Upgrading the Engine Mounts

Over past few weeks the engine mount team has focused on solving the vibration issues of vehicle and has made some good headway. Both Manny and Sherj spent time in the school’s Plastics lab to cast samples of polyurethane with varying durometer ratings. This durometer rating dictates the hardness of the polyurethane, which in turn affects other key properties of the polymer. The plan for this polyurethane is to insert it between the engine and the mount so it can act as an isolator, hence damp vibrations.

engine mount polymers
These different samples of polyurethane will undergo tests to determine specific properties, such as flexural strength and toughness. The data these tests provide will help the engine mount team to decide which sample of polyurethane will best suit the vehicle.

Once a desired durometer rating for the polyurethane is selected, it will be cast and machined into the desired geometry and installed on the vehicle.

 

Background Research

With these generic multi use engines, the possibility of mounting is quite large. For this particular example we took a look at everything from, compressors, water pumps and generators to ATV’s, UTV’s and racing karts to see if any particular method used could solve or help solve the particular issues we have isolated for this redesign.

The research into tools with similar motors mounted, didn’t really provide anything of use as most were just solid mounted with a simple design, due to it being a stationery design. The research into what we consider similar vehicles gave us an idea of how vibration is dealt with but not really anything in particular to help with our specific design. Most of these similar vehicles do not use solid mounts like our original, but rather have some kinds of anti-vibration materials added, (ie polyurethane or rubbers of different kinds). These ideas are great for those applications but rubber due to the excessively minimal slack allowed by the CVT is not really feasible for us, the polyurethane is something we may look into more due to its lack of flex.

Design wise there aren’t any mass market products that could be directly used or referenced. The most detailed and engineered design on the market currently would be used for racing shifter karts. These karts have similar issue as the Baja Buggy in that vibration and mounting point stress are very key in design.

 

The current car has competed in the 2015 Collegiate Design Series in Oregon. Aside from several components failing, there were other apparent issues. One of these issues were the members holding the engine. These members were unsupported for their entire length, causing the members to deflect a relatively large distance. Allowing the engine run in such a state for prolonged periods of time could lead to a catastrophic failure of the members and possibly damaging other valuable components. There were no calculations or simulations done to examine the unsupported member and whether or not it could fail through fatigue.

engine mounts
Figure 2: The Current V1 Engine Mounts

To solve this issue, the unsupported member can be braced using the engine mount and the frame members surrounding the transmission. This can be accomplished in a multitude of ways. The most simple of these is to weld the unsupported member to any adjacent frame member. The major advantage to this would be the amount of time and resources saved to fix the problem. The major downside is the welds would cause major restrictions. Currently, the engine can freely slide the entire length of the member it is supported by, allowing for easy tensioning of the CVT belt as well as a simple removal process for the engine. An engine mount that would allow for this freedom could involve a clamping system. This system would look very similar to what is currently being used but it would have an additional extrusion in contact with an adjacent member to act as the clamp. This extrusion would also consist of another piece placed on the other side of the member and bolts to hold these two pieces together. This design would allows for free movement after the bolts are removed, but would still provide support. Optimizing this design could also save weight as no simulations were done to test if material could be removed.

 

Vibration

 

Another issue with current engine mount is they are currently hard mounted to the frame. This causes a severe transfer of vibration to the member supporting the engine as well as throughout the entire car. This vibration has the potential to cause failure in a multitude of components such as the electronics, so it must be looked in to. There were no calculations or simulations done previously to determine the exact impact of the vibrations.

A solution to this problem could be the use of shims. The shims would be inserted where the engine mount clamps onto the frame. The shims could be made of rubber and would isolate the engine from the engine mounts. It is this isolation that would damp vibrations. A downside to these rubber shims is they may affect the tension in the CVT belt.

Other teams had varying views on the subject of engine vibration. Some teams had no need for vibration damping; they left the engine hard mount to the frame. There were other teams who had severe vibration and used either flexible or solid inserts to damp vibration.

 

 

Casting

Currently, the engine mount is stock 2×2 aluminum that has notches cut out with a ball mill. Holes were then drilled to bolt the engine to the mount, and then the mount to the frame. Instead of using stock aluminum, the casting of aluminum parts could be done. This has the major advantage of confirming the viability of casting future parts. This will allow future teams to create part geometries that would otherwise be very difficult to machine.

The new engine mount could be casted from a different aluminum alloy to maximise the desired qualities such as castability and machinability. A composition that would do this is Aluminum 319, which is an alloy containing 6% silicon and 3.5% copper. This type of aluminum alloy is commonly used for engine parts, which makes it a prime candidate for an engine mount.

Another aluminum alloy that meets the required machinability and castability properties is Aluminum 356. Aluminum 356 contains 7% silicon and 0.3% magnesium. It is also used for flywheel castings, automotive transmission bodies and pump bodies.

with the faculty at BCIT, casting different alloys is possible. This will involve using an uncontaminated crucible and sourcing the correct materials to achieve the desired composition.

V1 Electrical System Review

A few of the major improvements that needed to be made to the electrical system was that the power supply was too heavy, and that maintenance was going to be difficult if it needed to be done. Also, due to changes in the rules for the 2016 competition a new brake light needed to be purchased.
After some quick calculations, it was determined a simple 9V battery should do the trick, which is a significant weight decrease from a golf cart battery. This year, the car will not be equipped with reverse, making the overall circuit simpler and easier to install. In order to simplify installation and maintenance, more connectors will be used and the new brake light features two holes on the sides for mounting. Last year’s brake light was mounted using a grommet, so if the light needed to be removed, it was easier to take off the entire mounting bracket which was mounted a little too close to the firewall, making it difficult to use any tools. A new mounting bracket is going to be made this year once the brake light comes in and measurements can be taken, and will be mounted in a way that will be more easily accessible. The new brake light also allows for removal while leaving the mounting bracket in place.
-Oliver


Moving Forward

Moving forward is a surprisingly complex task in Baja SAE. Baja SAE subjects vehicles to a unique set of constraints, including a low-powered 10 HP Briggs & Stratton engine; shock loading and rough terrain; and dirt, grit, and mud. All of these factors make drivetrain design a critical factor in Baja SAE racing.

Off-the-shelf commercial and consumer products tend to be designed around applications that require different reduction ratios, or are relatively heavy due to their high power capacities. Off-the-shelf products are not optimized for Baja SAE.

Fig. 1: Dana H-12 FNR, commonly used in Baja SAE

On the other hand, student designed and manufactured gearboxes pose a different set of concerns. They must be precision manufactured; often requiring tooling not available at schools. Designing, verifying, and validating drivetrains requires a huge amount of time from students involved, making it an unappealing project to take on while balancing academics. Furthermore, because off-road racing has few similarities with products standardized for industry – lower reliability requirements, greater shock loading, low power – industrial standards such as AGMA present only a guidelines for design. Many student-designed gearboxes that perform well in competition are not designed to AGMA standards.

BCIT Racing designed it’s own gearbox last year, with a Forward/Neutral/Reverse mechanism. There were important lessons learned from this, such as the nuances of shift-mechanism design. The gear teeth showed little signs of wear, despite the failures that occurred elsewhere in the system.

Fig. 2: BCIT Racing’s custom FNR Gearbox

This past summer, starting in June, I began working on a new drivetrain design for BCIT Racing. I began this project early for two reasons, to keep my mind working over the summer, and to avoid designing a sub-par system due to straining academics. I decided to design a new gearbox for a number of reasons, but primarily because it is lighter and more reliable than chain drive systems, and may be optimized for Baja SAE to the greatest degree. With this in mind, the following parameters were specified:
  • ≤20lbs assembled, dry weight, a 40lb from BCIT Racing’s current gearbox.
  • One forward gear, approximately 12:1 reduction
  • CNC aluminum case
  • Minimal number of independent components.
  • Field serviceable; including the ability to inspect and replace oil without removing the gearbox from the vehicle.
  • Must be manufacturable in-house
  • 8in Centre-to-Centre shaft distance
  • 5in width maximum

Fig. 3: BCIT Racing’s gearbox being serviced at Baja SAE Portland

From here, the design process began. Interestingly, after independently studying various gear-design texts, researching, and running calculations, my gear design parameters came out similar to those of last years gearbox designers. Furthermore, after doing more research and talking with students from other schools – contacts I made through in Baja SAE Portland, – I found my gear design parameters were similar to theirs. Phew, I’m on the right track.

Embodiment design began last week, now that we are back at school I have access to Solidworks. I’ve already experienced some issues regarding permissions to modify ToolBox parts (gears) due to our school licensing – I’m working on remedying these with faculty. The case is being designed so that it can be manufactured with a 3 axis CNC so that the critical-features of each half may be manufactured in one setup.

So far, it looks like we are on track to achieve the design specifications. CAD renderings are under-wraps for now, but will be released soon. I promise the final design will be worth taking a close look at.

-Sanesh

Fig. 4: Shigley’s Mechanical Engineering Design lived in my backpack this summer

 

Summer 2015 Launch Meeting

I’m happy to report that BCIT Racing’s Launch Meeting for the 2015/2016 season was a great success! The turnout greatly exceeded our expectations with approximately 50 prospective new  members attending.
Dan kicked things off giving a crash course in the Baja SAE student design competition. Sanesh and Saf then took us on a journey through the 2014/2015 season, highlighting the Design, Build, and Competition stages of the project. After that I presented our goals for this season and beyond, and outlined the expectations for team members. Finally Dean wrapped things up by explaining the benefits to joining BCIT Racing and by sharing some of his personal experience honing engineering skills through working on the car this past season.
If you’re a BCIT student reading this and are interested in joining the team please see our application assignment here. Also feel free to email us with questions.
Looking forward to the season ahead,
-Jeff

Engine Mount Redesign

The core of BCIT’s baja team are already hard at work, designing new systems for the car, and an engine mount redesign is at the top of the list. Check below for some preliminary details.

The scope of this project includes the following elements:

  • Engine Mount Support Member
    • Reduce the travel of the member
    • Minimize the modifications of frame
    • Minimize amount of weight added
    • Examine the possibility of casting parts
  • Vibration Reduction
    • Attempt to minimize the vibration
    • Ensure that proper CVT belt tension is maintained

Team 2016

We look forward to introducing all our new 2016 team members! The core of BCIT’s baja team are already hard at work, designing new systems for the car, strategizing on how to make the team run smoothly, and getting these snazzy new headshots.

The team is eager to invite new students to the team during the first couple weeks of school. So keep your eyes open for these guys!