#video by #Harrison-Low on his jugglebot triumph. He finally switched from kevlar kite string to #UHMWPE for the linear actuators. Also he switched to #ODrive Pro electronics to control the motors. Featuring a #JLCPCB #3D-printing ad, sigh. Oh, also he burned out the hand motor because a sensor cable came unplugged. #robotics
on 02026-08-18#Harrison-Low’s Zulip site for his #robotics work #toread
on 02026-08-18#Harrison-Low #video about how his #Stewart-platform juggling robot finally can juggle, two balls anyway. He actually did switch from kevlar to #UHMWPE (Dyneema) which I thought wouldn’t handle the friction heat. He shows the pseudo-capstan “hand” #mechanisms that actually throw the juggling ball. Oh, and he's using Zulip instead of Discord to make it more open. #robotics
on 02024-09-15#Harrison-Low #video #toread about redesigning #robotics joint #mechanisms
on 02024-09-15#Harrison-Low #video about eliminating knotted string from his #robotics #mechanisms by wrapping his kevlar threads around screws and then squishing it under the screw heads by tightening them. Maybe he should have just used a trucker’s hitch?
on 02024-09-15#video about improved high-speed linear actuator #mechanisms design using carbon fiber for #Harrison-Low's juggling robot. Now his motor is in the linear actuator itself, and its shaft has two reels on it, one to let out string (kevlar kite string?) and one to take it up, or vice versa when moving the other direction. He’s also added TPU sleeves to the six bearings he was using as rollers to constrain the shaft’s motion to one degree of freedom. I think it's about 500mm of stroke. He’s able to get 3.4m/s and >50k cycles endurance. The theoretical precision is 8.4μm, which is more precise than his ±20μm Mitutoyo calipers, but with a pulley mechanism he got a standard deviation of 57μm, which is pretty good. The string breaks at about 70 or 80 newtons. #robotics
on 02024-04-28#Harrison-Low #video about a #mechanical linear actuator design for a juggling robot, capable of a full 263mm stroke in 100ms. He’s mostly using carbon-fiber reinforced plastic tubes, with six 6001RS cartridge bearings for rollers (one too many for #exact-constraint), held in place by a piece made by #3D-printing, with interchangeable spacers to adjust the fit in 100μm units to the imprecisely-sized tubes. He’s doing the actual actuation with a kevlar-kite-string cable drive, with the cables actually run through teflon Bowden tubes so the motors don’t have to add mass to the actuator joints; the motor pulley has two V grooves for the two ends of the cable. This seems like a good way to do robotic #mechanisms in general. This replaces his first hydraulic design made out of syringes and a second iteration using a ballscrew which was too slow and (I assume) also super expensive. He has an AS5048 magnetic encoder for positional measurement, coupled to the actual moving parts with a constant-force spring, whose rotation is what it measures, but so far he’s just using encoders on the motors themselves (which I guess are brushless since he’s using #ODrive; in fact, the motors are ODrive-branded, model D6374-150KV). He says ODrive's current sensing “completely removes” the need for limit switches. His attempts to clamp the three frame tubes with a flexure from the inside failed, but I don’t know why he doesn’t clamp them with a flexure on the outside, instead relying on hammering them in. He uses a thin wire with a hook bent on the end as fish tape to pull the kevlar string through the teflon Bowden tubes, but doesn’t always need it because of how stiff the kevlar string is. On one occasion the kevlar string was able to friction on the 3-D printed plastic and just cut right through it, presumably from heat (a big advantage for kevlar over UHMWPE, except when you want to cut it; presumably kevlar will creep less for the same reason). #robotics
on 02024-04-28