I used to own an arcade, and we had claw machines, they are total cash cows and this is how they work
You have 2 setting you can change, one for the power when the claw is at the bottom, so it grabs the booty, and one for the power by the time it reaches the top of the machine, so the power reduces as the claw lifts, and so it drops the booty while its lifting it up, very very occasionally (ie almost never) it will ignore the setting and give a win (assuming you managed to grab the booty in the first place), its always good to have a mug, sorry, punter walking around the place with cheap chinese knock off bart simpson under his arm.
If you want punters to win just max out the power at the top claw position, the electromagnet holds the prize and you win.
Another trick was wrapping some 5/10/20 pound notes round a tube, mugs - sorry, punters would always go for those, except the tubes where loaded with marbles, so you could pick them up but as soon as the marbles moved the tube would slip from the claw.
now, who wants to know about fruit machines lol