Overview: Mobility

In this post, I will talk briefly about the basic mobility base that the roverbot will be built around.

The roverbot will be based on a commercially-available radio-controlled vehicle chassis.  While it may not have the "geek appeal" of designing a mobility base from scratch, this approach will have the advantage of using a known-good platform to start with, which will allow me to concentrate on control, navigation, and other systems, instead of spending all of my time hammering out little physical details.  I have nothing against scratch-building a base - my initial plan was to start with a three-wheel differentially-driven tail-dragger design, eventually migrating to a custom-built treaded design using some really nice track units from Lynxmotion.  Unfortunately, right now I just don't have access to the tools or building space that I would need to do it properly.  I would rather defer it until a later project and do it right than to do a half-baked job using what I have available right now.

In addition, I have already had a bit of experience in working with radio-controlled vehicles.  I used to race R/C trucks some years ago, and so am at least somewhat familiar with the mechanics of getting them to do what I want.  Not surprisingly, things in the hobby have changed considerably in the years since I dropped out of racing, but the fundamentals are still the same.  There will no doubt be a learning curve involved, but it shouldn't be too rough.  After a good deal of poking around and re-learning a few things, I sat down to assess what features I was looking for in a robot base, and compare them to what was available on the market.

In the end, I went with a rock-crawler model from Venom Racing (now apparently Atomik), called the Creeper.  

Venom (Atomik) Creeper (photo source: Atomik website)

It features high-articulation suspension for terrain handling, along with provision for adding rear-wheel steering, and a single, centrally-mounted motor (as opposed to two motors, mounted on each axle, as some models use).  Many rock-crawler models have permanently locked differentials on the ends - essentially just solid axles in a differential-shaped housing - to eliminate wheel spin.  The Creeper features working diffs that can be locked manually.  Since I'm actually interested in having the differential action in the roverbot, I'll be leaving mine active.

The ability to upgrade to four-wheel steering was another plus.  I may have given up the zero turning radius of a tracked base, but the ability to steer sharply with both ends of the rover should help to keep the turning radius tight enough for a reasonable amount of maneuverability.

Finally, there's the suspension.  The extreme deflection of the rock crawler chassis may be a bit of overkill, but whether driven manually via a video link or running in autonomous navigation mode, it is certain to run up against a good number of obstacles that will simply be missed by the control system, so the ability to handle large bumps and obstacles will surely come in handy.

There are some definite quirks to the Creeper chassis design, which I will cover in more depth in a later post, but for the most part, it seems to be a pretty capable chassis which will serve well for this project.

My next post will take a look at the wireless link from the control station to the roverbot.  Of all of the rover's subsystems, the control link has gone through the most changes so far.  More on that next time.