Hobby Plus CR18P Terranaut 8x8 Active AWS

The kind of vehicle the maker sells it as. It sets what the car is built to do and which cars it is fair to compare it with.

• Crawlers are built for slow, controlled climbing over rocks: very low gearing, flexible suspension and locked axles.

A brushed motor carries current through carbon brushes that rub on the commutator.

• It is cheaper and smooth at low speed.
• The brushes wear and the motor loses power over time.
• That low-speed smoothness is why so many crawlers use one.

Ready to run: built at the factory with the electronics installed.

• Some come without a battery or charger; the maker's box contents say which.

The maker's nominal size compared with a full-size vehicle. It works more as a class label than a measurement.

• A 1/10 monster truck is far bigger than a 1/10 touring car, so compare length and weight for real size.

The small gear on the motor shaft. Fewer teeth gear the car shorter: quicker acceleration, lower top speed and a cooler motor. More teeth do the opposite.

• It depends on the motor you fit, so the maker does not list one.

The large gear the pinion drives. A bigger spur with the same pinion gears the car shorter.

• Pinion and spur must have the same pitch, or tooth size, to mesh.

Every reduction after the spur, multiplied together: transmission, transfer case and axle gears.

• That chain is why a crawler's figure is much higher than other classes'.
• It is fixed by the design; the gearing you change is the pinion and spur.
• This is the high range, which sets top speed and is what the calculators load first.

How many times the motor turns for one turn of the wheels. A higher number is shorter gearing: more acceleration and pulling power, less top speed.

• Among 1/18 crawlers & trail trucks in the catalog, the middle half run between 20.4:1 and 38.5:1 on stock gearing; this one is 31.2:1.
• Crawlers run far higher ratios than other classes, so the truck can creep and hold on a climb.
• This is the high range, which sets top speed and is what the calculators load first.

The final drive in low range, where a crawler spends most of its time: slower and stronger, for climbs and fine control.

• It is 4.0 times the high range.
• Switch the calculators to Low to work in this range.

This vehicle has a two-speed transmission: a high range for speed and a low range for crawling.

• A small servo moves the shift fork, so the range changes from a switch on the transmitter, even on the move.
• Both ranges share the pinion and spur.

The outside diameter of the mounted tire, tread to tread. A taller tire covers more ground each turn, which gears the car taller.

• Crawler wheels are named by rim size, such as 1.9 or 2.2 inches; that is the wheel, not this tire diameter.

How far the car moves for one turn of the motor: tire circumference divided by final drive.

• It lets you compare gearing across different tire sizes; more rollout is taller gearing.
• Here it is 6.1 mm.
• This is the high range, which sets top speed and is what the calculators load first.

How far the truck moves for one turn of the motor in low range.

• Here it is 1.5 mm.

What the shocks are and how they are built, as the maker describes them.

• Oil-filled shocks damp with silicone oil; friction shocks, found on some entry-level cars, damp with a sprung plunger and cannot be tuned with oil.

Brushed motors are rated by can size and turns rather than KV, so there is no KV to show.

The highest LiPo cell count the maker rates the electronics for. Each cell is 3.7 V nominal and 4.2 V fully charged.

• 2S is 7.4 V nominal and 8.4 V off the charger.
• Running more cells than this risks the ESC and motor.
• Many cars also run on fewer cells, only slower.

The motor fitted at the factory, as the maker names it.

• Brushed motors are often named by can size, such as 540 or 550, and by turns: fewer turns is faster.

The electronic speed control. It feeds power from the battery to the motor as you work the throttle, and usually powers the receiver and servo too.

• An amp figure in its name is normally the maker's continuous rating.
• A brushed ESC cannot run a brushless motor.
• Crawler ESCs usually have a strong drag brake, which holds the truck still on a slope when you let off the throttle.
• Set its low-voltage cutoff for LiPo, so a pack is not run flat.

The plug on the battery lead. Your battery needs the same plug.

• An adapter works, but it adds resistance and another joint that can work loose.

The size of the stock motor's can, as the maker names it.

• 280 is a standard can size; a larger number is a longer can with more torque.

The current the stock speed control is rated to carry, as the maker states it.

• The continuous figure is what it can carry all run; the burst figure only for moments, such as a launch.
• A motor or pack that pulls more than this risks the ESC.

The stock transmitter, the radio you hold.

• Two channels are steering and throttle; more channels work extras such as a two-speed, lights or a winch.

The stock receiver in the car, which takes the transmitter's signal to the servo and ESC.

• Another transmitter works with it only if it speaks the same protocol.

A brushed motor has no KV rating, so no theoretical top speed is worked out. Compare gearing by rollout instead.

The vehicle's weight as the maker states it.

• The maker does not say whether it includes a battery.
• On a crawler, where the weight sits matters as much as how much: weight low and in the axles helps it climb.