Spline Thieving Makes Hobby Servos Even More Useful

For years the proprietary spline pattern of rc servos has been a dealbreaker for hobbyists who want to add custom shafts and gears to their servos. First, different servo sizes have different spline sizes, and each vendor equips their servos with different patterns. True, some special vendors sell custom gears that mate to these patterns, but, overall, the hard-to-replicate pattern has severely limited the output options for servos.

This pattern didn’t deter [JB], however. With some clever CAD skills, and two working implementations, he’s demonstrated that these spline patterns can be (1) harvested and (2) added into custom components, opening a new suite of design opportunities involving servos.

To capture the spline, [JB] imports an image into Solidworks, and traces the pattern on a properly scaled image. From there, he can embed this pattern directly into a physical model for fabrication.

To make parts that preserve this pattern, [JB] has two options. With his FormLabs printer, he can print components that already have the pattern feature, allowing him to press-fit custom links directly onto servos. Alternatively, for a sturdier component, he presents the milling method. With this technique, he drills a circle of bolt holes onto the desired output shaft and then mills out the center. From here, the shaft can also be directly pressed onto the servo spline where each spline groove fits snugly into the edge of the previously-drilled holes.

So, how well do they work? According to [JB] he’s actually managed to do some damage to himself before damaging to the 3D-printed part while trying to strip the pattern. The end-goal is to insert these¬†shafts into transmissions for a miniature combat robot, another one of [JB’s] projects which is well-underway. Until then, we’re looking forward to seeing more servos tightly-integrated into upcoming projects.

Build a ROBONOVA-I


On the latest episode of Systm, they talk to [David Calkins], founder of the RoboGames competition, about humanoid robotics. The robots featured in the episode are Hitec’s ROBONOVA-I. The ROBONOVA is about a foot high and has 16 servos with support for up to 24, all connected to an Atmel controller. The episode is quite long: At around 15 minutes, they demonstrate the programming enviroment. You can program it traditionally or pose the bot to work out the motions. At 30 minutes, [David] mentions that next year’s competition will allow airsoft weapons to be attached, but bots have to be controlled from a first person perspective. If you’re interested in one of these kits, they have a ROBONOVA special of $900 or as low as $500 for educational institutions (that’s us, right?). Now is the perfect time to get one since you’ll have nearly a full year to prepare for RoboGames.

Related: You’ll hear builder [Matt Bauer]’s name mentioned several times.

[via BotJunkie]