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El Gecko

Big Bubba redux - adventures in homebrew chassis design

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Prompted by @Nikko85's suggestion, here's the build thread, if you want to call it that. It's definitely not planned out, so I'm not sure it can be called a build... more like an ongoing experiment in chassis design, in the cheapest way possible.

But let's start at the beginning, probably around 1990 or so. This was the 2nd "wireless" RC car that came into our household, and it was used and slightly abused, but still had some life left. Dad used popsicle sticks, duct tape, and rubber bands to "fix" the battery door, and things just got glued back on the body when they broke off. We had a ton of fun with it, but at some point, the 4WD system was causing problems, so Dad removed the dogbones to make it RWD only. Unfortunately, that put more stress on the rear gearbox, which eventually destroyed all the gears (but not before we had a ton of fun driving it around RWD--it was faster that way after all!)

Fast forward a bit, and this is what it looked like when I pulled it out of storage last year (I had stolen the tires for the Blaster already, and Dad sawed a wheel off years ago trying to fix the gearbox). It still had all the original electronics (including headlights) but none of it works anymore. I'm hoping to save and reuse the headlight pod + wiring as well as the battery plug and original on/off switch.

The chassis is a two-deck setup, with the fender wells, front winch and rear bumper incorporated into the top deck. I was originally thinking of just using that part as the chassis base, and attaching a new front bulkhead and a gearbox in the back, but the way it's lining up, I think I'll be using both decks still--the two biggest parts of the old chassis. As you can see, there are a bunch of gears that came out of it--and they're all basically unusable. So my first thought was... do I have enough spare parts to get a new gearbox sorted out for this thing?

big_bubba_redux_before_01.jpg

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big_bubba_redux_before_03.jpg

big_bubba_redux_before_04.jpg

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And in case you haven't seen my posts in the "So what have you done today" thread, the answer is: Yes, I do have an extra gearbox that might work!

It's an old Traxxas box that truly belongs on my Hawk, but the Hawk is running a gnarly ball diff trans right now, so this is the extra. This one has the original planetary diff setup, so it should be nice and strong (not that I'll be running much power through it).

I don't have a motor plate for this one, and the Fox spur is a different ratio than the standard Traxxas one, which means I couldn't use one of my other motor plates to locate the spur gear hole, so I really just did a best guess and it actually worked (with a bit of "massaging"). The motor plate I ended up with is actually the one from the original gearbox (you can just see it at the top of the 3rd pic above). It had a 90 degree bend about halfway through, so I bent it back flat and drilled some holes to mount it to the gearbox. The metal is a bit soft and weak, and I will probably need to replace it at some point, but it will do for now.

The original 280 motor in the "gears" pic above was still gasping and wheezing, even after lubrication, so I binned it in favor of a fresh 380 with the original pinion reinstalled.

Once that was all sorted and running smoothly, I moved onto the driveshafts. I had the standard plastic Traxxas slider shafts installed at first, but they'll be way too long and would make the track too wide. I could easily just cut them down to size, and I may later on, but for now I have another idea.

Nikko driveshafts. I was sitting there looking at the pile of parts leftover from taking the whole truck apart, and an idea struck me. What if I could actually use the old Nikko shafts to drive the truck somehow?

I found that some of the drive cups had hex shafts attached, which were pretty darn close to fitting into the diff, and they slid right in after I filed them down some!

So once I knew I could drive the diff via the hex shafts, I machined down (turned down) the diecast metal on the cups to fit 1150 bearings. The pic below shows them before I cut the shafts shorter and filed another flat part on the ends to slide into the diff interface. They're just a press fit into the bearings, but even if they come loose, I doubt very much they'll escape. With these installed, the gearbox runs super smooth and quiet (which is strange for this type of box).

big_bubba_redux_gearbox_00.jpg

big_bubba_redux_gearbox_01.jpg

big_bubba_redux_gearbox_02.jpg

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The latest development in the story is the stub axles to finish out the driveline. It just took some careful drilling, a bit of hammering, some through bolts, and voila! Stub axles!

Got the original tires back on some CCP Blackfoot rims (missing a bit more tread now), and lined everything up, and it's starting to look like it might actually work! The next step was going to be sorting out axle carriers, but my cousin may have just solved that dilemma for me :D

big_bubba_redux_stubaxles.jpg

big_bubba_redux_gearbox_03.jpg

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That takes me back. My first “full function” r/c was the Sears Lobo, which was a rebadged Big Bubba. Great little truck to bash around. A friend eventually got a Big Bubba and since they were identical, we would drag race and tug-of-war to see who’s was better.

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It works! The lower arms need a geometry tweak to counter some binding issues, but the whole drivetrain runs nice and smooth! Looks like it will end up about 5mm wider than a Hornet/Lunchbox rear end, and it should have about 1" of suspension travel once I fix the arms :D

big_bubba_redux_gearbox_04.jpg

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Awesome. Much more involved than any of my fixes. Out of interest what's the wheelbase on the BB body?

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4 hours ago, Nikko85 said:

Awesome. Much more involved than any of my fixes. Out of interest what's the wheelbase on the BB body?

The body itself is around 168mm wheelbase, and the old chassis was around 175.

I haven't mounted up the new gearbox but I'm hoping for a similar wheelbase as the old chassis, maybe a few more mm's on either end for increased stability.

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