After deciding on a design concept for our electric vehicle, our team went on to planning and ordering parts – to bring our concept into reality! In order to decide on the major components of the powertrain (motor, controller, wheels), we did some initial calculations to find out the power that we needed to supply to our vehicle in order to achieve the desired top speed of approximately 10m/s. However, due to insufficient research and haste, we ordered the ‘wrong’ motor and controller as we did not look out for the right things in the specifications.
Motor: We made an order for the Turnigy D3548/4 1100Kv Brushless Outrunner Motor. However this turned out to be a wrong choice. We learned that in choosing motors, we should be looking out for the following two specs – rpm constant (kv) and internal resistance. For this order, we only looked at the “max power”. Thus we will have to order another motor with a much lower rpm constant below 200Kv.
For our 1100Kv motor, it will not produce enough torque to propel our vehicle forward with a high-enough acceleration. It will only be enough for this:
Controller: Cost $150 – By far our most expensive purchase thus far: KBS24121L,50A,12-24V, Mini Brushless DC Controller. When looking for controllers, we should look out for its “operating voltage” and the “motor current limit, 10 seconds boost” and match it up to our motor. The controller that we have already ordered should be able to work, but we will have to redo some calculations and revise our budget to see if we can purchase a more optimal controller.
Rear wheel: We ordered an 8″ wheel that comes with a band brake assembly, and with belt sprocket.
Front wheels: We decided to order another of the 8″ pneumatic wheel that was given free.
Summary of calculations: We made calculations to find the max velocity and the acceleration, and did up a spreadsheet. These were more important in helping us choose our core components as compared to simply basing our calculations on power transmission.
Second week into building our EV, and we realise that we should have been more careful in ordering our parts. However, all is not lost. Doing more research and asking our instructors more questions beforehand would have probably prevented us from making costly mistakes. For the coming week, we will continue to refine our calculations, and continue to work on the CAD drawing of our vehicle. We intend to submit another BOM this Friday, and we may then begin to build our vehicle next week!
Lesson learnt this week for me (Anissa):
Cheers and have a great week ahead invisible readers!