TwchDuk's Micro4 build

[twchduk]

Hey crew, I'm realizing a little late that I probably ought to be sharing this journey with more people.

Ultimately this journey began last winter when someone shared a trailer for Mario Kart Live with me which got my attention immediately. I hade done a little FPV drone racing previously (mostly the palm sized TinyWhoops that you can "safely" race inside). The synthesis of augmented reality and electronics seemed amazing. However this excitement quickly turned to ash when I saw how slow and ponderous they were in reality; my drone racing background now catching up to the reality of the karts. Fast-forward a month and we had 3 buggies rigged up for FPV with new race tracks every time it snowed (there is nothing like the cold dark months of winter to spark creativity).

It wasn't long before I found micro crawlers and started playing around in that space, which brings us to today where there sits a fleet of micro crawlers in our home.



I've still got a bit of the racing itch so we've been looking at the 1:1 Ultra4 racing format as an interesting combination of an engineering problem and skill challenge. With that in mind we've been working towards our own Micro4 (Ultra24?) racing in the back sand pit.

I switched away from the tried-and-true Axial SCX24 platform due to the worm gears; I love the clearance and torque conversion of the axles, but I am concerned about the long-term wear of the worm gear at race speeds. This pushed us to the Team Associated Enduro24 and Hobby Plus CR-24.

I did some initial work on the Endiro24 to relocate the battery more centrally (and lower) rather than hanging off the back end. Also sliders. Who doesn't love sliders? (I think I ought to close up the holes between the tubes so it doesn't get snagged there)



More recently I've been working with a the Cr-24. Initially I built new tie rod since the servo arm and drag link would hit it during compression. This only had a minor effect during regular flexing and would only effect the steering if compressing both sides (say from a steep down, adding too much weight to the body or after a jump). Also dropped in some new wider hexes to prevent rubbing the springs by the taller tier tires I had put on. Ultimately there was too much flex steer for my liking due to the servo orientation and arm length, so I designed a quick and dirty servo carrier to mount the servo on the axle (and switched to a higher torque servo in the process). Sorry I don't have any of the interstitial pictures or pictures of the problems here, but we're a little too far down the rabbit hole to go back now. Right, also a high clearance bumper and sliders got designed and installed in during this period.





Yesterday my my CR-18 axles came in and I finally got around to building heads to mount Carisma MSA-1E shocks to this truck. I could buy the front steering hubs to mount to the existing CR24 axles, but had to build new wideners for the rear axle. The rims I am using have a relatively deep offset so I was able to make smaller hexes and increase the track width only slightly from stock while still maintaining clearance to the springs. I picked up the new axles rather than building new rims with a negative offset in order to minimize the steering scrub. A new steering linkage polished off the front end (this is using a new 4mm ball in order to keep the original drag link and shoulder bolts from an Enduro24 parts kit to keep down the friction and maintain tighter tolerances than is feasible with regular screws). And somewhere in there I had built another new front bumper, now too shallow for the stock body (ultimately this current form is just a temporary layover/test bed for a new tube chassis.





Still to-do for today is build a new front-mounted battery tray. Then it is on to the heavy-lifting.

[twchduk]

So I built up a quick battery tray using the rubber band style securing used on the CR24 and Enduro24 putting the battery up front and as low as I could.

I started building a cage body rather than a full frame/chassis replacement because I am ultimately that kind of lazy (I think replacing the rails is in the cards somewhere, but ultimately I'm here to drive. I took some cues from motiracer38's KOH build and broke the build into several pieces to screw together mostly driven by build times (/potential print failures on bug builds) and my print footprint. For the test prints I put in a pile of holes in case of adjusting plans.











After a few iterations refining the fit, and deciding that I did want to commit to a nano FPV camera at this stage, we ended up with this final shape. Personally I feel like the tall mid-section feels silly and I'd rather keep it lower and swept back more from a styling perspective, however the FPV really benefits from moving the camera as high as possible.









up next is actually mounting the body to the frame (I am thinking a swing-up style) and relocating the battery tray above the motor for better clearance to the shock mounts

[twchduk]

IT LIVES!

Over the weekend, we took the FPV rig for a spin!



Running video.


After a few night laps, I think I need to cover the headlights from the inside. I'd like to keep the hood open in order to see the tires if things get more technical. I'd love to get a proper drone-like HUD with a digital horizon for when things squirrely and a roll-over is imminent, but installing a whole flight controller just for a horizon and maybe voltage seems like overkill.
Other thoughts are that the course ought to be flagged better; that low angle really hides a lot of my markings that are otherwise very visible from above.

And in other news, it is time to build the fleet and have a real race. I think the Team Associated Enduro24 is next up for modification.