Shortcoming - Steering
It comes as no great surprise that the greatest area for improvement on YogiCub is the design and implementation of the wheel assemblies. This concerns three areas on the current implementation:

A second, more intermittent, problem was the loss of a wheel after performing a long sequence of steering maneuvers. The successive lateral loading on the wheel caused by repetitive turning and forward movement prompts the fastening pins to pop out of their mounts within the wheel. Once one pin is out, it is only a mater of time before the others follow suit - Quite funny to watch a wheel with independent thought going it alone.

Conclusion
Have a second fasting method utilizing the axle of the wheel (Not used currently).

The third area for improvement focuses on what wasn’t implemented, as apposed to what was. It stems from my (in hindsight) inexperienced assumption that the duration required to turn the Rover through a prescribed angle (say 90º) would be consistent – As it turned out, it wasn’t!

When turning YogiCub’s wheels always rotate through 45º. Having reached this, individual wheels are driven to turn the Rover through the desired angle of turn (whether 90º, 180º, 360º, or whatever). My downfall was having no way to accurately measure this. I assumed it could be measured as a time based event rather than a controlled event.

YogiCub’s turning relied on a calculation involving Rover dimension, wheel circumference, motor speed, and time. Assuming all of these factors are consistent during operation no problem. Rover dimension and wheel circumference don’t change. Time for the most part is relative, and we perceive it as being consistent. This leaves motor speed as the culprit. It does change quite considerably during operation and this renders any time-based calculation useless.
As it turns out, (a no-brainer in retrospect) motor speed varies with available battery power and wheel resistance. The less battery power the slower the wheel will turn. Therefore less distance traveled during a specified time period. The more resistance applied to the wheel, the more power required to turn it, slightly reducing the motor’s speed. – I can’t win.

Conclusion
Build a Rotation sensor into a Wheel assembly to monitor actual wheel revolutions as they happen (as apposed to predicted). Even better, have two (mounted to wheel assemblies on either side of the rover) and have the RCX average out the two readings for more accurate turning. This will enable consistent interpretation of a calculation based on Rover dimension and wheel circumference only. We don’t need to worry about motor gearing and speed – simple.

Shortcoming - Speed
YogiCub is fast, maybe too fast for autonomous control. While straight line speed is desirable, it comes at the expense of control and traction. Consistently in the field trials it would have been desirable to have a lower top speed for some more raw climbing power. When faced with a moderate obstacle YogiCub's slowed quite suddenly, almost shuddering. My initial gearing selection of 3:1 need needs to be revised to smooth out wheel drive and increase traction.

Conclusion
Increase gearing to 24:1

Shortcoming - Systems Control
Even to perform very simple steering tasks the programming and coordination of wheel assemblies and drive motors is pushing practical the limits of the LEGO® Mindstorms software. The primary limitation is the software’s interface itself. Programming is quick at a superficial level but quite repetitive and obstructive when trying to program anything with Object Orientated (OO) logic.

Conclusion
Use Bricx CC and NQC for future programming and development.

The Future
Where to from here? Apart from making the design modifications identified above the next logical step is to incorporate a working ‘rocker-bogie’ suspension system.

This will entail scaling up the Rover’s size and weight by about 40%. All drive and power trains will require strengthening, and the wheels and their assemblies will be re designed to support the extra weight.

I plan to implement a new steering control system, (both mechanical and software) based loosely off Miguel Agullo’s innovative 'skid-steering' solution.

This new Rover will also carry a simple sensor payload enabling it to measure and record its environment.

I am very happy with the design of YogiCub, as it meets all the engineering goals and criteria I established at the start of the project. You will be pleased to know that YogiCub’s bigger brother is already in development and taking shape. Watch out for him this coming winter.

Stay tuned and play well.
Tom Beattie