Just starting a build blog for the Mr. Basic Challenge II. When I get some more progress I will post pics and make a robot page.
I'm still developing ideas, but I liked Gareth's work on a suspension system for the original Mr. Basic Challenge, so I'm starting with that. My suspension will use steel cable instead of polymorph for a flexible power transfer system. Ultimately,I want to try a four wheel independent suspension, but I will start with the front axis being on one suspension platform and the rear on another.
Note: This is a reverse chronological blog. Newest entries will be on the top. Go to the bottom for the beginning.
Update: 2009-12-02
Well, I bought my new 4-40 thread tap, fabricated my last coupler and tapped the remaining threads. I need to go buy some more 4-40 set screws.
I also noticed that the way the Mr. Basic main drive shaft is mounted to the gears, I won't have the clearance I need to attach the couplers on the rear side of the drive shafts. I'll have to pull the shafts out and re-set the gears a bit further down the shaft. I think I have enough room to spare on the front side of the drive shafts to allow this. We'll see.
Oh, one more note. I held off building these couplers for a while because I couldn't get my hands on a 2.5mm drill bit to match the drive shaft diameter on Mr. Basic. However, once I got the proper sized bit, it turned out that the hole was too tight a fit and I had to use the next highest standard equivalant drill bit so the shaft would fit. So I had the bits I needed all along. Live and learn.
Er, two more notes. I thought I'd mention that I've gone back to my original suspension design where the cable drive is just underneath the chassis, as shown in the first picture from the update on 2009-09-04. Like this:
The only difference is now instead of springs between the main chassis and the plexiglass wheel mount, I am using a loop of steel cable as the suspension springs.
Update: 2009-11-29
Got my auto center punch. Love it. Drilled all the needed holes in my four couplers, and was very happy with the result. All that was left was to tap the holes with 4-40 threads, install the set screws and put them on the bot.
As I was tapping a hole on the second coupler, the tap broke. I was reversing the tap a 1/4 turn for every turn forward, and going nice and slow, but it broke anyway.
The good news it is a Craftsman hand tool, so they should replace it for free. The bad news is I will NEVER, EVER, EVER, be able to get the broken bit out of that coupler, so I'll have to build a new one. Oh well.
Update: 2009-11-24
I got a good start in on the four couplers for the rear platform, but I cannot find ANY of my center punches, and I own several. I ordered a new auto center punch, which should be good for this job. It arrives tomorrow.
In the meantime... pictures!
That's the rear platform pictured above. Just awaiting couplers so I can mount it to the drive shafts.
Above you can see the original front platform. I never bothered to remove the blue plastic film over the plexiglass. I guess I will eventually. Note the use of the steel cable as a suspension system. You can't see it, but steel cable is also used as a flexible linkage for the drive shaft. Useful stuff.
This is one of the couplers from the front drive system. Actually, it is the first coupler I fabricated successfullly. I had various failures before getting it right.
Update: 2009-11-21
Rear Wheel Platform
Stole a little time today to do some fabrication. I had to re-do the rear wheel platform after I managed to munge up the first attempt. My drilling was just not accurate enough (even with a drill press) and the drive gears didn't quite mesh up right. I turned a curse into a blessing, and started from scratch. I'm much happier with the result. I made the platform a bit wider front to back than last time. I wasn't happy with the stength of the original once I had all the necessary holes drilled in it.
Next step: More couplers!
Update: 2009-11-19 (leaking over into the next day)
A Successful Test!
After many weeks away from this project, I finally got some work done. I managed to buy the 2.5mm drill bits I needed, and drilled half-way through each of the four drive shaft couplers I've fabricated so far. This way they can fit on the drive shafts of the Mr. Basic kit.
I used two 1-inch lengths (I hope you all like the mix of Metric and English measurements in this blog) of steel cable as flexible drive shafts. Another piece of steel cable several inches long acts as a sort of sping between the Mr. Basic base and the front wheel platform. I hooked up some batteries and WHAM! Awesomeness!
With the extra flex of the suspension in front, Mr. Basic easily drove right over the top of my shoe without stopping. I think the basic premise of this suspension will work.
Now I need to fabricate a second suspension platform for the rear, and four more couplers. At least now I think I know what I'm trying to accomplish.
Pictures will come later, when I've had some sleep.
Update: 2009-11-11
Return to Building
Well I picked up a few 2.5mm drill bits a few weeks ago, but I've been travelling so much I had no time to use them. I'm home all next week and hoping to get some serious work done on Mr. Suspense.
If I can get a working drive system going, I can move on to the suspension system, which is what Mr. Suspense is all about.
Update: 2009-09-29
Mr. Basic Motor Control PCB
Last night I tried out my Mr. Basic motor control board, after reading how several LMR members were having trouble with theirs. Mine wasn't working either, but it all turned out to be user error. During installation, it seems we all over-heated the BD681 Darlington transistors and blew them up. I found an alternative Darlington transistor, the TIP120, which I was able to pick up at my local electronics store.
After some mangling to remove the old transistors, I successfully installed and tested the new TIP120s and they worked fine.
Coupler Fabrication
I also returned to coupler fabrication. After some blunders, I finally got four reasonably good couplers. I'll need four more for the other wheels, but a set of four will let me test the front suspension. Actually, I still need a 2.5 mm drill bit to complete the couplers. Hmmm, maybe I can stop by the store today. They are hard to find in the US.
Update: 2009-09-08
Coupler Fabrication
I made a quick attempt at fabricating one of the couplers. I knew this was going to be a test run, since I still need to go out and buy a 2.5mm drill bit. Nevertheless, I wanted to get started, and I have 3 feet of 1/4 steel rod from which to make a few centimeters length of couplers, so no big deal to waste a bit.
I found the cutting wheel of my Dremel very effective for cutting off a 1cm piece of steel rod. I was a bit afraid it was going to fly off the end of the bar like a piece of hot shrapnel, so I grabbed it with a pair of plyers and one handed the Dremel as I completed the cut.
It was easy and fast. Much better than trying to hack saw through the thing. I wouldn't want to try this with my angle grinder though.
I was a bit rushed when I drilled the hole through the axis of the coupler, and it came out off-center. However, I did find that the 3/32 drill bit was perfect for the smaller diameter steel cable I bought. I plan to make the through hole 3/32, and then widen just half way through with a 2.5mm drill bit to fit the drive shaft from Mr. Basic.
I certainly won't use this piece in the build, but I learned it was easy enough to fabricate the part. I'll just need the right drill bit and then a jig to make sure I center punch the exact center of the face of the coupler.
Oh, I still need to practice drilling the side holes, which will then be tapped for a 4-40 thread so I can insert set screws to hold the steel cable and the drive shaft. So I can use this junk piece to practice that part of the fabrication.
Mr. Basic Motor Control PCB
After dinner and getting the kids settled, I decided to switch gears and build the motor control board. It was easy enough with the info provided and the schematic OddBot posted. If you get one of these boards, I recommend a heat sink compound be used when attaching the transistors to the provided heat sinks.
Later, I will add a power regulator to the open prototyping area of the PCB, using the design I posted here. I'm not ready to do this yet, as I'm not sure what else I'll need on the board. So other than testing the board with the motors, I'll set this part of the project aside for now and focus on building the suspension and practicing fabrication techniques with brass tubing.
Early day tomorrow, so that's all for tonight.
To address TeleFox's comment below, I have added some totally tubular cable guide, to prevent the shaft from thrashing about.
I would make this out of brass tubing, which I would bend, cut and solder or braze. I’ve never worked with brass tubing before, so I’ll have to do some research and experimentation.
Additional Update:
It pays to sleep on a thought… or lie restlessly in bed on a thought. Instead of just a short tube guide section, I will make a custom tubular roll cage for the whole bot. Part of this roll cage will act as the guide for the flexible shaft.
I’m still thinking about using brass. Maybe I’ll go for the polished brass and wood look. I wonder if I can find brass springs? ; j
Additional Update:
Here’s an updated design drawing (now to scale!) showing part of the tublar roll cage/flexible drive shaft guide. Even if I don’t opt for the crazy over the top drive shaft design, I’ve decided to go for the brass tubing roll cage. It’s going to look very cool.
I picked up two sizes of brass tubing today, plus some springs, steel cable, and everything I need to fabricate the new couplers (except some metric drill bits). I also picked up some brass plate, and I may replace the plexiglass with brass for a cooler look.
I can’t wait to start experimenting with the brass tubing, but the couplers and some prototyping on the flexible drive comes first.
Update 2009-09-04
Here’s a diagram of the front suspension. I’ll post pics of the actual work when it is ready.
All the parts are from the Mr. Basic kit except for the new couplers, flexible drive shaft and the plexiglass mount.
Additional Update
I just thought of a way to keep the wheel base at close to its original length. I would have to route the flexible drive shafts up and over the top, as shown in the diagram below.
This would give Mr. Suspense a very unique look. I have to see if it is practical.
But you’re smart! 
