Stair climbing robot: group 4 – Nick Adriaens – Lowie Lagrin – Vince Muyshondt- Report

Design Project

 

Stair climbing robot

By Nick Adriaens
Lowie Lagrin
Vince Muyshondt

Second Bachelor, Industrial Engineering
2013-2014
Vrije Universiteit Brussel

 

Robot 

 

Introduction

 

The assignment of the Design Project was to build a robot which could climb the stairs. The goal of the project was to use all the theoretical background of the lectures and put the theorie to practice. Another objective of the Design Project was learning how to work with all the machines in the Fablab because it is important for other projects in the future. It all started with the construction of an example robot, followed by building an own stair climber.  The purpose of this website is to make this project more comprehensible for those who want to duplicate the robot. Our design and construction procedures are described on the website, which materials are needed and how to control the robot by using a computer. To climb stair, it is necessary to pay attention to different aspects of the mechanical and electronical difficulties to make it work.

 

Bill of materials

 

3mm MDF : 1m²

Screws and nuts : M2 ,M3,M4,M6,M8

Iron bar : Ø8 Length 70cm

4 linear barings

2 NEMA steppers

1 Dc motor

Small back wheel 3 cm

3 switches

1 range sensor

2 belts length

LiPo battery pack

1 Circuit breaker 2,5A

2 plastic connectors : 3 lines

Wires

5 Resistor 470Ω

Capacitor: 6*100nF – 3*100µF(pol) – 6*47nF

10 LED light

Diode: 1N5817

3 H-Bridge: L298D

Arduino connectors

Pin Header

 

List of machines/programs

 

LaserCutter

3D printer Makerbot

Pcb frees

Drilling machine

Altium designer

Inventor

Boardmaker

Arduino

 

Design

 

For the body of the robot, a simple rectangular design is chosen. Extra functionalities are added to enable it to go up the stairs. In the front, 2 conductors are added to make sure the robot can slide smoothly against the stairs. At the back of the robot some holes are drilled for a conduction system that contains the rack. The system from the gear-rack is the hardest part of the design because the gear rack system has to fit perfectly in the main body without too much friction. 

Stepper motors (in this robot NEMA 14) are used to drive the wheels. They are connected to the wheels with a belt. Because the motors are relatively weak, a reduction of 4 on the gears is used to make sure the robot can carry around his own weight.

The robot is not able to drive on 2 wheels, so an extra smaller wheel is added at the bottom back site. This wheel is not driven by any motor and is just there to keep the robot in balance. Preferably it is better to use a wheel that does not turn because this can cause problems while descending the stairs. This will be explained later.

 

Advantages

 

The concept of this climbing robot has some interesting advantages. Firstly, it does not really matter how much weight you want to lift. A robot with a weight of 2 kilo or a robot with a weight of 4 kilo will both go upstairs. The only factor that decides how much weight can be lifted is the gear on the DC-motor to lift the robot. It is advisable to make the gear a little bit smaller, so the motor has to revolve more to make the gear rack move an even distance. As a result, the robot will go slower up and will be able to carry greater amounts of weight.    

Secondly, by adding the necessary accessories it is not too difficult to make the robot to move automatically with some knowledge of electronics (which is required to make this robot anyway).  This excludes the possibility of crashing by making human control mistakes. But naturally, the use of all these accessories does not take away the fun of using the robot as it  is still possible to control it manually.

Thirdly, all of the electronics are super protected and fit in the inside. This makes it really hard to damage the electronics from the outside even if the robot would crash unexpectedly.

Fourthly, it is rather easy to drive around and to turn 360 degrees on the spot which makes it more flexible to navigate in small areas. This movability is useful to climb the stairs.

Last but not least, the parts in the robot are fairly easy to replace. If it is necessary, the top side can be removed which makes that the parts can easily be reached.

 

Climbing the stairs

 

This section explains the idea behind climbing the stairs with the robot.

First of all, the robot moves forward until the micro switch on the front conductor detects the stairs. Now the gear rack is pushed down. The moment the gear rack hits the floor, the robot will start to go up to the next step. Once it has reached his highest position, if everything went as planned, the wheels should be touching the next step. If the robots drives forward, it puts itself further on the stairs. At a certain point the gear rack will hit the border of the step, which makes it impossible to move any further because a micro switch is pushed in. At this point the robot will pull up the gear rack and now the robot will repeat all the previous commands.

The combination of mechanical and electronical components makes it possible for the robot the climb the stairs. Both will be discussed now.

 

Mechanical principles

 

The mechanical part contains the gear rack system together with the gear which is attached on the DC-motor inside the main body.

The purpose of the gear rack system is actually to reduce the friction from the rack with the body of the robot.

Conduction systemPicture 1

The gear rack is placed parallel in between two aluminum bars in a conduction system (Picture 1). Those two aluminum bars fit perfectly in linear bearings, which are fastened inside the main body of the robot. This allows to slide smoothly without friction. The 2 aluminum bars and the gear rack are fastened together with two wooden plates. One plate is located at the top of the conduction system and one at the bottom. On the bars, an exterior screw thread is drawn, which makes it possible to fasten the bars with ordinary bolts. To fasten the gear rack, two metal connectors are used at each side of the gear rack. One bolt is used to fasten two metal connectors at the same side from the gear rack. Another bolt is used to fasten each connector to the wooden plate on which also the aluminum bars are fastened.

To fasten the gear on the DC-motor a clever trick was used. At first the problem was that the gears on the DC-motor would break or the DC-motor axis would scrape out the hole made in the gear material. Because of this problem the DC motor out the gear. The solution for this problem was to reshape the axis of the DC motor into a rectangle. By doing this, the risk on scraping out the hole is reduced, making the robot more reliable.

 

Electronical principles

 

Electronically, some features are added to make the robot work automatically. These features will be discussed in this part. Three micro switches are placed on the robot: two on the conductors at the front and one at the back.

The sequence starts by pushing down the gear rack. The robot starts to move up until the gear rack is not able to move any further. To make sure the robot stops moving up at this point, a switch is placed at the top of the main body of the robot on the spot where the top wooden plate of the gear rack-system hits the robot. When this switch is pressed in, the robot starts driving forward until another switch located at the front conductors is pressed in by hitting the vertical side of the next step. In the next stage, the gear rack will be pulled up during a certain length of time programmed in the robot. Once the gear rack is pulled up, the robot starts driving forward until another switch at the front conductors hits the border of the next step. To make sure the robot is positioned parallel with the border of the next step, it will drive forward until both of his conductors hits the stairs. Once this process is done, everything can start over again. The program code is written on Arduino and is sent from the computer to the Arduino on the robot by using X-bees.

BinnenkantPicture 2

Four pcb’s (Printed Circuit Board) were made to ensure a good and safe electronic system. Two were made for 2 steppers and 1 for the DC-motor. And one X-bee Shield to communicate with the X-bee in the computer(Picture 2).

 

Difficulties

 

Although the building of the robot went very smoothly in general, there were still some difficulties. One of the difficulties was finding the right grip. The first rubbers that were tested did not suffice. After a long time of searching, a solution was found. The final solution was a silicon that was poured in a mold. Another problem was finding the right material for the gear. Both MDF and plexi did not satisfy our needs. In the end, the solution was making the gear out of nylon and by flatten the DC-motors axle.

 

Calculations

 

Pmotor = (2*pi*n*T)/60

n = revolutions per minute
T = torque = 30N.cm

P = 2*pi*0.30N.m*2revolutions/sec

=3.7699 W è power

Height of Stair +- 17 cm

Weight of robot: 3 kg ( approx)

t=W/P = (4kg*9.81m/s²*0.17m)/3.77W =1.8s ideal

 

Discussion/conclusion

 

Although the project was not always easy, finally it worked out. Once we had our idea, every step of the way went pretty smoothly thanks to our good teamwork and spirit. It is important to make compromises when working in a team, when the opinions of the different team members differ. Because we spent a lot of time, working on the robot in the Fablab Brussels, we had enough time to add some extra features, such as the complete automatisation. The most important thing while building something is to never lose faith and keep going. It is not a shame to ask for help when struggling. We completed every deadline on time. In the end we are satisfied by the result.

 

Downloads

Robot elektronica PCB’s

All parts



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