Plane Crazy mech arms rely on a combination of motor-driven shoulder pivots, elbow joints, and articulated wrists to achieve natural motion and combat poses. In the Roblox physics sandbox developed by Plane Crazy Developers, mechanical joints must balance freedom of movement against block collision to prevent the limb from locking up. Choosing between a single elbow or a double-jointed assembly determines whether your mech can bend past 90 degrees once outer armor plating is applied.
Single-Joint vs. Double-Jointed Mech Elbows
Builders in Plane Crazy typically implement one of two primary elbow configurations depending on how much articulation and exterior plating the build requires.
| Joint Configuration | Bending Range | Motor Setup | Armor Clearance | Best Use Case |
|---|---|---|---|---|
| Single-Joint Elbow | Up to 90 degrees | Single motor | Restricted once armored | Simple, lightweight mechs |
| Double-Jointed Elbow | Past 90 degrees | Dual motors (alternating controls) | High clearance around bulky armor | Advanced, heavily armored builds |
A single-joint elbow uses a standard motor to handle arm flexion. While simple to wire, adding armor blocks around the forearm and bicep quickly restricts its motion, capping its practical bend around a right angle.
A double-jointed elbow incorporates two motors placed in sequence along the elbow frame. This design bends past 90 degrees even after the arm is layered with protective plating. When configuring a double-jointed elbow, the motor controls must be inverted or switched relative to one another. Alternating the keybinds ensures that both motors pivot in tandem rather than fighting each other or tearing the joint apart during activation.
Essential Blocks and Clearance for Arm Joints
Physics jamming is the most common issue when constructing articulating limbs in Plane Crazy. If standard solid blocks sit directly adjacent to a rotational axis, the surfaces will weld or collide, freezing the arm completely.
- Cutters and Cylinders: Place a cutter block or a cylinder inside the pivot gap. These parts provide clearance for the rotating axis without catching neighboring geometry.
- Wedge Assemblies: Build the joint casing using half blocks, standard blocks, wedges, and half wedges down. Wedges create angled negative space that allows the forearm to fold inward without physical clipping.
- Text Signs for Low Friction: Standard solid signs often catch on adjacent surfaces. In tight joint housings, particularly those utilizing compressors or motor locking, using regular text signs helps avoid collision problems because they do not carry heavy collision hitboxes.
- Motor Lock Settings: While unpowered or unlocked joints can yield loose swinging motion, locking the elbow motors is often preferred on complex builds. Locking helps stabilize the assembly against server lag and physics glitches that can cause loose joints to vibrate out of alignment.
Shoulder Swivels and Wrist Articulation
Functional mech arms require multiple axes of movement beyond simple elbow flexion. A full arm assembly connects to the torso via shoulder mounts that dictate overall arm spread.
Spacing the shoulders slightly outward gives the central torso assembly room to house cockpit equipment, compressors, or internal mechanics. The shoulder base requires a swivel motor configured for up-and-down elevation, allowing the arm to raise forward or aim mounted equipment.
At the end of the forearm, an articulated wrist provides two axes of movement: vertical pitch (up and down) and horizontal yaw (side to side). Structuring the wrist with compact blocks gives hands or weapon mounts independent aiming capability. As demonstrated in community combat builds like the Striker Eureka Jaeger showcase, articulated arms can be mapped to swing forward to mimic melee punches and blade strikes. However, builders must ensure weapon components—such as forearm sting blades or integrated cannons—do not overcrowd the surrounding housing, or the arm will lose its ability to clear the torso during swings.
Sizing and Proportioning Mech Arms
Proper limb proportions prevent a mech from looking like a rigid block and keep the arms from clipping into the terrain during a walking cycle.
- Torso Taper: Treat the upper and lower torso as an inverted triangle, moving from a wider shoulder span down to a narrower waist. This provides a wide platform for arm mounts while leaving hip clearance below.
- Arm Length Target: As a general rule of thumb, mech arms should hang down to the mid-thigh or lower-thigh region.
- Knee Clearance: On a standard humanoid frame where the thigh measures roughly seven blocks down, the arm tips should end four to five blocks above the knee joint.
The exact block count of the bicep and forearm can be adjusted to fit your specific build aesthetic. However, keeping the wrists above the lower leg ensures that ground-level steps or split-leg walking motors do not drag the arms across the plot floor.
Frequently Asked Questions
Why does my mech arm freeze when I activate the elbow motor?
Mech arms usually freeze because adjacent blocks are colliding or auto-welding together. Replace solid blocks directly touching the motor pivot with cylinders or cutter blocks, and carve out space along the inner elbow using wedges and half wedges.
How do I configure keybinds for a double-jointed elbow?
Set the two motors to share the same forward and reverse functions, but reverse the control inputs on one of the motors. This alternating setup allows both segments of the joint to fold inward together naturally instead of rotating in opposing directions.
Should I lock or unlock my mech arm motors?
Locking the motors is generally recommended for detailed or heavy mechs. Unlocked motors allow the arms to swing passively, but server lag and heavy armor blocks often cause unlocked joints to sag, wobble, or glitch out during movement.
