Compatibility Between LEGO and fischertechnik Kits
The kits are not readily compatible. Physically, both have metric parts, but this doesn't really help. LEGO Technic has a base unit of 8mm and FT has a base unit of 15mm. Electrically, LEGO is I²C and FT is analog. The LEGO brick supplies 5 volts and FT supplies 9 volts.
But, these challenges can be overcome with some effort.
Comparison of LEGO and fischertechnik base units
Although these systems were not designed to be used with each other, any construction set worth its salt should be able to attach to objects that are not part of the system. This includes parts from other kits.
A quick observation: you could say that by nature, rods are "continuously adjustable" along their length. Likewise, the slots on the fischertechnik blocks are continuously adjustable. These fairly obvious ideas can be leveraged to connect the two kits.
Some ideas on mixing LEGO and fischertechnik parts
From left to right
- This is an FT metal rod, with a few FT blocks attached to it in typical ways. A LEGO beam can be stuck on it too, although the hole is a larger diameter and there's a bit of play.
- A couple of FT blocks are connected lenghthwise to a LEGO beam. This connection is also a little loose.
- The LEGO rods are a larger diameter than the FT rods, so they won't fit through the standard holes in the FT blocks. However, FT has a block that is used mainly for holding down wires which can be used here. It's a little loose, but this assembly makes a pretty good hinge.
- Once again, the base unit for FT is 15mm and for LEGO Technic it's 8mm. 15mm is pretty close to 16mm, so sometimes you can fudge things a little. The LEGO sensor connects to the FT beams using the 3cm plastic FT rods with end caps. The FT rods are smaller than the holes, but of course they're not quite centered in the holes either. The two factors basically cancel each other out and the whole assembly fits together pretty well, without any forcing. It's certainly good enough to hold a one ounce sensor.
- The last one is a LEGO sensor connected to FT wire holder blocks, using LEGO rods and small pulleys as end caps. It makes a nice compact assembly and won't rattle if the end caps are snug.
The purpose of construction sets is for prototyping. Prototypes are allowed to be ugly. Therefore, duct tape and other fasteners are permissible.
The next question is naturally, how do these kits match electronically? That's a little bit more challenging. I showed the sensors in the photo on purpose to spark a little curiousity in this area. Mindstorms are I²C and I noticed the extension ports on the ROBO TX are also I²C, so maybe there's something to work with there...
Of course, it's best to avoid mixing kits unless there is a good reason for doing so.
It's probably also worth mentioning that LEGO Mindstorms are not entirely compatible with standard LEGO blocks.
Compatibility Between LEGO Mindstorms, LEGO Technic and LEGO Blocks
Physically, LEGO Mindstorms are only somewhat compatible with LEGO. The base unit for the stackable LEGO blocks, is 8mm wide X 8mm deep X 9.6mm tall; the system is not cubic. LEGO does a lot of business and this is their flagship product, so that's just how it is. It's fine for building static structures, but as soon as you add rotating parts it gets really weird.
On the other hand, LEGO Mindstorms base units are cubic - the beams are 8mm tall, 8mm thick, and the holes are spaced 8mm apart. The 9.6mm measurement is not to be found. LEGO Technic has parts that can plug into either system. If this sounds confusing, it is. It's also well-documented. The goal here is to point this out to people who are not familiar with LEGO.
A larger incompatibility is that LEGO Mindstorms (and for the most part LEGO Technic) are based on pins on beams instead of interlocking blocks. There is no way to attach a beam to a standard block.
Although LEGO Mindstorms are physically compatible with LEGO Technic, they are not electrically compatible. Mindstorms are I²C and physically connect using the proprietary RJ12-like connnectors. LEGO offers the Power Functions product line, which are physically compatible with both LEGO Technic and the blocks, and use block-style electrical connectors. This is difficult to put into words, the easiest way to understand it is to visit the LEGO web site and look around.
It is possible to mix the LEGO systems. From left-to-right is a stackable block that accepts LEGO Technic studs, a LEGO Technic motor (which is also stackable), and a converter cable which enables an NXT microcontroller to drive it (part 8528).
It would be possible to make sort of an "automated dollhouse" by taking one of the many building kits that LEGO makes, adding actuators and sensors, and controlling it with an NXT brick. Such a project would require a lot of hybrid parts, but it could be done using only off-the-shelf components from LEGO.
For most robot projects you're better off to stay with Mindstorms as much as possible and ignore the other stuff, for simplicity and to hold down the costs. The NXT 2.0 kit does not contain any of the studded parts or Power Functions accessories.