 This is the board we've been working with for the record playback controller and you can see that I brought the controls out onto a piece of plexiglass and here's another implementation of that where the plexiglass has been mounted on top of the project box and the board has been mounted inside. I brought the heat sink out through the back. Power comes in here. There's an on-off switch and this is the potentiometer that controls the speed of the trolley. If you turn it clockwise or to the right it goes fast, faster and faster forward. If you turn it to the left or counterclockwise it goes faster and faster backwards. The record playback switch determines whether you're going to record a session or playback. The stop-lock button activates the relay which kills power to a section of track that's between these two screws on the platform so that you can resynchronize the position of the trolley each time you run it. Okay let's give it a try. We're going to fire it up. We're on record. We're going to turn the pot a little bit to the right, get the trolley started and while it's starting up I'll zoom out so you can see a little better and as it approaches the top of the hill I'll slow it down and stop it. Now notice it's right in the middle of the top of the hill. I'll bring it to the bottom of the hill. I'm going to stop it right about there. Let's back it up once, bring it the trolley around. Pretend we forgot a passenger way back here. Okay and then back up again. I'm going to hit the stop-lock button because we're only going to run it around once this time. You could run it around 10 or 15 times. That's no problem and as we approach that stop-lock I'm going to slow down and when it hit that last section of cut track it stopped. I like to let it run forward just for two or three or four seconds before I shut it down and flip it over to play. That allows the trolley to get into the stop-lock even if it gets a little bit out of sequence. Okay let's see how this repeated run goes. You may recall our first stop was pretty much in the center of the top and that's pretty close. It's a little bit beyond. The next one was down at the bottom and then we backed up so it's fairly repeatable. What you're going to find is that if the trolley is at roughly the same temperature, in other words has been run about the same amount when you play it back as it was when you recorded, it'll be fairly repeatable. By the way it's going to stop when it comes into that stop-lock. The relay just clicked. There it's going to stop and it's going to pause for a couple of seconds and it'll start that sequence over again. The things that make it not as repeatable as you would like is that all of the recording is based on time. It's taking 50 readings per second and it's playing back that exact same speed on the playback. But as I mentioned, as the trolley heats up or cools down, its speed based on a particular voltage will change. The power supply can heat up and change its voltage as time goes by. The track can become cleaner or less clean over time. But it is fairly repeatable, particularly with that stop-lock. You see it's off a couple of inches on stopping at the bottom there and it's going to come around one more time and of course this would go on forever and ever and as long as you leave power it'll continue to repeat that sequence. As it approaches the stop-lock, it's going to stop for this second time and so are we.