Fail of the Week: Hard Lessons in 3D-Printed Bushings for a Giant RC Car

Can you turn 47 pounds (21 kg) of PLA filament into a gigantic working 3D-printed RC car? No, no you can’t — at least not if you eschew proper bearings in favor of printed bushings.

That’s the hard lesson that [Joel Telling] learned with his scaled up version of the OpenRC F1 car, an RC car that can be mostly 3D-printed. The small version still has its share of non-printed parts, mainly screws and bearings. In his video series documenting the build of the upsized version, [Joel] elaborates on some of the reasons for going with printed bushings rather than bearings, which mainly boil down to hoping that the graphite lubricant powder he added would reduce friction enough to prevent the parts from welding themselves together.

The car came out looking great, and even managed to scoot about nicely for a few seconds before its predictably noisy and unhappy demise. But what was unexpected was the actual failure mode. The plastic-on-plastic running gear seemed to handle the rolling loads fine; it was the lateral force exerted on the axle by the tension of the drive belt that was too much for the printed bushing to bear.

As [Joel] rightly points out, it’s only a failure if you fail to learn something, so kudos to him for at least giving this a try. And all that PLA won’t go to waste, of course — everything else on the car worked fine, so adding one bearing should get it back on the road. He should check out our primer on bearings for a few tips on selecting the right one.

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Power Wheels Gets Real With Real Wheels

We’re no stranger to Power Wheels modifications, from relatively simple restorations to complete rebuilds which retain little more than the original plastic body. These plastic vehicles have the benefit of nostalgia to keep the adults interested, and naturally kids will never get tired of their own little car or truck to tear around the neighborhood in. Many toys come and go, but we don’t expect Power Wheel projects to disappear from our tip line anytime soon.

Today’s project starts with a straightforward Power Wheels restoration story: [myromes] picked up a well-worn Jeep and decided that it needed a fresh coat of paint and some tweaks before handing the keys over to the next generation. But in an interesting spin, he decided to try mounting proper pneumatic tires on it in hopes they might imbue the pint-sized Jeep with some of the abilities of its full scale inspiration. But as it turned out, the project wasn’t quite the Sunday drive he was hoping for.

For one thing, the new wheels were much thicker than the old ones. This meant cutting away some of the plastic where they mounted so he could get the shafts to slide all the way through. At 5/16″, the original Power Wheels shafts were also thinner than what the axle the wheels were designed for. Luckily, [myromes] found that a small piece of 1/2″ PEX water pipe made a perfect bushing. Then it was just a matter of buying new push nuts to lock them in place.

That got the front wheels on, but that was the easy part. The rears had to interface with the Jeep’s motors somehow. To that end, he cut out circles of plywood and used an equal amount of Gorilla Glue and intense pressure to bond them to the new wheels. He then drilled four holes in them which lined up with the original motor mounts so he could bolt them on.

Things were going pretty well until he tried to replace the Jeep’s rear axle with a length of threaded rod from the hardware store. It wasn’t nearly strong enough, and sagged considerably after just a few test rides. He eventually had to place it with a correctly sized piece of cold rolled steel rod to keep the car from bottoming out.

While the new wheels certainly perform better than the original hard-plastic ones, there’s a bit of a downside to this particular modification. The slippy plastic wheels were something of a physical safety to keep the motors and gearboxes from getting beat up to bad; with wheels that have actual grip, the Jeep’s stock gears are probably not long for this world. But [myromes] says he’s got plans for future upgrades to the powertrain, so hopefully the issue will be resolved before the little ones need a tow back home.

For more tales from the Power Wheels garage, you might want to take a look at this fantastic rebuild complete with digital speedometer or just head straight to the big leagues with some seriously upgraded rides.

Simple machining process repairs broken control knob

[Francisco] is helping his mother with a repair to the headlight knob on her Ford Ranger. Above you can see the broken knob on the left, and what it is supposed to look like on the right (taken from [Francisco’s] own vehicle for reference). We’ve encountered split shafts on plastic knobs before and decided it was not something that could be fixed. But he didn’t give up so easily. He mentions that you can purchase a replacement for a few bucks, but he has the means to repair the knob by machining a metal bushing.

The idea is that you mill a metal ring whose inner diameter matches what the outer diameter of the plastic shaft should be. By inserting the broken knob in the ring, the plastic is held tightly together as if it had never broken. In the video after the break [Francisco] uses a metal pencil body from his junk box and a mini-lathe to cut the bushing to length, and mill the inner diameter to his specifications.

He talks about the difficulty of getting replacement parts in Chile, where he lives. But we think this kind of thrift is a great example for all hackers. If you’ve got the tools why not use them? And if you don’t have them, here’s a great excuse to procure them!

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