Acorn Frequently Asked Questions

If you have some basic questions about Acorn, please ask them here and I will update this FAQ with answers. For more complex questions feel free to make a separate post.

What does Acorn do?

Some day, Acorn will use computer vision and tools to help perform weeding, planting, and more. Right now we are working on perfecting the basic vehicle which will carry those tools over each plant at the farm.

How much does Acorn cost?

Acorn units are not currently for sale, and we have not determined an estimated price for the system. Acorn is designed to be low cost.

In your announcement video, you say you want Acorn to become community supported. What does that mean?

Later in 2021 we plan to launch some kind of monthly donor support program. Like Patreon, though we may use Open Collective. There are many advantages to this approach which we will discuss in the future.

When will you offer kits for sale?

Robot development is difficult to accurately predict, but we hope it is possible to offer the first kits for sale in approximately one year. We already have a “Version 2” design which we are fabricating now.

What pronouns should I use for Acorn?

Acorn uses it/its pronouns. As in the sentence: Acorn loves to be outdoors and it feels warm and happy when sun shines on its panels. :sun_with_face:

Very interesting project. How does it navigate at the present time? Is it using only GPS? Or is it being remotely controlled?
I’m assuming you are using a Raspberry Pi as the central control unit.
thanks!

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Yep you are correct! We are using a Raspberry Pi and RTK GPS for autonomous control. It was all autonomous in our announcement video, and in the last 7 days acorn has traveled 58 kilometers autonomously. Some of those were slow days as I was working on it, but it had a new best day recently with 14.3km on pure autonomous solar power. It is currently just driving back and forth down the winding test row you saw in the video as we work on making sure continuous daily operation is reliable, and we will be expanding the driving area soon. :slight_smile:

It looks like your code base has a lot of Python in it. Are using RTK with Python? Is there a library available?

Regarding RTK, can you input “fusion” sensor data for possible dead reckoning?

We are using RTKLIB for RTK which is written in C++:

I’ve not tried to inject data in to the calculation. I would probably use a separate kalman filter if I was going to do that. This page talks about how it would be done in ROS, but serves as a good overview generally:
http://docs.ros.org/en/melodic/api/robot_localization/html/integrating_gps.html

I am also evaluating this as a possible GPS+IMU solution:

It looks like Acorn has no suspension, so I wonder how it handles bumpy ground. If one wheel rides up on a bump, won’t Acorn teeter diagonally?

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Yes that’s true. I think long term I like the idea of a flexible frame to account for this, but the simple rigid frame may be fine. We need to see if the rigid frame really ends up being a problem. It does teeter on uneven surfaces, but the ground should be somewhat even where precision work is required. Or suspension may be required. TBD.

For fast-moving ATVs, 4 wheel independent suspension is a typical  solution,   but I wouldn't recommend that for Acorn.

The usual field tractor solution to keep all 4 wheels on the ground in rough terrain is to have the font axle on a subframe with a pivot pin along the forward direction. Tractors are heavier at the rear axle, so vertical tilt of the tractor is controlled by the ground tilt between rear wheels.
My understanding is that the solution for Mars rovers is to have the front axles on a subframe, and the rear rocker-bogie axles on another subframe, and mount the rover body on a differential joint between these subframes, in such a way that the body tilt is the midway point between the two axle subframes tilts.

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I’ve also realized that since we are moving to a custom fork, we can have versions with or without suspension. I do think there is room for a variant without it and this would save cost, but it would be possible to add suspension at the fork without any other changes.

Most robots in my post today in competition section use wider wheels, at least wider per diameter, than Acorn’s prototype mountain bike wheels. They all are using cantilevered wheels as well, some with crab steering, some not. Not many have suspension, or an obvious way to handle non-planar fields.
Large tall field equipment for light duty tasks like spraying or carrying corn detassler crew, also use cantilever wheels on stilts. With a cantilevered one-tined fork, there is half as much opportunity to get trash stuck between fork and wheel.

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Yes I think there’s a lot of opportunity beyond the basic fork design we have now. We plan for our first release rev to be simple and robust, but I expect we will go through many versions. So far the mountain bike wheels are pretty good. Suspension would be very helpful. Also I loved my Cannondale lefty fork. A single tine fork would make tire repairs a breeze!