chrisb

I use an MT6701 magnetic rotary sensor mounted on the motor shaft, running in AB[Z] mode. This is used to measure the angle of the motor, and generate the correct PWM signals for the three motor coils. My inner current-control loop runs at 15kHz, using a PI controller.

The linked article is misrepresented.

Two points regarding blade recycling techniques taken straight from the top of the article:

- Cement co-processing and chemical dissolution are primary viable methods, yielding $27.57/ton and $199.71/ton returns respectively.

- Chemical recycling achieves top circularity (PCI=0.7) and notable carbon reduction (−0.475 t CO₂/ton).

Chemical recycling is not yet ready for industrial use; cement co-processing is.

Nice to meet an SRC investor :)

Yes, it was all very sad the way SRC ended.

Coincidentally, we're based fairly close to where they operated. We are in touch with some of the people that used to be involved with SRC, and have been able to learn from some of their experiences. There is agreement that the UK can be difficult for this kind of startup, but also about the importance of the product area.

My knowledge of ROS is a couple of years out of date, but primarily that reproducible testing and simulation, with precise time/clock management, which is essential for a reliable product, was very difficult in ROS.

I also felt the ROS build system more convoluted than necessary; and seemed rather brittle - it was too easy to break it with OS or other updates.

We found that many off-the-shelf ROS nodes didn't do quite what we wanted, and ended up spending much more time than expected rewriting code that we expected we wouldn't need to. It is quicker, and we end up with less & more maintainable code, by writing it ourselves.

I expect this could have been resolved, but when testing ROS we also ended up using more compute resources on-robot than we expected.

Using our own system allows us to build exactly what we require, which has become more important as our system gets larger and more complex; and means integrations into other systems (including testing) are easier.

Before we started building we considered many different designs, including legs. However, it introduces significant extra mechanical and control complexity, with more complex failure modes - e.g. one leg gets stuck in the mud; it also would be more expensive to build.

So we decided to stick with wheels, at least for this product iteration!

These are apparently not large EV-type rechargeable lithium batteries, as I immediately assumed.

From the article: "Aricell makes lithium primary batteries for sensors and radio communication devices". A "primary battery" is non-rechargeable; and given the use-cases mentioned I expect each individual battery is fairly small.

Of course, when there are 10s of 1000s of them together that's still a lot of energy to burn.

The subsequent prequel "A deepness in the sky" is also well worth a read.