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Rethinking 2wd Buggy Design

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Rethinking 2wd Buggy Design

Old 12-13-2017, 09:57 PM
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Default Rethinking 2wd Buggy Design

Current state of the project.



From the beginning:

After extensive testing of my last 2wd Buggy where I extensively modified a TLR 22. The main objective was to test the idea of reducing the polar moment of inertia by centralising the mass as much as possible. I also heavily tested front and rear weight bias to fully understand its affect.

Mistakes made in re-designing the car have taught me more about steering and suspension geometry.

Toward the end of this project I have started to play with aerodynamics and making the car light weight.












Most of the light weight stuff I tried worked well but I had a number of none results in the aero department. The one that really stumped me was any wing I tried on the front tower had no effect. I only have pics of my first try. I think there was some weird interaction with the front window and the window canards I put on the increase the window surface area. By the way the window canards WORK REALLY WELL!


BUT...... I am reaching the limit of what I am able to do with the cars design. AND this car was built for dirt, in the winter here we have a carpet offroad track where we run slicks. This car shouldn't work! But its not bad.... I know I could make this work but it would mean major changes and it wouldn't work on dirt. Soooooo.........

I wanted to build a new car. I wanted to design another car. Some of you might remember the Theory.


But things have changed in the rapid fabrication world. The one thing that I got excited about was 3D printing. So I picked one up and have started playing with it. And yes I know that the parts aren't perfect and aren't as strong. But there are new materials that have peaked my interest and I am going to give them a try. (More on that later)

Also, since I designed my last car the CAD programs have come along in leaps and bounds. The school I work at uses Fusion 360 and I thought I would give that a try. And WOW! In a short period of time I was able to get a car more or less designed. Probably under 50 hrs. The design still needs a bunch of little things to finish it off but I had to show it off.

OK, back to the beginning. While looking for design inspiration for the 22 based car I noticed that things haven't changed much since the original RC10. Granted that was (for it time) an ingenious design. But look at the development that has occurred in electronics. And the cars haven't really changed. Yah mid motor was a big change but that was due to track conditions changing.

So, taking what I learned from my last project and implementing a bunch of stuff that I want to try. I decided that for my first project in Fusion 360 I would design this....


OK...... There is a lot to unpack here!

I wanted to make something that is a major departure from current buggies. And the first thing I noticed was that shock towers haven't changed since the RC10. They are big aerodynamic slabs that run perpendicular to airflow. Yes I know offroad cars will always be aerodynamically dirty but I want to clean up this car and see what happens. So I came up with this.

Next, when doing sketches trying to figure out the aero the kick up on the front always stood out as a source of lift. So I came up with this idea for a blow through bulkhead. It might not produce a bunch of down force but it won't create lift!

Bottom view


Top view


Can't wait to build a wind tunnel to see what this does.

Another idea I had a while ago was to turn the arms into aerodynamic devices. I will say up front I don't like the front arm design. I am trying to come up with something that is more organic and flows better with the chassis. I think I am happy with the rear arms. I have printed some samples of these and they just need some slight tweeks before the final print.

I have tried making the upper shock mounts aerodynamically cleaner. This is also where the wings are going the be mounted. The wing and body will be vacuum formed out of lexan. The body, which I have sketches for, will start at the end of the monocoque front chassis and I think will bolt onto the car. More on this later.

The front chassis is an F1 inspired monocoque. This will bolt to an aluminium 22 3.0 chassis at the back. This section of the chassis will have braces that were inspired by the ones on the last car. I will be able to add and remove bolts to adjust chassis flex.



Inside the front monocoque is the servo that will be able to slide back and forth to help change weight bias. There will also be room for an ESC and reciever, or they could be installed on the side of the TLR laydown transmission for more rear bias. The last car had the ESC on the end of the motor (this worked really well).

Front view

Originally I had a wing on the lower member of the front arm and changed it to an air foil thinking it might clean the air getting to the rear arm/wing.

Side view


At this point I am calling this car the M-Theory.

That's all for now. My goal is to get most of the rolling chassis done over Christmas break (only two weeks) maybe even running? Just waiting for some parts to modify my 3D printer for this project. All I have to do now is get the design done and not miss any details. I will be posting my progress so stay tuned.

Last edited by NitrousBIG; 06-22-2020 at 11:11 PM.
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Old 12-13-2017, 10:00 PM
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Great job. Check Out Oople, many homebuilt narrow buggies to inspire you!
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Old 12-13-2017, 10:46 PM
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nice work thus far!
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Old 12-13-2017, 10:55 PM
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This is cool. I mean, just the fact that you're doing something different than just assembling RC lego pieces is commendable. I am often discouraged that all my ideas of things to make for an RC car are already being made and available to purchase online. Apparently I'm not being creative enough. (Now I'm remembering how I've imagined inboard front disc brakes for my 1/8 buggy...that'd be pretty sweet...but probably isn't gonna happen.)

Is the front kick-up necessary? Since you're doing a complete redesign...I always figured it's mostly there for rough surfaces. On road cars don't have kick-up like that, so I'm wondering if it's still necessary for indoor? (I assume you're running indoor by the tires...) In my limited 2wd ST experience, I've never been happy with tuning the front suspension, which I attribute to the kick-up angle. It's probably a lot to do with the weight of the tires/wheels on an ST, but my thought is that RC cars are more and more becoming on road cars that go over jumps. You're essentially building an F1 car, and adapting a more on road suspension might be advantagious.
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Old 12-14-2017, 02:40 AM
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I suppose my initial thoughts are that while an interesting project, and while an approach like that might yield results... does the end result end up even looking buggy-like, or does it become something else entirely? Then again current buggies already aren't all that "scale" in look in comparison to full-size racing buggies, like those in the Lucas Oil races or such.

As for the front kick-up... can't say I have too much knowledge on the subject, but based on how things move and what I've seen happen on the track I imagine it'd make things more difficult if there was none, when landing jumps even on smooth tracks? Unless you manage to land pretty much level. Kickup absorbs the impact more toward the chassis when you land a bit nose first, as is often the case. I can imagine that with zero kickup you could end up in trouble if the shock travel was fully vertical. Real cars may do jumps without kickup, but they don't generally do ones so big compared to their size.
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Old 12-14-2017, 05:36 AM
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Either way, the homebrew / homebuilt cars are always awesome! And most of the time, its nice to have something not many do.

Here is a pic from Oople, its a B4 that was narrowed down, and he even made his own narrow body by reforming a coke bottle on his own mold.
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Old 12-14-2017, 08:51 AM
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Originally Posted by NitrousBIG View Post
And yes I know that the parts aren't perfect and aren't as strong. But there are new materials that have peaked my interest and I am going to give them a try. (More on that later)


The way I see it, if you can make accurate 3d print parts, a guy can use those parts to make a mold and replicate the part in carbon fiber! (or Fiberglass or Kevlar...) That'd be sweet, right?

I've built fiberglass canoes, I built a kevlar SC body once, and I happen to have a vacuum pump for vacuum bagging...just sayin'.
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Old 12-14-2017, 08:52 AM
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Originally Posted by fredygump View Post
The way I see it, if you can make accurate 3d print parts, a guy can use those parts to make a mold and replicate the part in carbon fiber! (or Fiberglass or Kevlar...) That'd be sweet, right?

I've built fiberglass canoes, I built a kevlar SC body once, and I happen to have a vacuum pump for vacuum bagging...just sayin'.
Hint hint!
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Old 12-14-2017, 09:02 AM
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...

Like this 3D printed Laydown Transmission with Hydradrive and Cover!
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Old 12-16-2017, 10:50 AM
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Couple of old threads I found cool that are similar

New project, Slim B4 +12mm chassis

New project, Slim B4 +12mm chassis
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Old 12-16-2017, 03:44 PM
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Originally Posted by fredygump View Post
This is cool. I mean, just the fact that you're doing something different than just assembling RC lego pieces is commendable. I am often discouraged that all my ideas of things to make for an RC car are already being made and available to purchase online. Apparently I'm not being creative enough. (Now I'm remembering how I've imagined inboard front disc brakes for my 1/8 buggy...that'd be pretty sweet...but probably isn't gonna happen.)

Is the front kick-up necessary? Since you're doing a complete redesign...I always figured it's mostly there for rough surfaces. On road cars don't have kick-up like that, so I'm wondering if it's still necessary for indoor? (I assume you're running indoor by the tires...) In my limited 2wd ST experience, I've never been happy with tuning the front suspension, which I attribute to the kick-up angle. It's probably a lot to do with the weight of the tires/wheels on an ST, but my thought is that RC cars are more and more becoming on road cars that go over jumps. You're essentially building an F1 car, and adapting a more on road suspension might be advantagious.
Yes, design elements of this car are heavily influenced by F1, like the monocoque chassis component.

As for the kick-up idea. 2WD buggies do require kick-up for weight transfer. The more kick-up the more transfer. Less kick-up = less transfer. The greater the front weight bias the less kick-up required. That's why 4wd buggies have less kick-up.

This car does not have adjustable kick-up, so if I want to change it I'll have tho print a new front chassis.
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Old 12-16-2017, 03:58 PM
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I've got some more details done.

Buggy 7

I split the front monocoque chassis in half to work on a few things. When I think its done I'll mirror it before printing.

I also added an access hatch to the top to get at the steering. You can also see the servo mount and the slide track it sits in. I really like the honey comb pattern, unfortunately you wont see it.

You also get a good view of the blow through bulkhead and the webbing on the inside of the monocoque.

The bell cranks haven't been tested yet. I have to build the arms, knuckles and figure out how to make motion work in Fusion 360. I can use this to test the travel as well as check ackerman.

Buggy 9

Buggy 8

Buggy 10

Got the motor mount roughed in. I already have these pieces made in aluminium and just have to be tweaked once everything is printed. Notice how the motor mount floats over the chassis braces. This is so the chassis flexes the same on both sides.
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Old 12-16-2017, 04:29 PM
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Originally Posted by NitrousBIG View Post
The greater the front weight bias the less kick-up required. That's why 4wd buggies have less kick-up.
.
4wd has less kick up because of front drive & braking. With the same kickup as a 2wd, it's the same as 20* of anti squat in front.
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Old 12-16-2017, 05:07 PM
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Very cool!

Always like the Predator X10 myself.. seems like that would improve aero as well

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Old 12-16-2017, 07:41 PM
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My son Paul has a degree in Physics and Masters in M.E., including courses in aerodynamics which we applied with our X Factory bodies. He found there are no aerodynamics on a 1/10 off-road R/C car. The cars are far too slow. We've tried all sorts of aero things, including wings on the control arms, canard fins, etc. The only thing that helps with vehicle handling is to produce downforce by adding drag, so size and tilt angle of what pass for air dams is all that matters.

We also discovered that weight is like squeezing a balloon. If you narrow the weight in the chassis you must either make it longer or taller. Those parts have to go somewhere. We quickly found balance is more important, that weight needs to be placed to maximize balance considering both fore-aft and side-to-side. An unbalanced car is impossible to drive fast. Somewhere near the edge of theoretical perfection you fall off a cliff and the car is undrivable.

Coupled with weight distribution is flex. You must control both how much flex there is and where it is. Every track lay-out and every surface requires different amounts and position of flex. And the conventional rule-of-thumb -- loose as a goose outdoors and tied right down indoors -- often is not correct.

Lap times tell the only story that counts.

This is rocket science. And so much fun.
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