- Generate mobs and kill them for drops
- Vanilla-style spawners are an effective, inexpensive method
- Players must be a certain distance away for them to work
Vanilla rules dictate that hostile mobs naturally spawn 24-128 blocks from any player on any full (or top-half slab) block of light level 7 or lower. This mechanic can be manipulated to produce a renewable source of mob drops under safe conditions.
All mob spawner/grinder systems follow the same general design and require the following basic components: A "Mob Spawner" or spawning area, a transportation mechanism to the killing zone, killing-zone or "Mob Grinder", and a collector for the drops. All of these components can be done in vanilla Minecraft but several mods have made this a more reliable process allowing players to spawn specific mobs and kill them to get their mob specific drops.
While spawners and grinders and even transporters exist in many forms across several mods and mod packs you can mix and match any of them into any configuration to design a complete system to meet your needs, resource availability or just your personal taste.
Vanilla Minecraft has naturally occurring spawners in fortresses and mine-shafts that can be re-purposed (without even moving them) by adding transport, killing and collection methods to them. Also, any sufficiently dark area within the spawn range defined above (24-128 blocks) will naturally spawn mobs provided there is nothing present to prevent it. Using the F7 key you can easily identify where these dark areas are located. Popular mod specific, on-demand spawners include: MiceFactory Reloaded's Auto-Spawner and EnderIO's Powered Spawner. You can also relocate naturally occurring spawners using Diamond Dollys, Force Wrenches and a few other tools. More creative options are available in many packs that you can research as you get deeper into the game.
The most common methods for moving mobs to a kill zone in vanilla Minecraft is with either flowing water or gravity (suspended spawners can simply drop mobs to their death).
For modded Minecraft, the most popular methods seem to be MineFactory Reloaded's Conveyor Belt or the OpenBlock's Fan. The Conveyor Belt does a good job controlling mob movement but they wont work very well for floating mobs (like the Ghast). Fans work well for most mobs and are easy to make if you design the "air flow" correctly.
Methods used for killing mobs in mob farms can vary greatly. You can drop them from a significant distance and let the fall damage kill them. You can drown many of them in a flowing water system. You can even pass two or three block tall mobs through a suspended section of lava where the lava touches the top of the mob but doesn't destroy the drops at the bottom (but you can lose some drops this way). Another popular method is to transport them to a 1x1 area and use a sticky pistons to force a block into the area with them which causes them to suffocate.
Modded items that are popular for this purpose include the MineFactory Reloaded Grinder which collects the drops for you and also supplies the Mob Essence needed to make the Auto-Spawner work. You can also use Spikes (Iron, Gold or Diamond) to kill them and get the drops. Gold spikes will also cause them to drop the experience orb which can be collected in your collector and a Diamond Spike will cause them to drop both the experience orb and any "Player Only Drops" (mainly for Xeno's Reliquary items). Another popular option is the Autonomous Activator from Thermal Expansion - a highly flexible item which can be fitted with a sword to kill off the mobs (this also produces "player only drops").
For vanilla Minecraft, mob drops are typically collected in a regular Hopper (or a group of them working together). There are other, "kludgy", ways to do it but a Hopper is very easy to build and use.
Modded collection utilities (in addition to the Grinder discussed above) have to include the Vacuum Hopper from OpenBlocks which will also collect the experience and convert it to a liquid form which can be stored in tanks or drums. Obsidian Transport Pipe from BuildCraft can also pick up items for storage.
[please add any design examples you feel are relevant]
DeVco Mob Spawner RulesEdit
Here is a list of rules for their use on the DeVco servers:
1. Spawners must have some form of off/on switch be it levers or rednet cables. Whatever you choose. But it most be able to be turned off or staff will destroy your spawners with no refunds.
2. Mobs must be killed at a faster rate than they are being spawned. The build up of mobs lags the server.
3. Mob farms cannot be chunk loaded. You can use iron block loaders, but not diamond block loaders.
4. If your mob farm is causing server lag staff will break your spawners and there will be no refunds.