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NXTway-GS (Self-Balancing Two-Wheeled Robot) Controller Design

version (11.3 MB) by Yorihisa Yamamoto
NXTway-GS Model-Based Design based on Embedded Coder Robot NXT.


Updated 01 May 2009

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Editor's Note: This file was selected as MATLAB Central Pick of the Week

NXTway-GS is a self-balancing two-wheeled robot built with LEGO Mindstorms NXT and a Hitechnic gyro sensor. This demo presents sample models and documents describe the following contents.

How to Build NXTway-GS
Mathematical Dynamics Model of NXTway-GS
Controller Design for Balance and Drive Control
NXTway-GS Model Illustration
Simulation and Experimental Results

You can simulate NXTway-GS model and generate controller program that can be executed on the NXT. You can watch the movies of NXTway-GS simulation and control experiment at the following URL.

This demo uses Embedded Coder Robot NXT Demo as MBD environment. You need to download it from the following URL before trying this demo.

LEGO(R) is a trademark of the LEGO Group of companies which does not sponsor, authorize or endorse this demo. LEGO(R) and Mindstorms(R) are registered trademarks of The LEGO Group.

Cite As

Yorihisa Yamamoto (2021). NXTway-GS (Self-Balancing Two-Wheeled Robot) Controller Design (, MATLAB Central File Exchange. Retrieved .

Comments and Ratings (31)

Thanks sir it helped me lot in understanding concept


Hello. I run into this? how can it be reolved?

Failed to load library 'ecrobot_nxt_lib' referenced by 'nxtway_gs_controller/Battery Voltage Interface'

Failed to load library 'ecrobot_nxt_lib' referenced by ''
Component: Simulink | Category: Block error

Mandela ouafo

Guolong Jiang

Need to be updated to version R2017B.

graig leno

castle zhang


Marjan Sarafimov

Is it possible that i have not connected a NXTway-Gs with my PC yet, because i just wanted to make only a simulation on my PC..?

Unable to open model file 'nxtway_gs_controller.mdl'.

Shawn Tang

I have a problem in the two generalized
coordinates you choose.the first one is θ: Average angle of left and right wheel,why do you think it equals 1/2(θr+θl) ,the second one is φ: Body yaw angle,why do you think it equals R/W*(θr-θl).the two generalized coordinates has been puzzled me for days,and I am in deep affliction for it.would you please explain this two Eqs. of the generalized coordinates to me for the for the further?

weichen li

Unable to load block diagram 'ecrobot_nxt_lib'



Hello! thank you for your working.
I have some problems, it didnot work with me. I have a matlab R2013.
When I run the simulink file "nxtway_gs_vr.mdl", it has the error:

Error evaluating 'InitFcn' callback of Battery Voltage Interface block (mask) 'nxtway_gs_controller/Battery Voltage Interface'.
Caused by:
Undefined function or variable 'NXT.Signal'.

Anyone know how to fix it? please help me, thank you very much

zhu qunchao


cheung kwan

can anyone tell me what modification i have to make to use the Lego small wheels?

thank you

Deyan Dobromirov


phillip did you ever find out about the observer implementation?


I tried simulating this controller in simulink but i get errors for stating (source function do not exist) such as sfun_bt_tx, sfun_bt_rx, sfun_soundtone, sfun_expfcncallsscheduler. This is weird beacuse with the download of ecrobotNXT in the environment directory these do exist in a C file and as .mexw32. Could the problem be that I'm running this on X64 bit windows 7? Any help will very very much appreciated


Juan Luna

Philipp, i have completed the controller becoming both dynamics into one, and close the loop control in the wheel dynamics, but i calculated the remain states from the on-board sensors. the controller can track lineal and angular velocities. but the idea of an observer was made by Takachi in his early nxtWAY in with use a ligth sensor to determinate the states (ecrobot exmples).

Nguyen Hieu

Philipp B


has somebody implented an observer based strategy for the non measured states? Great work by the way, but from the view of modern control theory an observer based method would be even better.

Juan Luna

> Yorihisa Yamamoto

Hello, I first want to say that a person who designs a system so well, as seen in the archives of NXTway-GS, you should take time to support, from the fact that the documentation leaves some empty, they took me a while to realize that control the direction of the robot is in open loop.

Juan Luna


I'm trying to enhance (expand) the autonomous mode that controls the NXTway, this by implementing the pure pursuit algorithm, which is executed when these option is chosen.

During the simulation, I found to have some doubts:

1. Why to calculate the current position of the robot you do not use the equation 3.1 on page 7 of document (revision 1.1)?, but instead you use this one:

Z = integral (thetadot * R * cos (phi)) + initial Z;
Y = integral (thetadot * R * sin (phi)) + initial Y

I know that you renamed the coordinates of the robot (pg 56), but despite of the change of coordinates I think the equations are not equivalent.

2. As I could see in the file param_controller.m the maximum linear velocity is 0.3 [m / sec], but you do not put the equivalence with the angular velocity, so: If I put in the gamepad phidot_ref=10, how much it is equivalent in angular velocity?, what I see is that what you do is to add and subtract power to the motors (with a maximum of 25 pwm).

I really appreciate your attention. Thanks in advance, any help you can give me and I am attentive to your answer.

Sam Mirsky

Well done. Good documentation. This demo impresses everyone I show it to.

Yorihisa Yamamoto

> Anand
This file is archived with "Compressed (zipped) folder" shortcut of Windows XP. Please try to decompress it using WinZip or other utilities.


I am not able to unzip this file. please help

yipeng tang



Tatsuya Kikuchi

I watched the Self-Balancing Two-Wheeled Robot at Embedded Systems EXPO in Tokyo. It looked like a clown on a monocycle. I think this robot is joyful study case for students.

Anas Obeidat

it's Excellent Simulation to NXT robot and Documentation is perfect.

Diego Barragán


MATLAB Release Compatibility
Created with R2007b
Compatible with any release
Platform Compatibility
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