The ARC funtion is somewhat similar to expo, the difference is that expo gives a curved response to the input of the wheel or trigger, where ARC gives a dual-slope response. As with expo, a negative rate value makes the reponse to the initial movement of the wheel or trigger milder, then the response increases at the point in the wheel or trigger travel corresponding to the "point" setting... The higher the "point" setting value, the further along the wheel or trigger travel before the response increases.
For example, if you wanted a softer response to the initial movement of the steering wheel, you'd set a negative number for the "rate". Changing the "rate" number will dictate how soft the initial response to the wheel is. If you tried -20, let's say, and wanted even softer response, you'd then try something like -25 or -30 until you get to where you like the feel.
Now you decide where in the travel you'd like the response to increase. The higher the "point" number, the further along the travel you'd go before you felt the increased response. If, for example, you find yourself thinking that the steering feels good off neutral, but you're moving the wheel too far before the response picks up, you'd try a lower value for "point" to make the quicker response start happening earlier in the travel.
To answer the specific questions in the original post:
For the ARC Steering - I want the steering to be slightly slower in the begining of the travel. I find I try to turn a little bit and the car turns more then I want. So do I set a negative or positive value? And the value from 1-100 is percent of trigger pull right? Can you change how drastic the slowing down is or no? So if it is set to 20% it will be slower until 20% and then go to regular speed?
You'd set a negative value for "rate" for initial tests I'd suggest -20 or so on rate. I'd set the "point" to 50, so the rate will increase from the lower value
to normal at the 50 percent point of the wheel travel. Adjust from there to suit your taste.
For the ARC Throttle - Is it possible with an electric car or is that only for nitro cars that use a servo for throttle? If it is possible I am looking to get more power faster. So say the first 20% it gives more throttle then normal and then goes to regular. Would that be a positive or negative value?
Yes it works for electric OR nitro. To get more power earlier in the trigger pull, you'd set a positive value for the "rate" number, then set the "point" value for the place in the trigger travel where you want the normal response to come in, for example 50 would be at half trigger.
Remember you have to set ARC to enabled before you'll actually feel any changes... the function is inhibited by default. I've only used the Caliber, M8 and M11, so I don't have specific knowledge of the MX-3, but on the M11 you can set the ARC function independently for the throttle and brake sides of the trigger. I'd guess the MX-3 as well.