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“This [issue] includes all the parts you need to fit the two arms at the top of R2-D2’s body. These are motorised, and the parts provided include the motor, the operating linkages and the mounts that hold them inside the front panel.”

Again, the Understanding Robotics section of the magazine is missing again. THREE BIG issues in a row!



Materials: The Clutch Pressure Plate is the only metal part in this issue – the rest of the non-electrical parts are plastic.


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Assembling the Pivots

Steps 1-3

The Upper Arm (marked BP-50) has a T-shaped hole in the round end. Pass a Pivot through this hole so the two central tabs stop it in the middle of the Upper Arm, as shown:

Step 4

Fit the slotted end of the Double Crank over the tab projecting out of the Pivot:

Steps 5-6

Secure the Double Crank to the Pivot with one (1) 2.3×6 mm black screw:

Steps 7-9

In a similar fashion, pass the other Pivot through the T-shaped hole in the Lower Arm (marked BP-51) until it stops in the middle.

The instructions say this is part BP-42, but it is marked BP-51:

Steps 10-11

Fit the slotted end of the Single Crank over the tab projecting out of the Pivot, and secure these together with one (1) 2.3×6 mm black screw:

Step 12

The two arm assemblies should look like this:

Building the Clutch

Steps 1-3

Fit the Clutch into the Clutch Backplate as shown. It does not matter the position just yet:

Steps 4-6

Fit the Clutch Pressure Plate over the Clutch and secure it into place with two (2) 2×6 mm black screws:

Assembling the Clutch Linkage

Steps 1-4

Fit the tabs on the end of the Clutch shaft into the matching slotted recess of the Clutch Lever. Then, secure the Clutch Lever to the Clutch with one (1) 2.3×6 mm black screw as shown:

Step 5

Turn the Clutch Lever until it is aligned with the Clutch Backplate, then fit a Pivot Pin up through the hole in one end of the Clutch Lever, exactly as shown here.

These Pivot Pins were not easy to install – they require a lot of effort to press into place:

Steps 6-7

Take one of the Con Rods (it doesn’t matter short or long) and snap one end into position over the Pivot Pin:

Steps 8-9

In the same way, press another Pivot Pin through the other end of the Clutch Lever in the same direction as before. Then, snap the end of the other Con Rod and over this Pivot Pin, exactly as shown:

Fitting the Arms

Step 1

Collect both arm assemblies, two more Pivot Pins, and the Clutch assembly and lay them out like this. The Lower Arm goes on the right, along with the Long Con Rod side of the Clutch Assembly (marked with an ‘R’):

Steps 2-4

Snap a Pivot Pin down through the end of the Long Con Rod and then through the Single Crank on the end of the Lower Arm, as shown:

Step 5

Snap the other Pivot Pin down through the Double Crank on the end of the Upper Arm, as shown:

Step 6

Then, press this Pivot Pin down through the Short Con Rod, exactly as shown here:

The completed arm fitting assembly should look like this:

Installing the Arms

Steps 1-2

Feed both arms through the matching openings from behind the Front Panel:

Step 3

Slide the Lower Arm all the way through until you can press its Pivot into these matching notches above and below the opening:

Step 4

Fit the Pivot of the Upper Arm into its matching notches in the same way:

Step 5

Adjust the linkages to center the Clutch assembly and seat it on this bracket, as shown.

The arms are in the closed position here:

Step 6

Make sure that both Arms are sitting flush with the Front Panel:

Steps 7-8

Take the Left Pivot Mount and fit it over the Pivot of the Upper Arm. Then, secure the mount in place with two (2) 2.3×6 mm black screws:

Step 9

Fit the Right Pivot Mount in the same way with two (2) more 2.3×6 mm black screws:

Fitting the Motor

Steps 1-2

Feed the shaft of the Motor through the hole in the Motor Cover Base, this way up:

Step 3

Secure the Motor to the Motor Cover Base with two (2) 1.6×3 mm silver countersunk screws:

Step 4

Fit the Motor Cover Top to the base with the arrow pointing towards the Motor shaft:

Step 5

Secure the Motor Cover Top into place with two (2) 2.3×6 mm black screws:

Steps 6-7

The Motor shaft is D-shaped. Fit this shaft into the matching hole in the top of the Clutch assembly:

Step 8

Fit the Motor Cover onto these posts of the Front Panel.

I had to twist/turn the motor and clutch parts to get this to line up correctly:

Step 9

Make sure the Clutch is seated in its bracket and secure the Motor Cover to the Front Panel with four (4) 2.3×6 mm black screws:

The Front Panel should now look like this. The arms should stay fully seated when in the closed position (even when leaned forward as shown):

If your arms are floppy and/or fall away from the panel when in the closed position, try rotating the Clutch as shown to tighten them up:

Testing the Arms

Retrieve the electronic testing rig we last used in Issue 82. If it needs to be reassembled, refer to the first section of Issue 53. Uncoil the Motor lead and connect it to the Sensor Control Board socket marked with an ‘M’:

Step 3

Hold the S2 button on the Test Board to open the arms. Do not keep holding the button after the arms reach the fully open position:

Step 4

Hold the S1 button on the Test Board to close the arms. Do not keep holding the button after the arms reach the fully closed position:


This issue was crazy long and intricate. So many little moving parts! Happily, the arms work as expected. Make sure you store the arms in the closed position to prevent any damage to them or the linkages. We will attach this panel to the rest of the body panels in Issue 86.

Next Up

 Issue 85 – Right Front Body Panel, Shoulder Seal, Side Plate/Grille, Front Plate/Grille

9 thoughts on “ISSUE 84”

  1. Hello, how are you …
    I have a problem with retracting the left robot arm. The outward movement works very well. When retracting, the linkage blocks because it has passed a point at which no more movement or force can be transmitted in the direction of retraction or is possible. (kinematic joint, self-locking). I can imagine that this has to do with the position of the clutch and the position of the linkage in relation. Can you help me. I’d be happy to send you a picture too…thank you.
    Greetings from the Baltic Sea coast (Stavenhagen M/V Germany)
    Roberto (61yo)

  2. I reached the conclusion that they don’t give you enough 2.3×6 mm black screws. By the time I reached step 9 I was out of them. Fortunately fir me, I had a few flanged ones in my spares box thst came in a past issue, and I replaced the ones in the switches box with those, then used the ones from the switches box there.

    1. I had enough screws, plus a ton extra at the end. Perhaps you used the 2.x3x6 someplace earlier that should have been a different screw?

      1. I made sure I followed all the instructions to the letter. I always make sure all the screw packs are retrieved and stored aside after opening each pack. So no lost screws either.

  3. the arms move in the wrong direction when I press the S1 and S2 buttons, do I need to get a different motor or can I just rewire it to turn the right way

  4. Has anybody had issues with removing the wire after testing the arms my test went smoothly but when i went remove the wire from the Sensor control board the wire holder separated from the board and I can’t get the wire out i ended up calling fanhome and i am now waiting on a replacement Sensor control board and motor from issue 84 cause in trying to remove the wire came out of Socket.

    1. This happened to me but you can just slide the wire holder back on, it is the pins coming up from the board that are soldered. My neutral wire from the motor seemed loose after struggling to remove it from the test board so I had to test it again – it was ok and the wire holder worked fine.

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