I thought I'd give this an update as the electric vehicle system is now up & running and ready to go for a first production batch.
The plan is to get at least half a dozen of our electric vehicles equipped with this for the 2015 season to give a good initial test of reliability.
The first prototype above ended up with a few tweaks as shown in the picture below. I had to change the regulator to a switchmode type (hence all the components bodged on) as the linear one was getting hot. I also added a reverse diode on the power relay contact so that if the relay dropped out while the motors were being driven it didn't overvolt & destroy the drivers.
This worked reasonably well but the motor driver chips were on their limit running our smaller vehicles. These use a cheap direct drive wheelchair motor / wheel combination geared for a top speed of 5 - 6 MPH. Since we run at maximum 3MPH these therefore need more current running at 12V than if geared for the correct speed at 24V. The system worked fine running with a 12V battery, however all our vehicles out there (30+) run on 24V and the chargers are well over £100 each. The cost of changing, plus the operational nightmare of some vehicles running 12V and some running 24 doesn't bear thinking about.
Therefore, on the second iteration I doubled up on the driver chips running 2 in paralell for each motor. This effectively halves the current and therefore quarter the heat for each chip - halving heat generation overall. These are now working well and I'm hopefull may be powerful enough for our 2 tracks with hills.
The complete system for an electric vehicle is now a control unit plus radio on the chassis with a single loom plugging into the larger socket on the control unit. The body carries a junction box for joystick and fire button, plus the elctronic unit for the anti-collision sensors - a bought-in parking sensor system. This links via a single 12 core cable to the small socket on the control unit. Ultimately, I will probably put a small canbus interface in this junction box then the body can connect via a 4 core curly telephone type cable.
The radio and control units are communicating via canbus, and the radio has a USB interface so I can plug in a laptop and get full diagnostic information out. Basic 'error codes' are also passed via radio to the control system on the track / arena to provide plain text fault messages to the user, and then also send me a text message alerting me to the problem. (All our coin units / track control units have a GSM modem).
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If at first you don't suck seed, try drier grain.