Daily Archives: October 3, 2008

On-board computing

Thanks to the Pioneer’s background as a research ‘bot, it comes equipped with a rich C++ API allowing for easy programmatic access to the microcontroller, via a serial link from the on-board PC.  This has given us a great head start getting control software for equipment like the robot arm and motor control working quickly and effectively.

As mentioned in one of the previous posts, we’re using a simple 802.11-based wireless ethernet link between the lander site, the navbot and our Pioneer rover.  Our ground control station will consist of a setup of laptops and large screens, allowing us to view the various video streams and telemetry from the rover, as well as controlling its movement, track deployment and arm control.  Mobile Robots provide a small suit of control applications designed for use over a wireless link, which we have applied and combined with additional applications to allow us complete control of the rover while it is performing its mission (or at least thats the theory!).

We have tested these application thoroughly and had great success in remotely controlling the rover once out of visual range.  So control in the crater shouldn’t be a problem.

Integrating everything into the Pioneer shell

So the Pioneer, while a great base for software development for rover control and autonomy, wasn’t really designed to undertake quite such a heavy set of physical modifications as those we have applied.  As we’ve spoken of before, the large, wet-cell batteries were replaced with a smaller, low-profile Li-Ion battery in order to make room for the additional equipment we have designed.  This was just the beginning…

Without going into specifics, the new rover has a refined drive system, track pitch drivers and a reshuffle of the other odds and ends the rover needs to run (the microcontroller and OBC…!).  Let’s start with the base model.

The Pioneer 3-AT is a four-wheel drive, wheeled rover.  Internally there are 4 electric motors, with two each driving a pair of wheels each via a belt.  The remainder of the internals are fairly inefficiently stacked around these motors and the wet-cell batteries.

So, while our new battery saved some space, we had to fit additional motors inside to adjust the the tracks and still retain enough space to fit all the original equipment back inside!  Here’s the mounting bracket with the motors attached, ready to be fitted inside the chassis.

 

Motor mounting

Motor mounting

Once securely in place we attach our replacement drive chains, providing a more compact and stronger drive system for the tracks.  The remainder of the internals just about fit over these.

Our tracks are currently being tweaked to get the best performance and we hope to have them finalised early next week.  The axles, while similar and in the same positions as the originals, have again been modified to allow the track structure to rotate independently of the track belts, not the easiest of problems to overcome, but so far our solution seems to be doing the trick!