Saturday, October 15, 2011

Giving Gravity a Big Middle Finger Once Again

So I received my laser-cut parts from Ponoko a few days ago, rendering my balance project juuuuust about complete. At a glance, I wasn't as impressed with these parts as I was with the acrylic chassis for my suction car, but considering the material this time is over twice as thick, the parts look pretty awesome. I was too excited to take a picture of them as I was popping them out, but here's the aftermath:

Yes, I know, those two pieces in the middle look like little androids.

After realizing that I might have made the tolerances on these parts a little too tight, followed by having to hammer all the parts together as a result, a little balance vehicle was born.

I'm extremely happy with how the laser-etching looks. I'm going to have to do that with every subsequent project now. Also, this thing is SOLID. I designed it as if it would need to handle drops off of really tall buildings. Oops. Oh, and here are the gears:

So...not as pretty and precise as I would have liked. It's understandable though. This is the thickest material that Ponoko offers for laser cutting. And they will work, they just might have to be broken in a lot.

So at the time I got all the laser cut parts in the mail, I had everything else I needed to put this whole project together. Everything but the drive shaft, that is. You know, the main component that I need to make this thing move. I needed a steel shaft that was 170mm long and 5mm in diameter, but the problem was that I needed to buy it already down to size, since it's really hard to machine something that long down to that small of a diameter without it bending. I couldn't find a 5mm shaft anywhere for a while, but then I remembered that my favorite website ever, SDP-SI, sold shafts in metric sizes. I gave their site a visit and sure enough, I could buy a 180mm long, 5mm diameter stainless steel shaft for about $7, which I was very happy about. So I ordered one, but it didn't arrive until two days after I had everything else! What was I to do in the meantime?

Well...the night I had put everything together and was waiting for my 5mm shaft to arrive, I discovered that Walmart sells knitting needles, and that knitting needles come in metric diameters. I'm sure you can see where this is going.

So here we see a picture of a knitting needle cut to length and used as a drive shaft. Hey, I was desperate to test this thing out! The needle was actually solid aluminum too, which was kind of nice. I was certain it would be hollow when I bought it.

Completely assembled at last! Well, almost. Now all that was left was to wrap a half-pound of lead tire-balancing weights at the very top of the carbon tube.

There we go.

I definitely don't plan to leave these weights wrapped around like this. Mr. Machinist over here is going to make me a nice brass weight to serve the purpose that this huge roll of ugly lead is currently serving. I should have pictures of that up in a couple days.

So...initial test runs were tough. It was a lot harder to balance than I thought it would be. It's not super fast, so once the vehicle tilts more than about 5 degrees from vertical, it's going down. If you mess up a little and don't keep it almost completely vertical, it's game over. This is the reason the bigger 70mm wheels are mounted on it in all the pictures: I needed more speed. Also, a little problem that needed correcting was that the vehicle isn't exactly wide enough to prevent it from rocking from side to side. This results in the thing randomly turning towards some unknown direction very quickly and engaging some unsuspecting audience member in a surprise jousting match. And of course, the laser-cut spur gear does work, but not nearly as smoothly as it needs to. All of these things made balancing a little harder than it should have been.


In true human style, Alex and I were able to adapt to all of these issues and within a few short hours had the vehicle balancing for upwards of 20 seconds. It just took practice, really. The main issue with the vehicle wanting to rock from side to side was somewhat solved with a combination of being really careful not to jerk the throttle too much, driving it on soft carpet, and luck.

Then of course, a couple days later my stainless steel drive shaft arrived. I installed it and, since it was a little longer than I needed, I used that to my advantage and used some extra hubs I had ordered as spacers to widen the whole vehicle by 10mm, to help with the rocking issue.

Bam, done.

In the past couple days I've practiced a little more with this thing and despite how incredibly challenging it was to balance at first, on average I can keep it balanced for about 30 seconds now. One time I had it balanced for about a minute. It just takes a ton of practice, but that's what makes it fun.

I'll have a video posted soon.


  1. This is awesome. Next time anyone asks me how to build a segway robot I'm going to tell them to build this and just practice driving it for a few weeks.

    I also love the ducted fan car.