When Combat Robot Wheels Need To Be Nice And Cheap (But Mostly Cheap)

It started with [CHORL] making a promise to himself regarding constructing a new combat robot: no spending of money on the new robot.

That rule was violated (but only a little) by making his robot’s wheels out of EVA kneeling pads. EVA (Ethylene-Vinyl Acetate) is a closed-cell foam that makes for durable yoga mats, kneeling pads, and products of a similar nature. [CHORL] found a way to turn them into light but serviceable wheels for his robot: the Susquehanna Boxcar.

Nested hole saws create concentric holes. Perfect for wheels.

Here’s how the wheels were made: [CHORL] began with two hole saws. Nesting a smaller hole saw into a larger one by putting both on the same arbor created a saw with two holes, both of which were centered with respect to one another. The only problem was that this hole saw was not actually deep enough to cut completely through the thick foam. Luckily, cutting roughly halfway through on one side, then flipping the sheet over and cutting through from the other side was a good workaround. That took care of turning the thick foam sheet into round wheels.

A 3D-printed part served as a wheel hub as well as gear for the drivetrain. We want to call attention to the clever method of reinforcing the connection between the parts. [CHORL] didn’t want to just glue the geared hub directly to the surface of the foam wheel, because he suspected it might separate under stress. To address this, he designed six slots into the hub, cut matching slots into the foam wheel, and inserted six spline-like reinforcements in the form of some ABS strips he had on hand. Gluing it all together with E-6000 and leaving it to cure overnight under a weight resulted in a geared wheel assembly that [CHORL] judged to be about as round and rigid as a wheel should be, so the robot had a solution for nice light wheels that were, above all, cheap!

Lots of robots need wheels, and unsurprisingly, DIY solutions are common projects. [CHORL]’s approach here looks pretty scalable, as long as one can cut some accurate holes.

Interested in knowing more about the robot these wheels are destined for? [CHORL]’s still working on the Susquehanna Boxcar, but it’s almost done, and you can read a bit more about it (and see a few more pictures) here.

Yellow Robot Wheels Rolling Out

Small wheeled robots are great for exploring robotics and it’s easier than ever to get started, thanks to growing availability and affordability of basic components. One such component is a small motorized wheel assembly commonly shown when searching for “robot wheel”: a small DC motor mounted in a gearbox to drive a single plastic wheel (inevitably yellow) on which a thin rubber tire has been mounted for traction. Many projects have employed these little motor + gearbox + wheel modules, such as these three entries for 2018 Hackaday Prize:

BoxBotics takes the idea of an affordable entry point and runs with it: build robot chassis for these wheels out of cardboard boxes. (Maybe even the exact box that shipped the yellow wheels.) Cardboard is cheap and easy to work with, making cardboard projects approachable to any creative mind. There will be an audience for something like a Nintendo Labo for robotics, and maybe BoxBotics will grow into that offering.

Cing also intends to make a friendly entry point for robotics and they offer a different chassis solution. Instead of cardboard, they use a circuit board. The yellow gearbox is mounted directly to the main circuit board making it into the physical spine, along with its copper traces serving as the spinal cord of the robot. While less amenable to mechanical creativity than BoxBotics, Cing’s swappable modules might be a better fit for those interested in exploring electronics.

ROS Starter Robot caters to those who wish to go far beyond simple “make it move” level of robot intelligence. It aims to lower the barrier to enter the world of ROS (robot operating system) which has historically been the domain of very capable (but also very expensive) research-oriented robots. This project could become the bridge for aspiring roboticists who wish to grow beyond hobbyist level software but can’t justify the cost typical of research level hardware.

All three of these projects take the same simple motorized wheel and build very different ideas on top of them. This is exactly the diversity of ideas we want to motivate with the Hackaday Prize and we hope to see great progress on all prize contestants in the month ahead.

DIY Tank Tracks Give Tons Of Traction

If you’re building a robot for off-road or rough terrain, chances are you’ve thought about using a tank-tread style drive. There are a ton of kits available with plastic tread and wheels, but they are typically really expensive or pretty flimsy. Instead of going with an off-the-shelf solution, [Paul B] designed a heavy-duty tank tread made with common bike chain and conduit.

Some DIY tread designs we’ve featured just use a single bike chain on either side of the tread pieces. This gets the job done, but each section of tread is usually bolted through the chain. This means that you can’t use a sprocket to drive the chain since all the bolt heads block where the teeth engage. Instead, these designs typically use drive wheels inside the tread, which are prone to slip under a heavy load. [Paul B]’s design is a bit different: it uses a DIY double-wide chain so he can bolt tread segments to the chain and still use a drive sprocket.

Constructing the double-wide chain took quite a bit of work. [Paul B] completely disassembled a couple of bike chains with a delinker tool and then reassembled the chain in a double-wide configuration with M3 bolts instead of the original chain pins. Each section of tread (made out of cut pieces of plastic conduit) bolts on the outside section of chain, and a sprocket runs on the inside. His DIY chain approach saves him money too, since double-wide chains are pretty expensive. Since his sprockets directly engage the drive train, his design should be able to handle as much torque as his drivetrain can put out.

Reinventing The Wheel Makes For A Better Wheel…

When robots take over the earth, it will be important that they maneuver across various types of terrain quickly and effectively. Bipedal motion is a tricky feat to accomplish for machines, so [Carter Hurd] decided, why not invent a better wheel? Even wheels can be improved, right?

Making excellent use of the prototyping capabilities of a 3D printer, [Carter] designed a set of bulb-shaped mechanisms which act effectively to drive themselves around on a smooth surface. The bulb is split radially into a series of wedge slices which can articulate outward, transforming the robot into something of a spiky razor-beast, able to tear through piles of fall leaves or wakes of loose sand. In order to unfurl itself however, the shaft driving the central mounting plate of the wedges has to fight the robot’s own weight. To solves this, [Carter] modified his design so that the rest of the wedges would unfold around the one supporting the load, the wheels would then rotate to shift the weight, allowing the last piece to extend.

[Carter] shows a proof of concept from earlier this year, explaining his hinge design which stretches a tendon-like connector in order to tension the wedges in one state or the other. Since then it looks like his transforming wheel has evolved a bit. You can get a better view of his robot in action here :

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