Not really a guide or solution, there are enough of these on youtube, but some general tips to show you which options are available in the game to solve the challenges yourself.
Numbers needed for each challenge in every chamber:
Chamber #: portals (bronze/silver/gold) steps (bronze/silver/gold) time (bronze/silver/gold)
Chamber 13: 9/5/4 30/20/10 0:40/0:30/0:19
Chamber 14: 6/4/2 55/20/10 0:50/0:20/0:10
Chamber 15: 23/21/14 75/65/55 1:45/1:25/0:54
Chamber 16: 9/4/2 70/55/40 1:10/1:00/0:52
Chamber 17: 4/3/2 215/175/150 2:20/1:45/1:27
Chamber 18: 30/25/16 150/120/85 2:10/2:00/1:13
Some general tips:
- First work on the least-portal challenge and try to reach gold, you will need the shortcuts for the step and time challenges.
- Crouch while jumping gives you a little extra reach.
- When entering a portal in the floor, jump to increase your exit speed.
- Jumping in a floor entrance portal from a higher level, launches you just as high out of a floor exit portal.
- Try to place your portals strategically, so you can reuse them as entrance or exit portal.
- When you entered a portal for more then 50 percent, it is possible to shoot a new exit portal. Make sure you move back to the entrance portal before the new exit portal hits the wall, for the right effect.
- Cubes, cameras and turrets can be used to redirect energy balls.
- You can throw objects a little further by using the left or right trigger on your controller. Combine this with a jump and a little forward movement to launch objects over quite a distance.
- It is possible to grab objects through a portal.
Some tips to save steps:
- When you have to walk, make your moves in one single motion. Every little correction to your move adds an additional step.
- Jumping while moving saves steps and crouching while jumping saves even more steps.
- Spawning a portal under your feet saves steps.
- When jumping between two floor portals (from which the entrance portal was created by shooting it under your feet while standing on the ground), removing one of them when above it (by shooting another portal of the same color somewhere else, where doesn't matter, since it is only used to remove the portal bellow you) and landing on the floor, costs no steps. This is the same effect as described by 'a laundryman'.
- Make sure you don't end up too close to corners, since you will not be able to enter a portal below you without using steps.
Some tips to save time:
- Using your exit portal as the entrance portal of your next move saves time.
- Focus less on saving, since it disrupts your flow.
- Practice a lot...
Maybe some spoilers:
- Every vertical elevator with an open top can be reached without powering it up (meaning in all six chambers only one elevator has to be powered up).
- Every horizontal elevator can be passed without powering it up.
- Use the trick with entering a portal from a higher level with two floor portals and crouching to jump onto elevators and over walls.