Here's the advantages that crawler trucks have over other 4WD trucks:
*** WHAT IS RC ROCK CRAWLING? ***
RC rock crawling isn’t a fast-paced sport. It's not about speed but it is about power and maneuverability -- navigating obstacles and extremely uneven, rocky surfaces that many other RCs can't handle. While some RC monster trucks and truggies can handle rough terrain, a specialized class of RC -- rock crawlers -- are designed to perform even better on the rocks.
RC Rock Crawler Characteristics
Although you don't necessarily need a specialized vehicle -- stock RC monster trucks can handle some casual rock climbing -- more and more specialized RCs are available. There are also a few features that are common to most RCs used for rock climbing whether they come that way out of the box or the features are added when modifying monster trucks or other RCs for rock crawling fun. This list is not intended to be a comprehensive look at RC rock crawlers but it does introduce a few key characteristics.
For rock crawling you want more controlled power (torque) rather than high speed and high RPMs. Rock crawlers can use stock electric motors and lower gear setups that deliver steady power at low speeds to help get up and over those rocks.
High Clearance / Low Center of Gravity.
. You don't want your chassis dragging over the rocks but you also don't want an RC that's going to tip over when climbing a steep rock hill. The large tires on a rock crawler help provide the necessary ground clearance. When you raise that vehicle up high you could end up with an RC that tips over too easily so you'll want to balance clearance with a low center of gravity. And you'll want to be sure the weight is not all in the rear where it can pull the RC back and not allow it to climb as well. Putting things like the battery to the front instead of the rear can help with weight distribution.
. Rock climbing has uneven surfaces and involves a lot of twisting and turning so rock climbers need good soft not stiff suspension and steering. Most rock climbers will have 4-wheel drive and many have 4-wheel steering as well.
Abbreviated 4WS, 4-wheel steering has been around in the RC hobby since at least the 1980’s (that I know of). It means that all 4 wheels have the ability to control what direction the vehicle turns. If you were to look at the vehicle standing over it looking down and turn the front wheels to the left the back wheels would be facing right. With the right 4WS setup you can also do side stepping or crab walking where all four wheels turn in the same direction.
What 4WS means for RC rock crawlers is a better ability to maneuver in small areas, get over the uneven surfaces, and have better traction. One of my favorite RCs growing up was the Tamiya Clod Buster monster truck which was equipped with 4-wheel steering. Not all RC rock climbers have 4WS but it is a common feature and a common upgrade.
Unlike other types of RC driving, with RC rock crawlers you'll also want locked differentials. Not all wheels are in contact with the ground or rocks at all times. If not locked, the differentials may send power to the wheels that are off the ground rather than the ones that need the power to get over the rock.
The term "dig" comes from the fact that if only 1 set of tires are spinning (front or rear); they tend to dig a hole in the dirt. If only the front tires are spinning, it is called a front dig. If only the rear tires are spinning, it is called rear dig. Sometimes it is advantageous for the unpowered axle to be locked and dragged by the powered axle. This is called locked dig. Other times, the unpowered axle is left to spin freely. This is called unlocked dig. Read on to see which is best to use in particular situations.
the most popular use of dig is the locked dig. Most RC crawlers with three channel radios only have a two position switch for the third channel, and locked dig is what most crawlers commonly set their rigs up for. There are three situations for which to use locked dig.
The most commonly used locked dig is the turn. Locking the rear axle and steering the front wheels to full lock will allow the crawler to pivot. Almost a perfect rotation can be achieved. Making a sharp pivot-like turn allows a driver to reduce the amount of reverses needed to line up for a gate. Each back-up costs a driver one point. Those points can quickly add up. This feature alone is worth installing dig in your crawler, as competitions are often won by just a few points.
The use of locked dig is during steep descents and drop offs. Locking the rear allows a crawler to slow a descent by dragging its rear down a steep slope. Slower is often better in crawling as it allows the tires to maintain traction instead of bouncing down the grade, risking a flip or rollover which will cost the driver five points. You need to be ready to throttle out if the rear loses grip and tries to swap ends with the front.
This is locking the rear when getting ready to attempt a steep climb. Doing this allows the front tires to bite harder and wrap up on the wheels. Then it quickly pops back into four wheel drive and uses the resulting spring to give him a little boost up a difficult slope.
2 Styles of DIG System
There are two types of dig systems that are employed by RC crawlers. One is an electrical system used in crawlers that have motor driven axles such as the classic Clod Buster axles or the new Berg axles. Since these axles are motor driven, they do not have a center transmission or drive shafts tying the two together. Since no driveshaft needs to be disengaged, dig is achieved by using either a pair of separate ESCs for each axle or a switch system that cuts power to one of the motors. Mixing with a stick radio allows for use of both front and rear digs, but a pistol grip radio such as the Spektrum DX3R may also be used.
The other dig system is a mechanical type that relies on a servo to engage and disengage the drive shafts and lock the axles. This is the most popular at the moment as most completion 2.2 crawlers are shaft driven. Most of the mechanical dig systems in this article were designed to be used in the Axial AX10 (front dig only) and the Losi Competition Crawler (front & rear dig), but can also be used in other crawlers with a bit of imagination.
Narrower off-road tires and rims are common on rock crawlers. A narrower rim puts more tread on the sidewall and gives rock crawlers better traction all-around because the tires aren't running on a nice, smooth surface like you find on RC tracks -- on-road or off-road. Rock crawler tires typically have deep, chunky treads and are fairly soft. Although you can glue tires and rims, some rock crawlers like to use bead-lock rims. One of the advantages is that the tire doesn't separate from the rim easily when subjected to the stress of rock crawling.
More than you ever wanted to know, eh?