1 reply to this topic

[dalek]

I like my Third Eye controller because of it's light weight, thin light cord and good trigger feel.

 

However, as the other guys where I race know, adjusting the brakes for any given car, can be difficult because the amount of braking changes a lot with only a small amount of knob turn when between 4 and 4 1/2 on the dial.

 

To solve this problem, I modified my Third Eye by moving the brake pot (a 5K pot) from it's original position and installing it in the middle of the board, then putting a 500 ohm pot in the brake position and wiring them in series.  

 

So to adjust the brakes, the 5K pot (what I would call the range pot) is adjusted to bring the 500 ohm pot (the brake pot) into range so it can be used to fine tune the brake setting.  

 

The knob on the range pot has detents so it makes the pot act like a rotary switch which is ideal for this type setup.

 

This past Friday I used the controller and got the impression that the range pot will stay in the same position for most of the cars we race and if a change is needed, it won't be more than a click or two.

 

 

[Bill Seitz]

I haven't explored how Third Eye wires the brake pot, but likely V+ is connected to one end and ground to the other. The pot can then select a voltage between V+ and 0 to turn on the brake FET. Over the years, MOSFET's have been optimized for their major role as switching devices, and for minimum loss, designed to turn on rapidly above their minimum threshold voltage. The FET's I'm currently experimenting with turn on at around 2 volts and are 99% turned on at less than 6 volts. Most MOSFET's are specified to be 100% on by 10 volts. For all practical purposes, the pot range from 6 volts to V+ (12-14 volts) doesn't change the brake response, and the pot range from 0-2 volts doesn't turn on the brakes at all. So as you've noticed, the actual useful adjustment range from no brakes to 100% brakes is less than half the pot travel and can vary with the track voltage. As you've done, adding some additional resistance in the circuit helps put the brake pot into the useful narrow voltage range where it has greater adjustment effect.

 

This same phenomenon with FET's also effects a FET throttle circuit, and Third Eye has some additional circuitry in their controllers to accommodate this. It's curious why the same additional circuitry wasn't used in the brake function.