A Three Wheeled Design, Why?

By now, our hardware design is finished. Since the line tracking assignment and the final contest are separated no more than a week we decided to create a rover that can do both tasks without needing adjustments in the design. Furthermore we would like to be original and think for ourselves so we're not using any of the standard designs.

The most important requirements we determined during our first meetings were;

-It should be able to explore the mars landscape with the camera without going back and forth, the rover should be able to turn around its vertical axis.

-Because we will have to use encoder values in order to measure the length of the tape, the wheels are not allowed to slip.

-Hysteresis on the steering mechanism should be minimized, so we can be very sure about the direction we're going with respect to our previous position.

-The risk of getting stuck in a lake should be reduced much as possible.

At first these constrains resulted in a caterpillar like design, but since the wheels that drive the caterpillar might slip within the track, this idea was dropped. Then a more ingenious design with two wheels on the left and two on the right that allow the rover to steer in a caterpillar like way was proposed. But since these tires could also slip, and because one of the wheels could get stuck in a lake, this design was also dropped.

Our final design uses three wheels. Steering and driving is all done on one wheel which reduces hysteresis on the steering mechanism. Because we're using three wheels, the rover is not 'statically over-determined', which reduces the risk of slipping wheels (for the line tracking). Using less wheels also reduces the risk of wheels getting stuck in a lake but it goes at the cost of less stability. That's way we had to put the heaviest parts (the Bricks) low as possible. Below the finalized design is shown with some more explanation.

A – Light Sensors are in line tracking position, the onces on the side can easily be moved more to the side for the Mars mission.

B – Direct connection between wheel itself and steering gear in order to reduce hysteresis. Steering wheel can be turned 90 degrees to allow the rover to turn around its vertical axis.

C – Eyes of the rover are like small crosses, it makes the robot look drunk but this is just to mislead people.

D – We were too late with collecting extension cords, only the very long onces were still available...

E – The motor that moves the temperature sensor up and down is placed in the back to improve weight distribution.

F – Handle to lift the rover without Lego parts falling of.

G – Gear ratio has been slightly changed, compared to standard designs, to make it go faster. Of course it goes at the cost of torque. 

H – To increase stiffness of the steering axis a sliding surface is created with Lego bricks that are placed upside down is created. Scotch tape is used to reduce friction.