Problem Overview
The competition
proposed is to design a 4 speed manual transmission that optimizes power and
speed. By applying knowledge of physical concepts such as angular velocity and
torque into the design of the transmission the group aims to produce the most
efficient, powerful and fastest transmission possible. The competition will be
based on finding the transmission that produces greatest torque and also the
most speed. The problem that the project is addressing is making the most
efficient transmission possible.
Design Constraints
The constraints for the project are as followed. To design at least a 4
speed manual transmission designed using Pro Engineer. It has to be
tested using the Pro Engineer software animations. It also will be
printed using the rapid prototyping 3 dimensional printer. When
assembled the transmission must fit the pre-made support structure as
seen in Figure 1. The gears also must be compatible by using a Lego NXT
motor, to power the transmission. It will be tested using two criteria;
one to see how much torque the transmission will produce, and two to see
how much speed the transmission can produce.
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| Figure1: Pre-made support structure with NXT motor. |
Existing Solutions
The manual transmission has been around for almost as long as
automobiles themselves. In fact, up until 1938 when General Motors
started offering automatic transmissions, all cars had manual gearboxes
that required the drivers to control the gear shifting themselves. The
function of any transmission in any automobile is transferring engine
power to the drive-shaft and then to the wheels. Inside of a
transmission there are usually at least four different gears that when
shifted, adjust the vehicle's drive speed and it's torque. Lower gears,
which actually have a higher gear ratio are used to get the vehicle
moving from a standstill. The two main existing manual transmission
designs are the sliding-gear type and the constant-mesh design. The
older, now obsolete design, the sliding-gear type is not used any more
in modern cars. The difference between the two types is that in a
sliding-gear type transmission, the only thing turning at all times is
the main drive shaft, which gets shifted along one axis and at specific
points, meshing the gears together and allowing the car to move. Then,
in order to shift into another gear, the main drive shaft would have to
completely disengage with one gear, in order to move on to the next. The
reason why the constant-mesh design transmission is so much more
efficient is that the gears on the main drive shaft are constantly
meshed with the gears on the cluster shaft. The reason that this is
possible is because the gears that are on the main shaft are not
directly attached to it and can rotate freely around it. [2] These
transmissions are used very widely in today's vehicles. Different car
companies create their own transmissions and tweak them in ways that
they see fit, but most all manual transmissions today have the
constant-mesh design as a foundation.
Another important concept that is necessary for this project is the idea behind gear ratios. The technical description of the gear ratio of a gear train is the ratio of the angular velocity of the input gear to the angular velocity of the output gear. It can be thought of as how much one gear revolves when the other completes one single revolution. Different gear ratios are important for achieving different gears in cars, allowing for more torque in lower gears by having a higher gear ratio, and more speed in higher gears by having lower gear ratios.
Another important concept that is necessary for this project is the idea behind gear ratios. The technical description of the gear ratio of a gear train is the ratio of the angular velocity of the input gear to the angular velocity of the output gear. It can be thought of as how much one gear revolves when the other completes one single revolution. Different gear ratios are important for achieving different gears in cars, allowing for more torque in lower gears by having a higher gear ratio, and more speed in higher gears by having lower gear ratios.
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| Figure2: A diagram of a typical constant-mesh transmission. |
Design Goal
The most clear goal that the group is designing towards is a transmission that can output high speeds and that can withstand high torque. Because half of the competition is based upon the torque that the transmission can withstand the group plans to create a relatively simple transmission that will have fewer chances to catch somewhere and break under heavy force. With torque in mind the group chose to stick to a 4-speed transmission. The group plans to base some of the design on Sariel’s compact gearbox [1]. The compact gearbox should be beneficial because it minimizes torque. The formula for torque is torque equals the product of force and radius. Because torque relies on radius if the group keeps the gear shafts short theoretically it should reduce the magnitude of the torque.
High speed also is a major goal for the group. To maximize the speed proper gear ratios will need to be figured. It is obvious that the group wants a have a large gear ratio that will increase the output of the transmission. Smooth transitions from one gear to the next are also a major goal as rough transitions can easily lead to a broken transmission due to stress. The compact gearbox utilizing shorter, stronger, shafts makes this design unique from the standard automotive transmission that has longer linear shafts. Using the unique design of the compact gearbox as a basis the group will be able to add modification creating a even more unique and hopefully efficient design.
The most clear goal that the group is designing towards is a transmission that can output high speeds and that can withstand high torque. Because half of the competition is based upon the torque that the transmission can withstand the group plans to create a relatively simple transmission that will have fewer chances to catch somewhere and break under heavy force. With torque in mind the group chose to stick to a 4-speed transmission. The group plans to base some of the design on Sariel’s compact gearbox [1]. The compact gearbox should be beneficial because it minimizes torque. The formula for torque is torque equals the product of force and radius. Because torque relies on radius if the group keeps the gear shafts short theoretically it should reduce the magnitude of the torque.
High speed also is a major goal for the group. To maximize the speed proper gear ratios will need to be figured. It is obvious that the group wants a have a large gear ratio that will increase the output of the transmission. Smooth transitions from one gear to the next are also a major goal as rough transitions can easily lead to a broken transmission due to stress. The compact gearbox utilizing shorter, stronger, shafts makes this design unique from the standard automotive transmission that has longer linear shafts. Using the unique design of the compact gearbox as a basis the group will be able to add modification creating a even more unique and hopefully efficient design.
Project Deliverables
There are two main deliverables for this particular project. The first deliverable is an assembly drawing of our transmission drafted in Pro-Engineer. The assembly file must properly animate the processes of the transmission. It also must give calculated data on the theoretical output of the transmission for each gear ratio. The second deliverable is the actual printed and assembled prototype. The prototype must be capable of being hooked up to the NXT motor and then run through the torque and speed output testing.
There are two main deliverables for this particular project. The first deliverable is an assembly drawing of our transmission drafted in Pro-Engineer. The assembly file must properly animate the processes of the transmission. It also must give calculated data on the theoretical output of the transmission for each gear ratio. The second deliverable is the actual printed and assembled prototype. The prototype must be capable of being hooked up to the NXT motor and then run through the torque and speed output testing.
Project Budget
The budget for this project is being estimated as if it were
being made of actual steel gears and shaft material. The approximate pricing
for the materials needed are as follows: 6 X Steel Bored, 32 Pitch, 40 teeth,
Outside Diameter of 1.31”, for $28.51 a piece. 4 X Steel Bored, 32 Pitch, 18
teeth, Outside Diameter of .63”, for $14.16 a piece. 18 inches of 1/16” Steel
Shaft $9.98 [3]. This would bring the total price up to $237.68.
Project Schedule
In week 2 outline design proposal and divide up work load and finish on own time. Do research on how transmissions work and try and find appropriate gear and tooth ratios. In week 3 make hand sketches of how basic transmission. Calculate theoretical gear ratios. Sketch a basic gear in Pro/Engineer. Week 4 make actual gears in Pro Engineer. Week 5 make assembly in Pro Engineer. Week 6 start making simulation In Pro Engineer. Week 7 continue making working on Pro Engineer simulation. Week 8 print out pieces using the rapid prototyping 3d printer. Week8 assembly and fix any problems that occur. Week 9 competition. Week 10 make presentation.
References
[1] Sariel. (2010). Lego 4-speed compact linear gearbox [online].
Available: http://www.youtube.com/watch?v=xISN9U56yBY&feature=related
[2] Cook. (2009). Manual Transmission Basics [online]
Available: http://www.edmunds.com/car-technology/manual-transmission-basics.html
Available: http://www.edmunds.com/car-technology/manual-transmission-basics.html
[3] Carr. (2012). McMaster-Carr [online].
Available: www.mcmaster.com
Available: www.mcmaster.com
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