The document presents a project to design and build a gearbox from laser cut acrylic sheet that will lift a weight between 0.5-1m using a DC electric motor spinning at 9000 rpm. Tables show calculations for different gear ratios to determine the optimal design that lifts the weight in the shortest time while withstanding shocks and vibrations from the overhung load on the output shaft. The gearing orientation and mechanical properties of acrylic are also considered in the design process.
1. Project Summary
To design and build a gearbox from laser cut acrylic sheet which will be used to lift a weight
(at least 8 kg) from a height (greater than 0.5 m and less than 1 m) as quickly as possible.
The gearbox will be powered by a standard DC electric motor at 9000 rpm.
CREATIVITY JOURNEY
Hurdle
What is the input speed and torque?
What is the gearbox target output speed or output torque?
Will it need to withstand shock and vibration?
How overhung is the load on the output shaft?
How will the gearing be orientated?
2. Proposed Concept
Using a reduction gearbox to reduce input rpm while increasing torque to
lift a certain amount of load.
Pinion
Pinion Intermediate shaft
Output shaft
GearGear
Motor
3. Mechanical properties of Acrylic
Tensile strength, yield 72 MPA
Modulus of elasticity 3.102 GPA
d^2y/dx^2 = M/EI
4. Reason to choose a Reduction gearbox?
To reduce input speed of 9000 rpm from motor to a much slower speed while
increasing output torque.
To reduce speed in stages to avoid damage to gearbox
Simple design.
6. Design Limitations
Face width of the gear is 3mm
Gears will be laser cut on Acrylic sheet.
Spur gears is the only choice for the project as teeth are cut parallel to shaft.
Axial length of gearbox housing will have to be as minimal as possible to
achieve a greater performance.
Addendum diameter of pinion gear on motor is approximately 18.22 mm
Super glue will be used to connect the shaft and the gears
Mechanical properties of Acrylic
Tensile strength, yield 72 MPA
Modulus of elasticity 3.102 GPA
8. Areas of improvement involve gear arrangement.
Speed and torque of the gearbox output.
Calculating most efficient torque required to lift weight.
Stacking acrylic gear next to each other for greater strength.
Experimentation with gear ratio
Possible Improvements
9. !1
Observations (HCR)
The maximum tooth load is ~63% of transmitted load due to the sharing
of teeth
Vibration-signature amplitude is approximately ½ for equivalent
for gears not in contact and that are at the same load and speed.
With HCR gearing three pairs of teeth share the load: Entrace
Through the pitch point at the exit of the mesh
Applications Possible gear design
Electric fork lift truck transmission Noise reduction
Heavy lift helicopter HCR gearing
Propeller reduction drive gear (aircraft) HCR gearing
10. Gear optimization Contact ratio
Gear Parameter Changes Contact Ratio
Increased Ratio Decreases
Increased Addendum Increases
Increased Centre Distance Increases
Increased pitch diameter Increases
Increased Centre distance Increases
Amount of Profile Modification Decreases
C.R = OD° −TIF°
360 ° /N
No. T = 360 ° C.R
OD ° - TIF °
11. Pros:
Can handle extremely large reductions
Good load distribution, giving huge torque capability
High efficiency, with a general loss of only 3% per train
High power density
Cons:
More difficult to manufacture
High precision required
Loud at high speeds
High stress at the output shaft
High bearing loads