CCNY Mini Baja
Conceptual Designs
Prof. Sadegh
ME 47300/2PR
Introduction
The Society of Automotive Engineers (SAE) in conjunction with various colleges and automotive companies hosts a Mini-Baja competition event. The event involves building a Mini-Baja off-road vehicle, testing it, and then racing it in five to six events. Although there are strict rules set by SAE there is enough room to make our design unique.
This project has many parts but in the initial concept phase we focused on six main parts:
- Frame
- Front Suspension
- Rear Suspension
- Rear Steering
- Drive Train
- Floatation
The frame is the most important part of the design since it must be sturdy enough to survive the abuse of the racecourse. It must also conform to the latest SAE rules and fit all the components that will make the off-road vehicle run. An evaluation matrix was drawn up where the higher the score means the better the concept.
Frame
We made a rough estimate of we believed to the most important points when making and assembly the frame. Thinking about straight tubes with gussets or bent tubing as a group we were split evenly. The matrix did not help as much as we would hope. We are leaning towards the bent tubing because the manufacturing would be simpler and we need to manage our time efficiently.
Frame/Joints | Straight W/ Gusset | Bent Tubing | |||
Weight | Rating | Score | Rating | Score | |
Manufacturability | 3 | 3 | 9 | 4 | 12 |
Weight | 4 | 3 | 12 | 4 | 16 |
Durability | 5 | 4 | 20 | 3 | 15 |
Component Protection | 3 | 4 | 12 | 4 | 12 |
Safety | 5 | 4 | 20 | 4 | 20 |
Cost | 1 | 4 | 4 | 2 | 2 |
Adjustability | 4 | 3 | 12 | 3 | 12 |
89 | 89 | ||||
To see how the bent tubing would look we made two frames. Design A is more complex but offers a stronger design and would not need any gussets. Design B is simpler and adding gussets would be possible.
Figure 1: Frame design A and B.
Figure 2: Side view of Design A.
Since we are leaning towards the first design, it is the one we choose to build it out of PVC as a full-scale model. We started building the model at the SAE shop on Tuesday and it should be done soon and the final design will be chosen.
Figure 3: Deign A dimensioned.
Front Suspension
Having done the double A arm in the past wear attempting to make an short-long arm (SLA) this time around since it would be better in cambering. The two designs show little differences overall.
Front Suspension | Double A Arm | SLA | |||
Weight | Rating | Score | Rating | Score | |
Manufacturability | 3 | 3 | 9 | 2 | 6 |
Unsprung Weight | 4 | 4 | 16 | 4 | 16 |
Durability | 5 | 4 | 20 | 4 | 20 |
Component Protection | 3 | 2 | 6 | 2 | 6 |
Cambering Effects | 4 | 3 | 12 | 5 | 20 |
Cost | 5 | 3 | 15 | 3 | 15 |
Adjustability* | 4 | 0 | 0 | 0 | 0 |
* could not verify yet | 78 | 83 |
Rear Suspension
For the rear suspension we tried to think of all the possibilities to gain an edge on power, maneuverability, and durability during the race. The swing arm would not work well with rear steering due to independent movements of the arms. The multilink is something we feel would work well but we have little experience and we are testing that and the swing arm in Solidworks, Figure 4 & 5.
Rear Suspension | Double A Arm | Swing Arm | Multilink | ||||
Weight | Rating | Score | Rating | Score | Rating | Score | |
Manufacturability | 3 | 3 | 9 | 1 | 3 | 3 | 9 |
Unsprung Weight | 4 | 4 | 16 | 2 | 8 | 4 | 16 |
Durability | 5 | 4 | 20 | 3 | 15 | 4 | 20 |
Component Protection | 3 | 2 | 6 | 3 | 9 | 3 | 9 |
Cambering Effects | 3 | 3 | 9 | 0 | 0 | 5 | 15 |
Cost | 1 | 3 | 3 | 1 | 1 | 4 | 4 |
Adjustability* | 4 | 0 | 0 | 0 | 0 | 0 | 0 |
* could not verify yet | 63 | 36 | 73 |
Figure 4: Design B with swing arms on rear and double A arms on the front.
Figure 5: Deign B with multilink on the rear and double A arms on the front.
Rear Steering
Rear steering was also highly debated but we ended up going for the mechanical steering since the servo tend to be less reliable and less durable in extreme conditions. We expect this vehicle to be subjected to a harsh environment and violent shaking.
Rear Steering | Servo | Mechanical | |||
Weight | Rating | Score | Rating | Score | |
Reliability | 5 | 4 | 20 | 5 | 25 |
Weight | 1 | 4 | 4 | 4 | 4 |
Durability | 5 | 3 | 15 | 5 | 25 |
Component Protection | 3 | 4 | 12 | 3 | 9 |
Cost | 3 | 4 | 12 | 2 | 6 |
Adjustability | 2 | 5 | 10 | 2 | 4 |
73 | 73 |
Drive Train
Again, due to the expected harsh conditions a chain would prove to be more troublesome. We all have more experience with gears but we are still open to the idea of a chain if an inexpensive and large enough change can be found.
Drive Train | Chain | Gearbox | |||
Weight | Rating | Score | Rating | Score | |
Manufacturability | 3 | 5 | 15 | 3 | 9 |
Weight | 4 | 3 | 12 | 5 | 20 |
Durability | 5 | 3 | 15 | 5 | 25 |
Component Protection | 3 | 3 | 9 | 5 | 15 |
Reliability | 5 | 2 | 10 | 4 | 20 |
Cost | 1 | 5 | 5 | 3 | 3 |
Adjustability | 4 | 1 | 4 | 1 | 4 |
70 | 96 |
Floatation
Part of the competition involves going on to a lake turning around and driving out, without sinking of course. This part would be one of the last things done to the Mini-Baja car but it is critical since flooding will cause considerable damage to the rest of the systems. Closed cell foam is more versatile and less bulky. We saw other Mini-Bajas that use wood but they are not as appealing. Part of the water competition involves a timed trial to get in and out of the car safely. We believe the giant wood block may interfere with this challenge.
Floatation | Wood | Closed Cell Foam | |||
Weight | Rating | Score | Rating | Score | |
Manufacturability | 3 | 4 | 12 | 1 | 3 |
Weight | 5 | 2 | 10 | 4 | 20 |
Durability | 5 | 4 | 20 | 2 | 10 |
Component Protection | 3 | 3 | 9 | 3 | 9 |
Effectiveness | 5 | 2 | 10 | 4 | 20 |
Cost | 1 | 3 | 3 | 2 | 2 |
Adjustability | 4 | 3 | 12 | 4 | 16 |
Appearance | 1 | 2 | 2 | 4 | 4 |
78 | 84 | ||||
Conclusion
Each member of the group has their own section of the vehicle they will focus on and we are relying on their expertise to explain their choices. The current choice is a bent frame design with SLA in the front and a multilink on the back. The steering will be controlled mechanically and a gearbox will be used. The floatation will be done using closed cell foam.
Even though we are fairly set with our designs we are still open to change since most of the choices were very close in scoring. Some of the design elements like floatation are dependent on the size, shape, and weight of the overall vehicle so these will be fine tuned as the vehicle is built.
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