Hands-On With Joint Modules at the Show: A Few Things Not on the Spec Sheet

I compared Puxi Guangjing's setup—the drive module plus the joint module—against several common integrated joint solutions on the market, and actually ran it through its paces. The thing works, but it's not meant for someone touching a joint for the first time. If you already have a full-machine architecture, write your own comms layer, and know exactly how much torque each joint needs to output, then it saves you hassle. If you want to unbox it and just run it, you'll most likely get stuck at the calibration and comms steps.

A joint module is an integrated actuator unit that stuffs a brushless motor, reducer, encoder, and driver into one housing—basically every movable joint on a humanoid robot needs one. Some reports have broken down the cost, and this thing can account for about half of the body, so if you pick slightly wrong on the module, the whole machine is way off.

Last month at a robotics expo, Puxi Guangjing's booth had a set on display—the grayish-white drive module sitting still on an aluminum profile rack, with a laptop hooked up next to it. I had their engineer jog it on the spot, and I also flipped through a few pages on the host software myself. The interface isn't complicated; once you connect over CAN you can see three curves for position, speed, and current, and you can set the zero position and limits. The engineer demoed a zero calibration for me. Release the brake, manually turn it to the mechanical zero, write it in, then lock it down. The motion was smooth, but that's a sequence he's done dozens of times.

Where I got stuck was two places. First, the CAN message format and error codes—the manual doesn't give enough detail, so on site it basically came down to the engineer explaining it verbally, and I jotted down half a page. Second, current limiting. When I got back I tried it myself with an adjustable DC power supply, and the first power-up tripped the supply into protection—same problem as that post I wrote before about powering up a joint module: current limit wasn't set right, and I didn't follow the proper sequence.

The pleasant surprise was the dual encoder. There's also a reading on the output side; when I back-drive the output shaft by hand I can feel the cogging, but it's not too stiff. This is useful for people doing sim2real, because back-drive characteristics are hard to match in simulation, and a small discrepancy on the real machine gets amplified at the policy layer. Also, the integration is genuinely high—one housing in, and out comes position, speed, and torque, all three controllable, saving me all the wiring of cobbling together a motor plus reducer myself.

The downsides have to be mentioned too. The bundled host software is more of a demo; for data collection you still have to write your own scripts. Metrics like force-control precision can't be felt on a show floor—you'd have to go back and do step responses to look at overshoot and settling time, and I don't have a full test rig here, so I can only give a reserved opinion. I didn't ask in detail about delivery or pricing either, so I won't speculate.

This module suits teams that have already figured out what torque, what comms, and what control cycle they need. It's not suitable as a beginner's teaching aid.