Limitless Liberty's "Unlimited" dream speed build - Stretched Arrma Limitless

[BashingBrian]

I have some ABEC-7 ceramic bearings on the way.

Mmmmmm nice..??

 

[LibertyMKiii]

The CFD software I have used so far is decent showing air flows, but that is about the extent of what it can do. I was looking for data on downforce distribution. Too much force in the rear could cause the front to lift etc... I spoke with a few companies about trial software and that appears to not be an option at this time. Autodesk CFD for example is a subscription for 1 year at $10k. Consultation companies charge around $2-4k. Wind tunnel time is outrageous.

SO it looks like I may build a scale wind tunnel in the garage with 4 sensing pads (1 for each wheel) to measure downforce, plus a 5th sensor in the rear measuring drag force. Based on some calculations it appears I can get wind speeds up around the 120-150mph range through a small test area. This may be my summer project.

Also it may provide some side money providing test simulations for other test projects at some to be determined fee.

-Liberty

After digging into the wind tunnel idea I have determined it is not feasible on my budget.

Summary of the plan. This part was do-able:
Variable frequency drive controller with large shop fan 110v capable of around 12,000 cfm.
Wooden tunnel pull through method with thousands of straws to clean the air flow in the inducer/reducer with plexi-glass test area of 8x12x36 (H, W, L) angled diffuser section to fan.
Simulations capable around 200mph wind speed possible.
Eagle Tree air speed pitot tube system usb datalog capable via their eLogger.
4 wheel scale to measure downforce balance/distribution.
Additional weight scale for drag force measurement.

Problem area:
Boundary layer forms on the surfaces making simulations only good for wings suspended in the middle of the test area. Rolling treadmill type design is the only feasible solution to eliminate the floor boundary layer (match the floor speed with air speed). BUT I would need this belt moving over 120mph to do any simulation that would be usable. The challenges around this are limitless! I looked into belt sanders and conveyor systems. Everything would have to be custom built of course for my needs, but ultimately I can't see it being accurate enough for my needs. (some simulations have differences of 10mm which belt flex could easily make up that tolerance)

This means I am going with the test and crash method! Woo Hooo

Had some great aero inspiration this past week on Vacation:

-Liberty

 

[BashingBrian]

Is that a Transformer or the real thing..????

 

[Lazy Bushman]

Really think so? (honestly interested in any thing that might help) I have a few of them.
Seems like they do not kick in or do anything until the car has some significant angle differing from the direction of travel. From my experience above 80mph once a car is sideways it is game over. The car takes flight and does more flips than the Olympics.

My thoughts are they are better suited for off-road use. My cars typically drive very straight if my alignments are good and throttle application is smooth. I am getting a bit shaky as I get older...


CFD images from design V2. Identifies a few areas that can be improved (orange), which had mostly to do with my laziness during the drawing. Testing at 67 meters per second (150mph)
Yes that means that 200mph is nearly a football field per second. CRAZY!

View attachment 38109

View attachment 38110
View attachment 38111

-Liberty

I think I just dropped a few IQ points reading this?...but I did gain a headache....good stuff

 

[LibertyMKiii]

Is that a Transformer or the real thing..????

We all know that if it was a Transformer it would be a Decepticon (the bad guys always got the cool planes)

It was simply amazing to finally see one of these in person. Hard to believe it's first flight was in 1964 (who knows how long it was in development before that). A plane from that era doing what it did and still holds true as a speed demon for today's time.
2,510mph or (Mach 3.3+)

 

[DoNoHarm]

This is craziness how much detail it takes to hit these insane speeds nowdays. Nice to see that you’re going with the dream build! I’ll be sitting on the edge of my seat until it’s done lol.

 

[LibertyMKiii]

This is craziness how much detail it takes to hit these insane speeds nowdays. Nice to see that you’re going with the dream build! I’ll be sitting on the edge of my seat until it’s done lol.

Ha thanks! This project is going to be a very slow one. This release of the Arrma Limitless is going to slow me down, since I just have to play with thing a little...

BTW these bearings are simply amazing!
ABEC-7
Ceramic
no oil/grease

 

[BashingBrian]

@LibertyMKiii ... If you don't mind me asking, how much did those bearings set you back..??

 

[LibertyMKiii]

@LibertyMKiii ... If you don't mind me asking, how much did those bearings set you back..??

I originally looked at BOCA bearings, and I have used them before but the full set of orange seal ceramics were $200.00 usd
this time I looked at Ali Express and got some from china. Full set was around 80.00 (I can't find my receipt at the moment)
I took a risk on this but so far appears to have paid off.

-Liberty

 

[LibertyMKiii]

I have been doing some intense research on my aerodynamic design.
It appears I will need to pursue custom foam wheels/tires with a significantly taller diameter.

My ground effect methods are only functional at higher distances off the ground. Quoting a research paper with extensive testing:
"For very small ground clearances, the boundary layers developed on the wing lower surface and the ground get closer to each other, decrease the airflow below the wing and ultimately decrease the generated downforce significantly"

#Engineeringproblems

I suspect with these findings that the diffuser and underbody on the Limitless/Infraction are most likely all cosmetic.

-Liberty

Citation: Mokhtar, W. and Lane, J., "Racecar Front Wing Aerodynamics," SAE Int. J. Passeng. Cars - Mech. Syst. 1(1):1392-1403, 2009, https://doi.org/10.4271/2008-01-2988.

 

[BashingBrian]

I suspect with these findings that the diffuser and underbody on the Limitless/Infraction are most likely all cosmetic.

-Liberty

Citation: Mokhtar, W. and Lane, J., "Racecar Front Wing Aerodynamics," SAE Int. J. Passeng. Cars - Mech. Syst. 1(1):1392-1403, 2009, https://doi.org/10.4271/2008-01-2988.

I was thinking too that would be the case, but one can only dream..??

 

[LibertyMKiii]

I have what I believe is a solid plan for the center driveshaft and motor mount setup now, which was one of the big hurdles left on my list before cutting out the chassis (carbon fiber)

I have decided to share my aerodynamic design since I highly doubt anyone is going to attempt "stealing" this concept.

Despite some concerns mentioned in above post #30 I have decided to push on. To explain how I got here trying something different. The concept is used heavily in college solar car competitions. Concepts behind this design is to reduce drag and in their application you can see the curve on the top surface of the body (acting as an airfoil). This is used to create a neutral lift/downforce at their target speed which isn't very high due to the range of their race.

The above image does a good job of illustrating the drag behind a car that it has to "pull" in addition to its own aerodynamic frontal area.

Adapting this concept to my uses the side "pontoons" house the LiPo batteries between the front and back wheels on each side. I am undecided if I will use 4 LiPo batteries to mitigate voltage drop (weight is also an enemy and my LiPos are 2 lbs each). The center section is shaped like and inverted airfoil and utilizes the space between the center and the ground as a venturi. This is also known as ground effect, but not the application used in aircraft. The low pressure zone would effectively suck the car to the ground with less drag penalties than a standard wing on top of the vehicle would. This is very similar to a diffuser/splitter setup on cars but a much larger use of those concepts. This center section would also be what we typically see in a RC car where the ESC and motor will sit.
The side pontoons would also minimize wing tip effect also which is a plus

Now for the good stuff (It already looks fast right?):

Front:

Rear:

On CFD fast moving air starts with white then to orange and finally red. Blue is slower moving air.
Fast moving air creates low pressure zone where negative lift or what we call downforce from the venturi effect exists.

-Liberty

 

[Just a Basher]

This is good stuff. Looking forward to this coming together.

 

[BashingBrian]

I love reading your updates, but my brain always hurts afterwards..???

 

[Notorious J]

I have what I believe is a solid plan for the center driveshaft and motor mount setup now, which was one of the big hurdles left on my list before cutting out the chassis (carbon fiber)

I have decided to share my aerodynamic design since I highly doubt anyone is going to attempt "stealing" this concept.

Despite some concerns mentioned in above post #30 I have decided to push on. To explain how I got here trying something different. The concept is used heavily in college solar car competitions. Concepts behind this design is to reduce drag and in their application you can see the curve on the top surface of the body (acting as an airfoil). This is used to create a neutral lift/downforce at their target speed which isn't very high due to the range of their race.
View attachment 41884
View attachment 41882

View attachment 41883

The above image does a good job of illustrating the drag behind a car that it has to "pull" in addition to its own aerodynamic frontal area.

Adapting this concept to my uses the side "pontoons" house the LiPo batteries between the front and back wheels on each side. I am undecided if I will use 4 LiPo batteries to mitigate voltage drop (weight is also an enemy and my LiPos are 2 lbs each). The center section is shaped like and inverted airfoil and utilizes the space between the center and the ground as a venturi. This is also known as ground effect, but not the application used in aircraft. The low pressure zone would effectively suck the car to the ground with less drag penalties than a standard wing on top of the vehicle would. This is very similar to a diffuser/splitter setup on cars but a much larger use of those concepts. This center section would also be what we typically see in a RC car where the ESC and motor will sit.
The side pontoons would also minimize wing tip effect also which is a plus

Now for the good stuff (It already looks fast right?):

View attachment 41876

Front:
View attachment 41877

Rear:
View attachment 41878


On CFD fast moving air starts with white then to orange and finally red. Blue is slower moving air.
Fast moving air creates low pressure zone where negative lift or what we call downforce from the venturi effect exists.

View attachment 41880
View attachment 41881

-Liberty

Arrma Aerospace in the house! If you bring that body to fruition, you may just change the speed run game. What will you call it now that Limitless is taken?

 

[LibertyMKiii]

Arrma Aerospace in the house! If you bring that body to fruition, you may just change the speed run game. What will you call it now that Limitless is taken?

That is a good question and it is very likely I will make a custom body for the Limitless also...

 

[LibertyMKiii]

Oddly enough @Notorious J I have had some issues with my 1/10 scale diffs along with concerns of the abilities of the dog bones holding the power I plan on using. Long story short this build is evolving into a Limitless build now. The exception is I wont be using the Limitless body or aero so it may not resemble the production Limitless very much beyond the guts on the inside. The plan is to make it the way I feel the Limitless should be (maybe a future view into the V2 Limitless?) Can't wait to get the Limitless and begin ripping it apart

 

[Notorious J]

Oddly enough @Notorious J I have had some issues with my 1/10 scale diffs along with concerns of the abilities of the dog bones holding the power I plan on using. Long story short this build is evolving into a Limitless build now. The exception is I wont be using the Limitless body or aero so it may not resemble the production Limitless very much beyond the guts on the inside. The plan is to make it the way I feel the Limitless should be (maybe a future view into the V2 Limitless?) Can't wait to get the Limitless and begin ripping it apart

Have you considered using the dog bones from a different brand, possibly one geared more to racing? In fairness, the Limitless was designed to go fast, so I imagine that the parts included in the roller should be able to hold up. Food for thought then. Looking forward to seeing that body once the designs are final. That catamaran design seems ideal, but I just can't grasp how you would form it around and existing chassis. I leave the aerospace to you. I just like to break stuff ?

 

[LibertyMKiii]

Have you considered using the dog bones from a different brand, possibly one geared more to racing? In fairness, the Limitless was designed to go fast, so I imagine that the parts included in the roller should be able to hold up. Food for thought then. Looking forward to seeing that body once the designs are final. That catamaran design seems ideal, but I just can't grasp how you would form it around and existing chassis. I leave the aerospace to you. I just like to break stuff ?

I did look into other brands and I own a nice 3 axis lathe/mill (Emco Unimate SL) so the option of building my own from tool steel was looked at also. Ultimately it is the scale of the 1/10 parts that had me concerned handling 10+hp. The Arrma stuff will do much better and is very accessible at low cost, which is the other consideration for this build.

The body forming will certainly be a challenge. I will be doing that part in clay then forming the final copy in fiberglass. It should be lots of fun!

-Liberty

 

[LibertyMKiii]

Good deal came up locally that I just had to have... It has a TP 4060 motor inside, savox servo, and mm2 esc.

All the other parts of the Limitless probably won't be used on my build anyway. (Chassis, diffuser, splitter, and body) so this seemed a wise purchase.

Got the 2 Limitless 168mm dog bones for the extra long chassis. Should ballpark around a 20" wheelbase.

Can't wait to start cutting the CF chassis, but it's 96-99 degrees the next 7 days