Magic behind Thar Roxx's IntelliTurn & CrawlSmart features: Explained

The Lead for All-Terrain Capability Development for the Thar Roxx and other Mahindra vehicles walks us through how these advanced features work.

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So, the Mahindra Thar ROXX has been introduced into the market with some best-in-class off-roading features and, probably, for the first time in India features. Being the Lead for All-Terrain Capability Development for the ROXX and all other Mahindra products, I thought it'd be best to have a detailed thread on Team-BHP about what these features are and how these features work (on a holistic level), at least in the ROXX, so that fellow members can put these features to good use.

IntelliTurn (Intelligent Turn Assist)

Intelliturn is a feature which lets you manoeuvre through tight off-road terrain (turns) with ease. Basically, it brakes the inner rear wheel and facilitates a tighter turning radius than geometrically possible by the vehicle architecture.

To start off, let me tell you how to activate the feature in the Thar ROXX. Driver montoring and drive away intent is ON for safety so, you will need to start with:

• Sitting in your seat.
• Engine ON.
• Doors Closed.
• Seatbelts ON.
• E Parking Brake OFF.

Once your intent is to drive, set the:

• Transfer Case in 4Low.
• Gear in D.
• Choose the terrain you want to drive on - (Snow, Mud or Sand).
• Then press the IntelliTurn Switch on the right side driver switch bank.

Now you will see a green cluster symbol light up, similar to the switch you pressed. This means the feature is ready and it will facilitate a tighter turn whenever you turn your car. The feature will stay ON till 30 seconds after which it will go off, and you will have to press the switch again.

However, if you enter a turn, then the timer is reset and it will go off only if you don't use it for the next 30 seconds. Once you are in the Turn and the feature is 'actively working', it will do so for 15 seconds, which is more than enough for you to complete the turn. After which, the feature will turn off. The max speed at which this feature works is 15 kmph, which is more than enough for a tight turn off-road, beyond which it turns off.

How it works:

On a broader perspective, it brakes the inner rear wheel when turning. So when you are taking a right turn, it will lock the right rear wheel and vice versa when you are taking a left turn. There are multiple sensors at play here, which I'm not getting into detail. However, the basics would be the steering angle sensor, which sends input to the control unit, which figures out based on multiple sensors that the vehicle is intending to turn and increases the brake pressure to the inner rear wheel.

To visualize the turning effect, consider the centre of gravity as the reference point around which yaw moments are generated due to longitudinal and lateral forces generated by the tires. Usually, it's the lateral force generated by the front tires because of the steering geometry.

In this case, since one of the rear wheels is being braked (the inner), because of the differential, the outer wheel on the rear axle rotates at a higher speed. The higher rotational speed of the rear outer wheels, when compared to the inner wheel, will induce a yaw moment about the CG in addition to the forces generated by the front axle (steered tires). This will induce a skid steer in the rear axle, and the turning radius of the car is reduced than what would have been achieved with just the front axle steering the car.

Now, since it's a skid steer feature, the efficiency of the turn achieved will depend on the surface μ (Mu = Frictional Co-efficient). Ideally, lower the μ, better the turn, as the inner locked wheel can slide more easily. Another factor is the μ between the front axle and rear axle, too (off the road, you always tend to have different μ in all 4 wheels). This is also why the feature is differently calibrated for different terrain modes, and you need to choose the correct terrain mode you are driving on for the feature to work efficiently.

Here are a couple of videos illustrating how the feature works.

• Video 1
• Video 2

P.S. - I hope our Indian market evolves with respect to using features safely and responsibly so that the limit of features like these can be extended to make things really fun to drive.

Crawl Smart (Smart Crawl Assist)

Now, at least for me, I can say this would be the most useful feature off-road. It completely transforms your car into a Traction Generator. To explain it in a very basic sense, the car accelerates and brakes itself for you in off-road so that the driver can focus all his attention on steering the car through the obstacle. More on it later. Again, to start off, let me tell you how to activate the feature in the Thar ROXX. Driver monitoring and drive away intent is ON for safety, so you will need to start with:

• Sitting in your seat.
• Engine ON.
• Doors Closed.
• Seatbelts ON.
• E Parking Brake OFF.

Once your intent is to drive, set the:

• Transfer Case in 4Low.
• Gear in D.
• Press the CrawlSmart Switch on the right side driver switch bank.

Once done, and you remove your foot from the brake pedal, the car will start accelerating (and braking if required). The driver is given 7 levels of speed control. The default set speed is Level 2 and the driver can use the cruise speed keypad on the steering to set the speed to higher or lower as per the terrain demands.

This feature can be used for two purposes:

• Getting through difficult obstacles. The car will decide/generate the optimum traction, acceleration & deceleration for the given obstacle. (Excellent when used in loose sand and rocky obstacles) for you to cover it.
• Like an off-road cruise control to have a slow but controlled speed. This is ideal when driving through a forest where the idea is to see what's around you. Removes the stress from having to operate too many controls, and lets you enjoy the scenery.

How it works:

The overall operating logic of the CrawlSmart is pretty complicated, and I will stick to the basics. Like mentioned above, off-the-road, you always tend to have different μ in all four wheels. The idea of having the best off-road performance sometimes is to optimise & make use of the μ on each wheel to have the best forward acceleration of the car.

In CrawlSmart, the system uses multiple sensors (eg: Wheel Speed, Forward Acceleration, Yaw, axle torque etc) to figure out and demand torque on each wheel and gives ONLY the exact amount of torque and not more to each wheel. This is done through controlled brake interventions and engine torque modulation, effectively redistributing torque between wheels.

The beauty of this system is that if the demand torque based on the surface μ is different for all 4 wheels, the system will optimise the engine torque and brake pressure to achieve variable torque to each of the 4 wheels. This will help each of the wheels to make optimum use of the surface μ to generate forward motion of the car. The system will also try to maintain a constant forward motion based on what the terrain demands by increasing/decreasing the engine torque and the brake torque.

While the idea of the system was to democratise off-roading and enable more and more people to enjoy the beauty of off-roading, on rare occasions, the system even betters where expert drivers fail (eg: sand).

A couple of videos to showcase how the feature works:

• Video 1
• Video 2

P.S - This is a long video with a lot of other content too. Feel free to watch only the relevant part.

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