Robot Operation

Calibration Procedure

Robot calibration saves the zero position of each encoder relative to a known physical pose, and is necessary any time that any encoder has moved relative to the physical robot. This should only happen after replacing or reassembling parts of the robot, and so the calibration procedure should not be performed unless you are instructed to do so by Agility support personnel. The procedure makes use of the calibration jig and hardware that the robot was shipped with.

1. Remove the shin protective shells as described here.
2. Remove the battery and replace the front shell
3. Set the calibration jig on a flat surface and place the robot on the jig such that the bottom of the pelvis fits into the vertical stand as shown below
4. Using the four M6x18 flat head screws provided with the robot, fasten the pelvis to the stand via the holes indicated in the picture below. Note: it can be tricky to get the pelvis mounting holes aligned with the calibration jig holes. Also, if the mating surfaces are not flush, the screws can bind, so take care with alignment

5. To access the rest of the mounting screws, carefully tilt the jig forward until robot is resting on its front cover. You may want to place something soft for the shell to rest on to prevent marring of the cover
6. The flat part of the knee joint is bolted down to the surface of the jig using the four M8x25 flat head screws provided. In the final configuration, the thigh segment will be oriented vertically, with the legs folded up behind the robot. The easiest way to move the legs into this configuration is to move the toe down against its hard stop, fold the leg up as far as it will go, and tilt the thigh forward and outward until it is vertical relative to the pelvis, but abducted away from the pelvis body and off of the stand. This configuration is shown below. From this position it is easy to rotate the thigh towards the pelvis into the correct position.

7. Line up the threaded holes on the knee with the through holes on the bottom of the calibration jig and start threading in the screws (do not tighten them yet)

8. Align the legs so that they are parallel to each other and to the calibration jig. It is easiest to compare the straight lines on the calibration jig (illustrated below) to ensure that the legs are parallel.

9. When the legs are parallel, tighten the screws from the bottom of the jig.
10. Move the toes downward all the way against the hard-stop. Since the toes will extend below the bottom of the calibration jig in this position, prop the back of the jig up on a small object. Do not prop it too high, as subjecting the leg compressing DOF to gravity will compress the springs and cause an offset in calibration. In the final configuration, the robot should look like the pictures below

11. Replace the battery, plug in a USB drive with the calibration model loaded (this was provided with the software package), and turn on the robot
12. Calibration should take less than a minute. To check progress, you can connect to the robot via Simulink Real Time Explorer (instructions here). If Cassie is set up as a target PC in slrtexplr, you can type the following from the Matlab command window to view the screen:

tg = slrt;
tg.viewTargetScreen;

When calibration is complete, there will be a message on the screen indicating calibration was successful. If you do not see the message after a minute, make sure the model you are using is correct. If you still have issues, seek assistance from Agility support.