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Aims
Aims
Design and construct a compact low power battery operated (3V-9V) electric screwdriver meeting the following criteria:
The dimension of the screwdriver should not exceed the limit (length-200mm, width200mm and height-150mm).
The screwdriver movement should be reversible and will be able to push in and out of a screw ( see screw details in appendix) on the softwood or similar materials.
The output speed of the designed electric screwdriver should be downed between 150- 300 rpm by using a suitable gear mechanism.
Concept Design 1 -->
Concept Design 1 -->
Simple Design for easy manufacture
Battery Operated
LED Light
Trigger Switch for increased control
Storage for Additional Screwdriver Bits
<-- Concept Design 2
<-- Concept Design 2
Bits holder
Slide switch
Switch
Female micro-USB
Hex female adapter
Chargeable
Concept Design 3 -->
Concept Design 3 -->
90-degree adjustable head
Removeable battery pack
Slide switch for clockwise and anti-clockwise rotation
Interchangeable drill bits with hexagonal female adapter
Grip on body for ease of use
<-- Concept Design 4
<-- Concept Design 4
Ergonomic grip
Quick-change battery tray with locking cap
Large trigger (easy to use with gloves)
Concept Selection Matrix
Concept Selection Matrix
Using a Concept Selective Matrix to systematically compare the different design concepts against the selective design criteria. Such as Performance, Ease of Manufacturing, Reliability, cost and so on.
Ben’s design scored high in the criteria of performance, ease of manufacture, ergonomics and safety.
Whereas Zach’s design ranked the least while scoring high in aesthetics and ergonomics.
Development of Chosen Idea
Development of Chosen Idea
The chosen design idea was developed following some initial research regarding the required electronic components and manufacturing processes.
The storage compartment was repositioned. vents were included to ensure the motor didn’t become too hot over time. A detachable torch replaced the LED light to reduce the draw on current and the complexity of the circuit.
The handle was made more ergonomic to increase the user’s comfort.
We decided to use a planetary gearbox as it would enable us to achieve the required gear ratio within a more compact space in comparison to a standard gearbox.
The design would involve fewer shafts meaning the support structure design would be less complex.
Gear Ratio & Torque
Gear Ratio & Torque
Tangential, Wear and Static Load
Tangential, Wear and Static Load
Incremental and Dynamic Load
Incremental and Dynamic Load
The specification of the electric motor and the target rpm within the brief allowed calculations to be produced. This enabled us to determine the required gear ratio and output torque.
We conducted research into low-powered electric screwdrivers and found that we should aim to achieve an output torque of at least 0.2Nm. Once we had determined the gear ratio, we began to work on calculations related to gear design. We began by deciding on the size of the ring gear based on the size of the motor. Equations were used to determine the number of teeth for the sun, ring and planets that would achieve the required gear ratio and mesh correctly.
Once the properties of the gears had been decided upon safety calculations could be produced. The calculations confirmed the gears would be safe for this application as the wear load was greater than the tangential load. Furthermore, the static load was greater than 1.25 times the dynamic load confirming the design is safe.
Gear Box Assembly (Test Model)
Gear Box Assembly (Test Model)
A gear box test model is first developed in Fusion 360 following the data from the theory. The gear box consists of a Ring Gear, Driven gear, Planet gear and Plant Carrier.
Once we notice that the is no meshing between the gears, an updated model can be developed.
Gear Box Assembly (Updated)
Gear Box Assembly (Updated)
Following up from the theory section, the width of the gears were increased to 6mm. A hex bid holder was added to the second stage planet carrier and a orbital housing was designed to fit the gearbox and have an adaptable grip.
Final Design
Final Design
The final design incorporates 3 switches to control to physically turn on the motor, activate the motor, and dictate the direction of rotation. Other features included are a storage compartment for additional screwdriver bits, a battery compartment to access batteries and a detachable Mini Torch to use.
The finished product is manufactured almost entirely out of 3d printed components, including the gear mechanism. The motor, battery and other electronics were acquired separately.
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