Creative JourneyPaul Ryan, Jonathan CHOW AND YALAINDRA SHUGUMAR
RequirementsHad to lift 8Kg weightHad to lift it a height of 0.5mMade only from acrylic sheets & GlueShould not fail (crack/fail)Gearbox needs to be optimised
How it will be Evaluated
Our Approach-We first looked at the performance equation-found which were constants-determined the motors influence on the equation-this led to whether we want it to be reliant on efficiency or power-This brought the variables t & D to discussion-We will apply a factor of safety-Over engineer by 20%
What type of Gear is most suitable- Through calculations of the performance we looked at the difference between variablesWe then compared these to discover the types of gears we wanted to useOriginally we wanted helical
Advantages and disadvantages of eachSpur Gear+Good at low speeds -Low amounts of +Torque+Easy to cut-Very noisyHelical Gear+High capacity for Torque-hard to manufacture+Less noiseWorm Gear+Holds position when stopped-Inefficient+High capacity for Torque-Bad at high speeds
gearsGears are used to increase speed, or to increase torqueConservation of Energy law states that the total energy in a closed system remains constant; energy cannot be created or destroyed. Therefore any increase in speed would have to be accompanied by a decrease in torque, and any increase in torque, would result in a decrease in speed.
gearsIn order to increase speedEnergy applied to a large gear, which is connected to a smaller gearIn order to increase torqueEnergy applied to a small gear, which is connected to a larger gear
Gear ratioA Gear Ratio is the ratio of the number of teeth between two gears. E.g. a 48 tooth spur gear to a 16 tooth pinion would have a gear ratio of 48:16, which factors down to 3:1. For every revolution of the 48T spur gear, the 16T pinion gear rotates three times. Using the gear ratio of a set of gears, we can calculate the output speed/torque from the input speed/torque.
Gear ratioUsing a 3:1 gear ratioEnergy in: Motor at 900rpm, 60Nm. Increase in speed (Energy applied to the large gear, 3:1 ratio) Energy out: 2700rpm, 20NmIncrease in torque (Energy applied to the small gear, 1:3 ratio) Energy out: 300rpm, 180Nm
GearboxesGearboxes usually contain multiple sets of gearsThis allows for a greater gear ratio in a smaller spaceThe gearbox ratio (total gear ratio) of the gearbox would be determined by multiplying the individual gear ratios of each set of gearsE.g. A gearbox containing three sets of gears, with the ratio 3:1, 4:1, and 5:1 would have a resultant gearbox ratio of 60:1 (3*4*5=60)
Energy transferThere will be losses in a physical gearbox system due to multiple factorsThese factors include: FrictionBacklash (Slip) Imperfect meshing of gear teeth
Optimizing the gearboxIn order to optimize the gearbox, we would need to calculate the torque required to lift the weightOnce thats done, we would need to increase our goal torque by 20% as a factor of safety. This is so that we dont overwork the motor. Then, we would calculate the required gearbox ratio, and thus the number of teeth in each set of gears
Our gear arrangement will be a Compound configuration with a step reduction in each set.The number of gears that will be in the configuration is still being assessed.- The gear configuration needs to be strong to withstand the forces of the weight.
Housing for the gears (Gearbox):The housing for the gearbox will have some space on either side of the step compound gears which may leave room for movement of the gears, to prevent this we are considering creating bushings to prevent any significant movement of the gears. The shape of the gearbox may look something similar to the shape of a bike chain configuration or we may decide on choosing just a regular rectangle shaped box to avoid stress fractures near the edges or near the output shaft.