Sabertooth R/C DIP Switch Settings
"The Long Answer"
The R/C signal fed to the S1 input controls the forward/backwards motion of the vehicle. This is usually connected to the throttle channel of a pistol grip transmitter, or the elevator channel of a dual stick transmitter. The R/C signal fed to the S2 input controls the turning of the vehicle. The most common use of this feature is to control a differential drive.
A differential drive is one where the driving wheels are driven by different motors. Turning is accomplished by either reversing or stopping one of the wheels, or multiple for a four-wheel differential drive system. It allows great maneuverability and lets the vehicle to turn in place, at the cost of losing some speed when turning at top throttle.
The signal fed to the S1 input directly controls Motor 1 (M1A and M1B) and the signal fed to S2 controls Motor 2. Use this if you want your two motors to function independent of the other.
With Linear control, your signal exactly equals the input. This can make it hard to make fine adjustments if your top speed or max turning rate is high, or to get the control you need.
In the case of the Sabertooth R/C, throttle signals range from 0 to 255, with 128 being a full stop. Linear control directly converts signals into input, driving the motor by the exact percentage that the stick is set to. Exponential modifies the signal in a, well, an exponential fashion. For the curious, the formula is 128+(sign (input-128))*(Input-128)^2/128.
What this means is that at lower throttle signals nearer the center point, larger adjustments to the signal will result in smaller changes to the input, allowing you to smoothly guide your vehicle without requiring you to be move the stick a precise 1.75 millimeters to the left. Vehicles with high top speeds or fast max turning rates will benefit greatly from this, as linear control will give you an exact percentage and make life difficult if you want to only make a small turn or increase in speed. Exponential will soften stick control to make this easier while preserving your blistering-edge maneuverability, should your R/C car happen to need to make a fast getaway from the Batmobile. For a more thorough explanation, especially with regard to remote-controlled aircraft, please see here.
A lithium battery starts its output voltage at 4.2V per cell, and continually decreases as the battery is discharged. A lithium cell is considered fully discharged at 3.0V. Though some packs are more forgiving than others, exceeding this point will usually begin to damage the battery. Drop too low, and it will never recharge again.
Fortunately, you don't have to worry about this too much. The Sabertooth autodetects the number of cells in your Lithium battery and flashes that number on the Status 2 LED. Don't use it while battery is severely discharged as it may detect an incorrect number of cells and fail to cut off properly. The Sabertooth when in Lithium mode at the cutoff voltage goes into a feedback loop that reduces throttle, helping preserve the battery and making control sluggish when it's time to go recharge your batteries. The gradual scaling back of throttle makes it easier to return your vehicle to base, where a hard cutoff would simply make you walk.
Just what is acceleration ramping?
If you have ever built a heavy robot or other moving project, you have probably ran into the problem of using too much current on fast accelerations. This mode will help you out!
When enabled, this mode will spread out fast acceleration over the course of a half of a second. While you may not accelerate as fast, you will (potentially) greatly reduce your current spikes. This will cut back on the annoying stutters that come with trying to draw too much current from your source.
With this mode off, your acceleration will be proportional to how quickly you move your control device. There will be no delay.
Autocalibrate detects your zero stick point when you first power up your transmitter. After that it detects your highest throttle signal thus far and interprets that as 100%, and your lowest as -100%. After it's been powered to full throttle and full reverse, the driver will have a proper idea of what your throttle settings actually are. This is good for pistol grip transmitters and the like that don't have a perfect 100% to -100% setup.
Some receivers, such as the Spektrum AR6000, will output servo pulses before a valid transmitter signal is present. This will cause the Sabertooth to autocalibrate to the receiver's startup position which may not correspond to the center stick position, depending on trim settings. This may cause the motors to move slowly even when the transmitter stick is centered. If you encounter this, either consult your receiver manual to reprogram the startup position, or adjust your transmitter trims until the motors stop moving. Alternatively, you can simply disable autocalibration.
A microcontroller won't need to autocalibrate since it can be programmed exactly how you like, and you can just slightly adjust your signal if you find the zero throttle point is a little off. In addition, your range is basically whatever you want it to be.
The timeout failsafe causes the Sabertooth to shut down the motors if it misses ten signals in a row from your transmitter. This should only happen if you are encountering heavy radio interference and your vehicle has lost signal. As it may have been traveling faster than you (or any human) can run, a vehicle without a timeout failsafe can keep going until it runs out of fuel, wears the batteries down, crashes into something or all three.
The system will turn on again immediately if it receives new input, so don't worry that the failsafe will put you in a catastrophic position. Just hurry and catch up to your vehicle before it realizes what stopped it from ditching you and going to Vegas.
If, however, you are running from a microcontroller, interference is rarely a problem. Disabling the failsafe also opens up some options for running motors at set levels until their next instruction. You may find this useful, especially on slow microcontroller such as a basic stamp.