Lego: use Spike chassis to build Explorer robot

To quickly change the Spike into an Explorer robot, you can strip legs, claws and tail, leaving the chassis as a basis to build the Explorer robot.
Then add wheels, a bumper with touch sensor and an ultrasonic sensor mounted on a motor.

Strip legs, claws and tail

Add two wheels to the motors

Make rear wheel

Follow step 7-9 of the Castor bot building guide to make the small wheel. Then add it to the rear:

Add bumper with touch sensor

You may use your imagination, added with the instructions for the Bumper car and the examples below to add a bumper.

Add motor on top with ultrasonic sensor

The motor will be mounted in such a way, that it can be quickly removed.

Mount the ultrasonic sensor. Replace the axle with a slightly longer one, and add an extra pin to ensure a firm connection to the motor (the sensor will rotate, so it must be connected well):

Connect the cables. Extend the cable if necessary with a extra set of female-female jumper cables:

(how to connect the sensor to the servo-headers of the shield was explained here)