Lobst3r, a walking robot

[Aswin]

This is Lobst3r, the walking robot that can walk in any direction. It goes forward, sideways, it can turn and even rotate on the spot.

Robots that can go in any direction are called holonomic or omnidirectional robots. Most holonomic robots are made with special wheels. This robot however is a walking robot. Its legs implement  Klan linkage to walk. But the real trick is in the toes of the legs. The wheel on the tip of each leg is the secret to its holonomic capabilities. This small wheel is mounted perpendicular to the direction of the leg. As a result, the leg can roll sideways without any friction whilst still having friction in the walking direction.

The base of the robot is triangular, the simplest form to create a holonomic robot. On each side are 4 legs that are linked to a single medium EV3 motor. An additional NXT motor under the tail of Lobst3r powers the claws of the robot. The robot has two ultrasonic sensors that are used to detect objects in front of the robot. If it sees an object it will try to walk around it. If that doesn't work it will snap it claws in self defence, back up, rotate and walk away. The US sensors are switched on and off to prevent one sensor picking up the echo's from the other sensor. As a result the robot seems to blink with its eyes 

The program is written in leJOS. LeJOS offers standard code to implement holonomic robots.  

 

[JJ2]

Very interesting creation, the legs are very cool to watch, could you program it to be IR?

Its always fun to see an out of the box build like this.

[Leonardo da Bricki]

That is really cool! Thanks for showing such an interesting build.

[Sariel]

Best and funniest build I've seen in a long time :D

[1980-Something-Space-Guy]

I am very impressed. Not only does it function pretty much perfectly, but the lobster detailing and claws look and work really well. Do the gray pins manage to hold the wheels strongly enough? I was wondering if they ever slip out during a step.

[agrof]

HAHA, very cool creation! I love the leg mechanism, and the whole creature a lot! 

It would be great to see such product line within Technic: animals, human hand, robot arm, things a bit out of the box.

[grum64]

A cool and very interesting build.

[Aswin]

Thanks for all the positive remarks!

Regarding the questions.

At first I had two IR sensors as eyes. But also these interfered with each other. I know they shouldn't but still they do at fixed intervals. The IR sensors are much harder to shut down in leJOS than the US sensors. Therefor I switched to US. Also, the range of the US sensors is much larger and therefor better suited for a robot this big.

The grey pins that hold the wheels haven't slipped out a single time. There is not much strain on them. The main reason is that the robot accelerates in a controlled way to its final speed and from one move to another. Also, the four legs on each side are synchronized with a quarter phase shift between each leg. There is always a leg on the ground already when another one steps on the ground.

 

Edited September 27, 2016 by Aswin
engrish removed

[oracid]

Good ideas !

[Oliver 79]

That's an awesome machine! Did you model the legs in linkage yourself? I've just downloaded it myself, but I haven't had a chance to play with it yet. 

[Rascko]

Cool looking mecha-lobster, and a smooth-functioning too!

[Lipko]

Sweet!

I used the same linkage in my wind-up crab:)

 

[1980-Something-Space-Guy]

 

19 hours ago, Aswin said:

Thanks for all the positive remarks!

Regarding the questions.

At first I had two IR sensors as eyes. But also these interfered with each other. I know they shouldn't but still they do at fixed intervals. The IR sensors are much harder to shut down in leJOS than the US sensors. Therefor I switched to US. Also, the range of the US sensors is much larger and therefor better suited for a robot this big.

The grey pins that hold the wheels haven't slipped out a single time. There is not much strain on them. The main reason is that the robot accelerates in a controlled way to its final speed and from one move to another. Also, the four legs on each side are synchronized with a quarter phase shift between each leg. There is always a leg on the ground already when another one steps on the ground.

Very interesting. When you say controlled, do you mean closed loop?

11 minutes ago, Lipko said:

Sweet!

I used the same linkage in my wind-up crab:)

Wow! Those are awesome too!

Edited September 28, 2016 by BrickHat

[Imanol BB]

That is really cool, the legs are pretty amazing, the way they can move in various directions is great and clever with the use of the wheels, nice work.

[Aswin]

@Lipko I did use linkage to model the legs myself to find optimum dimensions using lego units and existing lego parts. This was fun to do. I like the crab a lot. 

@BrickHat With controlled acceleration I mean that I am able to specify the maximum acceleration (both linear and angular) of the robot. Whenever I issue a move command the brick calculates how long it would take to go from the current speed (both linear and angular) to the desired speed when taking the max acceleration into account. The brick also measures the current speed of the motors and calculates their end speed given the desired move and shape of the robot. Using the difference between the two and the time needed for acceleration it calculates the desired acceleration of each of the motors.  This is all done by a standard leJOS class called the Chassis, so I don't have to bother with it. (Although I wrote this class myself some time ago.) the acceleration and end speed are then issued to each of the motor drivers. The leJOS motor drivers offer excellent speed and acceleration control. As all this functionality is provided by leJOS. All I had to do for this robot is to tell the Chassis object what move to make next, like for example make an arc (with some parameters to define the arc). Everything else to get smooth moves and transitions is done by the chassis and motor drivers. As a result the program for this robot is very short. I used about 25 lines of code to implement the behavior of this robot. 

both the Chassis and the leJOS motor drivers are featured in articles on leJOSNews if you want to know more about them. 

[1980-Something-Space-Guy]

7 hours ago, Aswin said:

@Lipko I did use linkage to model the legs myself to find optimum dimensions using lego units and existing lego parts. This was fun to do. I like the crab a lot. 

@BrickHat With controlled acceleration I mean that I am able to specify the maximum acceleration (both linear and angular) of the robot. Whenever I issue a move command the brick calculates how long it would take to go from the current speed (both linear and angular) to the desired speed when taking the max acceleration into account. The brick also measures the current speed of the motors and calculates their end speed given the desired move and shape of the robot. Using the difference between the two and the time needed for acceleration it calculates the desired acceleration of each of the motors.  This is all done by a standard leJOS class called the Chassis, so I don't have to bother with it. (Although I wrote this class myself some time ago.) the acceleration and end speed are then issued to each of the motor drivers. The leJOS motor drivers offer excellent speed and acceleration control. As all this functionality is provided by leJOS. All I had to do for this robot is to tell the Chassis object what move to make next, like for example make an arc (with some parameters to define the arc). Everything else to get smooth moves and transitions is done by the chassis and motor drivers. As a result the program for this robot is very short. I used about 25 lines of code to implement the behavior of this robot. 

both the Chassis and the leJOS motor drivers are featured in articles on leJOSNews if you want to know more about them. 

Thanks for the detailed explanation, Aswin! That seems like a very powerful tool indeed. It works like a charm. And thanks for the link!