MightyCog has eleven free remote-control Technic-style builds, and they turn in three different ways: a servo steering the front wheels, one motor per side (skid steering), or a single front wheel that swings on a turntable. The best first RC build is the First RC Car (Servo): one M motor drives, one servo steers and channel A and channel B of the remote control them, in about 50 minutes. If you would rather spin on the spot, start with the RC Tank instead.
Every model below uses an IR receiver and an IR remote, has an animated step-by-step guide and a free printable booklet. They are all in the Remote control builds collection.
The eleven RC builds at a glance
| Build | Level | Minutes | How it turns |
|---|---|---|---|
| First RC Car (Servo) | 4 | 50 | Servo turns a steering rack |
| Front-Drive Servo Trike | 4 | 50 | Servo swings the whole front wheel |
| Floor Express | 4 | 40 | No steering: a train that drives forwards and back |
| Diff-Lock Mud Truck | 4 | 60 | Off-road truck with a differential lock |
| RC Tank | 4 | 60 | Skid steering, one motor per track |
| Skid-Steer Loader | 4 | 65 | Skid steering, one motor per side |
| Robot Arm with Servo Claw | 4 | 60 | Turns on a turntable; the servo works the claw |
| RC Racer | 5 | 75 | Servo and rack, differential at the back |
| Independent Rally Car | 5 | 90 | Servo and rack with Ackermann arms |
| AWD with Central Diff | 5 | 90 | Servo turns the front axle on a turntable |
| Twin-Motor Dozer | 5 | 100 | Skid steering, one motor per track |
Way 1: a servo steers the front wheels
A servo is a motor that does not spin round and round. It turns to the position the remote asks for and holds it, like your hands on a steering wheel. In the First RC Car and the RC Racer, the servo turns a small pinion on a steering rack, and the rack pushes the front wheels left or right. That is rack-and-pinion steering, the same as on the hand-steered Go-Kart, only now the remote does the turning.
The Independent Rally Car adds one more idea. Its steering arms are angled so that the inside wheel turns more than the outside one. That is Ackermann steering: in a turn, the inside wheel rides a smaller circle, so it needs a sharper angle.
The AWD with Central Diff steers a different way: its whole front axle swings on a turntable, with the servo standing on top.
Way 2: one motor per side
The RC Tank, the Skid-Steer Loader and the Twin-Motor Dozer have no steering at all. Each side has its own motor: an M motor on one side and an L motor on the other. Both forwards and it drives straight; one forwards and one backwards and it spins round on the spot, skidding its tyres or tracks. On the loader, a row of three gears on each side links the front and back wheels so they always turn together.
Skid steering is simple to build and can turn in its own length, but it scrubs the tyres sideways in every turn. Read Tracks vs wheels to see when that is worth it.
Way 3: the front wheel swings
The Front-Drive Servo Trike works like a forklift. The front wheel hangs in a fork with its own M motor, driven through two 40-tooth gears. The servo stands on a turntable on top of the fork and swings the whole fork, wheel and motor together. It can almost turn on the spot.
Compare the turning circles
How tight can a servo-steered car turn? It depends on the wheelbase (front axle to back axle), the track (left wheel to right wheel) and how far the wheels can turn. Change them below, compare Ackermann with parallel steering, and see whether your car fits a U-turn in a 60-stud street. A skid-steer model is the extreme case: it turns round its own middle.
Interactive: Turning circle and Ackermann calculator. Change a car’s wheelbase, track and steering angle and see, from above, the turning-circle diameter of the outer front wheel and the ideal inner and outer wheel angles. Compare Ackermann with parallel steering and fit U-turns into a 60-stud street.
Which one should you build?
- First RC model: the First RC Car (Servo). One drive motor, one servo, one receiver.
- You love diggers and tanks: the RC Tank, then the Skid-Steer Loader.
- You want a "real" RC car: the RC Racer puts drive, differential and steering together.
- Big weekend project: the Independent Rally Car or the Twin-Motor Dozer, both level 5 and 90 minutes or more.
- Something that isn't a car: the Floor Express train or the Robot Arm with Servo Claw.
Before your first RC build, it helps to have wired a simple motor: see First motor build. If two models answer the same remote, One remote, several models shows how to give each its own channel, and How does an RC car steer? follows the servo signal step by step. For every motorized model, not only RC, see Motorized Technic-style builds.
Interactive: Check yourself. A few quick questions on the ideas in this guide, each with an explanation.
- How does the RC Tank turn without any steering?
- What is special about a servo motor compared with an M or L motor?
- In a turn, why does the inside front wheel of the Independent Rally Car turn more than the outside one?
- Which is the best first remote-control build?
