The Powered Rail is a block that is used to stop or increase momentum of moving carts. It was added as a response to the Minecart booster bug which was fixed with the release of Beta 1.6.[1] Powered Rails are operated by Redstone currents, whether this comes from a Lever, a Button, another circuit or a Detector Rail.
A simple launcher using four Powered Rails, a Button and a solid block
Powered rails, much like redstone wire, have two possible states: on or off.
A rail that is "off" slows any passing minecart by applying a frictional force. The force is generally strong enough to bring a moving minecart to a complete stop, or to hold a minecart in place on a slope.
A rail in the "on" state will accelerate a minecart if any of the following is true:
The minecart is already moving, in which case the cart is accelerated in the direction of motion
The minecart is stationary, but one end of the powered rail is up against a solid block. In this case, the cart is accelerated in the direction that is not blocked.
The minecart is stationary, but the powered rail is on a slope. The instant the powered rail is activated, the brake is released and the cart will start moving down due to gravity. As the cart is now moving, rule (1) applies and the cart is accelerated in that direction.
The second and third cases can both be used to create simple stone button-activated launchpads. When the powered rail is off, carts are held in place, providing a safe way to load and unload carts without them derailing like they would on pressure plates.
Powering
Power can be transmitted to the rail from any of the six adjacent positions (above, below, or any side) in the same ways that redstone wire is powered. Strangely, the rail can also receive power from the five positions immediately above those adjacent positions. In other words, the rail acts as if it is two blocks high, and can receive power through any of eleven adjacent spaces, just like a door. This works whether the upper space is occupied or empty. However, powering the rail through the upper space currently exhibits more bugs related to updating.
Powered rails will propagate power to each other if they are adjacent and part of the same track, for up to 9 blocks from the power source (1 being powered directly which is propagated to 8 adjacent rails) . They will also receive power from any adjacent detector rail (when a cart passes over it), even if they are not part of the same track (which follows from the rules above).
Because the detector rail powers attached rail it could be used to activate power rails only when necessary:
For one-way travel, place a detector rail before the powered rail
For two-way travel, place a detector rail on both sides of the powered rail
In practice it is far more efficient to have powered rails constantly active using other means:
Place a Redstone Torch either next to the powered rail or two blocks underneath it or use powered Redstone wiring to achieve the same effect
Place an activated Switch next to the powered rail
Momentum
The speed of a cart which is boosted using Powered Rails is calculated to be at the maximum of 8 m/s, however the cart maintains an internal "momentum" value that keeps the cart at the maximum speed of 8 m/s until the excess momentum is depleted.
A single powered rail on flat ground against a stop block gives an occupied cart enough momentum to travel 80 rail tiles on a flat surface, or 8 tiles for an unoccupied cart (in Beta 1.5, this was 64 blocks and 8 blocks respectively). Tests show that putting several powered rails in a row has observable diminishing returns with each additional powered rail on how much further a cart will travel.[2] This implies that the momentum gained is smaller if the cart's speed is faster and vice versa.
Practical examples show that it is possible to accumulate momentum with a small 3x3 loop with 4 powered rails, after which the minecart is released from the loop via a track switch, resulting in a very long travel distance while still cruising along at the speed limit until all the surplus momentum gets used and the cart slows down.[3] This is mentioned in greater detail in the Mechanisms section. This example also reinforces the existence of diminishing returns, because releasing the cart from the loop after a really long delay only gives a slight increase in altitude reached.
Tests show that climbing slopes impact momentum severely, thus the cart speed plummets fast. However, if there is enough surplus momentum, carts will travel up slopes with ease. Conversely, carts traveling down slopes gain momentum. Downward sloped powered rails will add both the momentum from the rails and the momentum from going downhill to your cart.
It is unknown if there is a limit to how much momentum a minecart propelled by Powered Rail can accumulate.
Climbing slopes
6 blocks up without additional boosting in beta 1.5, 10 in beta 1.6
Launching from rest via four powered rails, an occupied cart has enough momentum to climb a 1/1 slope 10 blocks high without further boosting and then travel horizontally at a very slow speed for at least a dozen blocks before coming to a stop. Such a cart does not have enough momentum to climb a 11 block high slope. An empty cart in a similar setup will only climb 5 blocks and then travel a few blocks horizontally.
When minecarts travel upslope without having sufficient stored momentum upfront, a powered rail is needed 1 every 4 blocks to sustain movement all the way to the top of the slope, Alternatively, 2 every 8 blocks are somewhat easier to supply power to. However note this is a worst-case scenario where there is no momentum to start with.
There is a great way to travel easily up a slope and that is to have more cart momentum to begin with. With just a few seconds of building up momentum in the 3x3 loop mentioned in the earlier Momentum section, it is very much possible to reach cloud level from sea level as the starting point by using just 4 powered rails.
Optimal Use
The following table lists optimal powered rail usage for occupied minecarts.
Disclaimer: The Patch 1.5 and 1.6 optimal values in the table below is pending a new set of tests that uses straight tracks instead of a looped track with 4 corner track pieces which will give more reliable results because corner tracks reduce the distance traveled which was not accounted for. Meanwhile, 1 every 36 blocks should be a pretty reasonable estimate for optimal spacing without having noticeable speed decrease. The video at http://www.youtube.com/watch?v=F7CyaCeS3fY shows the absolute optimal spacing for maintaining maximum speed in Beta 1.6 to be at 1 every 27 blocks because 1 every 28 blocks is slower by 1 pixel.
3 powered rails in a row on flat terrain is sufficient to boost a minecart from rest to the maximum speed of 8m/s.
Thereafter, the optimal spacing of powered rails on a level track is to use 1 every 42 blocks (that is, a repeating pattern of one powered rail followed by 41 normal rails, then another powered rail, and so on) which maintains a constant minecart speed of 8 m/s. If gold is in short supply, it is possible to use powered rails with more space between them at the cost of reduced overall speed:
One powered rail every 44 blocks: 7.92 m/s –1% speed decrease (quite negligible)
One powered rail every 46 blocks: 7.24 m/s –10% speed decrease
Using one powered rail every 43 blocks might be optimal seeing that 1 every 44 blocks is only a 1% decrease in speed (untested).
However, the optimal spacing of torches is 1 every 13 blocks in order to keep the entire track lit at lightlevel 8 and above. (hostile mobs can spawn on tracks, passive mobs will only spawn on tracks if the track is on grass), so for aesthetic purposes, it might also be desirable to space out powered rails every 39 blocks.
A diagonal track is a track that consists of the the pattern 'left corner' attached to a 'right corner' attached to a 'left corner' ... and so on. When minecarts travel on a diagonal track, the camera is held steady in the diagonal direction and the minecart visually travels diagonally along the track as well. It is discovered that the speed limit of minecarts is actually 8 m/s per cardinal axis, thus when traveling on diagonal tracks, the cart will travel 8 m/s in both cardinal directions of travel to result in a net vector of 11.3 m/s.
Because of this difference, there is also a difference between the optimal spacing of powered rails when used on a diagonal track when compared to straight travel on flat terrain. This is determined to be 1 every 52 blocks (counting tracks orthogonally, if you count blocks diagonally instead it is 1 every 26 blocks - orthogonally means every block containing a rail in this case). As Powered Rails do not curve and cannot be used at corners, a straight stretch of 3x1 track with the middle track being the powered rail is needed every 52 diagonal tracks. Because of this, diagonal tracks may be undesirable as the camera will swing left and right momentarily every 52 blocks before returning to the diagonal direction of travel.
A Detector Rail will power the 4 blocks adjacent to it as well as the 2 blocks below it when a minecart (both occupied or empty) is over it. It is thus possible to activate powered rails inline without the use of redstone torches or wiring.
In general it is possible to include a detector as a source to get the power to activate an adjacent powered rail but this is not recommended as best practice. For example if you place one detector and 4 subsequent powered rail you will see the cart gets stuck on the third or second powered rail since the moment the detector stops detecting the cart the power will get cut instantly and the powered rails return to their braking behavior.
However when just a single powered rail is used in combination with a detector in theory this lends itself to one-way powered rail lines by placing a detector rail before the powered rail (with respect to the desired direction of travel). This way, occupied carts will only be boosted if they are traveling the proper direction. Carts coming from the "wrong" way will be quickly brought to a stop by the inactive power rail. Notice however that when using this as described there will be a cart stuck on the track. The most likely way this is used in practice is not to block a wrong way cart but because the track is designed so there is only one way possible to start with.
A two-way line can be inefficiently created by placing detector rails on either side of the powered rail. In practice when choosing detectors to give power on a two-way track you will need a detector on either side of a single powered rail. Although they do work and can be effective for some specific reasons to give power inline it is not often used this way.
Placing alternate powered and detector rails up a 1/1 slope will not propel a cart more than 3 blocks upward if there was little momentum to start with, because the cart will be slowed down by the slope and fails to clear the powered rail before it returns to the "off" state due to the fact that the cart is no longer over the detector. The cart will become stuck unless it is in a "train" of two or more carts, in which case the last cart in the train will become stuck.
A better example to use detector rail would be have something activated or changed based on where the cart is in your track, or as failsafe devices. For example if you have a station with a cart waiting if may be a good idea to release the cart waiting at a station in case a rogue cart arrives instead of having both collide.
Curved power rails currently only exist in the case of a T-junction.[6] They do not currently function like regular rails in a curve (without being in a junction). It is possible to make a one-way curved railway using power rails, but not a bi-directional one.
When placing rails, regular rails prefer to curve towards the powered rail. In cases such as these, the south-west rule applies.
A cart traveling on a powered rail that collides with an object (wall, single block, player, other cart) will reverse direction. It will not reverse direction if it collides with a translucent block, such as Stone Slabs or Glass. If a track including powered rails is bordered by blocks acting as "buffers", the cart will indefinitely continue back and forth along the track. Having carts interact with each other on a short track designed this way can be used to chain multiple carts together as a "train". Once aligned, they will all move together at relatively the same speed.
How far the charge passes down adjacent rails is independent of the length of redstone wire. Even if the rails are connected to a redstone torch by 15 blocks of redstone dust, the 8 adjacent rails will still be powered normally despite the fact that they should be out of range for the torch.
Powered Rail Mechanisms
Stop Points
It is possible to make points in your track where a cart is stopped and then jumpstarted again by player input. This can be useful for creating checkpoints to certain sites of interest in your world. This can be done by using two powered track pieces on a one block incline, by having the first powered track piece going down, with the second powered track piece at the bottom and a button placed alongside the second powered track piece, so that the button is directly above the track. You can see an animated example of this stop point if you click on the image
Animated Gif of said example,click for the animated version
When the cart comes to this point it will stop On the incline, allowing the cart to use gravity to start the boost when the button is pushed. Players can then either stay in the cart and carry on to the next stop, or leave the cart at the station for themselves/other players to use later.
Starting boost
Creating a simple initial boost device using 2 powered rails. Dig a hole 1 block deep and 2 blocks long. Place the powered rails inside the trench, connect one end to the track that you wish the mine cart to exit. Finally place the mine cart on the powered rail. Once power is applied to the rail the mine cart will be boosted out.
Momentum boost /climb boost
It is possible to reach a remarkable height with just using 4 powered rail[3] by using a 3x3 loop with 4 powered rail that is connected with a T switch to the slope. A cart is placed on the loop and allowed to spin around for a few seconds to build up momentum beyond the speed limit. The best practice is to have a switch with a delay to switch the T section to alternate between a loop and the uphill section. The player switches the loop so it will go uphill, because of the delay the player can get in the cart and the cart will loop a few times building up momentum until the delayed switch of the T-section shoots the player uphill.
With just a few seconds of building up momentum, you will reach the cloud layer if sea level was used as starting point. You can implement this trick in a minecart arrival/depart station, as seen here.
Bugs
If a Powered rail is only powered by another Powered rail diagonally up or down, you can destroy the rail powering it and it will continue to look and act like it has power until the block is updated. This can be used to have little to no power sources in your track design and up to 2/3 less powered tracks for uphill parts.
When you power a track, 8 tracks in both directions (excluding the track being powered) will be powered. If you have a 19 Powered tracks in a row [1,2,3...18,19] and you Power track 10, tracks 2-9 and 11-18 will receive power. If you add power to track 9, after powering track 9, track 1 will not be powered, even though it is within the 8 tracks. After this, if you remove power from track 10, power will be taken from track 9, however, the same tracks will be stay powered (tracks 1 which should be powered is not, and track 18 which is powered, should be unlit). If you power track 2, (or 18), you will get power in the next 8 blocks.
Doing this, you can power infinite tracks with only 3 torches. 1) If you power track 1, up to track 9 will be lit. 2) Power track track 9 (or last lit track) and 10 (the last unlit track). Putting power in track 9 will keep the previous tracks lit, and 10 will power the next. 3) Then unpower 1, it will still be lit, as 9 is lit, and in the 8 range. 4) Now unpower 9. 1 is still lit. Jump back to step 2.
This also means you can't power tracks in steps of 1 (even if you make something fancy with redstone circuitry). You would have to unpower everything, then power the one 8 steps away (you need n carts + 8 for the number of tracks)
There are currently no textures for curved power rails. However, they still work when placed at T-junctions powered by Redstone.[6]
In Beta 1.6.5, if a Powered rail is flooded by water, it disappears.
When a minecart is on an unpowered rail and it powers up, the minecart may not move. (please confirm)
Trivia
For comparison of speeds, walking speed is about 4 m/s (4.27 exactly), thus using powered rail to speed up will almost double your traveling speed.
Powered rails will always show as powered in the inventory even if destroyed and collected while it was unpowered.
