Active Damper
While thinking of ideas for our senior design class ME 102B, a group consisting of four friends and I thought of the most ambitious project any of us had ever done: a damper that can have its stiffness controlled via magnetorheological fluid in a smaller form factor than anything currently existing. The challenges we overcame to make the idea a reality were formidable, but in the end we succeeded.
Motivation
Since all of us were members of Berkeley Formula Racing, we all had interests in ways to make our team's car (and cars in general) go faster. A car's dampers play a central roll in controlling its response to forces, but their functionality has some limitations. With a traditional damper setup, you can't tune for one type of response (bounce, pitch, roll) without affecting all the others. With an actively adjustable damper, it would be possible to change how the car behaves at any moment, either manually or automatically with the help of live sensor data. This would allow for a more adaptable car that can maximize its performance in all parts of a track.
Effect of damper settings on different modes of movement.
Design
For a baseline, we used Ohlins TTX25 shocks since they're what we use on our FSAE car. The upside of the Ohlins shock is their independently operating high-frequency and low-frequency fluid circuits that you can tune separately for both compression and rebound. The main design challenge was integrating a magnetic coil into the circuit. Our design put the magnetic coil on the damper plunger and forced fluid through the plunger's orifices. This somewhat compromised the adjustability of the low-speed circuit, but it had to be done to make the damper even possible to manufacture in our time frame.
An early whiteboard mock-up of the circuit.
Assembly
Once the parts arrived, the hardest part began - actually putting the project together and making it work. The parts fit pretty well together after some careful machining, but we realized a great error - the MR fluid we bought had almost no information online on how to use it, so as a result, our coil was nowhere near strong enough to actually make a noticeable difference in damping. On top of that, we didn't even have wires thin enough to make a better coil. And to top it all off, the seals we bought for the nitrogen gas canister didn't work and the gas itself wasn't properly connected to the rest of the damper, preventing it from working at all.
After ordering new wires overnight, redesigning the circuit on the spot, redesigning and rewinding the coil to produce 70x as much magnetic force, machining new custom parts, and figuring out a solution to the nitrogen gas canister, we finally had a working active damper. But as soon as it first got working, the thin wire snapped somewhere inside, so we had to disassemble and reassemble everything yet again, this time more carefully. Eventually, after multiple long nights, we had everything done and together at 6:00AM the morning of our presentation.
The inner tube, some circuit parts, and the main body of the damper laid out.
Test-fitting the damper using normal fluid.
Filling the damper with nitrogen gas.
