Mid Motor Rustler - V2

[rc10nick]

Towers and motor plate are done!





I tried CNC'ing the battery tabs at the same time, but the machining operation didn't work and destroyed them. Oh well. I'll get them later. It's nice to have all the CF on the car match now. I also bought some aluminum hexes while I was at it.

[Russ Winn]

This is an awesome build....I can't wait to see it finished.

[rc10nick]

I've got some cool progress to share today!

I finally decided what kind of Traxxas 2wd I wanted to make - a Bandit! TLR parts support has been going the way of Team Durango lately and I decided it would be best to have a backup or potentially a replacement to my TLR 22 5.0. I ordered bandit arms and links from a popular online chop shop and they showed up in the mail today. I just finished putting them on and taking some measurements with TLR 22 wheels/tires fitted on them. Surprisingly, with the 7.5mm truck hexes on the front axles the car is just at the 250mm limit with the TLR 22 front wheels. However the rear end does seem just a hair too wide with the TLR 22 rears and the 5.5mm hexes. I might need to research some more options for wheels/hexes/axles to see what I can do to make sure my car is legal.

Anyway, now for the pics. The car is really starting to come together! I just need to add a wing mount and I've decided to go with the b6's wing mount to make life easy for myself.

[tmaxx51]

Looks really good! If only for aesthetics, I think the narrow chassis is the right move.

Why are you machining your own arms vs using an off-the-shelf part like the ProTrac arms? The RPM long front arms are floppy and actually make the front wider than the rear with the same wheel offset, but they do get you wider.

The casting was unsuccessful for now. I used alumilite performance 80d and the casting had so many bubbles it was practically foam. It seemed to mix well with the dye and chopped fiber strands I put in. I'm sure that with some degassing before mixing the resins and a pressure pot, I could get decent parts. I don't want to deal with that so I have been looking at smooth-on task 6 resin because it has good strength and is supposed to be very easy to work. I did realize that I need to make a couple of changes to my transmission case design so I'm back to trying to fix my 3d printer before resuming the casting process.

*Edit - I missed your 2nd page and the arm question is kind of irrelevant now. Can't wait to see how it does on the track.

[rc10nick]

I finally got around to installing that wing mount. I printed a new tower with the holes for the mount and used that as a template to transfer the holes into the CF tower I already made. It worked, though one of the holes come out really wonky. Oh well, it still beats CNC'ing a new shock tower. I took the beat up wing from my 22 and threw it on just to see how it would look and I'm quite pleased with the result! At this point I just need a body and to throw in some electronics and it will be ready to go! I'm going to go with a modern bandit body and not the old school one I've used in other pictures. That old one is cool but I don't want to destroy it by making it a runner. They seem impossible to find now.

[rc10nick]

Getting closer!

I decided I want to set up the bandit to run slicks on a carpet track. I've seen some carpet tracks across the country switching to slicks to prolong the carpet's life and apparently the cars are easier/more fun to drive and have the benefit of near infinite tire life (downsides are slower lap times vs pins and you need to sauce the tires). I didn't have any clay slicks sitting around, but I did have some very old NIP pink compound Losi tires that I could take to my belt grinder. The fronts came out a bit wonky, but they're good enough for something I didn't have to spend any money on.

I settled on using a 10bl60 ESC with a cheap 10.5t motor I had sitting around. I finished wiring everything up only to discover the hard way I had reversed the polarity of the battery leads and fried the ESC. Such a dumb mistake... anyway a new ESC should be here this week, so when that shows up I'll finish the rest of the wiring.

The new body did show up in the mail so now I'm working on solutions to use velcro to mount the body. Since my new chassis design doesn't match the stock chassis shape there are large gaps between the body and the car. I've designed and printed some tabs to install on the rear of the car that let me use velcro. The front will be a bit trickier to figure out as there's no good places to add tabs, nor does the Traxxas body even conform to the shape of the stock traxxas chassis. I dremelled off the mounting tab on the front top plate so using a body clip isn't an option, not that I really wanted to anyway. I'll figure something out. Then I just need to paint the body and it will be nearly complete!

Last thing I want to do is refresh and re-install the ball diff. Apparently slicks on carpet is like driving on dirt so I'm sure I'll want the ball diff in the car for that. And now for the pics!

Electronics kind of stuffed in, and new body velcro tabs installed:


Unpainted body test fitted to the car:


Close up of new body velcro tabs and body:

[rc10nick]

Ready for action!




Things I did that you can see: Added the motor cooling fan, got the body mounted up with velcro

Things I did that you can't see: Swapped in a ball diff, added spacers between the motor plate and the waterfall brace, reprinted some parts at 100% infill for strength, gave the car a starting point shock setup

I'll be taking it with me tonight to the carpet track to give it a test run before racing starts. I'm pretty excited to see how it get around the track. So far on my little basement track it seems to drive pretty well.

[Frankentruck]

Basement track? More details please.

[rc10nick]

Basement track? More details please.

Nothing too fancy, just some 2x4's on the basement floor with a few jumps I built.



Update on the car: So as expected it didn't survive the night, but it broke in a way I hadn't anticipated and did far more damage than I expected! The idler gear broke free inside the transmission case and completely trashed the main gear on the ball diff. I also toasted two spur gears because the top shaft had so much slop it made setting the mesh near impossible.

But before everything broke I did get a minute or two of driving it on the track, and it was great! Probably could use some more steering, but overall driving that thing was the most fun I had all night. Running the slicks on carpet was really fun - the car felt so much easier and more consistent to drive without the extreme edginess you get on carpet tires and it still felt like I had plenty of grip. Pace was definitely far off of my 22 with carpet tires, but like I said the fun factor was huge. It's definitely something I'm going to try to get going in my area.

[Frankentruck]

Very cool basement track!

[rc10nick]

And it's basically done now!

I redesigned and re-printed the transmission case and it's much better now. I reinforced the area that broke and I figured out a design trick to really help with fitting bearings into 3d printed parts - add a small notched cutout on any bearing recess and use the slicer to force the z-seam in that notch. That way the z-seam blob doesn't screw up fitment/clearances. I've also been running it on my basement track non-stop the last couple of days and it's been very reliable.

I also got around to painting the body and I'm quite pleased with how it turned out. There's no mistaking it for anything other than a bandit now!

And finally to finish up the build I've got some carbide diff balls on the way. With all that done it will be ready to try racing on Friday night. I can't wait!

[Dangeruss]

Pretty car. Nicely built. I like how everything fits under the body all stock like.

[rc10nick]

Pretty car. Nicely built. I like how everything fits under the body all stock like.

Thanks! That was actually one of my major pet peeves about most mid motor traxxas builds and one of my most important goals. I wanted stock bodies to fit without any jankiness or hacking required.

Now that I'm done with the majority of the build, I'm thinking about how to take this further. I've been playing around with diffs lately and the lack of a quick access design in this has me a bit annoyed. So that is definitely a feature that I want to add.

Also, I want to try a 5 gear layout like the new B7 has. If I make the transmission case longer I can use it to brace the chassis instead of a waterfall, and that frees up the space the waterfall takes so I can move the motor forward even more in the car.

[rc10nick]

I took the Bandit out racing again this past Friday and this time nothing broke! I was able to run the car the entire night in the mod 2wd class and it drove really well. I managed to record the main by strapping a phone to my head - I'm sure I looked silly but the video came out great!

[Frankentruck]

Of course you didn't break anything, you're doing a quality job racing out there! It takes some whacks to break stuff.