Axle Loading Glitch
The axle loading glitch enables you to overlap anything attached directly or indirectly on a axle (spin motors, free axles, servos) inside anything else.
Widely used in stock, some of the better DSL builders use it as well.
Axle loading is considered as a cornerstone of modern stock building with the Snapper Loading Glitch, but is not a necessary requirement to be a good builder.
How To (Motor)
To do it, start out with a motor you want to axle load. You can have as many as you want, because this glitch will affect all motors in your bot. Usually you have to do it one at a time to be useful though. Wire your motor, spin it in the bot lab and then go quickly to another tab to stop it.
Now add an axle mount (or a motor, any component with a spinning axle will do). The motor will start spinning a little faster when an axle is added. Now quick click on another tab to stop it before it slows down : the goal here is to get the motor spinning so fast, the axle flies off.
Keep adding axle mounts and removing them as necessary and stopping the motor until the axle flies off into space, then stop it one more time. When you have the axle frozen out in space, attach something such an extender or a disc onto the motor. It will attach where it normally would, not on the axle. But we don't want that, so you'll need to spin the motor again, this time letting it slow down. The axle will go back to its normal position - but the component you attached will be floating in space!
You can now build out in space without the rest of your bot getting in the way, and put stuff in front of the motor that could not normally go there. When you're finished, go into the test garage and back out. The stuff you put on the motor will be back on the axle, and inside whatever is in front of it.
Other techniques
-Rather than adding and removing axles, you can simply spin the motor you want to axle load, then quickly change tabs while still spinning, the motor will stop. Then make it spin again, the motor takes more speed, change tab. Repeat until the axle starts to wobble and then will flies out.
That technique takes some time, sometimes it lasts frustratingly long, so you can add/remove extenders on the motor's axle to speed up the process (add the extender, make the motor spin, change tabs, remove extender)
-Another possibility is chaining motors. If you chain 2 motors so that the second motor is indirectly attached to the first motor and make them spin, and use the swapping tabs technique, the second motor will swiftly start to wobble and turn in circles rather than just spinning on it's center. You can then remove the motor and use the previous axle loading technique, it will help.
This glitch is usually used when one wants to have lots of components cramped to a small spot.