A. What you’re after is the Steering EPA (End Point Adjustment). That’s the limiter that prevents the servo from trying to steer the wheels past their physical limits.

On the top of the radio there’s a lid. Under the lid are three sets of controls:

1. the top switches are for channel reversing – you can ignore these unless you are making changes to the servo, motor or ESC at some later time.
2. the top dials are for setting Trim (point of center).
3. the bottom dials are for setting EPA (End Point Adjustment).

It’s the bottom dials we’re interested in. Steering is on the left and Throttle is on the right. Here’s how to adjust end point for your steering:

1. Turn the radio and the car on.
2. Dial the Steering EPA dial (the bottom-left one) back to zero.
3. Turn the wheels to their maximum limit to the left.
4. Increase the steering EPA dial (the bottom-left one) upward until the wheels reach their physical limit. Back it off just a shade.
5. Turn the wheels all the way to the right. Observe closely to see if the servo is straining or if there’s more reach available by dialing the steering EPA dial back and forth a little.

One of Left or Right will be more limited than the other. Your aim is to find the furthest the servo can move the wheels without straining. Check you’re happy that the servo isn’t straining beyond its limit either way by turning that steering EPA dial back a shade if it’s needed. Then you’re all set!

I found this a little difficult to explain but in practice it is a fairly intuitive process once you know which dial to adjust.

Happy driving!

-Craig

A. Overdrive (commonly referred to as ‘o/d’) is a rock crawling thing. Overdriving the front axle makes the front wheels turn faster than the rear wheels, typically by 5% to 15%, but there are implementations out there of up to 33%!

Overdrive can be achieved by driving the front axle faster or the rear axle slower. Ring and pinion gear ratios can be changed so the difference happens on the axle at each or either end. Alternatively some transfer cases have a provision to drive the front faster than the rear, such as the StealthX transmission from Element RC’s Enduro line.

Overdriving the front helps the vehicle maintain direction on difficult climbs where traction is low. It does this in two ways:

• It lets the front pull the rear onto and through problems.
• It also maintains a low loading effect on the suspension by way of that front/rear wheel speed difference. This is thought to aid traction on rock problems, though it would be undesirable on flat, high traction surfaces.

On steep ascents without overdrive, the rear has more of the vehicle’s weight on it and so often has more traction available than the front axles. With that extra traction, the rear will work to push the vehicle forward. This hinders it from turning in whatever direction you’re steering. It’s like a slow-motion, understeer effect that is undesirable on rock problems.

There are a few ways to address this understeer effect:

• DIG (DIsengageable Gear) locks the rear drive, such as in the VS4-10 Phoenix and SCX10 III. You can then drag the nose of the rig around with the front while the rear stays in place. (You can also use DIG to ‘DIG up’ by loading the suspension and drive line before popping the rear drive back on, but that’s for another discussion!)
• Remote locking and unlocking rear diffs (such as on the TRX4) also can help bring the vehicle’s nose to the direction you want by lowering the drive (or authority) over the vehicle’s direction from the rear.

Both of these options mean the front wheels do more of the work, pulling the vehicle round to whatever direction you want to face. Unlocking the rear diff isn’t as effective as DIG, but both have their place in crawling.

Overdrive is another way to address the understeer issue. By keeping the suspension slightly loaded and keeping more of the traction authority up-front with that higher wheel speed, your crawler will more consistently and reliably reach the line you’re trying to drive.