its extremities be E1 and E2.
  2. Pass the cable trough the hole (H) in the pulley.
  3. Block the cable on the hole H with some cyanoacrylic glue.
  1. Twine the cable on the pulley. The number of turns around the pulley has to be decided on the basis of the entrance and exit pulleys (P1 and P2): the cable should be tangential to the pulleys.
  2. Block the cable on the motor with some tape. This will allow you to maintain the cable positioned on the pulley.
  3. Take a piece of cable. Tie in a knot at one extremity. Take the other extremity (E3) and pass it trough the hole H1 on the pulley P3. Exit the pulley trough the hole H2.
  4. Take a tensioner and remove the left-hand (LHS1) and the right-hand screws (RHS1).
  5. Remove E1 from the tape that blocks it on the motor.
  6. Pass E3 trough the hole in LHS1. Pass E1 through the hole in RHS1.
  7. Tie in a knot (KN1) on E1. This knot should be positioned so as to have the tensioner in the middle of the admissible range of movements.
  8. Tie in a knot (KN3) on E3. This knot should be positioned taking into account the length of the tensioner.
  9. Twine the cable E3 on the pulley P3 (see the picture). Screw LHS1 and RHS1 on the tensioner.
  10. Take a piece of cable. Tie in a knot at one extremity. Take the other extremity (E4) and pass it trough the hole H3 on the pulley P3. Exit the pulley trough the hole H4.
  11. Take a tensioner and remove the left-hand (LHS2) and the right-hand screws (RHS2).
  12. Remove E2 from the tape that blocks it on the motor.
  13. Pass E4 trough the hole in LHS1. Pass E2 through the hole in RHS1.
  14. Tie in a knot (KN2) on E2. This knot should be positioned so as to have the tensioner in the middle of the admissible range of movements.
  15. Tie in a knot (KN4) on E4. This knot should be positioned taking into account the length of the tensioner.
  16. Twine the cable E4 on the pulley P3 (see the picture). Screw LHS2 and RHS2 on the tensioner.

TIPS AND TRICKS:

In order to increase the cable tension it is useful to unscrew the screws S1 and S2. After having completed all the described operations the cable tension can be increased by tightening the screws S1 and S2.

wrist_yaw and wrist_pitch coupling

---
Motor / --
Cable / Carl Stahl CG077063
  1. Take a piece of uncoated cable (more or less 10 cm). Let its extremities be E1 and E2
  2. Take the tensioner (Te1) out of its socket by removing the screw S1.
  3. Tie in a knot at E2.
  4. Pass E1 through the hole in the tensioner Te1. Pull the cable so that the knot will block the cable.
  5. Pass E1 through the hole H1 on the pulley.
  6. Put S1 back in place but leave the tensioner close to H1.
  7. Follow the cable path until the stopper St1.
  8. Remove the stopper St1 by unscrewing S2.
  9. Pull the cable and block it with the stopper St1 and with screw S2. Tie in a knot in order to prevent any cable slippage.
  10. Take a piece of uncoated cable (more or less 10 cm). Let its extremities be E3 and E4
  11. Take the tensioner (Te2) out of its socket by removing the screw S3.
  12. Tie in a knot at E4.
  13. Pass E3 through the hole in the tensioner Te2. Pull the cable so that the knot will block the cable.
  14. Pass E3 through the hole H2 on the pulley.
  15. Put S3 back in place but leave the tensioner close to H2.
  16. Follow the cable path until the stopper St2.
  17. Remove the stopper St2 by unscrewing S4.
  18. Pull the cable and block it with the stopper St1 and with screw S4. Tie in a knot in order to prevent any cable slippage.