The mechanical arm

This was quite easy as i followed all the instructions. i also learn about constraints while doing this. However, when doing this, i figured out that that there was one thing i don't know how to do and that is how to delete a key frame. I pressed backspace and my entire constraint got deleted. I than figured out that you must right click and select delete from the drop down menu to delete a key frame. Also, when doing this video, I have problem with the file size, its too big, causing it to lag when playing. I tried to convert it but every time gives a blank screen.