DIY Playground: A few build ideas from an ROV

This isn't a build log. And what's shown here wasn't built as a rover. It is a rover, sure, but it was built as a playground, a collection of dozens of separate experiments, trials, and ideas. I build this a few months ago, and I'm about to tear it apart and rebuild it based on the lessons I learned, but before I do that, I figured I'd share a bit. 

This was a relatively low cost build, for me, but it would not be inexpensive to reconstruct. I had many of these parts already, so I'll provide some details, but it isn't really a good idea to repeat this exactly. Even I would not build it like this a second time. 

The chassis is a Ruckus Monster Truck. I've been very happy with it. If you know about RC trucks, no doubt, you'll have lots to criticize with this bottom-end 1/10 scale vehicle, but it works just fine for autonomous roving on semi-broken ground and natural grass lands. If you have a lot of obsticles over 3.5-4" and you might need to upgrade to a crawler or something in 4WD.

I'm using an APM 2.5, a 3DR 5.8 FPV kit, with OSD, a Futaba R6208SB rx, a 3DR telemetry kit, a GoPro camera, and a previous generation 3DR LEA6 v1.1 GPS. Besides the 3D printed parts, I use a few #6 screws from Home Depot of various lengths, a 6-to-individual-6 pin'ed cable for the rx (because it was handy, I normally make custom cables from a kit of parts I got over at Hansen's Hobbies,) one 3 pin servo cable for power and channel 8 to the rx, and a few zip ties. 

I removed the shell and some of the plates provided to hold bits in place. One nice feature I made use of here is the twist wing connectors. They are supposed to hold a plate in place for the battery, but the velco strap holes are sufficient for that so I repurposed these twisting winged items as the way to hold the 3D printed body to the chassis. 

While you can see screws, these screws are not fixed. They are glued onto the orange 3D body, but they act strictly for alignment for the chassis, as pins. Why use screws? They are cheap and easy to source. A smooth pin would be nicer, but I had screws. 

I left a large space above the battery, allowing the battery to be inserted and removed easily without taking anything apart. The body and chassis fit together like a glove, stay rock solid while driving around, and come apart in seconds, but disconnecting the two servo cables is a bit of a pain. In the future, I might add a socket that causes the servo cables to connect/disconnect just by attacking the body. I suspect the guide pins would pay off even more then.

The 3D work was created in Google Sketchup, sliced on KISSlicer, and printed using Printrun (for Mac) on a PolyPrinter in ABS. PolyPrinter is a large build area (9x9x9") rock solid industrial-grade FMD printer creative iteratively by fellow Makers in the Dallas area based on their frustrations with less-reliable and more well-known printers. 

In the center of the lower plate, I experimented with integrating Tastywheat's Onmimac 3DR APM Anti-Vibration mount. It works just fine, and while it makes a nice looking stand-alone mount, I would not integrate it like this again. It is far easier to re-create the essential bits and not have to fix all the curves and intersections. You'll notice various arches and buttresses underneath. All of these printed perfectly, without any support, on my PolyPrinter, and they really add rigidity to the structure. While not shown, I did also add thicker triangular bands on the underside of the large surfaces, to add rigidity and reduce weight. This structure was printed in one go, with no issues, and it fits like a glove. The heated bed and fully enclosed space of the PolyPrinter, no doubt, are critical to printing large ABS components like this without lifting or warping. 

The protrusion on the front/left of the sketchup screenshot is the bottom of a GoPro mount. There were several experiments around the GoPro in this build. In the upper place, I included a springy tab that retains the GoPro when inserted. 

No tools, no screws, just slide it in from the side.

When it is fully inserted, the GoPro locks into place, but you can still operate all the controls, access all the ports, buttons, and see the all of the indicators. 

It comes out easily, by pushing up on the tab and pulling it out sideways, but will not come loose while driving around, even under hard driving. The back is also open, allowing for GoPro accessories. 

While this arrangement works well, I would not do it like this again, at least not on a rover. The lens gets far too dusty here in Texas, even with light duty. Because the rover is ground-based, weight is not as critical, so for future ground-based builds I will design around the supplied GoPro protective cases. For aerial systems I now use a variation of this arragement, with extra tolerances for a tiny bit of foam on the contact edges. This helps with vibration and gives a tighter fit overall. 

Another minor, but nice, feature of this build, and easier to do in 3D printing than in transitional plate/cut fabrication can be seen for otherwise "hidden" components like the telemetry module. Measuring out where the TX/RX leds would be situated under the top plate, I sunk the plate down over that area so that it is just ~.25mm thick. 

This creates an high quality effect similar to the hidden indicators found on Apple laptops. While I print in bright orange while prototyping and for my aerial components, I expect this effect would look even sharper when printed on black or some other dark color. Here is a shot of the top plate just as the 3DR telemetry radio LEDs light up. When it isn't lit, you just see orange, but it is so thin that when the LEDs light up, they stand out in the original LED colors. 

In future prints, I plan to fit the video and telemetry radios better, such that they do not twist at all when installed, but otherwise I'm very happy with how they work. 

I don't use the power module in this build. The rover chassis is powered on 7.2v 6 cell NiMH battery. To use the power module, I'd probably swap out to one of my in-inventory 3S lipos, but that would lead me to replacing the existing ESC and motor while I'm at it, so I've left it alone for now. 

There are a dozen or so other ideas expressed in this build, but I've hit the limit on embedded/uploaded images in a blog post, so I'll call this the end for now. My dialog is boring enough with the images, I will not subject anyone to my text sans photos. Happy hacking.

Views: 1678


Moderator
Comment by Michael Pursifull on January 13, 2014 at 5:02pm

Here are a few more photos.

Comment by Jack Crossfire on January 13, 2014 at 5:16pm

It's surprising just how expensive a capable chassis is.  It takes a lot of mechanics to distribute power to the wheels that can't be replaced by software or built with hand tools like a quad copter. 


Moderator
Comment by Michael Pursifull on January 13, 2014 at 5:32pm
I suspect many here could build a nice platform; for me, it wasn't the puzzle I was (at the time) interested in, so I bought something and built on it. My goal wasn't even to have a rover, so much as that a rover is a nice platform to work on collision detection and other features, to support some of my aerial trials. That being said, it is interesting how much engineering goes into these little RC vehicles, when you start looking at them in detail.

Moderator
Comment by Gary Mortimer on January 13, 2014 at 11:38pm

Interesting that you are working on collision detection, I know nothing about rovers does the current code look ahead?? Do those crawlers adjust their speed if they do come across an obstacle?? Those are probably very n00b questions.

Great work on the printing BTW 3D printers are still more expensive than the most expensive thing at a competition of expensive things organized by Forbes rich listers here in South Africa so I am still to start playing but I am itching to start.

Comment by mP1 on January 14, 2014 at 1:28am

How much did the printed plastic cost ? Im just trying to understand how cost effective it is to print rather than buy.


Moderator
Comment by Michael Pursifull on January 14, 2014 at 1:47am

As it happens, yes, rovers do have code for obstacle avoidance. Attach a MaxBotix to A0 and A1 and enable. However, you'll notice the absence of sonar in the photos. I've done some experiments with avoidance in the past, and when I built this, that was one of the original intentions. In a previous (stationary) platform, I constructed a "radar" like sweeping three-way sonar array, and controlled all three with an arduino uno. The Uno output a serial stream of seven column output with time, angle, and distances, and accepted a few commands (a speed setting and a couple of different operating modes) but the intent was to do more with it on a mobile platform.... including generating some mapping/memory matrix, and some behaviors. Not as fancy as some of the SLAM projects, but I was inspired by this. I haven't gotten back around to that, except for taping the rig to the top deck and taking it for a spin around the yard, and I've had plenty of other projects to keep me busy, but they have a way of coming together over time.

I cannot imagine being without my 3D printer now. It makes so much possible. Sure, there are simple cases and structures, but they are also useful at making connectors, tools, mechanical components... I have more projects to share :)

Even the local public library here in a small town in North Texas has just announced that they have public access 3D printers, and that they will be offering free public classes. Add this to the growing lists of Makerspaces world wide, and someone you know has one. Repraps can be made at home for less than the price of a drone if you are precision oriented and technical and patient. You can get an unreliable commercial unit for a tiny bit more, internationally. But 2014 is shaping up to be a very big year (even bigger than 2013) for 3D printing proliferation and reduced costs.  So many people are making them at reasonable price points that the real challenge is finding one that is reliable and will be around for more than the next six months. The better-known printer companies stand behind their products ... but the cost of shipping back for repairs is steep, because of the size.


Moderator
Comment by Michael Pursifull on January 14, 2014 at 1:50am

But for my part, I'm so happy with my PolyPrinter that I'd get three more if I had the space for them.


Moderator
Comment by Michael Pursifull on January 14, 2014 at 3:04am

@mP1: As it happens, I keep very precise records, so I can answer that. 

$5.583 USD for all printed parts on this build. 180.12g of ABS, 74679.6631mm extruded, which is sold by the kilo at $31.0 USD. You can get filament cheaper, if you shop around or buy off brand or in bulk. This was purchased from Amazon. If you are going to print a lot, you can even cut this cost by a factor of eight to ten, if you have access to a filament extruder (there have been several successful kick starters ~$400 USD) 

If I were printing these for other people, I might invest in the filament fabrication, and drop the material cost down to around 0.70 USD. But for my prototyping $5 USD in material costs is fine. For the cost of a McDonalds meal or a Starbucks coffee, I have large, complicated, custom Rover parts, printed a few times faster than I could have it shipped, next morning delivery.


Moderator
Comment by Gary Mortimer on January 14, 2014 at 7:07am

I wonder what my children will do with 3D printing its a brave new world.


Moderator
Comment by Michael Pursifull on January 14, 2014 at 8:13am
Well, there's one thing they will not do, that's appriciate how much time we spent cutting, sanding, drilling, glueing, planing, welding, routing, casting, folding, bonding, fitting, treating, laminating, moulding, bedding, laying up, pressing, stamping, etc.

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