會走路（但沒有頭）的貓

Background After listening to the children’s stories of “the little Major Tom”, my six-year-old daughter asked me to create a robot cat just as it is described in those books. That original cat can walk, talk, fly and knows about everything. Hence, the task of rebuilding this cat is obviously a bit too challenging, so I was going to make something simpler fit. Basically, I wanted to demotrate some simple kinematics – which are not that simple in the end… The resulting “cat” looks a bit incomplete. It’s quite simple and symmetric and you will find only some simple holes where the face and the tail should be mounted. The design of these parts (by print or paper) are up to anyone who is willing to recreate the cat. See the video at: Printing All parts are prepared to be printed with a layer height of 0,2mm and a 0,4mm nozzle. The parts do not require any supports, only the “shoes” might be easier to print with supports switched on. Print either the two plates or all parts individually. If you print the single parts, you will need (colo refer to the parts in the pictures): 2x (white) 2x (white) 1x (black) 1x (black) 2x (black) 2x (green) 2x (blue) 4x (yellow) 4x (black) 4x (black) 4x (black) 4x (blue) 4x (blue) 4x (blue) 4x (red) If you go for the plates, the second one might require some rotating before it fits your print bed. In case of trouble, print the body as single parts. Additional, non-printed parts In the given design, I have used the following non-printed parts: 17 screws: M4 x 10 mm. 17 nuts: M4. 17 washe: M4 (4.3 mm iide / 9.0 mm outside diameter, optional). 1 DC motor: Reely Vario Gear Motor RE140 (Reely part no. 240788, can be found at Conrad in Germany, see 1 Battery Box: Goobay Battery Box for 2 Mignon (AA) battery cells with switch (Goobay part no. 12443, available at Conrad, too, see Screwdriver, flat-nosed plie, hammer For the tramission, I have arranged the gea in the little gear box for the 625:1 configuration as shown in the data sheet of the motor. Assembly Step 1: Mounting the drive gea As a fit step, the drive gea () must be mounted to the drive shaft of the motor. The gea must be placed exactly on the both ends of the shaft. It is not yet necessary to shift the shaft itself in the right position. The two drive gea have a center hole with a diameter of 3 mm which is exactly the same as the shaft. For fixing it, just hold it vertically and use a hammer to move the shaft into the center hole of the gear. For me this worked fine for the fit gear. The second one was wobbling after mounting it this way, so I tried correcting this by pressing and pushing it. As a result, it was a bit lose. In this case, get it from the shaft, add some glue and remount it. The two wires from the battery box can now be directly soldered to the motor. I was glad that the box already includes a switch, so no extra “electronics” are required. After switching on the motor, both gea should rotate nicely with not too much unbalance. Step 2: Mounting one side of the body and the motobattery holder Use one side part of the body (), three screws and nuts for mounting it to the motor holder (). You can optionally add washe, but I skipped them for making the assembly easier. Then, use three screws and nuts, and mount the motor to the holder. Hint: The grooves at the (red) motor gear box are made for M3 screws. Hence, either use M3 screws or widen those groves with a drill as I did. Finally, add the battery holder () on top of the motor holder. The battery holder should just “snap” in. If it does not fit precisely, you may use a hammer just to “improve” the design and get rid of gaps. Be careful, and use the hammer “gently”. Remember that it is only plastic… Step 3: Adding the axles and complete the body Use one output gear () and put it on an axle (). Push one axle clip () to both sides on the axle to fix the gear. The position of the gear does not matter for the moment. Stick the axles in the holes in the middle of the rounded parts of the body. As shown in the pictures, make sure that one of the output gea is in front of its drive gear and the other one behind its drive gear (or, if you look from above and rotate it by 90°: one to the left and one to the right). Shift the motor shaft and the output gea in order to make the gear pai mesh with each other. You may rearrange this later again, but it will ease the completion of the body. Now, use three screws and nuts (…and washe, if you like…) to fix the other side part of the body. Finally, complete the body using the remaining 8 screws/washenuts and the body front and back elements (). Now, shift the gea to make them mesh. The orientation of the axles does not yet matter – you can rearrange the gea again. However, it is time to switch on the motor to check whether the axes are rotating. Step 4: Adding the excentre and the joint Move the four leg axles () through the round holes in the four eccentrics (Eccentric) as shown in the pictures. Snap the eccentrics on the main axle. This might require some intee force from your finge – or a little help from the hammer. Make sure that the eccentrics on both sides on one axle are looking in opposite directio (as indicated by the greed arrows in one of the pictures). Furthermore, loosen one of the output gea and adjust the eccentrics of both axles that they “look” to opposite directio (see yellow arrows in another picture). Then, bring the gea back into the meshing position again. Switch on the motor and check whether everything is running smoothly. If not, use oil or sandpaper to optimize the parts – or try to loosen the gea again and run-in the axles manually. Step 5: Adding the legs Move each leg () through its joint () as shown in the pictures. Shift each joint through one of the lower holes in the body and add one clip () to the top end of the leg. On the inner side of the body, add one clip to hold the joint in place (). Switch on the motor and look in which direction the “cat” seems to move forward. Press the shoes on the legs accordingly. “Conclusion” Finally, the “cat” should be moving. However, there might be a lot of friction in the system resulting from printing tolerances, assembly tolerances, and bad design. I got mine working by adding some oil to all moving parts and by loosening the gea and doing a “run-in” by rotating the axles, eccentrics, joints, and legs manually for a few minutes. In the end, the cat is working and thus it is walking. For sure, some crucial parts are missing: on the front and the back you will find two holes which are here to mount an individual face and tail that you can design using a 3D print or paper. Concerning the original objective: the cat is not falling to pieces easily, but it is not yet an optimal design for 6-year-old kids. Hence, any improvements and ideas are welcome (excluding the hint that you can buy about the same in various more pretty and robust desig in any toy-shop….). If you want to edit the design, feed free to use the FreeCAD file included in the package. Please let me know if there are improved veio.