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EV.4.1 Motors
EV.4.1.1 Only electrical motors are allowed. The number of motors is not limited.
Graphic - DC Motor
Graphic - DC Motor
This rule essentially tells us that we cannot use internal combustion to power our car. Alternatively, as stated, we are restricted to electric motors.
But how do electrical motors work?
By using principles of electromagnetism to convert electrical energy to mechanical energy.
When the power switched on, the brushes supply current to the commutators. These commutators are attached to the rotating coils, one to each end. Current passes from commutators into the coil, placed in between the poles of permanent magnets, called stators. When current moves in the coil, the magnetic field is induced around the coil. This magnetic field comes in contact with the magnetic field of the stators and the coil starts to rotate. When the rotor rotates the shaft attached to it also rotates, thereby converting the applied electrical energy into mechanical energy.
Pictured to the left is an animation which demonstrates these concepts.
Article - Types of Electric Motors
Article - Types of Electric Motors
EV.4.1.2 Motors must meet T.5.3
T.5.3 Motor Protection (EV Only)
T.5.3.1 The rotating part of the Motor(s) EV.4.1 must be contained in a structural casing. The motor casing may be the original motor casing, a team built motor casing or the original casing with additional material added to achieve the minimum required thickness.
Minimum thickness for aluminum alloy 6061-T6: 3.0 mm
If lower grade aluminum alloy is used, then the material must be thicker to provide an equivalent strength.
Minimum thickness for steel: 2.0 mm
T.5.3.2 A Scatter Shield must be included around the Motor(s) when one or both:
The motor casing rotates around the stator
The motor case is perforated
T.5.3.3 The Motor Scatter Shield must be:
Made from aluminum alloy 6061-T6 or steel
Minimum thickness: 1.0 mm
The above set of T.5.3 rules specify safety constraints for the structural casing and scatter shield, both of which are mandatory components of our build. Constraints such as material thickness, material composition, and component functionality are regulated.
Starting with T.5.3.1, this rule references a structural casing for the motor. Our 2023 team was able to use the original motor casing due to the fact that its thickness exceeds 2.0 mm and is constructed from stainless steel.
T.5.3.2 and T.5.3.3 both reference a component called the Scatter Shield, which is a steel or nylon guard placed around the bell or clutch housing to protect driver and spectator from flying parts in the event of part failure at high RPM. For our cases, we are only operating in one gear. Without a clutch or a flywheel, the driver is solely being protected from a failure of the chain.
Photo - Motenergy ME1616 Motor Casing
Photo - Motenergy ME1616 Motor Casing
Photo - Scatter Shield from the 2023 Vehicle
Photo - Scatter Shield from the 2023 Vehicle
EV.4.1.3 If used, Outboard Wheel Motors, where the motor, attendant cables and wiring do not meet F.11.1.3, must:
a. Include an Interlock EV.7.8
This Interlock(s) must Open the Shutdown Circuit EV.7.2.2 before failure of the Tractive System wiring when the wiring is damaged or the Wheel/Motor assembly is damaged or knocked off the vehicle.
b. Reduce the length of the portions of wiring and other connections that do not meet F.11.1.3 to the extent possible
This rule has dependent compliance on another set of rules from the tractive section, which should be reviewed for context. An explanation of EV.4.1.3.a and EV.4.1.3.b will follow.
As stated by F.11.1.3, all components of the tractive system (which in this case, includes the outboard wheel motor) must be contained within either the Rollover Protection Envelope or a fully triangulated structure defined in the Component Protection ruleset.
Rules Reference - F.1.13 (Referenced in F.11.1.3)
Rules Reference - F.1.13 (Referenced in F.11.1.3)
F.1.13 Rollover Protection Envelope
The Primary Structure plus a plane from the top of the Main Hoop to the top of the Front Hoop, plus a plane from the top of the Main Hoop to the rearmost Triangulated structural tube, or monocoque equivalent.
* If there are no Triangulated Structural members aft of the Main Hoop, the Rollover Protection Envelope ends at the rear plane of the Main Hoop
Starting with the Rollover Protection Envelope, this is an extension of the Primary Structure, inclusive of two tangent planes. The first connects the Main Hoop to the top of the Front Hoop, and the second connects the Front Hoop to the Rear Impact Protection.
Rules Reference - F.3.2.1.n (Referenced in F.5.16)
Rules Reference - F.3.2.1.n (Referenced in F.5.16)
Rules Reference - F.3.2.1.n
Rules Reference - F.3.2.1.n
Rules Reference - F.4.1.3 (Referenced in F.5.16)
Rules Reference - F.4.1.3 (Referenced in F.5.16)
F.4.1 Requirements
If any composite or other material is used, the SES must contain:
[...]
F.4.1.3 Calculations that show equivalence of the structure to one of similar geometry made to meet the minimum requirements for a structure made from steel tubing per F.3.2. Equivalency calculations must be submitted for energy dissipation, yield and ultimate strengths in bending, buckling, and tension.
If not protected by the Rollover Protection Envelope, the wheel outboard motor is required to be protected by a triangulated structure (or properly calculated similar geometry).
But what is triangulation?
Triangulation refers to frame members being assembled in a way that creates only triangles. If a member is only loaded at it's ends (i.e. a two force member), the member will only be able to translate axial loads, meaning the loads will be parallel to the direction of the member. In other words, members that are only loaded at their ends will be loaded in tension or compression, never bending.
Within this ruleset, the requirements for sizing of the triangulated tubing are specified as being Size C, defined in F.3.4.1. Shown in the table, the Component Protection application allows for alternative tubing material. This said, the material must be structurally equivalent to the predefined size. Calculations must be inclusive of the material's:
Energy Dissipation
Yield and Ultimate Strength In:
Bending
Buckling
Tension
Schematic - HVIL Within Shutdown Circuit
Schematic - HVIL Within Shutdown Circuit
As shown above, the HVIL for the outboard motors would be connected in series just after the High Voltage Disconnect (HVD) Interlock, and just before entering the Accumulator Container.
Photo - HVIL Example
Photo - HVIL Example
In this picture, a thick orange HV cable plugs into a motor inside of a wheel. A thin black wire with an inline autosport connector is attached to the wheel by a loop of safety wire. The black cable is routed out of view of the camera back to the chassis of the vehicle. The failure mode will be a detached wheel unplugs or breaks the communication cable.
Article - Outboard Motor High Voltage Interlock Circuit
Article - Outboard Motor High Voltage Interlock Circuit
Additionally, EV.4.1.3.b requires that wires and connections be as close to compliance as possible. There should not be a lot of slack in these, and they should really be as close as possible to fitting inside of the rollover protection envelope or other triangulated structure.
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