Our goal for the first prototype was to generate a mechanism that can produce enough suction pressure to collect the dry-leaves-waste. For that, we designed a wireless D.C. operated vacuum collector using Axial Flow Fan for suction pressure generation.

In comparison to the conventional methods, this is a less-tedious as well as time saving method for collection of dry leaves. Moreover, the battery-operated suction mechanism does not use fossil fuels for the generation of power, and hence has fewer adverse effects on the environment.

The major challenges for us in this phase were :

To create enough vacuum inside a closed environment (PVC pipes) for suction of dry leaves.
To choose a proper, durable material for the propeller which can generate the air flow for creating the vacuum.
To select a motor that can generate enough Rotations per Minute (RPM) of the axial fan.

The components used for creating the suction mechanism:

Motor
Customized axial flow fan
PVC pipes (pipe that collects the dry-leaves from the ground, suction cylinder)
Battery
Switch.

CAD Drawing for Prototype - 1

Link for CAD design (Fusion 360 Software): https://ahduni31.autodesk360.com/g/shares/SH56a43QTfd62c1cd968fbeee2d8cc4b13be

Orthographic Projection

Component-wise analysis of the manufacturing process

(along with the learnings and shortcomings)

In this section, we have explained the process that we followed for creating the suction mechanism along with the learnings and shortcomings.

A 12 volts rechargeable battery is used as the main source to power a DC motor. The specifications of the motor used are that, it exhibits 4000-7000 RPM at 12 Volts when the current reading is approximately 0.2 amperes. In order to decide the power of the motor to be used for creating enough vacuum, we performed the calculations (actually, after the prototype was built) which is shown in the pre-analysis calculations section in Prototype 2.

This motor is connected to the axial flow fan with the help of a flexible coupler. The customized axial flow fan, used to create suction, is made from a durable steel material whose flaps are bent at an angle to increase the amount of air it can displace.

The attached motor-shaft-fan is firmly mounted inside the PVC pipe of diameter 7 cm which is used as a suction cylinder with the help of a steel frame. The diameter of this cylinder increased to 11 cm at the opening of the fan.

Further, this suction cylinder is attached with a thinner PVC pipe (diameter 3 cm) also known as the collection pipe.

Selecting the Motor

Shortcoming

First, we planned to use a 3.7V drone motor (BLDC-brushless DC motor) which in theory provides 9000 RPM. However, this motor works the best for lightweight propellers and the propeller we have used is made of steel and quite heavy. Also, there was a significant size difference between the drone motor shaft and steel Axial Flow Fan.

Therefore, we were not able to employ the drone motor to generate sufficient vacuum.

Drone motor

Source: https://filmora.wondershare.com/drones/drone-motors.html

Learning

We referred to this video, for selecting the correct motor and according to that, a 12 Volt DC motor can generate enough air flow to create some suction power inside the PVC pipes. We decided to utilize a similar NFP-RK-360/365 SA motor which exhibits 4000-7000 RPM at 12 Volts when the current reading is approximately 0.2 amperes. Practically, this motor worked well for suction of the dry leaves.

However, we were not able to measure the actual RPM of the axial fan as we did not have an access to a tachometer.

Customizing the Axial Flow Fan

Shortcoming in deciding the fan material

First, we made use of a plastic propeller (same as the one shown in the image) with the drone motor.

This propeller instantly broke after a single collision with the wall as it was not designed properly to be used in a closed environment.

Source

Learning

From this incident, we realized that the material for this fan has to be strong enough to bear the smallest amount of collision in case the fan touches the wall due to vibrations.

In addition, the fan size should be such that it can easily rotate inside the PVC cylinder without collision.

Learning from that experience, we decided to make a customised axial flow fan out of mild, durable steel which can withstand the air drag force and shaft centrifugal forces because a ready-made, durable fan was not available in the size such that it fits inside the cylinder of 11 cm as well as it fits with the motor shaft.

We used a CPU panel as a durable steel material.

Shortcoming in making the customised axial flow fan

Due to lack of advanced tools like laser cutter and angle grinder, the first fan had rough edges and inappropriate shape which led to poor aerodynamics.

The image on the right hand side showcases the failed attempt to make the axial flow fan.

Therefore, we discarded it.

Learning

Following the same procedure, we built another axial fan with the same material, which had smoother edges and the flaps were angled in such a way that the fan was aerodynamically efficient and was able to generate higher levels of airflow.

The images on the right hand side show the process of making the final axial flow fan for prototype 1.

Mounting the motor

Shortcoming in mounting the motor in PVC pipes

Initially, we mounted the motor along with the fan inside a PVC pipe of constant diameter of 7cm using a steel frame which was also custom made.

This produced unnecessary vibrations as it was suspended freely and led to deformation of certain parts as the fan kept touching the surface of the pipes.

Learning

From this experience, we learnt that the motor should be firmly mounted inside the cylinder such that the fan doesn’t collide to the surface. However, we did not implement this in our first prototype. This was considered in the next phase i.e. in Prototype 2.

Things that went well

At the end of this phase, we were able to achieve enough vacuum such that the suction was created for the dry-leaves as shown in the video below. From the calculations the efficiency of the suction mechanism is 7.78 %.

Video of working model for Prototype 1

1 Prototype1.3gpp

Other shortcomings (Which are taken care of in the second prototype)

Planning for the next phase of making the product

Not enough vacuum

We were able to achieve the vacuum but the suction power was relatively less than expected. The reason for that was the gap between the axial fan and PVC pipe. So, we planned to scale up the previously made axial flow fan in the next phase of making the product (i.e. in Prototype 2). Furthermore, the hindrance in the fan speed due to collision with the surface might decrease the air flow for creating a powerful suction. To reduce the collision, we planned to mount the motor using screws on the cylinder surface which was also implemented in Prototype 2.

Space for the storage of collected dry leaves

In this prototype, our only goal was to create the vacuum for enough suction of the dry leaves. The collected dry leaves created a hindrance after suction inside the PVC pipe as we had not allotted a separate space for storing the collected leaves in this phase of the product which is a very important part of the final product. This was also planned to be completed as a part of Prototype 2.

Collection pipe size

In the current prototype, the diameter of the collection pipe was only 3 cm. For prototype 2, we planned to make this pipe broader so that the vacuum collector can cover a larger area.

Calculation - FindIng Efficiency for Prototype - 1

Calculations for Prototype 1.pdf

Component-wise analysis of the manufacturing process

(along with the learnings and shortcomings)

Other shortcomings (Which are taken care of in the second prototype)

Planning for the next phase of making the product

Calculation - FindIng Efficiency for Prototype - 1

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