Low cost window cleaning robot: Final Model

Hello readers! In last article Low cost window cleaning robot we explained the first prototype we designed. We also explained the short comings and failures of the design. But this was not the end! We did further literature survey and came across the video of this wall climbing robot on YouTube.
 It became our inspiration and we began to develop a robot using high speed brushless dc motor as seen in the video for creating vacuum between the surfaces.

As learned by previous experience the important parameter while designing the robot is the weight of body. It is important that the mass must lie at single point and by physics we commonly recall the concept as centre of gravity(COG).
The mass must be distributed in such manner that the entire system can be replaced by single point mass.
COG helps in reducing the recursive steps needed to calculate the force exerted by gravity on each component on the robot.
We designed the chassis on CAD and went for lazer cutting as shown in the article Sneak Peek.
The weight of the robot according to the new design had to be lower than or equal to 500 g. Our first design of the chassis was heavy and so we removed more acrylic in order to reduce the weight.
Finally when the chassis was designed, we placed our components as shown in the figure below.

Figure 1 Top View

 As you can see we have placed the brushless dc motor in the middle of the chassis and rest components like Arduino development board, motor driver and ESC around the motor. The motor driver we have used is to control the two gear bo motors for robot's motion along the wall.

Figure 2 Bottom View

  
But unfortunately as we proceeded to test our prototype we faced some problem with our ESC(Electronic Speed Controller). We had bought 30A ESC whose rating was lesser than the maximum current rating of the brushless motor.
Please keep in note that use ESC whose current rating is greater or equal to 30%-40% of the maximum current rating of the motor.It ensures that your ESC will not get short if the motor drives high load.
Since we were using our motor to create vacuum to support the weight of the robot, it was driving large current from the battery.In every test runs the ESC would get really hot and soon the motor stopped working properly.We solved this problem by replacing the old ESC with larger current capacity of 40A.
Next we faced the problem with the BO motors.The motors had 1.5 kgf torque which is not enough to push the robot upwards.The motors with high torque are heavy and could not be placed on the robot. We did some research and found out about mini geared high torque motors.Due to budget constraint we could not implement it in our project. 
But in the end, we were able to fulfill two out of four major objectives.

Low cost Window Cleaning Robot: Challenges and much more!

So, after having a look at last post Sneak Peak, you might want to know quite a lot of things. And here, we will discuss everything but step wise.

Why window cleaning?

The  exteriors of many buildings are being constructed with Huge glass Panes  which give an immense aesthetic beauty, but cleaning the outer part of the building is a tough job. Generally, human labor clean the outer pane by clinging themselves to the high storied building which involves high life risk factor.

So, the motive of building this project was quite simple, it ensures safety of human labor, and also cuts the maintenance budget of commercial buildings. But since, we are still working on the model, it can be used for our home glass window panes.

Figure 1: Human labor cleaning exterior panes which has high risk factor

Attempt in making the robot:

The main challenge is to manage the weight of the body, our original idea was to fabricate the wheels of the robot in such a way that it could stick to the window. The wheel used was a pulley wheel with 4 cm width and 6 cm diameter, where we used flat suction cups of 2 cm diameter, which were fitted on the wheel, by drilling holes on the wheel. In this way, we had got around twenty four to thirty suction cups on a single wheel. So, the wheel with so many suction cups does stick on the window, but with the weight of the robot? Does it? Even if it takes the weight, will it stick along with vertical motion of robot?

This was a challenging task!

Before moving on, I would discuss the components that we have used to make the robot:

1.  LiPo 11.1 Volts Battery: For powering up the controller as well as for driving the motors.
2. DC Motor (10 RPM high torque 10 kg-cm)
3. Arduino Mega: Control action
4. Dual DC motor driver 20 Amperes
5. Miscellaneous: Cleaning material.

Weight of the entire robot:

Components of robot	Weight (grams)
Wheels (Four)	152 gms
Acrylic Chassis	250 gms
DC Motor (Two)	360 gms
LiPo Battery 11.1V	140 gms
Arduino Mega	40 gms
Cleaning Purpose	40 gms
Total	980 gms

Now, we made a four wheel robot with all wheels fabricated with suction cups. The body is shown in figure. As per our calculations, the suction wheels took the weight of the robot perfectly. The robot got stuck to the window with all the components.

Designing our body:

Figure 2: Acrylic cutting

Figure 3: Mounting wheels in between

Figure 4: Mounting DC Motor

Figure 5: Final Acrylic chassis

So, keeping our fingers crossed we tried moving the robot, kick starting the motors the wheels didn't stick to the window and our robot fell down, which was heart breaking. This was the first failure and challenge we faced! So, our idea with having suction wheels went in vain, because by the time the other suction cup would come in contact with the window it slipped from the window.

Umm.. So what, we didn't give up that easily! We came up with other idea of creating suction the other way. The sneak peak post had the laser cutting fabrication of our new body, which would be discussed in the next post.

Figure 6: Robot stuck on window without motion

So readers, along with the weight, motion of the robot is also a challenging task of the previous model. But in the new model, we are not fabricating the wheels, we are changing the entire body, and made it quite compact, where we narrowed down the size and weight of the robot.

Low Cost Window Cleaning Robot: Sneak Peak!

Hello readers. It’s almost been six months since, we last wrote about the projects that we are working on. Hmm.. It might be quite interesting to know that we will soon come up with quite a bunch of projects and tutorials on different development boards.

To talk about this project, Low Cost Window Cleaning Robot , the title seems to intrigue interest and imagination! But we had a roller coaster ride in making one, and most importantly we were able to keep it low in cost! The ‘Window Cleaning Robot' was our Idea proposed under the Idea lab Committee, Nirma University about six months ago, along with our guide Prof. Vishal Vaidya to whom we are extremely grateful.The outcome of this project is supposed to be an autonomous robot that can clean any vertical windows, by clinging to it with the concept of suction.

The main challenge of the project was designing it’s body, we had failures which would be discussed by us in subsequent blog posts. We shall also discuss the motivation behind this project.

Since, we all know by now that robot has to climb the window or the wall vertically, it has to act against the force of gravity, so as you readers might be knowing the Newton’s Second Law of motion, F=ma, where a in our case is the gravity 9.8m/s^2, a constant.

So, managing weight(mass) of the body becomes an important parameter, thus we used Acrylic to build the chassis. One can fairly imagine the amount of suction required for clinging the robot onto the wall/window.

 

As this is a sneak peak, allow us to intrigue you further by showing you a small glimpse of our final body.

Figure: Acrylic Sheet Laser cutting

Some of you might have guessed it, and for the people who haven't, this is our acrylic sheet undergoing laser cutting. 
Accuracy plays vital role in this project and its role will be crystal clear with the upcoming articles.
Stay tuned for the upcoming posts!