LEGO Mindstorms vs. fischertechnik

Here are two simple robots to give an idea of what is being discussed. On the left is a 2-wheeled balancing robot with remote control built from LEGOs, on the right is a basic tribot from the FT Robo TX Training Lab.

• ARM 7
• 48 MHz
• B&W LCD display
• speaker with voice synthesis
• 4 sensor ports
• 3 encoder motor ports
• USB
• Bluetooth
• I²C
• no expansion ports

• ARM 9
• 200 MHz
• B&W LCD display
• no speaker
• 8 sensor ports
• 4 encoder motor ports / 8 analog outputs
• USB
• Bluetooth
• I²C
• 2 expansion ports

• Both systems are durable and will last many years.
• Both systems are metric.
• The cost of either sytem adds up pretty fast. (The cost of FT adds up a bit faster.) Of course, after you have a stockpile of parts you can reuse them, and to build a new project you can supplement your collection as needed.
• Both the NXT basic kit and the Robo TX Training Lab include motors with digital encoders
• USB and Bluetooth, I²C
• Pneumatics are available
• Nice touch - both the NXT basic kit and the Robo TX Training Lab include large paper "test pads" with markings for mobile robots to run around on.

The quick answer is, these kits are not readily compatible. However, hybrid projects are possible and there seems to be a fair amount of interest in doing this. Please see the compatibility page for more details.

• Great for mobile projects
• Great gift idea - the buyer does not need to do any research. Just get the basic NXT kit and batteries, and you're done.
• LEGO is what everyone else has.
• Clutch gears and differentials are available
• Compatible sensors and other parts are available from 3rd party vendors
• The NXT kit has a very high fun factor. The pea shooter is nice selling point.

• Great for stationary projects
• The system is very flexible in the variety of things that can be built with it.
• The FT system is more open, in the sense that an FT project can be connected to non-FT parts a little more easily than is the case with LEGO. Several fasteners and other hardware store items can attach to FT.
• You can plug anything that has wires into an FT microcontroller. (This is mostly good...) The FT bricks are somewhat similar to Arduino / Netduino in this respect.
• The microcontroller brick can be powered from a wall adapter.
• Both 16- and 32-bit bricks have built-in IR
• The Robo TX brick is small and lightweight. The battery pack is a separate unit, so there are more options for where to place these parts on the robot.
• The Robo TX brick supports telnet. On a Windows system you can attach to it with Hyperterminal.
• Nice touch - the kits include plastic bins which can be used for storing & organizing parts, at least temporarily

• Batteries only. (rechargeables help...)
• The 6-pin cables with proprietary connectors make the robot tidy, but it seems like you're always looking of a different length than what you have. They are expensive.
• The batteries are part of the brick, making it bulky and heavy. The lithium battery pack makes it even more so. LEGO robots tend to be designed around the brick and the motors.
• LEGO does not make compatible solenoids for its pneumatics - only manual valves. It's possible to physically toggle the valve with a motor, but this is slow and bulky.

• Due to the nature of the material, the nylon parts can't be molded to the same exact tolerance as the ABS parts. Occasionally you have to swap out a nylon part to find one that holds in place more snugly.
• Instead of using encoder or stepper motors, many of the 16-bit kits (such as the arm) come with plain electric motors and use a cam-and-bumper system to count revolutions. This leads to extra wires and strange prominences sticking out of your project. (32-bit kits like the Robo TX Training Lab have encoder motors.)

LEGO NXT has sold a lot of units and there are tons of books, 3rd party add-ons, project plans and web forums.

Of course you can find an amazing amount of stuff on eBay, both out-of-production parts and compatible parts, such as 3rd party sensors.

Having a large customer base is a plus in many ways, but there are disadvantages as well. In order to sell the product as a toy, each of the parts has to be proven safe for children - in every country where LEGO is sold. Regional laws vary, so this is a major limitation. LEGO does not sell compatible solonoids for its pneumatics, and it will not market some types of sensor. Aftermarket vendors do a pretty good job of filling in the gaps, however.

LEGO Technic is not as flexible as FT, but you can do a lot of things with it, and in most cases it's not a factor. If you're mainly looking for a mobile platform with sensors, LEGO is an excellent choice. It's a high quality product at a reasonable cost.

Battery life is an issue. AA batteries do not power a robot for long. There is a lithium battery pack available (part 9798) which stores a pretty good charge, which needs a wall transformer (part 9833, or substitute your own). The battery pack sticks out the back of the NXT brick about 1/2". This may be a consideration for some mobile projects. Rechargeables are another solution.

The NXT brick itself does not have a power jack, so even stationary projects require battery power. But if you do happen to own the battery pack, it can power the brick while it is being charged. Long story short - you will eventually end up buying the battery pack.

The encoder motors are nice but they are somewhat bulky and kind of an odd shape. They can sometimes be tricky to incorporate into your project. Basically you end up designing your robot around the brick and the motors.

The Bluetooth implementation on the NXT is a bit quirky in my experience. I found this article to be helpful.  It's dated 2006 but information is still useful.

mindsensors makes small servo motors as well as linear actuators for NXT. Linear actuators aren't as much fun as pneumatics, but practical.

For individual parts, the "pick-a-brick" page is often helpful - http://shop.lego.com/pab/

LEGO Technic has 2 types of wheels, coasting wheels that turn freely, and drive wheels which have a cross-shaped hole to attach to the axle. This is a nice feature, but be sure to order the right part.

FT is not as established in the USA as it is in Europe. Fischer has been making robot kits for a long time, among many other things.

Fischer targets the educational market, and there are many fun experiment kits as well as robotics. Some of the kits are intended for older students in a lab environment, so the selection of parts and sensors is not as restricted as LEGO.

A lot of interesting web content is available only in german.

FT is very flexible and great for prototyping. The parts are quite sturdy, but it's possible to combine parts in ways that fall apart. Using FT is an acquired skill. Once you learn to "think in fischertechnik", you can really do a lot of things with it.

Suggestion: if you're not familiar with FT, it might be worthwhile to get a low-cost kit like the Da Vinci Machines (part 500882) or the Universal II kit (part 93290) and build a few models to evaluate the system.

Gears and wheels attach to the axle with an adjustable wing nut. By keeping the wingnut a little loose, it can also function as a clutch gear. While there is some benefit to this design, in practice it can be quite fiddly. If the robot is a little heavy, drive wheels tend to slip on the axle when you don't want them to.

FT uses plain wires with connectors on the end, which are similar to banana plugs but much smaller. This makes the system fairly open. If you have a motor or analog sensor that operates within a reasonable voltage and current range, just put a connector on the wires and plug it in. This is a very convenient feature. The downside is, FT projects tend to have a lot of wires sticking out. Of course if you intend to keep the project assembled for a long time, the wires can be cut to length.

The pneumatic pump splatters a tiny amount of oil when it runs. It's not a big deal as long as you know about it first. Store your project on a piece of newspaper.

Be careful when purchasing robot kits so that you don't end up over-puchasing. For example, the Robo Mobile Set comes in 2 variations - part 93292 includes the 16-bit brick and software, part 96808 is the same kit but without them.

If you have the time, take a look at some of the projects built from the pneumatic kits (parts 34948, 500883, ...). You can do some interesting things with solonoid-controlled pneumatics. Fischer also manufactured hydraulic toys for a short time.

There are upscale FT robotic kits targeted to high schools and colleges. The school kits are generally pretty expensive. Some educational suppliers make lab kits that are based on fischertechnik parts.

Fischer sells aluminum girders of various lengths. Some 3rd party vendors manufacture FT-compatible T-slot girders and will cut them to length.

Fischer does sell stepper motors (part 32311) although they are pricey and hard to come by in the US. They're manufactured by Crouzet (part 82920001). There are also blogs on how to adapt other stepper motors for use with FT.

A good showcase of what can be done with aluminum girders, worm gears and stepper motors is the 2-D plotter that was sold back in the 80's. (part 30571)