Limitless Project Downforce for VTe2 and Limitless

[Lennart]

That turned out really nice! It appears your angle is far more realistic than the 25 deg. that Arrma used on the Limitless/Infraction/Felony.

I am in that same school of thought that the air gap under the car is too tight to allow enough airflow. There will be a boundary layer interaction with the bottom of the car and another with the ground. I don't think there is enough gap between those two for an under-car venturi to be useful.

BUT I have been wrong before

Yeah, I read a "normal" diffusor angle is like 7-10 degrees. But it is also important to get clean high energy flow towards the diffuser, which is probably not the case because of an exposed front suspension and many holes in the chassis. But it looks better

Ground effect on rc cars is not as powerful like on 1:1 cars, Maybe a higher ride height is better to stay away from ground boundary layer...

When the diffuser angle is too big and/ or not enough airflow under the car: The air gets suck back into the diffuser.
This car has too much rake, so not much air getting towards the diffuser.

@Lennart Don't worry about the 1717. You hear about all the 5 people that grenaded them but you don't hear about the 10,000 people that haven't had any issues.

I've run my at 55K RPM for speed runs with no issues, with that said, it could blow into pieces at any time. But it is what it is and I will run it till it doesn't work anymore. It's not something I worry about. Would I bash with tall gears and high RPM - ah probably not.

As for the temp 65°C is fine and shouldn't be even close to anything damaging. There's also a difference between running temp and resting (storage) temp. When I do a speed run, I might see 75-80°C when the run is done. If I let it sit, the temp gets much higher which tells me the temp sensor is starting to read the true temperature or the sensor is out of range and doing weird stuff. Either way it's just sitting there with no stress on it.

Their isn't much in the motors (magnets, coils and some sensors) I don't believe it's an electronics issue. Which leads me to believe the temperature issue (others pleases chime in) is mechanical. The first is the bearings and lubrication. The second is the thermal expansion. The third might be any insulation or bonding material thermal limits. But, again hot is different than hot under stress.

BTW I'm sure (or at least I hope) that Castle tests every motor that goes out the door for max RPM to make sure it doesn't fly a part.

Now I can sleep better...

 

[LibertyMKiii]

Yeah, I read a "normal" diffusor angle is like 7-10 degrees. But it is also important to get clean high energy flow towards the diffuser, which is probably not the case because of an exposed front suspension and many holes in the chassis. But it looks better

Ground effect on rc cars is not as powerful like on 1:1 cars, Maybe a higher ride height is better to stay away from ground boundary layer...

When the diffuser angle is too big and/ or not enough airflow under the car: The air gets suck back into the diffuser.
This car has too much rake, so not much air getting towards the diffuser.
View attachment 289529

Now I can sleep better...

Just don't go off the deep end and fully build a custom car around the idea

 

[Diem Turner]

Yeah, I read a "normal" diffusor angle is like 7-10 degrees. But it is also important to get clean high energy flow towards the diffuser, which is probably not the case because of an exposed front suspension and many holes in the chassis. But it looks better

Ground effect on rc cars is not as powerful like on 1:1 cars, Maybe a higher ride height is better to stay away from ground boundary layer...

When the diffuser angle is too big and/ or not enough airflow under the car: The air gets suck back into the diffuser.
This car has too much rake, so not much air getting towards the diffuser.
View attachment 289529

Now I can sleep better...

lol...what an awesome image. It literally looks like the cool air is cupping the car's balls from behind.

 

[Lennart]

Just don't go off the deep end and fully build a custom car around the idea

View attachment 289538

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View attachment 289540

I have seen this project a while ago. Would have been really interesting to see how it would perform....

 

[LibertyMKiii]

I have seen this project a while ago. Would have been really interesting to see how it would perform....

Might be a project for the fall/winter this year.
Having too much fun right now running my 1/7 scale.

 

[Lennart]

The cappack did reduce max ripple from 2v to 0.65volts (both at 170 amps). nice

And the first time 0-100 in under 2 seconds. And with all the aero the car is extremely easy to drive.

But I have one concern: Both diffs were very smooth in the beginning but now both are incredibly tight. I can't even spin the front diff with my fingers on the 17mm hex anymore. And you can feel every tooth count when turning the diffs. I already opened the front diff last time but there was nothing to see... no damage

Do I need to shim the diffs or something?

 

[Lennart]

An update every once in a while: I did change from a 21T/46T to a 21T/43T spool. Top speed is now 134kmh. Somehow max amps were reduced from 170A to 165A. And ripple voltage from 0.65V to 0.44V, maybe because I reduced from 10Hz to 5Hz data rate?

My biggest "accomplishment" is I finally found a way to measure G-Force accurately: with my Runcam Thumb pro camera! The footage can be stabilized in Gyroflow so the cam saves gyro data (1000Hz). A friend helped me to convert this data into beautiful charts via python code.

The program averages (in this case) 90 measurements to one point on the graph. Still not perfect but waaaay better results than my smartphone's jittery and unusable results.
At speed ~65kmh the car can drive slalom with over 1.6Gs ! On a different run I drove in circles with ~15m diameter and lower speeds it only managed 1.2Gs there. With GRP XM2 slicks

Here it accelerates at maybe over 1.6Gs but brakes a little better at over 1.8Gs.

0-100 is still 1.85s in the gnss app. And in the gnss app, the castle motor rpm telemetry and now this gyro data proofs that the castle system (with my settings at least) gives a second acceleration punch at over 90kmh with over 1.7-1.9Gs on some logs.... but I don't know that is causing that.

 

[Lennart]

First time driving with HD FPV and also the first crash with the car. Broke the two front wing airfoils, but they were still holding on afterward.

To fix the understeery behaviour I will try to add more caster and camber to the front.
The speed reading is nice to have but the Gforce reader is unusable because it somehow sums up all three force axis.
It is also nice to see the live voltage drop while accelerating.
Throttle percentage, distance from home and RSSI are not working because its not arming properly.

Here you can nicely see the wings pushing the car down at over 120kmh compared to 30kmh.
And driving FPV at 100kmh strangely does not feel as fast as normal line of sight driving.

 

[Jerold]

First time driving with HD FPV and also the first crash with the car. Broke the two front wing airfoils, but they were still holding on afterward.
View attachment 314448

View attachment 314449

To fix the understeery behaviour I will try to add more caster and camber to the front.
The speed reading is nice to have but the Gforce reader is unusable because it somehow sums up all three force axis.
It is also nice to see the live voltage drop while accelerating.
Throttle percentage, distance from home and RSSI are not working because its not arming properly.
View attachment 314450

Here you can nicely see the wings pushing the car down at over 120kmh compared to 30kmh.
And driving FPV at 100kmh strangely does not feel as fast as normal line of sight driving.

View attachment 314452

Very cool project.

I realize your testing and cutting a new path here, but I would say you probably don't want look at the data when you are moving fast or bad things can happen. That's what video and data logs are for.

 

[Lennart]

Very cool project.

I realize your testing and cutting a new path here, but I would say you probably don't want look at the data when you are moving fast or bad things can happen. That's what video and data logs are for.

Thank you

Totally true.
The most I managed was quickly glancing at the speedometer at slower speeds. At higher speeds the eyes are tied to the road.
I just realized those things when looking at the goggles DVR afterwards

 

[Lennart]

A new form of parking lot bashing

And I printed a new rear wing and also new front wing airfoils for more downforce.

 

[Tex Koder]

A new form of parking lot bashing

And I printed a new rear wing and also new front wing airfoils for more downforce.

View attachment 321431

That looks Fantastic!

 

[Jerold]

A new form of parking lot bashing

And I printed a new rear wing and also new front wing airfoils for more downforce.

View attachment 321431

Very cool. I love you well you can see the tire placement on the apex. How is the latency?

 

[Lennart]

Very cool. I love you well you can see the tire placement on the apex. How is the latency?

In the video latency, I see no difference compared to my old analog setup. But 25FPS( 40ms between each frame) vs 100FPS (10ms between each frame) probably reduces the Digital fpv latency further. And the full HD transmission really makes it easy to drive in such a parking lot. With my analog fpv I could only go up and down the straights. Cornering was not really possible with all the curbs there...

However, I think on a typical rc racetrack FPV would not not really give an advantage

The bigger problem now would be my radiolink transmitter, which starts to have control dropouts or short failsafes at over 200meters. And not really more latency but rough feeling steering and throttle inputs.

 

[Jerold]

In the video latency, I see no difference compared to my old analog setup. But 25FPS( 40ms between each frame) vs 100FPS (10ms between each frame) probably reduces the Digital fpv latency further. And the full HD transmission really makes it easy to drive in such a parking lot. With my analog fpv I could only go up and down the straights. Cornering was not really possible with all the curbs there...

However, I think on a typical rc racetrack FPV would not not really give an advantage

The bigger problem now would be my radiolink transmitter, which starts to have control dropouts or short failsafes at over 200meters. And not really more latency but rough feeling steering and throttle inputs.

It would be cool to have an FPV race series. I would be sea sick myself, but I'd probably watch it anyway.

 

[Lennart]

It would be cool to have an FPV race series. I would be sea sick myself, but I'd probably watch it anyway.

In case you have not tried any FPV: it's not as bad as you might think. Only when driving offroad over bumpy stuff you might need a break now and then.

FPV races with live onboard cam broadcasting would be cool, especially when "special" tracks would be driven. Maybe bigger tracks with blind curves, which could not be driven line of sight for example...

 

[LibertyMKiii]

Great updates and work so far.

As an FYI.
Hoboa released a V2 of the car. You would be able to take these rear hubs and some of the related parts to make the rear wing adaptive to the suspension load.

 

[Lennart]

Out of interest I made some aero hubcaps for the grp wheels. They just screw under the 17mm hex wheel nut. So I am not sure if this loosens them up over time, but I will test that... Maybe these will make a slight difference .