As my son and I build the Johnny 5, we run into some things that would benefit others who are about to build one to know. While build progresses I will keep adding comments, but feel free to add as it will certainly help the rest:
Get lots of small cups and trays ready. There are billions of different fasteners supplied. It makes sense to keep them all organized, lest they end up under the table. I also got a large Tupperware® tub to keep all the unused parts together.
Make sure you have a tiny and a small Phillips head screwdriver ready. Magnetize the tips on a strong magnet and you’ll thank me later right about when your fingers don’t fit where the screw must. A tube of Loc-Tite blue or purple isn’t a bad idea, but don’t use it where it will contact the Lexan®. (Use only on metal to metal parts)
The stand-offs for the chest (4 of them) are nylon, and EASY to thread-strip, so be VERY careful when you tighten the screws on them. I couldn’t get mine to hold the chest without play, so I ended up substituting them with some aluminum ones, but of course you are all more careful than me…
When you put the treads together remember the little tubes that go inside each tread link. I had to un-rivet a few because the instructions mentioned them on the next page, and I got carried away…
Its a good idea to have a pair of calipers handy in order to measure the screws as required in each step. Lots of screws are availiable at each step, but it is best to use the specified ones. Some differ by very little. Also, if you have a digital caliper its better because some of the fasteners are metric and others are imperial. A cheap digital one can be bought at Electronic Goldmine. It has a button to go between mm and inches! goldmine-elec-products.com/p … mber=G1709
5.1 Did you buy both batteries required? There is a 12 volt one for the drive and a 7.6 volt one for the servos…
5.3 The Serial cable that comes with Johnny 5 needs an adapter (USB to Serial) to your USB port. You probably have one, but get one if you don’t as most modern computers don’t have a serial port anymore. You will need it to run the sequencer application which is on your CD.
Did you buy the Basic Atom Bot board? (Optional, but mentioned in the building instructions if you want to autonomize the bot later)
Mini Atom Bot Board: lynxmotion.com/Category.aspx?CategoryID=66
(Don’t forget to order the Basic Atom microcontroller to go with the board)
Look at each picture carefully before installing a servo or its four hardware fasteners. Is the servo on top or under the flange? In the waist servos, some springs are attached, so be extra sure where the mount point that holds the spring is, because it is different from front to back!
Orient your parts exactly like in the pictures. Remember that the pictures were probably taken disassembling a debugged Johnny 5 so they are perfect. If you do this the range of motion of the servos will correspond to what was intended. Even though there are many mount positions for a servo, not all will give you the range of motion or motion intended.
Also be careful with the orientation of the top platform as you screw it on. If you look at the robot from behind, the notch for the serial port plug must be on your left. This is important because even though the Lexan® will fit up side down, the SSC 32 puts the servo ports closer to the base rotate if you do it as you should. (Orienting it right keeps the servo plugs out of harm’s way later on).
One pleasant surprise is that you will end up with lots of small spare parts useful for other projects. The Lynxmotionites have been VERY generous in this regard.
Take a piece of tape or sticker material and number the tag ends of the servos as you go along. While building it will tell you to plug the servo into the SSC board, but this is not practical until the very end. One obvious benefit is that you will be able to organize your cabling with zip ties or waxed dental floss ties (yes, this is how it was done in the dark ages of electronics) while not loosing track of what plugs where later on. Note: Don’t go tying cables until everything is assembled, since you need to make sure that cable bundles leave adequate length for range of motion… you catch the drift right?
Make a small block about 2 inches high that fits under the chassis of the Johnny 5. Chock the robot on top while you work out the sequencer stuff. This way the robot can be on your desk next to your computer without running away while you debug it’s programming. I glued bicycle inner tube to the top and bottom of the chock so it wouldn’t scratch my Lexan or the table top. Plus, it will be useful for other robot work as well.
When I’m working with small mechanical pieces - be it for kit assembly, or disassembly of something I want to put back together properly again, I haul out my workshop ice cube trays, a pen, and some paper.
In the case of building kits, each type of fastener and small part goes into a ice cube cup. If there are enough different types and sizes that it’s difficult to tell at a glance just what they are (1/4" versus 3/8" 4-40 screws, for example), they also get a slip of paper in each cup, or a bit of tape on the side of it, telling me what’s where. It takes a small amount of time in preparation before you get down to the actual building, but the time spent pre-sorting and labeling far outweighs the time and effort involved in measuring everything during the build process, and possibly having to back screws out to replace them with the proper piece later.
When disassembling for reassembly, the parts removed in each distinct step get a new cup from the others, along with a slip of paper letting me know where they came from. This may seem like overkill, but it comes in handy when you’re disassembling a notebook computer to get to a slot on the bottom of the motherboard that needs fixing, and the only way to get there is to disassemble the entire machine from the top to get there. Otherwise, it gets difficult to tell a 2x4mm drive cage screw from a 2x6mm case screw, in an application where using a screw that’s too long can potentially cause a catastrophic short and kill the computer outright.
(okay, sometimes I use little plastic sample cups, too - but ice cube trays are harder to knock over)
The 7.2vdc motors and batteries are on the way out. We used them out of necessity at first. But that was back in the day when you really had no options for motor controllers. You just used RC car controllers. Nowadays we are using Dimension Engineering controllers which work better at 12vdc anyway. Besides there are a lot more motor options at 12vdc.
Does that go for the GHM-04 motors too? I guess with the new 12V GHM-15 motors with encoders, I could see the GHM-04’s going away too, but some robots are small enough to not be able to handle the longer motors, and the GHM-04 is a nice fit (like on WALTER’s current body, for instance). If you only keep ONE 7.2V motor, PLEASE let it be the GHM-04 and QME-01 encoders. Otherwise I might have to buy some more (with encoders) before they go out of stock. I just don’t think a longer motor would be good on other wheeled robots I want to build.
Here are some pictures of additions I’ve made to my Johnny 5:
The first photo shows a wire travel limiter I added to the front and back of the robot. It prevents the torso from falling back when the robot power is turned off. This prevents the spring from over stretching. A similar limiter is added to the back of the robot in order to prevent the torso from falling forward on power down. Made with fishing wire and crimp on sleeves. It is attached to the same points as the spring ends are. As can be appreciated the servos can still work to move the torso, but they will be somewhat limited in their maximum travel. This is OK, because (in my case) if the servos travel all the way forward or backward, the torso cannot recover back to standing straight up.:
This next photo shows the left side of the backpack I made to hold the wireless transmitter and its antenna (Bluetooth Modem - BlueSMiRF RP-SMA). The interesting thing is that this part was made with two left over parts included with the robot. (I used one flat long servo bracket and one regular servo bracket.) Note that I put heat shrink tubing around the radio circuit board, and a little rectangle of inner tube between the radio and the servo bracket. It is held on by zip ties as can be seen.:
This next photo shows the right side of the backpack I made to hold de wireless transmitter and its antenna. I had to drill four holes for the zip tie to wrap around the transmitter module. Note that the bracket also serves to hold the wire bundle.:
I have the standard servos as came in the kit for the waist:
HS-645MG in position 1 (bottom)
HS-645MG in position 2 (top)
(Not as strong as I would have liked, but with my “patch” it won’t be a problem.
As for the transmitter, Yes it’s Sparkfun’s Blue SMiRF.
I was going to take it farther, but my laptop crashed and it’s taking zillions of years to reboot, so I might have to restore it from a backup tomorrow. I plan to give Johnny voice as well. -Migs
Migs, I hope you don’t mind, but I would like to add to your line of tips by adding an image of the bit that I used to assemble the SES brackets for my BRAT.
The right tool makes a big difference in assembly. The Driver I used has a built in magnet that made it a breez with assembly. The magenet holds the screws very well and if you slip, the screw tends to stay on the bit rather than fall on the floor.
The bit is about 20 years old but I think I got it at Sears. It was a Craftsman driver bit set that came with a bunch of hex bits in a nice molded plastic case.
