Hi All,

I need to make a custom motor controller to control a 240w 24v motor. Currently the motor is controlled by 2 relays which are used to isolate a single battery for 12v (For race start) and 24v used full throttle and these are just on or off, there is no PWM. The controller is to keep the motor as efficient over a race which is 1 hour. There are 2 12v 24Ah battery which power the car and used to power the motor.

The motor most efficient RPM is 1800 and current and voltage can both my monitored and logged very easily with an arduino.

Could the voltage be controlled to keep the motor at it most efficient point during the race as we just stay at full throttle as we do not need to brake and accelerate as we stay at a constant speed?
Could the current be limited to limited discharge of the batteries to minimise energy consumption?
One team can set there fastest lap at the end when the batteries should be dead, possibly s joule their circuit?

Picture of relays is attached!

 

Have a go with a PWM controller and see how it compares. With that, you can accelerate gently and that will save power over just switching the 12V to 24V.
Make sure you use over rated FETs and diodes to handle stalled motor conditions. If you want, a relay can be switched in across the FET for max power, but that may not be needed.
Monitor the current via a Hall current sensor for low loss. Then the controller can use that info to back off the PWM as required.
Do you need reverse? If not, it is pretty straight forward to make a controller, or buy one on Ebay for a starting point.
For example,
https://www.ebay.com.au/itm/10-50V-...h=item25dadc325c:g:9LoAAOSwg0pZYzOl:rk:2:pf:0
I have no idea what they are like but the price is not to bad for something to play with. But I would recommend you build a more intelligent one so more control and monitoring can take place. An Arduino will be a good cheap place to start. Arduinos cannot be beat for support and cost as they are so readily available and the development system is free. They may not be the best processors but are ideal to start with.
You will find it almost gets to be a "religious" argument as some people are dead against Arduinos. I cannot understand that attitude myself, but you will no doubt see the relies.
I use a mix of processors in my designs, PICs too. For protos, the Arduinos are so much easier to use. For example, I make an add on board for the Beagle Bone Black, and I will make an Arduino board to drive it for testing the boards as I assemble them as it is so much easier to get the Arduino code going.