When it comes to dominating offroad performance, many people’s first thought is of tracked vehicles. Bulldozers, tanks and excavators all use treads, and manage to get around in difficult terrain without breaking a sweat. Today, we’re exploring just what makes tracked vehicles so capable, as well as their weaknesses.
It’s All About Ground Pressure
Let’s first look at how tank tracks work. There are a huge variety of designs, with differences depending on application. Different trends have been followed over time, and designs for military use in combat differ from those used for low-speed construction machines, for example. But by looking at a basic tank track design, we can understand the basic theory. On tanks, the track or tread itself is usually made up of individual steel links that are connected together with hinges, though other machines may use rubber tracks instead. The tracks are wrapped around one or more drive wheels, often cogged, which directly pull on the track. On the bottom of the vehicle are the road wheels, which ride on top of the track where it lies on the ground. The weight of the vehicle is carried through the road wheels and passed on to the tread, spreading out the load across a broader area. Outside of this, the track system may also have one or more idler wheels used to keep the track taught, as well as return rollers to guide the track back around without touching the road wheels.
Master of 3D printed robots, [James Bruton], plans to do some autonomous rover projects in the future, but first, he needed a modular rover platform. Everything is cooler with tank tracks, so he built a rover with flexible interlocking track sections.
The track sections are printed with flexible Ninjaflex filament. Each section has a tab designed to slot through two neighboring pieces. The ends of the tabs stick through on the inside of the track fit into slots on the drive wheel like gear teeth. This prevents the track from slipping under load. The Ninjaflex is almost too flexible, allowing the tracks to stretch and almost climb off the wheels, so [James] plans to experiment with some other materials in the future. The chassis consists of two 2020 T-slot extrusions, which allows convenient mounting of the wheel bogies and other components.
For initial driving tests [James] fitted two completely overpowered 1500 W brushless motors that he had on hand, which he plans to replace with smaller geared DC motors at a later stage.
A standard RC system is used for control, but it does not offer a simple way to control a skid steer vehicle. To solve this, [James] added an Arduino between the RC receiver and the motor ESC. It converts the PWM throttle and turn signal from the transmitter, and combines is into differential PWM outputs for the two ESCs.
Tracked vehicles are cool, but can be quite complicated to build. [XenonJohn] wanted to skip the complexity, so he created Vector, an electric tracked motorcycle using only basic parts and tools. No machine tools required.
If it looks familiar, it’s because it was inspired by [Make It Extreme]’s monotrack motorcycle that we covered last year. [XenonJohn] liked the concept, but wanted one that was simpler to build. That meant ditching the custom machined parts like the wheels and the suspension system. These were replaced with three go cart wheels and axles mounted in pillow blocks, on a simple welded frame. An e-bike battery powers a 500 W golf cart motor that drives the rear wheel. Like [Make It Extreme]’s version, the track is an SUV tire with the sidewall cut off. [XenonJohn] used tin snips to do this, but from personal experience we would recommend a utility knife. This track design will have a tendency to collect debris inside it, so cutting some hole in the tread could help. As with most single wheeled/tracked vehicles, you really don’t want to try and stop quickly.
It looks like this bike works fine in straight lines, but there is room for improvement with the steering. [XenonJohn] has some ideas to do this, which we hope to see some time in the future. Let us know in the comments how you would make it turn better.
[XenonJohn] really like vehicles that can make you face plant. He built quite a few self-balancing motorcycles, one of which was supposedly designed with first responders in mind. It honestly seems more likely to create an emergency than respond to one.
One of the basic truths of ground vehicles is that they are always cooler with tank tracks. Maybe not better, but definitely cooler. [Ivan Miranda] takes this to heart, and is arguably the king of 3D printed tank projects on YouTube. He has built a giant 3D printed electric skateboard with tank tracks with the latest version of his giant 3D printer. Videos after the break.
The skateboard consists of a large steel frame, with tracked bogies on either end. Most of the bogie components are 3D printed, including the wheels and tracks, and each bogie is driven by a brushless motor via a belt. Some bends were added to the steel frame with just 3D printed inserts for his bench vice. The bogies are mounted to the frame with a standard skateboard truck, which allows it to steer like a normal skateboard, by tilting the deck. It looks as though this works well on a smooth concrete floor, but we suspect that turning will be harder on rough surface where the tracks can’t slide. We’ll have to wait for the next video for a full field test.
The large components for this skateboard were printed on [Ivan]’s MK3 version of his giant 3D printer. Although it’s very similar to the previous version, improvements were made in key areas. The sliding bed frame’s weight was reduced by almost 50%, and the wheels were rotated, so they ride on top of the extrusion below it, instead of on it’s side, which helps the longevity of the wheels. This also allows bed levelling to be done by turning the eccentric spacers on each of the wheels. The rigidity of base frame and x-axis beam were increased by adding more aluminium extrusions. Although he doesn’t explicitly mention the print volume, it looks to be the same as the previous version, which was 800x500x500. For materials other than PLA, we suspect a heated build chamber will be required have any chance of making big prints without excessive warping.
There will always be those of us who yearn for an iron steed and the wind through your hair. (Or over your helmet, if you value the contents of your skull.) If having fun and turning heads is more important to you than speed or practicality, [Make it Extreme] has just the bike for you. Using mostly scrapyard parts, they built a monotrack motorcycle — no wheels, just a single rubber track.
[Make it Extreme] are definitely not newcomers to building crazy contraptions, and as usual the entire design and build is a series of ingenious hacks complimented by some impressive fabrication skills. The track is simply a car tyre with the sidewalls cut away. It fits over a steel frame that can be adjusted to tension the track over a drive wheel and a series of rollers which are all part of the suspension system.
Power is provided by a 2-stroke 100cc scooter engine, and transmitted to the track through a drive wheel made from an old scuba tank. What puts this build over the top is that all of this is neatly located inside the circumference of the track. Only the seat, handlebars and fuel tank are on the outside of the track. The foot pegs are as far forward as possible, which helps keep your center of gravity when stopping. It’s not nearly as bad as those self-balancing electric monocycles, but planning stops well in advance is advisable.
While it’s by no means the fastest bike out there it definitely looks like a ton of fun. Build plans are available to patrons of [Make it Extreme], but good luck licensing one as your daily driver. If that’s your goal, you might want to consider adding a cover over the track between the seat and handlebars to prevent your khakis from getting caught on your way to the cubicle farm.
3D printing is well-suited to cranking out tank tread designs, because the numerous and identical segments required are a great fit for 3D printing’s strengths. The only hitch is the need for fasteners between each of those segments, but [AlwynxJones] has a clever solution that uses plentiful hard plastic spheres (in the form of 6 mm airsoft BBs) as both a fastener and a hinge between each of the 3D printed track segments.
Each segment has hollows made to snugly fit 6 mm BBs (shown as green in the image here) which serve both as fasteners and bearing surfaces. Assembly requires a bit of force to snap everything together, but [AlwynxJones] judges the result worth not having to bother with bolts, wires, or other makeshift fasteners.
Bolts or screws are one option for connecting segments, but those are heavy and can get expensive. Segments of printer filament have been successfully used in other tread designs, though that method requires added work in the form of either pins, or heat deforming the filament ends to form a kind of rivet. This design may be a work in progress, but it seems like a promising and clever approach.
Tracked drive systems are great, but implementation isn’t always easy. That’s what [nahueltaibo] found every time he tried to use open sourced track designs for his own rovers. The problem is that a tracked drive system is normally closely integrated with a vehicle’s chassis, mixing and matching between designs is impractical because the tracks and treads aren’t easily separated from the rest of the vehicle.
To solve this, [nahueltaibo] designed a modular, 3D printable rover track system. It contains both a motor driver and a common DC gearmotor in order to make a standalone unit that can be more easily integrated into other designs. These self-contained rover tracks don’t even have a particular “inside” or “outside”; they can be mounted on a vehicle’s left or right without any need to mirror the design. The original CAD design is shared from Fusion 360, but can also be downloaded from Thingiverse. A bit more detail is available from [nahueltaibo]’s blog, where he urges anyone who tries the design or finds it useful to share a photo or two.
3D printed tank tracks — including this one — often use a piece of filament as a hinge between track segments and sometimes slightly melted on the ends to act as a kind of rivet, which is itself a pretty good hack.