Mid Motor Rustler - V2

[SnowTheProto]

I was curious if you'd be considering releasing the files and maybe a simple guide to allow people to build on of their own, (i would like to build one).

[rc10nick]

Files have been released for a few weeks now - https://www.printables.com/model/890186-nickcnc-mid-motor-conversion-for-traxxas-bandit-ru

Warning, though, the transmission cases have a bit of a design flaw that causes melted internals and stripped gears. I fixed the issue but haven't yet updated the files on printables.

Unfortunately I just don't have time to make any kind of a guide outside of what's written on printables or what I've said in my youtube videos about the car. Maybe I'll get there when things slow down over the winter.

[rc10nick]

It's been a while since my last update so I suppose I'm a bit overdue for one. Since my last update I've had lots of fun racing this car, finding and fixing design issues, and dialing in a setup.

Since the last update where I blacked the car out and switched to the LD2 body, I've spent some time working on 3D printed inserts. Their popularity in the crawler world combined with another user on the rctech forums having success with his inserts inspired and motivated me to give them a try. Sparing the boring technical details about design, filament, and printing them, I've arrived at this design:



I've found they work quite well and it's for the same reason the crawler guys like them so much - they're really soft when you compress them, like an open cell insert, but the internal webbing gives you the most sidewall support you've ever had in your life. The result is a tire that grips really well yet is super stable and precise.

My bandit with these inserts in them allowed me to win not one but two races in a row.

Here's a video of my first win (skip to 1:54 for the start of the race):


I got a bit of help in that win with 2nd place having electronics issues, but even once his car got sorted out I was able to reel him in and nearly put him a lap down by the end of the race.

My second win was against a bigger and more competitive field, but unfortunately I didn't get that on camera at all.

It hasn't been all sunshine and roses, though. My transmission case had a bit of a design flaw that resulted in the idler gear slightly rubbing against the transmission case. I learned of this design flaw when I was at the track and stripped out the main gear on my ball diff. When I took the transmission case apart to see what had happened I noticed the recess for the idler gear shaft had melted and deformed which allowed the idler gear to move out of position and wreck my stuff up. A quick redesign later and now everything is good.

In terms of setup, I've noticed my car feels really planted and stable up until the moment it doesn't - it abruptly lets go and is difficult to control once that happens. Up until recently I was trying to tune the car to keep it locked in and prevent any kind of sliding. I think that was a mistake - when you think about it you're going to slide around on dirt no matter what, so you're better off tuning to optimize for a car that's easy to control when it does slide. I think it's also why my car felt like it didn't have any corner speed - it was too "locked in" and couldn't rotate through the turn without losing control.

With that in mind I figured from a physics standpoint the centralized mass of a laydown car would make it easier to control while sliding around so I swapped it back over to the LD config. Another motivating factor to switch back to LD is the fastest guys at the track are running laydown even though they could easily switch to standup. Seeing how fast they are made me start second guessing the idea that you need a rearward weight over the tires to be fast even in low grip conditions.

I also bought a set of Schumacher Honeycombs because I wanted a hard, long wearing tire to run on my basement track. The harder compound means tires last much longer than the clay slicks I was using on my basement floor, and with less grip it gives me a way to test my car's stability as it slides around.

I've spent the last few days testing setup changes like a mad man, but it was worth it. The laydown car is now easier to drive and faster than I could ever get the standup car to be. It's really easy to control as it slides which lets me hammer the throttle like an idiot and the car doesn't spin out (exaggerating a bit, but it kind of feels that way compared to how it was before). I also really like these Schumacher Honeycombs - they still drive surprisingly well and they have no visible wear even after days of hard driving on my basement floor. A similar bar tire in a clay compound would be 100% slicked out by now.

The next race is this Saturday and now I'm super excited to test out the car with this new setup!

[Luke66]

Very cool project. Planning on building a racing Rustler based off of your design. Do you think that the chassis needs any wheelbase changes or should it just be good to go wheelbase-wise?

[rc10nick]

Very cool project. Planning on building a racing Rustler based off of your design. Do you think that the chassis needs any wheelbase changes or should it just be good to go wheelbase-wise?

Thanks! Sorry the delay, I'm not too active on these forums anymore. The stock Rustler and Bandit both use the same chassis so no need to worry about wheelbase differences.

[Luke66]

Good to know! Thanks! Will post pics of my build when my project is through.

[Luke66]

Are you active on any other forums as of now? Like have you been posting about your build in other places or just not posting about it at all? (Minus YT) Trying to learn as much as I can about the design while I build mine!

[rc10nick]

I'm active on other places around the web, but the only place I talk about my design nowadays in on my youtube channel. And obviously I do still poke in here from time to time but that's just because there's an insane amount of knowledge here and the builds are some of the best around.

[Lavigna]

I just went through this entire build thread. Really incredible work. Car looks great all black. Pretty amazing you did all this yourself. Thanks for taking the time to share it all with us.

[rc10nick]

Thanks for the kind words!

Since I'm here I guess I can give a small update. I've decided to go super modern and take inspiration from the B7 and more recently the new 22x.

Last fall I designed a 5 gear transmission to use indoor on carpet and ran that all winter. I had some issues with other parts I had designed, but once I got everything figured out the car was pretty fast and competitive.

This summer I'm back to racing outdoor at Pit Stop and I've been running my 5 gear trans on the loose outdoor dirt. It's actually way better than most people would think despite having the motor so far forward on the car. The weight is about as centralized as I can get it which makes it pretty easy to control and it really doesn't feel like I'm lacking rear grip at all.

More recently, and I don't have a picture of this, I redesigned my 5 gear trans case to move the rear shock tower in front of the shocks like on the new 22x. This let me get the shock tower, wing mounts, and wings even more centralized into the chassis and I think it helped. I've also been trying to shave off as much weight as I can. The car was a bit of a pig when I started, roughly 1600g, but now I think I'm down to about ~1560g and it's made a huge difference.

Anyway, here's a pic: