I must build a device that moves autonomously from an ‘initial point’ and hits a wall of certain unknown distance, then return to its initial position.
No programmable devices to be used such as raspberry pi.
I was thinking of accelerometers or gyroscopes, but im not sure how to go about it.
If you guys have any suggestions, please let me know 
Thanks!
Gyroscopes and accelerometers need to be connected to a “programmable device” such as a microcontroller. It sounds like they want you to do it purely mechanically.
If you know the distance to the wall, you could essentially time it. A DPDT switch can reverse the polarity of a DC motor.
ah yes it has to be purely mechanical, and move **autonomously. **
I have already considered using gyroscopes accelerometer (not sure how to make them work without a programmable device).
the distance of the wall is unknown however the point of the project is that it must hit the wall and return to its original position (or at least close to it).
It’s a good challenge - design 1 course in Mechanical Engineering?
A DPDT switch will reverse a motor - perhaps just figure out how to mechanically “time” the distance?
Can your creation leave an object at the starting line? If so, you’re set…
If not, perhaps have something unwind?
If you can trim your motors to give you a straight course, then a pair of microswitches on the front of the 'bot will be able to trigger a latching relay and reverse the direction.
