Now that the quad A1 has been running faster, it has started “running” through its ad-hoc cable management too. After replacing a harness for the nth time, I decided to actually design something rather than just keep re-building over and over again.

My current best effort uses semi-flexible nylon split conduit, captured in 3d printed forms at each joint. Inside that conduit is basically the same harness I had before, with the cables selected to be more robust to repetitive motion. The nylon conduit is only semi-flexible, so it enforces a relatively large minimum bending radius on the wires within, while still sticking to the black quad A1 color motif.

In the last post, I described the newer gait engine which takes a desired command and produces a set of gait parameters. At that point, the gait engine needs to implement those gait parameters in a way that is stable with respect to disturbances and keeps the two legs properly out of phase with one another.

The gait variables that the gait selection procedure emits are as follows, each “leg” is actually a pair of legs.

As hinted in my earlier video I’ve been working towards some higher speed gaits with the quad A1. To accomplish that, I had to restructure the gait sequencing logic to permit changing cycle times and allow flight phases.

For now, I’ve tentatively broken down the trot gait into 5 regimes, based on how fast the machine is moving:

1. At the slowest speeds, the flight legs swing through a step in the configured maximum flight time. The interval between flight times is fixed at a configured maximum. Here the speed is determined by how far the flight legs move.
2. Once the flight legs are moving through their maximum allowed distance, then the amount of time spent with both legs on the ground is reduced in order to increase speed.
3. At the point when both legs are not on the ground at the same time, then there begins to be a flight phase. Increasing the length of the flight phase increases the speed.
4. When the flight phase reaches a configured maximum, then the swing time is decreased until it reaches a configured minimum.
5. When the swing time is at a configured minimum, the flight time is at a configured maximum, and the legs are moving through their maximum range, then the machine is moving at its maximum speed.

Depending upon the current commanded rotation rate and translation velocity, the distance available for the legs to travel through may change. This uses the same mechanism from the step selection technique to determine the maximum distance at each update cycle, then selects which of the above regimes is active based on the commanded speed.

Here’s another short video only update, I’ve been experimenting with flight phases on the quad A1. With the gait formulation as I have it now, it isn’t terribly stable, but with some coaxing videos are possible:

I’m continuing to make progress with getting the quad A1 to move at higher speeds, furthering my earlier video update. I’ll write up more later, but here’s a quick snapshot showing a 2 m/s trot:

I’ve started some development on higher speed gaits for the quad A1! No real details to report now, just a video showing the first time I tested it not in simulation. I will admit these clips were cherry-picked, as there are problems still, but it is a start!

I’ve worked through a number of different iterations of the stand-up sequence for the quad A1 (2019-05, 2019-09). The version I’ve been using for the last 6 months or so works pretty well, but because it drags the legs along the ground to get them into position, it can have problems when operating on surfaces with a lot of traction, like EVA foam, besides being uselessly noisy.

To make things just a bit more robust, I’ve now tweaked the startup routine so that the shoulders lift legs clear off the ground before positioning the legs, then lowers them back down into place. This makes the stand up routine much more likely to succeed on just about any surface:

Just a video update… I’m not generally offering the quad A1 for sale *yet*, but if you’re interested in an alpha version, you can write info@mjbots.com

You can of course already get nearly all the non-3d printed parts at https://mjbots.com

For some upcoming work, I needed to drive the quad A1 around without being tethered to a computer. To date, my control mechanisms have been:

• A web interface driven from a computer with joystick attached.
• A nrf24l01 link driven from a nrfusb attached to a computer.

Note, both of those methods involve being tethered to a computer, which makes it hard to be mobile. As a possibly short term solution to this problem, I went ahead and got a bluetooth “gaming” controller for my phone (non-affiliate amazon link):

I first wrote about the very very simple web UI for the quad A1 some time ago. That UI served its purpose, although it was largely inscrutable to anyone but myself, as the primary data display was a giant wall of unformatted JSON which filled most of the page. It was also pretty easy to accidentally pick the wrong mode, cause the robot to jump instead of walk, or cut power to everything.