A robot construction kit is a kit designed in a manner that allows reconfiguration, thus it allows one to invent numerous robotic creations. As a rule of thumb, these kits include actuators, sensors, structural parts and a controller.
Usually these kits are accompanied with software created specificaly for them. As everything is included and accompanied with instructions, robot construction kits are a great way to learn about robotics. Thus it is very appropriate to use them in educational institutions.
On the other hand, you shouldn't assume that this type of robot kits is useful for beginners only. Although the accompanied software and manuals are usually designed with an enthusiast without prior experience in mind, more sophisticated and flexible options are usually available for advanced users.
Talking about advanced users - a robot construction kit is an option to evaluate for research and idea prototyping, as often it is possible to avoid low level tasks and focus more on the problem at hand. Oh, and it's usually fun to do too.
I understand that at this moment you may feel that all robot kits of this type are more or less the same. This is only partially true. While it is essential that all these kits have actuators, controllers, sensors, etc, every kit has its strong sides.
Alpha Rex, photo courtesy of Lego for press use.
While this is true, it seems that initially there were some problems with new kits cannibalizing sales of other Lego kits. Luckily for us, they found a solution to their corporate problems and now Lego Mindstorms is often perceived as "something else" than other Lego kits, thus appealing more to older audience.
While it is easy to program Lego Mindstorms using the provided software, there are quite a few programming options from enthusiasts and other third party providers. In my opinion, this is the strong side of Lego Mindstorms robot construction kit.
It is simple enough for kids while it can get pretty advanced later. A simulation possibility in MSRS is another strong point. Read more in my article on Lego Mindstorms...
Fischertechnik is a German brand of construction toys. The same way as Lego evolved to Mindstorms, fischertechnik has their robot construction kit. Fischertechnik has never been only about fun, quite the opposite - their sets are always very educational and focused on engineering knowledge.
ROBO is no exception. The fischertechnik industry robots II kit is a great example of this commitment. You can build a 3-axis industrial pick and place robot using this kit. Other sets are available as well. Essentially, every of these sets include instructions on how to build various robots.
As other robot construction kits, fischertechnik ROBO comes with easy to use software designed to program robots made with this kit. Also, it is possible to program these robots in C; I'm not aware how much previous knowledge would be required in that case though.
Because of these educational qualities, this robot construction kit is used in numerous educational institutions worldwide. Because of the design, it is often possible to use Vex components for your own robotics projects. It can be quite troublesome to find needed metal parts, gears and other stuff, so Vex components can be used instead.
Also, the remote control capability also has to be noted. While it is possible to remotely control robots made with other construction kits, Vex comes with an elaborate remote control solution that is suitable for custom-made Vex robots, as it is designed in a way that allows custom function mapping, such as driving, crane operation, etc.
Vex is especially suitable for creation of mechanically complex robots that can be both - autonomous and remotely controlled. There are many Vex competitions held world-wide. There you can compete with other inventors. I'm not afraid of this designation as Vex robot designers can be called inventors. Read more in my article on Vex robotics design system.
I'm not really sure if Lynxmotion can be regarded as a robot construction kit, as Lynxmotion kits are usually designed to build one specific robot. Nevertheless, just like Vex, there are many Lynxmotion parts that can be bought separately and assambled as needed.
From this point of view it is a robot construction system. In my opinion, they are not suitable for robot builders without or with little robot building experience. On the other hand, if you are an experienced robot builder Lynxmotion offers everything you need to build virtually anything.
I especially like the software tools provided. Some are free, some are not. For example - Roborealm Vision software that allows you to integrate machine vision into your project costs around 90 USD. In either case, it's nice to know that such software is available.
I'm not going to say that Bioloid is a robot construction kit, that does this and that, as that would be too repetitive. Oh, I already did and that is what this article is about, right? OK, as other kits mentioned in this article, Bioloid has its "specialty".
A humanoid built using the Bioloid Comprehensive kit.
This robot construction kit is especially suitable for creation of articulated robots. This is done through a radically different communication method, if compared to other robot construction kits (with the exception of RoboBuilder). Bioloid's actuators are connected in a daisy chain, thus lesser inputs are needed on the controller and wiring becomes more convenient.
This allows you to form articulated arms, legs, limbs or whatever. Actuators are quite smart as well - they can be switched in either angular or continuous rotation mode, provide information on various parameters, such as torque, speed, internal temperature and more. You can read more in my article on Bioloid.
Bioloid is not the only robot construction kit designed to create articulated robots. RoboBuilder is another option if you are looking for that kind of kit. Just like Bioloid, it uses the daisy chain method to control its actuators.
As I haven't really done a throughout research on this kit as I have for Bioloid and some others, I may be wrong on some points. Still, as I understand, Bioloid is a bit more flexible patform in terms of expandability and reconfiguration and it seems that Bioloid's actuators are a bit stronger and software a bit more elaborate.
On the other hand, RoboBuilder kits are cheaper and it seems that robots made with this kit are more nimble than those made with Bioloid. Also, the network protocol is more universal and programming options are wider.
Also, it should be noted, that movements can be shared. A good example of this is the one arm handstand. You can find it on YouTube, if you search for "RoboBuilder one arm handstand". If you get a RoboBuilder and build the humanoid, you can get the movement file at robobuilder.net and your robot will do the same.
In either case, there is one thing that should be noted. There are many other humanoid kits out there, which seem just like Bioloid or RoboBuilder, when in fact they aren't. These kits I'm talking about are designed as one robot, you can't reconfigure them to make other robots unless you hack them.
Ollo is a kit manufactured and designed by the same company that manufactures the above mentioned Bioloid - Robotis. As you understand, most of these kits are not suitable for young kids. The Ollo kit is manufactured to rectify this.
Photo courtesy of Robotis
Ollo is designed for 7 - 10 year old kids as an introduction to robotics. There are three "levels" of this kit. Ollo figure that can be used to construct static figures, Ollo action that has a motor, thus movable figures can be made and Ollo bug.
Ollo bug is what makes Ollo a robot construction kit. Along with motors, a Robotis controller CM-100 and a remote controller are included. This controller is supported in the new Robotis software for Bioloid and Ollo - RoboPlus. I'm not aware though if this software is being shipped with Ollo right now. You can read more on Ollo and other beginner robot kits here
As you see, there are numerous robot construction kits and design systems. Each has its own strengths and weaknesses. If you want your kid to learn about engineering - fischertechnik could do the job. If you fancy competitions or RC devices - Vex robotics design system could be for you.
If you'd like to build a humanoid, a spider, or a robot with limbs - RoboBuilder, or Bioloid could do the job. In either case, I hope I managed to bring some info to you. I'm sure there are some other kits that could be regarded as robot construction kits. However, I believe that these are the most notable ones.