Mechanical Assembly
- Rafael Hostettler
How to mount/unmount the shells
Torso
The front an back shell of the torso are mounted to the structure of the torso by means of a clip-mechanism. The individual shells are fixed together with simple elastic straps (Pinky) or by means of a clip-mechanism (Brain) depending on the robot.
Disconnecting the shells
To unmount the shells you will first need to disconnect the front and back shell at their interfaces (blue and red marked.
Pinky
The front and back shell are connected with elastic straps. The following pictures show the locations of these straps.
The straps can be removed as well as mounted by using an Allen key or something similar.
Note that not all the hooks at the top interfaces are used, as it has shown to not be necessary.
Brain
To disconnect the shells you will first need to remove the clips, which are located at the interfaces of the shells at the bottom left and right, as shown in the following pictures.
Next you need to pull apart the shells at the top left and right as shown in the following picture. The shells are only stuck together, so only little force is needed.
Unmounting the shells (both robots)
After disconnecting the front and back shells at their interfaces, each shell can be unmounted by pushing the shell upwards. Each shell is fixed at two points to the structure of the torso by means of a clip mechanism. The locations for the front shell are marked in the following picture, on the back shell you will find them at the same height.
The clip-mechanism is shown in detail in the following picture. By pushing up the shell, the pin, which is fixed to the shell itself, will slide along the geometry and eventually escapet the slot.
It is recommended to use both hands, placing them centrally at the bottom and at the top edges. Then push slightly towards the robot and jerk the shell upwards using both hands.
Mounting the shell works similar. Use both hands and push the shell down, so the pin slides into the slot and snaps into the geometry. After that connect the shells at their interfaces, the same way you disconnected them.
Arms, Legs, Head
The Arm-, Leg- and Head-Shells are mounted elastically with a rotary-hinge and button-lock. The shells of the arms and legs always have two hinges, made of a dowel pin (which is not the hinges' axis) pressed into a 3D-printed geometry. This slides onto the grey FDM-printed hinge which is connected to the skeleton by rubber-dampers. In the figures below, you can see how the shells are sliding onto the hinges.
On the Other side of the shells, they get locked into the grey Button-Lock. This component is a spring-loaded button, which releases two shells when pressed. It is also connected to the skeleton by a rubber-damper (see figures below).
The lower Arms contain a small version of the Hinges and Button-Lock which function equally. All shells are marked with “L” or “R” for left or right. Do not force the shells in position to lock them. They should align with the Button-Lock. If they don’t, you might have the wrong shell. The Shells on the upper arms, however, require some force to snap onto the Hinges.
Faceshell
The face shell is mounted at three positions: one button-lock (see description above) on each side above the ear, a hinge at the chin. To unmount the face shell you need to complete the following steps.
First disconnect all cables which lead to the jetson inside the face shell. Next, loosen the two button locks, while holding the face shell with the other hand. Now slightly tilt the face shell to the front.
Next, move the shell downwards so that the hinge at the chin is free.
Following picture shows the hinge as seen from inside the face shell.
Now you can remove the face shell.
To mount the face shell follow the steps in reverse order.
Neck
How to mount Roboy
Roboy can and should be mounted using the three mounts inside the pelvis. As indicated in the following picture one mount is in the front (1) and two are in the back, left (2) and right (3). Use something solid with a firm stand on the ground to mount Roboy on.
The three mounts constitute an equilateral triangle with a side length of 121,244 mm.
Use M6 screws and nuts to mount the robot. The thread length of the screws should be at least 14 mm but not more than 16 mm plus the thickness of your mounting base (i.e. wooden plate with 30 mm thickness → screws with 44-46 mm thread length). For mount 1 the screw needs to be placed from the top and the nut from below. For mount 2 and 3 put the nuts in the corresponding socket first before fixing the robot with the screws to your basis plate from below.
How to mount/unmount a muscle
Torso
The first step is to unmount the shells as described above.
The torso contains 16 muscles, 8 in the front and 8 in the back. The muscles are arranged in 4 rows which are numbered as depicted in the following image.
First, you need to disconnect the bus cable which is connecting the motor boards of the muscles.
The cable can be disconnected by reaching underneath the torso and unplugging the connector.
When reconnecting make sure the orientation of the plug is correct. At the side of the plug is a fitting which needs to go in the hole in the board of the connector.
Before unmounting the muscle the corresponding motor board needs to be unmounted. This can be done by disconnecting the plugs ( blue markings) and by loosening the two screws (red markings).
Next, the tendon of the corresponding muscle needs to be detached. Therefore pull the tendon to unwind it as much as possible. Then cut the tendon as close as possible to the winch.
After this, the screws of the corresponding muscle can be loosened. Each muscle is fixed with 4 screws, 2 in the middle and 2 at the side.
For the muscles of row 2, 3, and 4: Loosen the screws of the muscle which needs to be unmounted and pull it out carefully.
For the muscles of row 1 a few extra steps are needed: Loosen the screws in the middle of row 2, 3, and optional 4 and rotate the muscles outwards as much as possible.
After that loosen all 4 screws of the muscle in row 1 and pull it out carefully.
Now the muscle can be exchanged and to mount the muscle all the steps described before need to be completed in reverse order.
Neck
The neck consists of 6 muscles, 3 per side. To unmount a muscle of the neck a few other parts need to be removed first.
First, the shoulder pad (blue marking) needs to be removed.
Therefore you need to remove the 6 threaded rods which are marked red in the following picture by loosening the nuts underneath the shoulder pad (1 threaded rod and the nuts are not visible in the picture).
After loosening the nuts, the threaded rods can be pushed through and pulled out.
Next, two screws must be removed which fix the shoulder pad to the bosh profile.
Now the shoulder pad can be removed. Be careful with the cables!
After this, the routing bar (red arrow) which sits underneath the shoulder pad can be removed as well.
Next, the routing bar (green arrow) needs to be removed. Therefore the muscles of row 1 of the torso of that side (front and back) need to be unmounted (see chapter before).
When the muscles of row 1 of the torso have been unmounted the screws (blue markings) of the routing bar need to be loosened, 3 in the front, and 3 in the back. After that, the routing bar can be lifted and the muscles of the neck can be exchanged. Make sure to unplug all cables from the motorboard which might be blocking the muscle.
After exchanging the muscles all the steps described before need to be completed in reverse order.
Upper Arm
The two M3-Units are screwed to the Aluminum-Bone with two screws. After unplugging all cables and removing the tendon from their routing-path to the wrist, the screws can be removed.
On the lower M3, the screws are next to the servo-motor.
On the upper M3, both Screws are on the inner side, screwed into the M3 from the back, marked in green in the figure below. Note, that one screw also mounts one MyoBrick like a sandwich.
The two MyoBricks are part of the structural system, as the elbow-joint is solely mounted to the MyoBricks. In order to remove one MyoBrick, unplug all cables first, that exit the MyoBrick.
Then, the yellow- or orange-highlighted screws need to be removed. It’s recommended to unscrew the Shell-Mountings (the upper hinge and the entire sheet-metal with the lower hinges, as seen above). As the MyoBrick is not mirrored, there might be no screw in the marked places. Check the tables below for all positions. There are always at least two screws on the front and back of each MyoBrick. The MyoBrick itself is slid into the elbow joint in distal direction. Unscrew all screws between the elbow and MyoBrick and slide off the elbow. Then you can remove the desired MyoBrick.
When you have to replace or disassemble the MyoBrick-Unit, note the orientation of the back part and which side the cables exit the unit!
Be careful with the sensor-cables, exiting the MyoBrick at their front.
Right Arm | Front/Anterior MyoBrick (Extend Elbow) | Back/Posterior MyoBrick (Contract Elbow) |
|---|---|---|
Inside (Close to torso) | 2x distal (at the elbow) 1x proximal (medial, proximal hole) | 2x distal 2x proximal (both proximal holes) |
Front | 2x proximal (both distal holes) | - |
Back | - | 1x proximal (medial hole) |
Left Arm | Front/Anterior MyoBrick (Extend Elbow) | Back/Posterior MyoBrick (Contract Elbow) |
|---|---|---|
Inside (Close to torso) | 2x distal (at the elbow) | 1x proximal, posterior |
Front | 2x proximal | - |
Back | - | 2x distal, 1x proximal (medial, distal hole) |
After exchanging the muscle, all described steps need to be completed in reverse order.
Lower Arm
The six M3-Units are screwed to each other with the aluminum-sheet in between. After unplugging all cables and removing the tendon from its routing-path to the wrist, the screws can be removed. There are always three screws per M3-Unit.
Take care of the M3-Unit on the other side, as it gets unscrewed as well.
Warning: Each M3-Unit has a unique housing, named “M3_5” for the fifth unit of the right arm or “M3_5_m” for the fifth unit of the left arm, which is the mirrored part of the right arm.
Pelvis
There are six MyoBricks inside the pelvis. The two ones for sideways tilt are accessible from the side. The other four ones have to be accessed from the top.
To remove one of these MyoBricks, you should dislocate the hip-joint on this side to remove the leg if nobody can keep it out of the way for you.
Unplug the cables and remove the tendon from its guided path.
Unscrew the screws, as seen below, and take out the MyoBrick.
When you have to replace or disassemble the MyoBrick-Unit, note the orientation of the back part and which side the cables exit the unit!
After exchanging the muscle, all described steps need to be completed in reverse order.
It is recommended to remove the torso first as the pelvis is quite stuffed with cables.
Before you can remove one MyoBrick, unplug and unscrew its motor-board and remove the tendon from its routing towards the torso.
If you need to remove one of the top four MyoBricks, unscrew the tendon-router first, that guides the tendon to the MyoBrick you need to remove.
Each MyoBrick is mounted with at least three screws. The figure below shows the pelvis from the top when Roboy is facing upwards. The screws are highlighted in yellow. Remove them and remove the MyoBrick.
When you have to replace or disassemble the MyoBrick-Unit, note the orientation of the back part and which side the cables exit the unit!
After exchanging the muscle, all described steps need to be completed in reverse order.
How to route tendons
Always make sure tendons are running on the pullies before moving Roboy. When tendons are not under tension, they can slip of the pullies and then get damaged when using the robot.
General Routing
Tendons of the lower limbs and arms are guided by PTFE-Tubes to protect them at small or multi-axial redirection.
This tendon router is embedded in the 3D-printed design. Inside, the PTFE-Tube, not shown in the picture, gets locked. When it is clicked in the router, it should extend to at least 10mm. To manufacture the fitting geometry of the tube, you can print this tool:
Here you insert the tube (in the right order) and cut out the material. With No.0 (printed on the back) you can cut an even end. With No.1 you cut a chamfer and with No.2 you cut out a "V" where the tube will get locked.
The dowel pin in this tool is optional. It is assembled with one M3 Allen screw. The current design is optimized for a 3mm outer and 1.5mm inner diameter tube (can be found on amazon.com). You can adapt those parameters in both designs to your tube. (Small adjustments regarding tolerances might be necessary)
To ease the routing-process, follow these steps:
Bend the end of the tendon to a U-shape and hold the long and short open ends with two fingers.
Use a sharp scalpel and cut the U at the lower part in one cut, to prevent a frayed end.
Pull on the tendon-end with three fingers to reduce the diameter of the tendon-end and get it into a round shape.
When you have to route the tendon around a pulley, form an arc so the tendon-end aligns with the pulley-surface and doesn’t get stuck at the guiding-surfaces.
Neck
The tendons of the neck facilitate the movement of the head. There are three tendons on each side originating from the topmost row of muscles and attaching to the head base.
How tendons are routed
The following picture shows the routing of the neck as seen from the front. Only the head base of the head is displayed, where the tendons are attached. Make sure to correctly route the tendons to avoid collisions with tendons of the shoulders.
How tendons need to coil
The following picture shows the correct way of how the tendons need to coil as seen from the left side. The shoulder is not displayed.
Shoulder
General
Each shoulder is actuated by 8 muscles, which are located on the respective side in the muscle. The tendons which facilitate the movement are routed from the muscles to the upper arm in 3 steps (levels of routing):
level 1: upwards from the muscle to the routing bar
level 2: sideways from the routing bar to the corresponding shoulder
level 3: from the shoulder to the upper arm
In the following pictures the routing of the left side of the torso is depicted. The routing on the right side works similar.
Level 1
The level 1 routing works the same for both sides as well as back and front. The tendon coming from the lowest muscle is routed to the outmost pully of the routing bar. Second lowest muscle is routed to second outmost pully, and so on.
Level 2
Level 2 routing works similar for the left and right side but is mirrored. Coming from the routing bar tendons are routed to a pully in the shoulder. Pay attention to how tendons cross and which tendon is running above the other. The following picture shows how to route the tendons for the left side (Roboys left).
The following picture shows how to route the tendons for the right side (Roboys right).
Level 3
Level 3 routing works similar for the left and right side but is mirrored. Coming from the shoulder tendons are routed to the upper arm. Pay attention to how tendons cross and which tendon is running above the other. The following pictures show how to route the tendons for the left side (Roboys left).
The following pictures show how to route the tendons for the right side (Roboys right).
It is important to pay attention to how the tendons coil on the winches of each muscle, meaning on which side of the winch the tendon is exiting the muscle. Coiling should be implemented as depicted in the following picture to avoid tendons touching other parts of the robot and thereby causing tendons to wear off more quickly. This picture is exemplary for both sides of the robot.
Arms
In the following, the routing on the right arm is described as both arms including their tendon routing are symmetric. The upper arms contain two MyoBricks for the actuation of the elbow joint.
The wrist ball-joint is actuated by six M3-Units. Two units are placed in the upper arm, rotating the hand around the axis of the arm. The other four are placed in the lower arm.
The tendons of the four M3-Units in the lower arm are routed as seen below. There, the tendons are routed through PTFE-Tubes between the M3-Unit and the wrist socket. The PTFE-Tube end should extend from the wrist socket about 5-10mm towards the hand. In the figure below, the outside (lateral) of the lower arm is shown. Medial, the tendons are routed the same.
The forearm rotation is realized within the wrist joint by the two M3-Winches, placed in the upper arm. The tendons are routed over the elbow joint without interfering with its angle/ actuation state! For this, the tendons are routed over pulleys around the two joint axes of the elbow and redirected straight again. The pulleys are hidden beneath covers that keep the tendons in the pulley’s groove. In the figure below, the covers are removed to show the routing from the motor to the hand. PTFE-Tubes are used again at the exit of the motor, the redirection on the lower arm and the wrist. At the wrist socket, long tubes are used as the tendon is wrapping around the socket of the joint. At the wrist, the tendons (blue and green) are routed beneath the other four tendons, seen below in orange.
At their ends, the tendons are tied to the hand-adapter. Use a washer beneath the knot to distribute the load into the hand-adapter and prevent the knot to be pulled through the hole.
Hip to Torso
The six MyoBricks that controll the spine are mounted inside the pelvis. Two of them are mounted in the lower section and controll the lateral motion of the torso (eg. bend it sideways).
The motors to bend the upper body to the side are placed on the very bottom of the pelvis. Their tendons are redirected over one PTFE-Tube through the shell next to the hip-joint socket (see figure to the right).
After the tendon enters the pelvis again, it is visible from the top. There, it is redirected by one pulley and exits the pelvis through a PTFE-Tube towards the torso (see figure below). This tendon goes straight up to the most lateral point of the torso, right next to the safety tendon.
The remaining four MyoBricks are mounted in the upper section and controll the extension/flexion and rotation of the torso (eg. bend it backwards/forward and rotate left/right).
The motors for this actuation are placed in the pelvis to be accessible from the top. After exiting their motors, the tendons cross each other inside long PTFE-Tubes, which are mounted on the tendon-guide. (For the motors to be removed, the tendon-guide has to be unscrewed.) At the pelvis-shell, the tendons are redirected by one pulley each and exit the pelvis through a PTFE-Tube towards the torso (see figure below).
After the tendons exit the pelvis, they are routed and attached to the torso as described below.
Torso and Pelvis are connected by five Safety-Tendons.
These Tendons are fixed to the torso and can be unplugged at the pelvis shell.
When the Spine should be actuated, the tendons should stop right before the spine reaches its maximal deflection.
When the Spine is not actuated, it is best to shorten the safety-tendons so the torso is stabilized without the MyoBricks stalling all the time.
Legs (optional)
For the knee, you basically follow the tendon leaving the motor’s winch tangentially to the next pulley. Then, search in the plane of the pulley for the next pulley so the tendon approaches this one tangentially again. Repeat this until you reach the thigh again, where it is tied to the threaded rod of one shell-mount.
How to maintain it
The rolling-joints (Elbow/Knee)
Instead of one joint axis, these joints consist of two cylindrical surfaces that roll over each other. This allows for a more durable joint with overload-protection. The kinematic behavior, however, is more complex, as the joint has two virtual joint axes. The bar inside the joint maintains the same angle to both connected limbs, the half of the joint angle between those limbs. Those two half-angles are measured by magnetic angle-sensors.
The connection between both rolling parts is realized by two cruciate tendons on each side of the joint (see figure below).
Each cruciate tendon is tied to a loop and wrapped around a path in a double-eigh figure. On this path, it passes a tension-screw which deflects the tendon and tenses it against small spring-steel-plates.
On the big 8-figure, the tendon is glued to the rolling parts using thermal glue, which is removable.
If the joint is loose, try to fasten the tension-screw with a 2.5 Allen Key.
If the tension-screw is at its limit, unscrew it to its limit and replace the cruciate tendon.
To replace the cruciate tendon, cut the old one, and remove it including the thermal glue, the tendon is fixed with. Be aware, that the joint is very fragile in this state! Do not move it around or bend it sideways, this might damage the sensor-mount inside the joint or unwind the other cruciate tendon.
Get some new tendon (D=1mm) and wrap it around the double-eight figure.
start between the joint parts and go around the big eight figure.
include the tension-screw as shown in the figure
cross the tendon at the joint axis, where the groove between the big and small 8-figure is removed
route the tendon around the small 8-figure
tense the tendon until both joint-parts connect and mark the spot where both tendon-ends overlap
release the tendon at the last loop and tie a knot slightly before the mark
put the tendon back onto the last loop while rolling the joint (which helps to get it into the groove)
fasten the tension-screw (the metal spring-sheets should not bend)
apply thermal glue to the big 8-groove where you removed it beforehand
The Spine
How to take it apart
Remove one hand
The hand is mounted to the hand-plate, on which all tendons of the wrist are attached to, by two screws.
To remove the hand, unplug the power and data lines and then, unscrew the two screws, highlighted in yellow:
For re-attachment, do the above in reverse.
Separate torso from lower limbs
Remove one leg at the hip joint
First, remove all cables and unplug tendons between thigh and pelvis (if applicable).
The ball of the hip-joint is screwed into the socket, tensed and locked in place by a toothed ring as seen below. This Fast-Locking-Ring is secured by a small part that is screwed into the joint-socket.
To remove the thigh, unscrew the safety-lock, highlighted blue in the following figure, beneath the ball-joint (from the back). Then unscrew the toothed ring (counter-clockwise for the left hip, clock-wise for the right one, due to symmetry).
To reattach the leg, arrange the bushing (yellow) and the locking-ring as shown below. Then move it like this into the socket and fasten the toothed ring (clockwise for the left hip and counter-clockwise for the right hip). Finally, screw in the safety-lock. make sure to fasten it softly and check the play of the joint during this. Fastening the safety-lock too far might lock the hip-joint or break the lock.
Remove one lower leg
First, remove all cables and unwrap the actuator’s tendon for flexion between the lower part of the knee and the lower leg (the two pulleys). Do NOT remove the cruciate tendons or cables from the knee itself!
To remove the lower leg beneath the knee, remove the four screws (two distal and two medial) as highlighted in red below.
After this, wiggle on the lower leg, to loosen the conical fit. The section beneath the rolling joint can be removed then. To re-attach it, some pressure might be required to fit the lower leg back into the knee and align the screw-holes.