AERO’s 7th generation racecar, and 3rd generation EV, CleanSpeed 3 (updated to CleanSpeed 3.5 for its second year) was started from scratch in September 2016 – very much a clean sheet design in terms of both electrical and mechanical design. Its most prominent features include a newly designed suspension, an improved battery pack, a new powertrain, a new control system, and a new chassis to contain it all.
At Formula Hybrid 2017, CS3 placed 2nd in the design competition, and 3rd out of 8 cars in the electric class. At Formula Hybrid 2018, CS3.5 placed again 2nd in the design competition again, and 3rd out of 11 cars.
|Battery Capacity||6.14 kWh|
|Battery Chemistry||Lithium iron phosphate (LiFePO4)|
|Battery Voltage||102 V|
|Batteries||GBS 60 Ah Prismatic|
|Burst Current||600 A|
|Motor Controller||Zilla 1K-LV|
|Motors||Dual LMC 200D95B, shaft coupled|
|Motor Type||Brushed DC|
|HP||55 hp @ 4,000 rpm|
|Torque||120 lb-ft @ 0 rpm|
|Track Width||56.5 in|
|Weight Distribution [F:R]||47:53|
|Wheels||OZ Aluminum Formula Student|
|Tires||Hoosier 20.5x7-13 R25B|
The suspension system for CleanSpeed 3.0 was a completely clean sheet redesign compared to previous suspension setups used in the past. The OTS wheel hubs, wheels, and dampers were the only components that were not redesigned. Senior member Greg Castaldi spent countless hours designing the system, with the primary design goals being adjustability, stiffness, and much improved geometry. New uprights were designed to replace the old, non-optimized ones that had been used previously, and were machined by AERO’s sponsor Tru Form Precision Manufacturing. The suspension geometry was modeled using software from Lotus Cars UK to ensure the dynamics of CS3 performed as intended.
CleanSpeed 2’s under-the-driver battery pack was ideal for keeping the center of gravity of the car low, but it was extremely difficult to access for maintenance and was susceptible to water damage. With that in mind, senior members Jack Thomae and Alex Raff designed a new battery pack around the same lithium iron phosphate prismatic cells, but made it relatively easy to remove from the car for maintenance to be performed. Compared to CleanSpeed 2’s pack, this year’s pack has 13% more charge capacity, which allows the car to drive farther and faster. Also, the battery management system was upgraded to a new, more configurable option from Elektromotus.
To boost performance from CleanSpeed 2, the decision was made to switch from an AC powertrain to a DC powertrain with dual, lightweight pancake-style permanent-magnet DC motors from Lynch Motors. Coupled with Manzanita Micro’s Zilla motor controller that had been used on the original CleanSpeed, the package proved to be fairly reliable. To send all that power to the wheels, a new, adjustable differential mount was designed by Junior member Moritz Thali, which provides an easy way to adjust chain tension and swap out different sized drive sprockets. Additionally, an electronic series-parallel motor switching system was implemented using contactors from GIGAVAC. In series mode the car has greater acceleration, and in parallel the car has a higher top speed, effectively allowing the driver to “change gears” without any extra moving parts.
To fix the noise and signal problems CleanSpeed 2 had, a new control system was designed by sophomore member Cullen Jemison. This system, based on the industry standard controller area network (CAN) bus, was designed to eliminate noise and minimize analog signal runs in order to allow the car to run reliably under all conditions. It also included new safety circuitry, which safely powers down the car within seconds of any dangerous fault being detected.