Millennium Force Anti-roll Dog System?

I'm working on a project for school and my team and I were wondering if anyone could give us a heads up on how the Millennium Force anti-rollback system works, because I heard that it is not active when the ride is moving up the lift hill.

The best I understand it, the rotation of the wheels in a forward motion powers a magnet underneath the car that holds up the anti-rollback dog. When the train stops moving forward, the magnet loses power and the dog is allowed to fall.

Again, this isn't direct knowledge, just what I've gleaned from discussions over the few years I've been here.

I love when people talk about the mechanical systems for my favorite rides, esp. Millennium force...:) Is that why it makes that grinding noise you hear from the midway below and not from the hill when you ride it?

I think JuggaLotus explained it pretty well.

Correct. You only hear the "grinding" noise when the train is coming to a stop and starting back up.

There are 6 anti-rollback dogs on each Millennium Force train. There is a pair on the rear of the first, fourth, and last car.

Each anti rollback dog is basically a large piece of steel that falls into the slots on the lift hill track.

Pic of lift track and slots:

The I beams double as the catch car track, and the anti rollback system.

The anti-rollback dogs work like any other roller coaster. If the train moves forward, the dogs lift up and clunk back down in the slots. If they try to roll backwards, the dogs fall into the slot and hit the back of the slot.

The special feature of Millennium Force's anti-rollbacks is that they have an eddy current lifter on each. The brakes on the ride are the same concept using eddy current "magnetic" brakes.

The lifters work with a tire that rides on top of the I-beams the outside of the slots. The tires rotate while going up the hill. The tire is mounted next to a ring with a slot on the inside with magnets located in the slot. The anti-rollback dog has a copper plate attached that hooks over the ring. As the wheel rotates, the back of the wheel moves upwards, which pushes the copper plate up which pushes up the the anti-rollback dog.

The brakes work with static magnets, and a moving train. The brakes resist a difference in speed of the copper plates on the train and the magnets on the track. The faster the train moves relative to the magnets, the harder the brakes work. The lifters work the opposite way. The magnets are forced to rotate. As a result, the lifters want to move with the magnets, and the only way they can move on the back of the wheel is up. The plates move up until the anti-rollback dog hits the bottom of the train.

A picture of the 4th car:

Notice the small tires on the inside of the road wheels. If you look carefully, you can see the copper hooks that are around the top of the metal ring with a slot. The copper plate is located inside the slot. You can't see the actual anti-rollback dogs, but they are forward of the tires and copper plate hooks. Also note the chain dog in the center of the car. There is only one chain dog one each train which is located on the 4th car. This engages the rear of the catch car and works exactly the same as the anti-rollback dogs except the chain dog does not have a lifter on it.

The anti-rollback dog lifters require a sufficient angular velocity of the tires (rotation speed) to lift the anti-rollback dogs. When the train is not in motion, the dogs fall and engage the slots. If the train is moving slowly forward, you will hear a clunk sound as the dogs are forced up and drop down in the slots. This does not do damage in itself.

Occasionally, the tires will not get sufficient grip. The locations that had the most issues when wet have traction strip glued down to help keep them rolling. The spots are the bottom of the lift and the top of the lift where there is curvature in the track. Sometimes the tires go flat and will not rotate as well or at all. This is worse when the track is wet. This slippage causes the anti-rollbacks to drop at full speed. High speed engagement is very loud and violent.

Any train that drags it's anti-rollbacks for more than a short period of time is required to be taken out of service immediately and repaired by a mechanic. Accelerating the train up the lift from a stop also causes this until the dogs are lifted up. To prevent damage to the dogs from normal starts in the station, black plastic plate was put in place over the slots in the station to hold them up until the train moves fast enough to allow the lifters to work correctly. The plastic is viewable on the official P.O.V. video.

If you are in the rear of the load station, you can watch the lifters work as the train leaves the station. Of course that doesn't help much during the off season.

Hope this helps,

-Marc

(Bad link fixed)

So if you are saying that the lifters can be seen from looking back then i guess the reverse POV shot by cedar point,you would be able to see these lifters in action right?
And also don't the catch car have a hand in the roll back process as well?

No, I think he means that you can look from the station at the back of a dispatching train to see them (i.e. under the rear of the train). This perspective is not possible from the train, and hence not from the reverse POV, presumably.

Rollback said:

A picture of the 4th car:

http://image05.webshots.com/5/4/41/62/65344162ELDZSR_ph.jpg

Marc, welcome to Pointbuzz. Hope you enjoy the site.:) I just wanted to let you know that this link didn't work too well. Could you re-post the link. Also thank you for the explaining of how the dogs work on Millennium Force. It's been a while since someone on here explained how that system works. One question I have for anybody on here is what prevents the train from accidental train rollback on the first hill?

I fixed the link and even tidied them up.

The anti-rollbacks are responsible for preventing the train fromrolling back on the first they. They work very well. The lifters donothing when the train slows down, and the anti-rollback dogs fallunder their own weight. Even if all of them did manage to stick atonce, which I can say will good assurance that it won't happen, thelifters will force them down during a rollback on the first hill.

I did notice that you can see the bottom of the right anti-rollback on the right car in the "4th car picture."

The black plastic is viewable in either of the official POV videos, but it is better viewed in the reverse POV. On the other hand you can't see the anti-rollbacks in the POV.

I took that photo of the MF train on blocks. I'll have to hunt around and see if I can find the original size.