Archive for August 12, 2013

Problem identification. The doldrums.

At this stage in the game, this project is on a clear path to completion, with no major revisions in sight. What I’d like to do is identify some issues that have made themselves apparent during the build and tweaking processes. Some are things that I would fix in the version 2, if one were to exist. Some I need to fix right now.

This also marks the end of the “let’s build something cool!” phase and into the “ugh. WHY isn’t this working?” phase. It’s a lot harder to stay interested in finishing, but I’m going to power through.

Here’s where I’m at:

  1. Limited rotation: any rotational movement that goes too far would tangle up cables that are driving the pitch gear motor. Everything in this system is designed to be battery-powered, so the obvious solution would be to mount the yaw motor on the rotating platform. That could mesh with an inside gear that’s been fixed to the base.
  2. Non-prime gears: this is one of the topics that have come up while doing ongoing research for what constitutes a “good” mechanical design. Generally, teeth shouldn’t continually mesh with exactly the same tooth and the opposing gear. That’s a good way to cause excess wear through dirt or inconsistancies in the the teeth hitting the same spot every time. To make sure that doesn’t happen, you want the gears to be co-prime. Right now, my two gear sizes have 55 teeth, and 280 teeth. That’s no good. Fortunately, 281 is prime, so that neatly solves that problem. The pitch gear doesn’t ever rotate all the way through, so that doesn’t fix the issue for those mates, but there’s nothing I can do about it, so why worry?
  3. Catching: the top gear(I’ve been calling it the pitch gear) catches up between the two gears providing support. When it gets caught, the gear likes to try and shove the rear support struts up and out of the base. This is the only problem(so far) that I haven’t foreseen. Fortunately, I was able to move that top support gear a little closer to the bottom portion using some holes that already existed. Anything less than 90 degrees seems to do the trick.
  4. Squeezed bearings: I used some flat washers on either sides of the bearings, but that still caused too much friction for them to rotate properly. I need to find some smaller nylon washers, or maybe flanged bearings.
  5. Wobbly base: the lower gear(I’ve been calling it the yaw gear) is mostly just sitting on a huge bolt that I had kicking around. I was hoping it would work, but no dice. It doesn’t quite. The gear wobbles around in relation to the base just enough to lose contact with the motor gear. When I can get some more laser cutting in, I’ll build another base with an additional cage around the bolt to provide more support.

Relapse (Build)

Putting it all together.


The materials I used are a little more than the final product requires, some material was used up in mistakes or scrapped in newer revisions, but here is what I started with:

  • 2′ x 3′ 3/8″ acrylic ($20)
  • 6″ x 6″ 1/8″ acrylic ($10)
  • 4x 3/8 bolts
  • 4x 3/8 lock washers
  • 8x 3/8 flat washers
  • 4x 3/8 nuts
  • 1x #6 machine screw
  • 1x #6 lock washer
  • 2x #6 nuts
  • 1x 5/8 bolt
  • 3x 5/8 nuts
  • 1x 5/8 lock washer (about $4 for all)
  • 1 cheap tripod for the head (can be replaced with 10mm bolts or threaded rod) ($3)
  • 2x bearings (26mm OD, 10mm ID, 8mm width) ($6)
  • 2x BLDC motors (I got these for free)

Relapse (Design)

In the time since I designed my timelapse camera gimbal, I’ve laid everything out for laser cutting, researched companies that offer cutting services, and very carefully decided not to send it out. As an initial draft, I wasn’t ready to spend $150 on a process that I’ve never used before.


Fortunately, the excellent Laser Cutter Cafe recently started up on a temporary basis. The deal is, you can come in, take a brief training course, and rent time on a laser cutter. Compare to online services, this is relatively inexpensive, and you can cut smaller test pieces and see the results immediately. For rapid prototyping, this is a valuable learning tool.

At the beginning, I was finding that many of my designs had fairly glaring errors that weren’t apparent until I was holding a physical copy. Throughout the process though, I was constantly tweaking and updating the design, and now I’ve got an excellent handle on what works and how everything will fit together.

The tweaking process involved adding, removing, and moving pieces around to fit better. Initially, everything was going to be glued together, but with a combination of finger joints and mortises, most of the individual components slot together and can almost friction fit. Naturally, glue will still be used, but the assembly of the final product is nearly idiot-proof now.



If I were to print this again, I’d arrange the shapes closer, merging the the coincident lines to save on laser-time, but that wasn’t a priority while printing up the prototype.