Really Easy to Assemble…

You know you are in trouble when the advertising material for a product says, "So simple even a child could do it" or "Really easy to assemble." You know that you are in really, really big trouble when the product manual says, "Just follow the diagram on the box." Unless you happen to have an eight year old around the house, you are about to drop off the edge of a cliff. In just a few minutes you're going to have a desktop covered with parts, an assembly drawing that may look great to someone with a lot of experience but is total gibberish to you, and a frustration level that's headed to the moon....

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That's where I found myself on Sunday afternoon - staring a desktop covered with tiny parts and trying to make heads or tails out of the assembly drawing. I was attempting to put together a Tamiya 70097 dual motor gear box for a robot I'm experimenting with. Some people might have been put off by the fact that the diagram on the box is almost totally in Japanese, but that wasn't my problem at the moment. I can do a reasonable job at reading the Japanese language, especially if I'm not rushed or working to a deadline. My problem was that the unit provides too many options, and too little step by step instruction. I know that most model car hobbyists wouldn't have a problem with this - but unfortunately I don't have that background.

Still, I decided to press forward and muddle through, even if I made some mistakes. I managed to get one half of the gearbox partially assembled before I had to go back and redo everything. And, of course, I managed to drop some of the small parts on the floor and had to stop working to search for them. After about an hour of assembly, disassembly, and searching the floor for parts, I managed to get the whole thing together. I was really happy, perhaps even smiling.

I decided to use a short tapping board as a prototype chassis, and used some self-tapping screws to mount the gearbox. Time to mount the wheels on the gear box shafts. The first wheel pressed on fine - no apparent problems. But, when I tried to press the second wheel onto the gearbox shaft I noticed that somehow the two wheels weren't evenly spaced relative to the center of the gearbox.... Something was horribly wrong....

I tried pushing them back to the center... Big mistake. Suddenly one of the shafts popped out, and several gears dropped out of the bottom of the gearbox... Back to square 1...

After reviewing the assembly drawing for a while, and turning the gearbox over and over in my hand, I finally realized that the two drive shafts butt up against each other. The only thing that keeps them in place is a collar and setscrew that you adjust very early in the process. Apparently in trying to push the wheels onto the shafts I had moved the relative position of one of the collars and loosened the setscrew, which allowed the shaft to slip and the gears to fall out....

The good news is that after taking a deep breath and calming down for a few minutes, I managed to reassemble the gears on the shaft and reposition everything. It meant dismounting the gearbox from the chassis since access to the setscrew is from the topside of the gearbox.

I finally managed to get everything assembled and working - quite an achievement for someone with fat fingers and almost no physical coordination. Nevertheless, it was amazing to me that so many sources for robot kits and parts sell the 70097 with only the assembly instructions on the box. Some one must have had the same experience I did, and must have figured out a better way.

So, I did what I always do in this type of situation - I went to the Internet and searched for assembly information.

It turns out that Camosun College (Electronics and Computer Engineering Technology Department, Victoria, BC) in Canada runs an excellent series of robotics classes and competitions, including mini-sumo. And, their mini-sumo reference design uses the same dual motor gear box that was causing me so much heartburn. Apparently to solve the same problem for their students they created one of the best sets of step by step assembly procedures I have ever run across. It includes numerous photographs of the assembly process along with supporting text. If you are planning to use the Tamiya Dual Motor Gear Box (70097) for any application I highly recommend that you read the Camosun assembly proceedures - before you start.

Sumo Robot Gearbox Assembly (pdf)

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