what is the best way to make a extendable arm?
the best way is to use the Vexlabs Linear Slide Pack. and then use some chain or rope to move the arm.
I bet you could rig some drawer slides to work, although they are somewhat heavy.
Or…you can use the peices that come with starter kit the angle 1x1 and lightly tighten a few bolts and it slides great and you can use chain or rope whatever you would like
You could fold an arm so to speak. Put motors at or near where the folds would be and then use the to open or close the angle, extending or contracting it.
I thought of that but it was not working well for me
Check out my new Vex based Linear Actuator, which I made for my Hero 2007 Robot. I included some construction hints in the photo captions.
https://vexforum.com/gallery/showimage.php?i=200&catid=newimages
https://vexforum.com/gallery/showimage.php?i=200&catid=8
What is the linear slide pack?
how would i get the arm to extend though?
You would attach a chain or rope to the bottom of the moving peice the run it up to the top over a pulley or whatever and then done to a motor that retracts the rope chain.
I’m stupid how did i not think of that LOL. Thanks
It’s good though that you asked for help instead of giving up. My team did some work with extendable arms with the FRC robots so I learned from that.
I know most people would have given up
Thank you 
HELP!! The rope i use keeps snapping half way up. I tried doubling it up and it did not help, and using fishing line was worse and illegal. what should i do.
nylon cord
Make sure it doesn’t rub against any sharp edges that could weaken it.
well personally i like doing a 2 jointed arm with a motor connected to an arm, then at the end of that arm put another motor and arm.
it can get just as great of reach as a linear slider arm even more depending on how you do it.
just my preference…
~Alex~