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Kai Ploeger

@kaiploeger.bsky.social

Somewhere deep down the wonderful rabbit hole of robot juggling and dynamic manipulation 🤹 🤖 PhD student @ IAS Lab, TU Darmstadt

Posts Replies Media

Kai Ploeger @kaiploeger.bsky.social · 07/07/2026

A prior on how to adapt is much more forgiving than a prior on what the optimal policy is. A simplified Newtonian model may struggle to predict exactly how to throw a ball, but it is very useful for deciding how to adjust the aim.

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Kai Ploeger @kaiploeger.bsky.social · 07/07/2026

How accurate does a model-based prior over search directions have to be? We rotated the analytic Jacobian prior to test this. At 90°, it fails as expected. But surprisingly, up to 30° the learning speed is barely affected, and final performance stays unchanged even up to 45°.

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Kai Ploeger @kaiploeger.bsky.social · 02/07/2026

Paper and videos: kai-ploeger.com/residual-juggling

kai-ploeger.com

Task-Error Residual Learning for Real-Robot Five-Ball Juggling

Stable three-, four-, and five-ball juggling from the second attempt, via directional task-error residual learning.

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Kai Ploeger @kaiploeger.bsky.social · 02/07/2026

The only method that came close is a far heavier composite Bayesian-optimization scheme, and it shares exactly those two ingredients. Same formulation, much more machinery.

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Kai Ploeger @kaiploeger.bsky.social · 02/07/2026

The pattern underneath: Keep the direction of the error instead of collapsing it to a scalar, and guide exploration with an analytic prior pointing roughly in the correct direction.

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Kai Ploeger @kaiploeger.bsky.social · 02/07/2026

We tried a whole zoo of ways to learn five-ball juggling throw corrections. The simplest thing on the board came out on top.

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Kai Ploeger @kaiploeger.bsky.social · 30/06/2026

Break this rule on purpose, enter the beautiful world of siteswap juggling, as my former student Mario Gomez Andreu did. His bachelor's thesis on it became an IROS paper, with mesmerizing videos: kai-ploeger.com/beyond-casca...

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Kai Ploeger @kaiploeger.bsky.social · 30/06/2026

Fun fact: Patterns with odd and even ball counts are juggled differently. Odd counts cross from hand to hand (the cascade), even counts stay on their own side (the fountain). This is the simplest way to keep two balls out of the same place at the same time.

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Kai Ploeger @kaiploeger.bsky.social · 30/06/2026

The progression. Three balls on the first attempt, four and five by the second.

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Kai Ploeger @kaiploeger.bsky.social · 24/06/2026

It runs on a deliberately simple stack: soft PD control, idealized ballistics, no visual perception in the control loop. A task-level residual absorbs the rest.

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Kai Ploeger @kaiploeger.bsky.social · 24/06/2026

Learning five-ball juggling on the second attempt, with two Barrett WAMs. Most humans take years of practice. Paper and videos: kai-ploeger.com/residual-juggling #robotics #juggling

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