Yeah, I hope I get to see this soon, love the arm action! I've been cleaning out the shed here and found the BotFest arena in there, sitting there ready to go.
Thanks! Really pleased with how the arm movement came out. I still need to adjust the horns at the back so it can self right, but aside from that it's perfect. Fingers crossed we get the all clear to fight again soon.

Do you have a way to stop the motor when the lifter gets to the end of its travel?
I do! It's called the floor . Because my transmitter has both sticks on spring return, just a quick burst of the motor is enough to get full extension. Don't think it's enough to burn the motor out, but proof of the pudding shall be in the eating.

I was planning on using a servo to stop it damaging itself, but it doesn't seem like a great power-to-weight ratio whereas that is super fast, looks more like a flipper than a lifter.
Servo should be fine. It's worth noting that a 4-bar arm requires different force depending which end is powered. The "crank" (rear arm) takes less force to lift than the "rocker" arm (front). If you're worrying about a servo not having enough power, you'll be better off linking it to the back arm. It should be sufficient. I'm only using an N20 because I'm using a Malenki Nano ESC, which works better for motors than servos.

If you're making a 4-bar, I recommend the AskAaron blog and geometry calculator/excel sheet for it. Took lots of trial and error, but was worth it in the end.

http://runamok.tech/AskAaron/lifter_FAQ.html