2010-05-04 » Is Bob just about done?

Some people might be thinking to themselves, “Is Bob just about done?”

If you are one of those people, the answer is: No!

It would appear to the casual reader that Bob might be nearing completion. After all, last week I already had the motors and wheels spinning independently and I had the Ardweeny controlling them. The whole thing even ran from battery power. This past weekend I spent many more hours working on him, so one might assume that I’m even further along, maybe even with a robot that moves. Such an assumption would be wrong.

In fact, Bob’s probably less together than he was the weekend before last.

A number of factors have combined to cause me to need to redo some of the parts that were already “working”. The main issues I’ve run into in the past week are:

• I found that the motor mounts I designed and built were not stable or sturdy enough.
• I found out that the JB Quik I used for the frame was not strong enough. (possibly due to not enough roughening)
• I took apart Bob’s motor controller so I could work on using the shift registers. (not started yet though)
• The other motors, controller, and shift registers came in the mail.
• I broke my 6-32 tap. (see image attached to this post)

While testing the motor mounts, I pulled one right off. This alerted me to two problems with my motor mount design. First, getting the motors mounted turned out to be a lot trickier than it should have been. Most of the problems were in getting the aluminum shims to stay in place while I tightened the set screws. After several tries, the motor mount in question came right off the frame. The second problem I was alerted to was that JB Quik wasn’t holding the frame together as tightly as I expected. I suspect this is mostly due to the fact that the aluminum was not roughened up enough before I applied the JB Quik. I’ll have to do some testing. The difficulty in actually mounting the motors though led me to review other options.

Over the course of the weekend I designed and built 5 new prototypes for mounting the motors. Each of these was made primarily of aluminum that I cut and filed using a hand file and a hacksaw. This took many, many hours and all but one of the designs I came up with were either too complex for me to build accurately or were still not sufficiently sturdy. Finally I came up with a pretty simple design that also seems pretty stable. I only have one prototype though, so I’ll need to see if I can make 3 more that also work.

The reason I only have one prototype of the new motor mounts is that in the process of redoing the frame, my tap broke. I had decided to screw the whole frame together to make it stronger than the JB Quik alone made it. Screws also play a prominent role in the new motor mount design, so I need the tap in order to finish the other 3. Luckily I was able to get one today from Canadian Tire.

Where does this leave Bob now? I am hoping to make some progress on the several of the following before next week:

• Finish reinforcing the frame
• Finish the other 3 motor mounts
• Begin testing with the shift registers
• Finish the new dual output power supply I’m building (6v and 5v)
• Attach the wire and connectors to the two new motors
• Attach the connectors to the second motor controller

For me, most of the fun is in designing and building Bob. I’m not in a hurry. In fact I’d probably rather not finish too soon. Since this is a hobby project, I have the time to keep working and reworking components until I get them to work to my satisfaction. And then I can still tweak some more! I’m learning a lot from both the things that work and the things that don’t. If everything worked the first time and I didn’t need to take things apart or redesign pieces I’d say I haven’t challenged myself enough.