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Sgvhak Rover; Rover built by San Gabriel Valley Hardware Hackers Group
Topic Started: Jul 13 2018, 10:20 PM (1,043 Views)
RogerRandom
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Hello everybody!

The San Gabriel Valley Hardware Hackers Group (SGVHAK) are honored to have been part of this Open Source Rover project as beta rover builders.

Unlike most of the other beta builders, we are not a school team. We are a group of science and technology enthusiasts who love to take things apart and see what makes them tick. We also build our own contraptions, taking on many hobbyist-level projects leveraging our members' skills. They range from electronics circuit design to mechanical design implemented via either 3D printing or machining. Given this background, it made perfect sense for us to assemble a team to run through rover construction documentation and give feedback on our experience.

In early January we had our kickoff meeting, and over the following two months we worked towards our self-imposed deadline: a public rover appearance at Southern California Linux Expo (SCaLE 16x) on March 8th, 2018. We got the motorized chassis running by our deadline, though we had yet to finish the LED 'face'. Since our debut at SCaLE 16x, our rover has been at several other public outreach events like the "Science for March" event at California Institute of Technology (Caltech).

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Mechanically, our rocker-bogie suspension system was built according to instructions and the main body box is only slightly different. Our largest changes were:

  • Wheel travel motors: We used the tires specified, but inside the tire is our own creation. It is a 3D-printed planetary gearbox driven by a powerful yet inexpensive motor. Inside this planetary gearbox is an integrated optical quadrature encoder, reading from a 3D-printed encoder wheel. Our wheel design is open source and publicly available.
  • Wheel steering motors: We upgraded our steering motors to a larger and beefier unit after breaking our first set. We also skipped the position encoders on corner steering motors. Without the encoders, we have to trim and zero wheels manually on every power-up. This loss of convenience was a tradeoff against cost.
  • Software: The reference rover software was not yet ready for public consumption when our mechanical construction got far enough to need software. So we started writing our own code and continued on a separate path for software. SGVHAK rover software is a HTML-based interface over WiFi so any web-enabled device can control the rover. It is also open source and publicly available. The source code was designed and documented to be easy for students to understand and pick up.

I was the software person and my personal blog has more details on the thinking behind our rover software. I also wrote about the mechanical side of our project, or at least the parts I knew about. This link will bring up all of my blog posts tagged with "SGVHAK Rover"

We have ambitions to make a more powerful and sophisticated (but less beginner-friendly) rover software package in the future, possibly based on ROS but nothing has taken form yet. We have also started working on a robot arm we could mount to our rover.

- -

Postscript:

During the beta build process, there were many discussions about alternative approaches, multiple ideas on tradeoffs we could make to drop the price of admission. One particular approach was to give up the Actobotics metal construction set pieces and the sophisticated Roboclaw motor controllers. In their place, use 3D-printed plastic pieces and using less powerful hobby servo motors that are a lot cheaper. In theory such a rover should be possible for under $500. I liked the idea so much that, after our SGVHAK rover build was complete, I accepted the challenge and created Sawppy the Rover for $500.
Edited by RogerRandom, Jul 13 2018, 11:29 PM.
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RogerRandom
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Emily, our SGVHAK rover team's Instagram expert, had posted a few items as our project progressed.

Click on a thumbnail to see the full image. Some of these are links to short videos and are marked as such, so people seeing this on expensive data plans are informed.



Wheel assembly:

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Frame assembly:

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It's Alive!

(This is a video.)
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(This is a video.)
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Our steering motor broke just before debut at SCaLE. We hacked in a RC servo to take over steering the broken corner.

(This is a video.)
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Climbing a curb

(This is a video.)
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Running with an older sibling

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Edited by RogerRandom, Jul 14 2018, 02:22 PM.
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Szymon
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Wow, I love the planetary gearbox idea! For sure we'll try to prototype that and use in the projects. Keep us with the good work!
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kris.austin

RogerRandom
Jul 13 2018, 10:20 PM
[*] Wheel steering motors: We upgraded our steering motors to a larger and beefier unit after breaking our first set. We also skipped the position encoders on corner steering motors. Without the encoders, we have to trim and zero wheels manually on every power-up. This loss of convenience was a tradeoff against cost.
First off, congratulations on an awesome build!

You mentioned the steering motors breaking and that you ended up using some RC motors because you were on a time constraint. What motors would you recommend for a new build? I'm gathering my parts list and I certainly don't want some problematic steering motors.

Thanks for any advice.
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RogerRandom
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We ended up using these guys and they've worked well for us.

16 RPM HD Premium Planetary Gear Motor w/Encoder
https://www.servocity.com/16-rpm-hd-premium-planetary-gear-motor-w-encoder

The motor's mounting pattern does not line up nicely with the hole pattern of an Actobotics beam, so an adapter will be necessary. We designed and 3D-printed one for our rover but unfortunately we've lost track where our CAD file went for that particular piece.
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Bdebevc

What about something like this?
https://www.banggood.com/GM4632-370-DC-12V-30RPM-High-torque-Turbo-Encoder-Motor-Worm-Geared-Motor-Reducer-Motor-p-1069461.html?rmmds=detail-left-hotproducts__5&cur_warehouse=CN

Takes about 20 days to get to the U.S. and I have had good luck ordering from this site.
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RogerRandom
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The advantage of a planetary gearbox is that loads are distributed across multiple gears and their teeth.

With a worm gear, all the stress is concentrated onto a single gear (tooth) which demands much stronger material for that gear.
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dcali

Just have to say, that looks incredible; great work! Also I hadn't heard of SGVHAK and this is right in my backyard. I'll have to look this up!
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