Robak 2 Suspension Upgrade

Update 04.10.2025: Some people who tried this upgrade found the original arms a bit thin with certain materials, so I’ve uploaded a strengthened version. Both versions are interchangeable. Lower arms are now 6 mm (were 4 mm), and upper arms 5 mm (were 4 mm). 📷 Image redacted — claim this model to add your own media Motivation: Robak 2 has been around for over two years now. During that time, I released two upgrades, v2.1 and v2.2, focused mainly on making the car more durable and reliable. Now, I can take the Robak out without worrying about it failing unless there's a crash. With its high-speed potential, I've been pushing the Robak faster and faster. While measuring the top speed, I noticed some stability issues. On rough terrain with roots, the car jumped, causing the wheels to lose contact, resulting in zero traction and poor handling. Entering corners at high speeds is tough due to the car’s high center of gravity (CoG) and low roll center, making it want to flip- something you don’t see in commercial RC cars. Clearly, something wasn't right. It’s a shame to have such a fast car that handles like an old school bus. This is the first step towards making the Robak 2 more fun to drive by improving its racing capabilities. This is achieved by redesigning the suspension geometry. Plus, the notorious steering block, often the weakest part, has been upgraded in this suspension mod package, hopefully making it last longer. Even if you’re just into bashing, good handling makes it more fun and helps avoid unnecessary crashes. Better handling also improves your driving skills. There’s much more room for improvement in handling than in bashing, where we’re nearing the drivetrain's limits. Reinforcing structural parts shifts the breaking point from cheap 3D-printed parts to more expensive drivetrain components. Changes Introduced by the New Suspension Parts: Raised Roll Center : This reduces the chance of flipping in corners. Adding an anti-roll bar could do the same but would complicate the design and require new hardware. Changing the geometry to raise the roll center was a simpler fix. 2-Degree Negative Camber : Both front and rear wheels now have a 2-degree negative camber, which increases as the suspension compresses, ensuring better contact between the tire and the surface in corners. This required changing the arm lengths so that the upper arms are shorter than the lower arms. You can adjust the camber settings by changing the upper arm length. Reinforced Steering Block : Now made of two pieces, with the arm printed separately for optimal layer orientation during printing. This allows for quick Ackerman steering geometry adjustments. Roll Center Location The roll center in a car's suspension is the point where two roll center lines intersect. A roll center line is the extension from the tire contact point with the ground to the instant center. The instant center is the point where two imaginary lines, which are extensions of the suspension arms, intersect on the opposite side. 📷 Image redacted — claim this model to add your own media Before (v2.2): 📷 Image redacted — claim this model to add your own media After: 📷 Image redacted — claim this model to add your own media A shorter Roll Moment Arm means a lower moment that wants to flip the car over in corners. General Advice: Print accuracy: Ensure the arms move freely without too much resistance, as the suspension performance depends on it. Tune your printer or correct the holes in the arms and/or hubs with a 3mm or 3.15mm drill bit. Lightweight Wheels : Small SCT wheels can be ~50% lighter than off-road/monster truck wheels. This drastically improves suspension performance, reduces overall weight, and lowers the center of gravity. With lower inertia, the drivetrain handles frequent starts/stops better, allowing quicker acceleration compared to monster truck wheels. However, smaller wheels reduce ride height and top speed. Lighter wheels can actually make you faster off-road because with less unsprung mass, the suspension stays more responsive and maintains traction better than with heavier wheels, which can cause jumping and traction loss. Suspension Droop : Set the suspension droop so the shocks are at 1/3 of their travel distance when the car is at rest (Lower Arms parallel to the ground). This allows the suspension to extend over dips and compress over bumps. Stock Injora spring rates should work fine with the classic Robak setup. If the car struggles to stand or requires maximum spring preload, you likely have suspension binding. Remove the shocks and eliminate any friction, ensuring arms move freely. Arm Design : The arms are thin by design, intended to break first during crashes to protect the drivetrain. If they break during casual driving, optimize your print settings in the slicer. I’ve tested them extensively, and they withstand jumps well, even with basic materials. It’s better to reprint a lightweight arm than replace a bent halfshaft or broken chassis. I rely on your feedback- if many report the arms are too weak, I will improve the design. HSP 102011 Steering Block: If you would like to use new front hub carriers with metal steering blocks, you will need to ensure the holding screw moves freely in the hub carrier. To do this, increase the hole size with a 3mm drill bit and use threadlocker to fix the screw to the steering block. Fasteners: Upper Arms8x M3x25mm DIN 912; ISO 47628x M3 Nylon-Insert Locknuts DIN 985; ISO 10511Lower Arms Hinge Caps4x M2.5x5mm DIN 912; ISO 4762Steering Arm to Block2x M2.5x12mm DIN 912; ISO 4762 Note for v2.1 Robak Drivers: Robak v2.2 introduced a 2-degree toe-in on the rear axle, which is carried over to this design, improving straight-line stability. You can upgrade directly from v2.1 to this new version. Credit for the wheel model used in my design goes to Phil Maddox. You can find it here: RC 1/10th scale Buggy Wheel & Tyre . Huge thanks for the fantastic model! 📷 Image redacted — claim this model to add your own media 📷 Image redacted — claim this model to add your own media 📷 Image redacted — claim this model to add your own media