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Mighty Mites

Author Photo
By Glenn Thompson

Radio-controlled trucks and tractors showcase small wonders.

two-engine-lead
by Glenn Thompson
If one gas engine is good, two are better.

The origin of the tractor pull predates the tractor. During the horse-farming era, farmers matched teams of horses against each other. A team would attempt to pull a heavy load a given distance or the horses would pull a sled for a certain distance while additional weights were added as the sled moved along. The weights sometimes consisted of rocks; other times, people stepped onto the sled.

blue-pickup

Image: by Glenn Thompson

Aim for the stars.

Tractor pulls date to the early 20th century. Organized pulls were recorded as early as 1929 in Vaughnsville, Missouri, and Bowling Green, Ohio. Pulls became popular across the country during the 1950s and ’60s. The National Tractor Pullers Assn. was organized in 1969. Today, many state and local organizations sponsor tractor pulls.

As late as the 1970s, pulls involved two classes of tractors: stock and modified. Stock tractors were those placed in competition as issued from the factory, while modified tractors usually had different and larger engines mounted on them. Since then, many types of modifications have been approved.

wheelie-bars

Image: by Glenn Thompson

Wheelie bars are there for a reason.

During the past decade, increasing attention has been paid to lawn and garden tractors. Pulls for these tractors are often held in conjunction with pulls for the larger machines. As with large tractors, lawn and garden tractors have been modified for competition. At a pull, it is not unusual to see a souped-up riding lawn mower or a garden tractor sporting one or two car engines.

In the past 25 years, another class of tractor and trucks has emerged: the radio-controlled model. Pulls for these machines are usually organized by small local groups and are generally unpublicized. Organized in 1987, the National Radio Control Truck Pulling Assn. provides rules and guidelines for pulls (these can be viewed at National Radio Control Truck Pulling Association). The organization also sanctions local, state, regional and national events scheduled by affiliates.

liquid-fuel-radio

Image: by Glenn Thompson0.

A liquid fuel-powered, radio-controlled model.

The National Micro-Mini Tractor Pullers Assn., founded in 1976, publishes detailed information about classes of pulling tractors. These can be viewed at National Micro-Mini Tractor Pullers Association. Both organizations intend to be national or international in scope, but are primarily active in the Midwest and Eastern U.S. Current information about these organizations is available on their Facebook pages.

The evolution of farm toys

The evolution of radio-controlled miniature tractors and trucks for pulling has been somewhat different than that of their larger siblings. When farm tractors were developed during the early 20th century, it wasn’t long before tin and cast iron toy tractors and implements became popular gifts for farm children. Eventually, these early models became collectibles.

Later, die-cast and plastic models added degrees of realism not possible with earlier production techniques. The Ertl Company was the first to produce highly realistic die-cast tractors and implements. This eventually led to production of model tractors for adult collectors that were too expensive and delicate to be children’s toys.

These models were sometimes sponsored by tractor manufacturers. When a farmer purchased a new tractor, the dealer often presented the farmer’s son with a model tractor. Model tractors made in the U.S. are usually produced in standard sizes: 1:64, 1:16 and 1:8, with 1:16 being the most popular. Model tractors produced in Asian countries are often 1:32 scale.

Model airplanes long a popular hobby

Model airplanes have a long history. Many adults today fondly remember long winter evenings of childhood spent assembling balsa wood, tissue paper and glue into small planes that were launched as gliders or powered by twisted rubber bands. A wonderful new hobby emerged with the availability of relatively inexpensive, tiny gasoline engines and that led to shows where model planes are shown and flown, sometimes competitively.

It’s easy to see how that led to the development of the drones used by the military today. Improvements to batteries and development of rechargeable and lithium batteries made it possible to power model planes with small electric motors.

However, many hobbyists prefer to use gasoline engines because they more closely resemble full-size planes. Transistors and other miniature radio components enabled development of sophisticated radio-controlled units, rendering obsolescent free-flight planes and planes whose flights were governed with control lines.

The long history of model cars tends to emulate that of toy tractors. Early tin and cast iron toys led to development of die-cast and plastic models that are very realistic. In many cases, the same companies that produced toy tractors expanded to issue model cars and trucks.

High performance engines and motors now commonplace

lead-weights

Image: by Glenn Thompson

A completed home-built, radio-controlled model. Note the lead weights.

During the 1970s and 1980s, collectors began experimenting with models powered by gasoline engines developed for model airplanes and later with small electric motors. As with model airplanes, specialty companies now provide motors, wheels, axles and radio-control units. Tractors and trucks built to a scale of 1:10 are common; however, machines in other scales such as 1/8, 1/12 and 1/18 are also readily available.

New materials and refined production processes have resulted in small engines and motors with astonishing power-to-weight ratios. The most popular fuel-burning engines are two-stroke glow-plug engines that burn “glow fuel,” a mixture of methanol, nitromethane and oil. Four-stroke engines burning gasoline are also common. Two-stroke engines are cheaper and easier to maintain; four-stroke engines are easier to start, develop more torque at lower rpms, are quieter and have a more realistic sound. Diesel engines and turbine jet engines are also available.

home-built-chassis

Image: by Glenn Thompson

A home-built chassis.

Radio-controlled tractors and trucks powered by DC electric motors have become very popular. Early motors with brushes, gearboxes and heavy nickel-cadmium batteries have been replaced by brushless motors and lithium polymer (LiPoly) batteries, resulting in power units that equal or surpass the performance of fuel-burning piston engines. Two- or four-cell 7.4-volt battery packs are used in many machines. They are compact and lightweight. Special chargers ensure that batteries recharge evenly.

Nitromethane engines at speed sound like angry bees; lithium polymer DC engines sound like power tools.

high-revving

Image: by Glenn Thompson

A high-revving electric motor.

How to start your project

Excellent “off-the-shelf” radio-controlled tractors and trucks are available online and at hobby stores. However, many enthusiasts prefer to build their own models. This allows them to customize their machines and experiment with varied configurations.

The first step in building a tractor or truck for competition is development of a detailed project plan. A Computer-Aided Design (CAD) program is useful. Once the design is finalized, items are acquired and construction begins. Aluminum sheets and tubes are preferred frame materials and are cut and shaped as necessary. The front axle, spindles and tie rods can be purchased ready to be attached to the frame. Some enthusiasts are skilled machinists and construct their own.

A brushed or brushless motor and a controller are attached to the frame, as well as a switch to turn the motor on and off. Although small, the motor develops amazing power from an armature rotating as much as 100,000 rpm. A series of gears are used to reduce speed and increase torque. Transfer cases are available for 4-wheel drive tractors and trucks; however, most machines are 2-wheel drive. Likewise, differentials are available, but the final gear is usually attached directly to a live axle connecting the two rear wheels. The front wheels, transmission gears and rear axle rotate on ball bearings.

Although front- and rear-wheel rims can be purchased ready for use, some hobbyists machine their own from solid aluminum stock. Tires are purchased. The front tires are solid; rear tires are thin and filled with foam before being pressed unto the rims. Rear tires usually have lugs. Rear tire traction can be increased by grinding down the back half of each lug with a Dremel tool and cupping it so that the leading edge is sharper and rests evenly on the track when under pressure. Rear tires spin rapidly during a pull and must be replaced occasionally.

servomotor-steering

Image: by Glenn Thompson

The servomotor for the steering mechanism.

Tie rods are attached to a servomotor, as is the motor controller. These are connected to a receiver that receives signals from a hand-held remote control. The remote control can operate on as few as two FM circuits: one for steering and the other to control speed. Remote controls with additional circuits are available to control tractors and trucks with other functions, such as reverse and lights. To avoid interference, each person competing at a pull has unique FM frequencies. A bind plug is inserted briefly into a connector at the beginning of each pull to lock in the frequencies. A hand-held radio control unit can govern the actions of a tractor or truck as far as 300 feet away.

motor-controller

Image: by Glenn Thompson

The controller for the motor.

Plastic bodies can be constructed by the builder or purchased ready to be attached to the frame, often with a hook-and-eye fastener for easy removal. Many styles are available and they are usually customized by the purchasers.

Multiple lead suitcase weights are usually attached at various points on the tractor or truck to increase traction and reduce the tendency of the machine to rear up during a pull. Some machines also have “wheelie bars” attached to the back to limit the degree to which the machine can rear up and reduce the likelihood of it tipping over backward.

tire-lugs

Image: by Glenn Thompson

The second set of step-down gears. Note how the lugs on the tire have been ground down and cupped to improve traction.

The pull sled is usually a miniature version of those used at pulls with regular tractors. A weight supported by the wheels is gradually moved forward by a chain drive. As it moves forward, it increases the weight resting on a steel plate sitting on the track. Additional weight on the plate increases the friction between the plate and the track and adds to the difficulty of pulling the sled. The pull track is usually 40 feet long and 4 feet wide. A mixture of clay and sand is carefully raked to eliminate pebbles that can become projectiles during a pull.

Self-taught machinist rises to new challenge

Two state-wide organizations sponsor radio-controlled tractor and truck pulls in Texas: The Lone Star State R/C Truck & Tractor Pulling Assn. and the Texas Truck & Tractor Radio-Control Pullers. Small local groups hold occasional competitions. One of these consists of six or seven friends in the Texas Hill Country who gather when time and weather permit. Two of these individuals have constructed 30-foot pull tracks at their homes. The group has its own printed rules establishing limits for weight, length, type of tires, height of hitch and battery size.

rc-tractor

Image: by Glenn Thompson

An RC tractor with a home-built body. Note the wheelie bars, which limit the degree to which the machine can rear up.

Allen Becker is a member of the Texas Hill Country pull group. A life-long resident of Boerne, Texas, he has run a small engine repair service for more than half a century. Allen has always had an interest and talent for making and repairing things. He is a self-taught machinist and is justifiably proud of his scratch-built miniature gas and steam engines. When he joined the local radio-controlled pull group a few years back, he saw it as a way to test his skills and immediately began building his first radio-controlled model. He now has three. Allen is not highly competitive; his greatest pleasure lies in building his machines and watching them work.

becker-rc-models

Image: by Glenn Thompson

Allen Becker and two of his RC models.

While some might say that competing in a radio-controlled tractor or truck pull lacks the thrill of actually sitting on the machine, others would counter with the reduced cost and ease with which the machines can be transported. However, whether competing with a full-size tractor, a garden tractor, or a radio-controlled model, the adrenaline flow and the thrill of winning are the same, as is the pleasure of associating with friends at a pull. FC


Glenn Thompson, professor emeritus from the Wisconsin University System, was born and raised on a farm in South Dakota. In addition to other pursuits at his home in Texas, Glenn rides herd over “an eclectic collection of dead and dying riding mowers and compact tractors.” Email him at uffda@beecreek.net.

Published on Dec 2, 2020
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