Circuit Design

This is the final design for the circuit we decided to make. When the ON/OFF switch (sw1) is set to the “ON” position this activates one of the micro switches (sw2) which in turn powers up the motor (m1). The motor then allows the arm to move out of the box and turn the switch (sw1) to the “OFF” position; this makes the motor go into reverse and retracts the arm back into the box. This also triggers another micro switch (sw3) which powers up the second motor (m2), this turns the shaft connected to the axel which allows the box to move 15cm before coming to a complete stop. The third micro switch (sw4) is the speed control switch; we put a resistor (r1) in with this to limit the speed that the box moved at. We added a diode (d1) to protect the motor from any charge that could possibly go back into the motor and destroy it.

Manufacturing Techniques

Laser Cutter

We used the laser cutter to produce some of our components and pieces of the box. Firstly CAD drawings in solid works had to be made, once this was done the files had to be converted to DXF format so the laser printer can take the profile of the component and cut it out. We used the laser cutter because using the laser creates a clean and accurate cut, also it is a good method to use to cut our acrylic. This is because acrylic is a brittle material which is had to cut any other way. The laser cutter uses a laser to cut through the material, this laser is a concentrated beam of light which is refracted up to the point of cutting. When the laser cutter is working it is important to have an extractor taking all of the harmful chemicals away from cutting the acrylic and to get rid of any residue from the acrylic.

CNC

We used the CNC machine for our base panel which had important slots and grooves which needed to be routed out. The CNC has a number of tools it can use on various materials, the tool we used on it was a 2mm end mill which spun at a high rpm. The CNC like the laser cutter runs on a computer program that needs to be programmed with code relating to our CAD designs on solid works. This code tells the machine where to cut, to what depth and the type of cut. The end mill takes away material similar to a drill and is effective at coming out with the desired finish.

Band Saw

We used a band saw, this was not a manufacturing technique that we planned to use as we had a different material to use and a time constraint that was not originally planned. The band saw was used to cut the wood that we used to create the exterior of box and part of the lid. We printed out our panel designs off solid works and cut them out and used them as templates on the wood. Then the panels were cut out however the band saw leaves a rough edge and finish to the panels. so we had to sand them down afterwards. The band saw is a blade held at both ends which vibrates in a vertical motion using a serrated blade to cut into the panels and remove material.

Evaluation

Overall the box works well despite the wooden exterior. The internal system almost works as it was designed to. There are, however, two aspects that it fails to do; slow down and achieve the desired distance.  
 

The resistor is not powerful enough to slow it down like we intended it to. This is due to an error with our initial calculations. 

 

It was supposed to travel 30cm but it only travels 14cm. It does not travel 30cm because we changed the diameter of the wheel. The wheel was changed to enable us to move the rear drive wheel further back proving more stability. We needed more stability as the box only has 3 wheels. 

 

I feel that it is better that it doesn't travel the full 30cm as it is suppose to be used on a desk and if it travelled 30cm it might run the risk of falling off and being damage or damaging something else. 

Problems That We Encountered During Manufacture

Throughout this project we have encountered many problems. 

 

The first of which involved the materials. We wasted several weeks waiting for the material and parts we need to be ordered and delivered. Once we had the material we wasted a couple more weeks waiting to use the laser cutter. This was a problem because it gave use less time to assembly the final product once the parts were cut.

 
When we finally had all of the material and part we needed and had access to the laser cutter we had another set of problems. The first of which was the machine bed on the CNC milling machine was not flat so the slot in the based plate was not even and had to be adjusted by hand. This lowered the overall accuracy of the project and used more time. The information, about the position of the mounting holes on both motors, was different on the manufacturer's website and on the actually motors. Due to this the central rib had to be cut twice.

 

Cutting of the panel on the laser cutter was also a problem as we had the sizes wrong and the panel ended up being too small for the base plate. This used up our material. As a result of this we had to use wood for the external panels.

 

Below is a picture of the original useless box.

 

Below are picture of our finished useless box.

 

 

Drawings

This drawing is of the arm that “switches off” the system. In reality, this arm actually switches its own motor into reverse whilst at the same time activating the drive motor.

This drawing is of the internal rib on which the arm and drive motors are mounted.

This drawing is of the cam that changes the drive speed, by actuating micro switches. This cam has been designed based around using 3mm thick acrylic.

Design Process

Firstly we studied current pointless boxes to find out exactly how they worked. Which is that the switch being turned on activates a motor with a gearbox upon it this then turns a shaft with the arm on it. The arm has a certain profile because of this it opens the box lid as it moves towards the switch, it then turns the switch off, the switch going off also triggers the motor to reverse to bring the arm back to its original position. We would be building upon these principles.

The same motor as used in other pointless boxes would be used, this motor would be mounted upon and internal rib mounted in the base of the box, the arm would be custom made by us, and this was due to the different sizing of our box in comparison to other pointless boxes. We would have to be careful that the profile of the arm was correct to lift the box lid, but not too fast or too slow. As with the other pointless boxes our arm would be mounted on the shaft coming out of the gearbox on the motor. This gearbox gave high torque and low RPM from the motor; this is exactly what we needed for the arm, as the switch is quite stiff. When the arm reached the top of its movement, and switches the main switch off, this would activate a micro switch which would then activate the second phase of the system. This micro switch would activate a second motor, which would be slightly more powerful than the other; this is because it would be powering the movement of the box.

We planned to have the box move roughly 30cm when the second phase was initiated. The motor has a gearbox on it already which again gives high torque and low RPM, but not as low as the other motor. The motor would be connected to a shaft which would power the axle, therefore the wheel. Also upon this shaft would be two cams interacting with micro switches, the first cam would be to turn the motor off after it had travelled 30cm, the second cam would slow the motor down by activating a resistor. This is because we needed to have some form of control over the automation.

The next phase was to design the panels of the box. The top of the box would split in the middle, where the switch would be mounted just over to one side. The other side of the lid would be on hinges so the arm can open it with the correct movement and profile. The sides of the box would be plain and simple. The side panels will all have slots and tabs in so they fit together perfectly and are easier to attach together. The base of the box would be more complicated, with slots needed for the wheels and various mountings needed for the internal workings. The panels themselves would be attached together with glue as this is the simplest and most effective way of mounting each component to one another.

Initially, the group agreed that the material to be used for the construction of the useless box would be 2mm clear acrylic. The thickness was sufficient to give the box the required strength and rigidity, but not too thick so as to reduce internal space and increase weight. However, after some consideration, it was decided instead to opt for 3mm thick black acrylic.

The reasons for this were:
1.) Clear acrylic would show off the internal workings of the device, which detracts away from the personification idea (although this would make the engineering design available to scrutiny)
2.) 2mm thick is a relatively uncommon size; 3mm is much more readily available and therefore considerably cheaper

This meant that some of the designs already completed would have to be altered, as they were originally based around working in 2mm thick material.

We would now use Solidworks to design all of our parts to be laser cut and order parts we needed to start making our box.

Assignment Brief

We have been tasked with the design and manufacture of a toy/device that utilises a mechanical system with feedback via sensors to alter mechanical behaviour.

Our group has decided on a variant of the “Useless Box” (http://youtu.be/aqAUmgE3WyM). The useless box is activated with a toggle switch, an arm appears out of the box which then turns the device off. Our variant adds an extra degree of motion, in that once the arm has turned the device off a drive motor then causes the box to “back away” from the operator.

This system uses motors, limit switches and some basic circuitry in the design.

Other criteria that the device must adhere to include:

- Have moving parts.

- An on-board power source.

- Parts produced using CNC and manual processes.

- Fit inside a 250mm cube.

- Cost no more than £40.