First test session with the Agni motor

 

The first run of Stealth Aero with the new Agni 143 motor was held as part of a Greenpower test day at Goodwood Motor Circuit on 26th March. Our main aim was to collect as much data as possible on the new motor and to ensure that the car chassis can handle the speeds we will need to be averaging for the duration of the world record attempt.

 

As we do not yet have the lithium polymer batteries that we will be using for the record attempt we decided to use the standard 33Ah lead acid AGM type used in F24 and F24+ racing with Greenpower and continue to run with the PG drives i70 motor controller that the car has used for a number of years whilst competing in Greenpower. We knew that this controller would not be suitable for the record attempt itself but believed it to be capable of withstanding the increased current draw over the test session.

 

The good news , was that the car chassis proved quite comprehensively that it can more than handle the speeds we need to aim for in the 24h record attempt and the motor ran well. Our fastest lap saw us average 42.5mph with top speeds in excess of 48mph which is very close to the pace we hope to achieve.

 

Unfortunately, however, we quickly discovered that the i70 couldn't handle the rapid higher currents that are generated when initially starting the motor or during regenerative braking, this is largely down to the low motor winding impedance of the Agni motor. By the time the safety mechanisms inside i70 react to these high transients, the MOSFETs are already deteriorating and so after the first three laps of Goodwood, they failed. The mode of failure was regenerative braking out on the circuit avoiding a slower car which saw us retreating back to the paddock on the back of a recovery vehicle.

 

Fortunately we had a second spare motor controller so fitted that and sent the car out again with a different driver for another four laps before the same thing happened prematurely ending our testing session.

 

During the our second session the average power usage was lower than we expected at some 825w (some 1.1hp) this was in part down to the low capacity batteries that we were running.

 

So in conclusion a mixed day but some good progress not least the car handled the speed and extra power well. The next step is to source the controller for the record attempt, fit the lithium polymer batteries and have another practice session giving more of the drivers a chance to experience the car running at higher speeds.