OpenDog Version 3 Is Ready To Go Walkies

We've been following [James Bruton]'s open dog project for a little while now, and with his considerable pace of work - pandemic or no pandemic - development has been incredibly rapid. The latest milestone is the public release of version 3 (Video, embedded below.) This upgrade to the system adds 3D printed cycloidal gearboxes, removing the previous belt drives. [James] had immense fun tuning the motor controller parameters for these and admits they're not completely dialed in yet. He notes that the wider gearbox body means that the robots geometry needed to change a little, and the previous belt-drive version may have a bit of an edge, but he's confident he can make it work (and given his incredible previous robotics builds, we totally believe he'll nail it!)

Silicone overmolding around a 3D printed former, using a 3D printed mould

Older versions struggled with slippery plastic feet; the advantage of a predictably smooth contact shape of a rounded foot is somewhat offset by the limited contact patch size, and that means not so much grip on some surfaces. [James] solution was obvious enough - just learn how to make 3D printed silicone moulds and cast a nice rubber foot around a plastic former, and problem solved! Unfortunately he neglected to add some recesses for a lever to get in between the mould halves, so it was a bit of a struggle to separate after curing. A beginner's mistake that won't be repeated, we're sure.

Full source for openDogV3 is now available on the GitHub page. Here's the playlist for the whole project, as well as direct links for the cycloidal drive development (part1, part2, part3.) But before you all go diving in to start 3D printing your own pooch, [James] tells us that the total cost would be around $2000 all in, with the bulk of that being the motors and ODrive units, so this one for the serious builder only!

We've covered robot dogs a fair bit, a particularly nice example is The Dizzy Wolf, and if you're wondering just why on earth you'd want a robot dog, then Ask Hackaday has you covered as well.

#robotshacks #3dprinting #cycloidalgearbox #jamesbruton #opendog #robotics

Bungee And Cam Assisted Actuator For OpenDog

One of the challenges of many walking robot designs is the fact that they draw current just to stay upright. This was exactly the case for one [James Bruton]'s quadruped robots, where the knee motors were getting too hot to touch. Adding springs to take some of the load is not as simple it might seem, so [James] created a bungee assisted cam mechanism to do the job.

For a normal spring-loaded lever, force is proportional to how much the spring is stretched, which will require the actuators to draw more and more current as it lifts the leg higher. For the spring force to remain constant throughout the range of motion, the length of the lever arm must become continuously shorter as the knee is bent. [James] did this by stretching a bungee cord around a cam. The added bulk of the cam does however cause the knees to knock into each other in some scenarios, but [James] plans to adjust the robot's gait to avoid this. He didn't get around to actually measuring the current draw reduction, but the motor temperature has dropped significantly, only being slightly warm after a test run.

These tests were done with OpenDog V2, but [James] is already working on the design of V3, which will use 3D printed cycloidal gearboxes. At the moment, that build is still being delayed thanks to the global component shortage.

#robotshacks #bungeecord #jamesbruton #opendog #robotactuator