One of Dash's most important parts is the powertrain, which reaches from his battery to his legs. What we usually mean when we talk about the powertrain though, is the motor and transmission. We have 3 main goals for Dash's powertrain:
- Deliver power effectively from the motor to the legs
- Be easy to assemble (this is a kit after all!)
- Have the proper stiffness for power transfer
Delivering power effectively is largely a function of the motor choice, gear ratio, and stiffness of all the elements, but today we're going to focus on goal 2, and ease of assembly. We could build the best powertrain in the world, but if no one can put it together, it's not much use.
Andrew and I troubleshoot gearbox design
The first major component is the motor, which we source from a supplier. We use a coreless, brushed DC motor. These aren't as powerful as a brushless motor, but they're far less expensive and easier to control.
Our sample motors, each of which we need to test to find the one that fits Dash best
The transmission is a custom piece that we design and build ourselves. It consists of gears that are sourced from a supplier, and a 3-D printed housing. The housing has gone through a few iterations recently, to support the goal of easy assembly. Our original design was very straightforward, with two separate housings for each motor, each of which also held the rear of the opposite motor. This housing is very light and simple, but difficult to assemble when integrated with the whole robot.
One way that would make assembly easier, would be if the housing were a single piece. This would eliminate any fiddling with lining up the motors. A design that never made it out of the digital realm was quickly drawn up:
However, this would be difficult to integrate with the cardboard structure. The cardboard has to fit in or around the transmission, and glue does not bond the two well, some physical lock is needed. Hence, the current design, with slots cut down the transmission for the cardboard to fit into.
The whole thing fits into an assembly, which carries the motors, gears, and an output bushing to connect to Dash's hips and legs.
The powertrain is much easier to assemble now, though it may receive a few tweaks in the coming weeks still. The next goal for this component is to make sure we're using the very best motors and gear ratios so that Dash can run fast, maneuver around obstacles, and more!
Next week, look out for some electronics updates. Thanks for reading!