Go Back  R/C Tech Forums > General Forums > Electric Off-Road
Creating and developing a 2wd buggy >

Creating and developing a 2wd buggy

Like Tree24Likes

Creating and developing a 2wd buggy

Old 01-22-2018, 04:11 PM
  #61  
Tech Initiate
 
Join Date: Jan 2018
Location: Blaine, MN
Posts: 31
Default

And that's why I didn't get the Prusa, mine doesn't have belts nor plastic parts. It weights quite a bit but feels very solid. Shame about the printing part I am almost sure it's a software problem maybe my windows install was wonky... Will try again in the next days.[/QUOTE]

Yeah I just looked up your printer and it looks high quality. Hope you can figure out your calibration issues. If not, shoot me a PM and I can get it printed for ya.
Lukeman269 is offline  
Old 01-22-2018, 04:49 PM
  #62  
Tech Elite
Thread Starter
iTrader: (1)
 
Join Date: Sep 2010
Location: My house.
Posts: 3,569
Trader Rating: 1 (100%+)
Default

Originally Posted by Lukeman269
Yeah I just looked up your printer and it looks high quality. Hope you can figure out your calibration issues. If not, shoot me a PM and I can get it printed for ya.
Will do, by the way which software are you using? I'm using blender and the one giving me calibration issues is Repetier.
30Tooth is offline  
Old 01-22-2018, 04:55 PM
  #63  
Suspended
iTrader: (1)
 
Join Date: Oct 2017
Posts: 781
Trader Rating: 1 (100%+)
Default

30tooth,

Have you heard of the Tekin Active Link suspension?

Adding an extra linkage to the inner camber mounts has been done before. Turns out the added complexity was not worth the hassle.

It's really hard to build a better mousetrap. There are pics of my car on the 22 4.0 page for anyone that cares to see my ability to evolve a platform. Before the 4.0 came out my 3.99 was a legit .75 seconds a lap faster than a stock 22 3.0.

Who knows though, if 30tooth can get the extra linkage to work that much better, then maybe the next generation of cars will have to have it too.
urnotevenwrg2 is offline  
Old 01-23-2018, 01:52 AM
  #64  
Tech Elite
Thread Starter
iTrader: (1)
 
Join Date: Sep 2010
Location: My house.
Posts: 3,569
Trader Rating: 1 (100%+)
Default

That would be the DAX suspension, not the suspension design I talked about in the beginning of this thread which is the multi link.

I've seen your car and the 4.0 still has suspension geometry issues. With suspension designs like this you have to make compromises but whoever designs the cars at TLR just can't seem to pick which compromises to make, that's why Yokomo and AE are racking up more wins.
30Tooth is offline  
Old 01-23-2018, 06:54 AM
  #65  
Suspended
iTrader: (1)
 
Join Date: Oct 2017
Posts: 781
Trader Rating: 1 (100%+)
Default

Originally Posted by 30Tooth
That would be the DAX suspension, not the suspension design I talked about in the beginning of this thread which is the multi link.

I've seen your car and the 4.0 still has suspension geometry issues. With suspension designs like this you have to make compromises but whoever designs the cars at TLR just can't seem to pick which compromises to make, that's why Yokomo and AE are racking up more wins.
This last weekend I had the pleasure of driving at a new track about an hour and a half away from where I live. They had the stickiest clay I have ever driven on in 28 years of rc racing. The dirt was so sticky that you could see exactly how much contact patch you were using. My outside rear tire would come off after a run pefectly clean, save for maybe 5mm of the inside edge. If I had added maybe a half degree of negative camber I could have moved the contact patch enough to make that tire come off with no clay stuck to it at all. Not that I would want any more contact patch with that much grip anyway. The working patch of every other tire on my car was centered and even. Doesn't really sound like much of a geometry problem to me if I can use that much of the tire.

Last edited by urnotevenwrg2; 01-23-2018 at 07:33 AM.
urnotevenwrg2 is offline  
Old 01-23-2018, 07:50 AM
  #66  
Tech Addict
iTrader: (8)
 
Join Date: Aug 2008
Location: CT
Posts: 715
Trader Rating: 8 (100%+)
Default

Alright question and hopefully not derailing but theres lot of interesting talk in here about arm length.

So .....

Looking at that Dax front end picture it seems like the kingpin is moved closer to the arm hinge pin vs what the stock C' probably would be.

Buggies and stadium trucks kingpins are out farther then the hing pin so to me its short arm.

4wd and Touring cars have the hinge pin located farther out then the king pin ....

Why? I know 4wd has to clear the front cvd and all that but what is the tuning/geometry reason? Is it just the difference in the vehicles or could the 4wd hingepin/kingpin geometry work on a 2wd or vice versa?
Robbob is offline  
Old 01-23-2018, 09:51 AM
  #67  
Tech Elite
Thread Starter
iTrader: (1)
 
Join Date: Sep 2010
Location: My house.
Posts: 3,569
Trader Rating: 1 (100%+)
Default

Originally Posted by urnotevenwrg2
This last weekend I had the pleasure of driving at a new track about an hour and a half away from where I live. They had the stickiest clay I have ever driven on in 28 years of rc racing. The dirt was so sticky that you could see exactly how much contact patch you were using. My outside rear tire would come off after a run pefectly clean, save for maybe 5mm of the inside edge. If I had added maybe a half degree of negative camber I could have moved the contact patch enough to make that tire come off with no clay stuck to it at all. Not that I would want any more contact patch with that much grip anyway. The working patch of every other tire on my car was centered and even. Doesn't really sound like much of a geometry problem to me if I can use that much of the tire.
That's because you don't know how the camber curves are. Look how the tire is being used the fullest.



Ever wonder why 2.4" tires were ripped out of their beads? Where's why.

Originally Posted by Robbob
Alright question and hopefully not derailing but theres lot of interesting talk in here about arm length.

So .....

Looking at that Dax front end picture it seems like the kingpin is moved closer to the arm hinge pin vs what the stock C' probably would be.

Buggies and stadium trucks kingpins are out farther then the hing pin so to me its short arm.

4wd and Touring cars have the hinge pin located farther out then the king pin ....

Why? I know 4wd has to clear the front cvd and all that but what is the tuning/geometry reason? Is it just the difference in the vehicles or could the 4wd hingepin/kingpin geometry work on a 2wd or vice versa?
If you are referring to the suspension on the tekin car that's no DAX front suspension, it's a type of pillow ball suspension using pan car suspension parts.
That's my focus on the front end, the 2wd cars don't have space and axle joint constraints so I'm choosing to have the kingpin centred in the wheel. Typically 4wd cars have to run larger scrub radius than 2wd cars because it's very difficult to package the axle joint and the wheel bearings. That works better on 1/8th buggies because there's more space and for the record I'm designing an upright that does just that.
Getting rid of the current scrub radius is one of the goals of this project, if zero or negative scrub that remains to be studied. Let me add that MercedesGP and RBR went with negative scrub radius on their 2017 F1 cars.
Robbob likes this.
30Tooth is offline  
Old 01-23-2018, 10:50 AM
  #68  
Suspended
iTrader: (1)
 
Join Date: Oct 2017
Posts: 781
Trader Rating: 1 (100%+)
Default

Originally Posted by 30Tooth
That's because you don't know how the camber curves are. Look how the tire is being used the the fullest
Funny you chose a picture of that 22.

Are you aware of the weight jacking induced by the scrub radius and front caster angle problem that that generation of 22 had? Using that picture is not an accurate representation of what my car even is. Additionally, you have no idea the adjustments I have made to the geometry on my car. Through the entire range of travel my car has no bump steer, and a little bit of camber gain. If I want more steering, I just have to turn the steering wheel more. Because I have moved every bit of weight I can between the front and rear axle, my car can change direction very easy, and with tiny amount of deflection. You can simulate all you want, I tune my stuff by driving it at the limit, making an adjustment, then driving it again to see if the limit moved.

Last weekend I could see (in the real world not in some computer simulation or theoretical model) exactly how much I was using my tires based on how they came off the track. If I had to put a % on it I would say the front tires and inside rear were at 97% use, and the outside rear was at 99% use.

A few weeks ago, the track where I raced last weekend had a pipe burst. They couldn't water and the track dried way out. Huge cracks everywhere. They rehydrated the track and the grip was the same as before it got dry, but now the track was ROUGH, like the roughest smooth sticky clay I have ever seen. My fastest qualifying round was round one as the grip came up the more we ran on it. I didn't make any adjustments to my car all day, just slightly adjusted my driving style. A tiny bit more grip would have made the car slower.
urnotevenwrg2 is offline  
Old 01-23-2018, 11:06 AM
  #69  
Tech Champion
iTrader: (159)
 
Krio's Avatar
 
Join Date: Mar 2008
Location: At dirt tracks in Michigan!
Posts: 5,718
Trader Rating: 159 (99%+)
Default

Originally Posted by Robbob
Alright question and hopefully not derailing but theres lot of interesting talk in here about arm length.

So .....

Looking at that Dax front end picture it seems like the kingpin is moved closer to the arm hinge pin vs what the stock C' probably would be.

Buggies and stadium trucks kingpins are out farther then the hing pin so to me its short arm.

4wd and Touring cars have the hinge pin located farther out then the king pin ....

Why? I know 4wd has to clear the front cvd and all that but what is the tuning/geometry reason? Is it just the difference in the vehicles or could the 4wd hingepin/kingpin geometry work on a 2wd or vice versa?
Some designs are intentionally looking to achieve longer arms and that is why you see the hinge pin inside or outside the king pin. Other times, there are design constraints or other suspension choices that have been predetermined that make the hinge pin location change.

Using the AE B6 and B64 for an example:

AE uses the same arm length (hinge pin to hinge pin) on the B6 as the B64. The B6 C-hub is just like you mentioned on other 2wd vehicles with the hinge pin further inside than the king pin. The B64 hinge pin is pretty much in line with the king pins. For AE, the main reason for this difference is compensation for the wider differentials on the B64. The inner hinge pins are further apart on the 4wd, so the outer hinge pins are that much further out. They have an arm length they chose to stick to, so they design the rest of the suspension around that.

More to the point of what you pointed out on average, there are two main things you need to keep in mind when it comes to the roll center:
1. Where it is when the car is sitting at ride height
2. How quickly it moves up and down due to the suspension compressing/rebounding

Where the roll center is at ride height determines how quickly the car initially reacts to lateral forces due to steering input. How quickly the roll center moves up or down is one factor that determines how quickly the car settles as you are taking the corner. Other things like roll bars and springs can change this, but that's the gist.

Lets assume that we have cars that are identical, but one has long arms and one has short. They also have the same spring and damping rate at the wheel. Also, at ride height, the arms are parallel with the ground. This means they both have the same roll center when the car is at ride height and will react identically the instant you turn the steering wheel. Once the suspension compresses at all, they are now going to react in different ways.*

With everything else equal, a longer arm will make the roll center move less as the suspension compresses. This means the car will settle into the corner more quickly because the chassis will roll less. A shorter arm does the opposite. The shorter the arm is, the more the chassis wants to keep rolling as the suspension compresses. In the example outlined with two cars where everything is equal except the lower arm length, the one with shorter arms will roll more and take longer for the chassis to stop rolling as you enter a corner. Whether this is beneficial or not totally depends on a multitude of factors, such as the traction level, class of vehicle, how rough the track is (thus changing the oil and springs that are used), and even the drivers skill level.

2wd offroad vehicles usually benefit from being a tad slower reacting. Quick changes on the loads the tires experience is a good way to break the rear end loose and cause a spinout. On the flip side, a car that reacts too slowly can also become unpredictable when you need to make quick directional changes such as through a chicane or if you need to dodge a car that is crashed on the track. It's a never ending tug of war to find a balance, but on average the roll center and arms on a 2wd offroad vehicle are lower and shorter than an somewhat equivalent 4wd vehicle.

For 4wd offroad vehicles, the additional stability, grip, and speed they typically experience means you want to take advantage of a suspension that reacts more quickly. Longer arms do this, but you can also make the suspension react more quickly with stiffer springs and swaybars. The stiffer they are, the more quickly equilibrium is reached between the forces trying to roll the car (roll center acting on the center of gravity and centripetal force loading the outer tires) and the forces that are resisting that roll (swaybars and springs).

When you get to on-road, you are looking at even faster left/right changes in direction, so you want an even quicker reacting car. This leads to suspension arms that put the hinge pin out past the king pin to make it as long as possible without resorting to unique inner arm mounting locations. They also want the center of gravity to be closer to the roll center than on offroad vehicles.

*disclaimer: all examples above assume that the static roll center at ride height is below the center of gravity of the vehicle. If you move the roll center above the center of gravity by raising the inner hinge pin really high, the roll center now resists roll instead of aiding it. This is a bad idea 90% of the time, so it is ignored.
Robbob likes this.
Krio is offline  
Old 01-23-2018, 12:52 PM
  #70  
Tech Elite
Thread Starter
iTrader: (1)
 
Join Date: Sep 2010
Location: My house.
Posts: 3,569
Trader Rating: 1 (100%+)
Default

@urnotevenwrg2, seek help.

@Robbob and @Krio, arm length is chosen by what you can package and what the intended geometry calls for. One or the other can be made to give the "same" outcomes if you play with stiffnesses and so on.
30Tooth is offline  
Old 01-23-2018, 01:01 PM
  #71  
Tech Elite
iTrader: (1)
 
Join Date: Mar 2011
Location: Houston
Posts: 2,766
Trader Rating: 1 (100%+)
Default

Originally Posted by Krio
AE uses the same arm length (hinge pin to hinge pin) on the B6 as the B64.
Associated has used the exact same arm length and shock mounting points since the B3. They were even the same on the B44.
30Tooth likes this.
fredswain is offline  
Old 01-23-2018, 01:05 PM
  #72  
Tech Addict
iTrader: (8)
 
Join Date: Aug 2008
Location: CT
Posts: 715
Trader Rating: 8 (100%+)
Default

Originally Posted by Krio
Some designs are intentionally looking to achieve longer arms and that is why you see the hinge pin inside or outside the king pin. Other times, there are design constraints or other suspension choices that have been predetermined that make the hinge pin location change.

Using the AE B6 and B64 for an example:

AE uses the same arm length (hinge pin to hinge pin) on the B6 as the B64. The B6 C-hub is just like you mentioned on other 2wd vehicles with the hinge pin further inside than the king pin. The B64 hinge pin is pretty much in line with the king pins. For AE, the main reason for this difference is compensation for the wider differentials on the B64. The inner hinge pins are further apart on the 4wd, so the outer hinge pins are that much further out. They have an arm length they chose to stick to, so they design the rest of the suspension around that.

More to the point of what you pointed out on average, there are two main things you need to keep in mind when it comes to the roll center:
1. Where it is when the car is sitting at ride height
2. How quickly it moves up and down due to the suspension compressing/rebounding

Where the roll center is at ride height determines how quickly the car initially reacts to lateral forces due to steering input. How quickly the roll center moves up or down is one factor that determines how quickly the car settles as you are taking the corner. Other things like roll bars and springs can change this, but that's the gist.

Lets assume that we have cars that are identical, but one has long arms and one has short. They also have the same spring and damping rate at the wheel. Also, at ride height, the arms are parallel with the ground. This means they both have the same roll center when the car is at ride height and will react identically the instant you turn the steering wheel. Once the suspension compresses at all, they are now going to react in different ways.*

With everything else equal, a longer arm will make the roll center move less as the suspension compresses. This means the car will settle into the corner more quickly because the chassis will roll less. A shorter arm does the opposite. The shorter the arm is, the more the chassis wants to keep rolling as the suspension compresses. In the example outlined with two cars where everything is equal except the lower arm length, the one with shorter arms will roll more and take longer for the chassis to stop rolling as you enter a corner. Whether this is beneficial or not totally depends on a multitude of factors, such as the traction level, class of vehicle, how rough the track is (thus changing the oil and springs that are used), and even the drivers skill level.

2wd offroad vehicles usually benefit from being a tad slower reacting. Quick changes on the loads the tires experience is a good way to break the rear end loose and cause a spinout. On the flip side, a car that reacts too slowly can also become unpredictable when you need to make quick directional changes such as through a chicane or if you need to dodge a car that is crashed on the track. It's a never ending tug of war to find a balance, but on average the roll center and arms on a 2wd offroad vehicle are lower and shorter than an somewhat equivalent 4wd vehicle.

For 4wd offroad vehicles, the additional stability, grip, and speed they typically experience means you want to take advantage of a suspension that reacts more quickly. Longer arms do this, but you can also make the suspension react more quickly with stiffer springs and swaybars. The stiffer they are, the more quickly equilibrium is reached between the forces trying to roll the car (roll center acting on the center of gravity and centripetal force loading the outer tires) and the forces that are resisting that roll (swaybars and springs).

When you get to on-road, you are looking at even faster left/right changes in direction, so you want an even quicker reacting car. This leads to suspension arms that put the hinge pin out past the king pin to make it as long as possible without resorting to unique inner arm mounting locations. They also want the center of gravity to be closer to the roll center than on offroad vehicles.

*disclaimer: all examples above assume that the static roll center at ride height is below the center of gravity of the vehicle. If you move the roll center above the center of gravity by raising the inner hinge pin really high, the roll center now resists roll instead of aiding it. This is a bad idea 90% of the time, so it is ignored.

Thanks for taking the time - gives me some good reading.
Robbob is offline  
Old 01-23-2018, 01:42 PM
  #73  
Tech Elite
iTrader: (1)
 
Join Date: Mar 2011
Location: Houston
Posts: 2,766
Trader Rating: 1 (100%+)
Default

Originally Posted by urnotevenwrg2
Funny you chose a picture of that 22.

Are you aware of the weight jacking induced by the scrub radius and front caster angle problem that that generation of 22 had? Using that picture is not an accurate representation of what my car even is. Additionally, you have no idea the adjustments I have made to the geometry on my car. Through the entire range of travel my car has no bump steer, and a little bit of camber gain. If I want more steering, I just have to turn the steering wheel more. Because I have moved every bit of weight I can between the front and rear axle, my car can change direction very easy, and with tiny amount of deflection. You can simulate all you want, I tune my stuff by driving it at the limit, making an adjustment, then driving it again to see if the limit moved.

Last weekend I could see (in the real world not in some computer simulation or theoretical model) exactly how much I was using my tires based on how they came off the track. If I had to put a % on it I would say the front tires and inside rear were at 97% use, and the outside rear was at 99% use.

A few weeks ago, the track where I raced last weekend had a pipe burst. They couldn't water and the track dried way out. Huge cracks everywhere. They rehydrated the track and the grip was the same as before it got dry, but now the track was ROUGH, like the roughest smooth sticky clay I have ever seen. My fastest qualifying round was round one as the grip came up the more we ran on it. I didn't make any adjustments to my car all day, just slightly adjusted my driving style. A tiny bit more grip would have made the car slower.
I saw your "3.99" as you called it. Your mod to move the rear shocks ahead of the rear arms was already a conversion kit that X-Factory had offered for a while. Yours did look more factory by using the Associated bulkhead though as opposed to a carbon fiber spacer and long standoffs. It was pretty obvious that this would be a feature on the 4.0. My mid motor Durango ran shocks in front of the arms with a 3 gear setup 5 years ago. It didn't have a laydown gearbox though. I built a mid motor RC10 30 years ago that also had the shocks in front of the rear arms. It's a nice setup on modern high grip tracks but on true off-road dirt it's nearly useless. Design around the conditions though and use what works best.
fredswain is offline  
Old 01-23-2018, 02:14 PM
  #74  
Tech Adept
 
Join Date: Feb 2015
Posts: 163
Default


Originally Posted by 30Tooth
That's because you don't know how the camber curves are. Look how the tire is being used the fullest.



Ever wonder why 2.4" tires were ripped out of their beads? Where's why.



If you are referring to the suspension on the tekin car that's no DAX front suspension, it's a type of pillow ball suspension using pan car suspension parts.
That's my focus on the front end, the 2wd cars don't have space and axle joint constraints so I'm choosing to have the kingpin centred in the wheel. Typically 4wd cars have to run larger scrub radius than 2wd cars because it's very difficult to package the axle joint and the wheel bearings. That works better on 1/8th buggies because there's more space and for the record I'm designing an upright that does just that.
Getting rid of the current scrub radius is one of the goals of this project, if zero or negative scrub that remains to be studied. Let me add that MercedesGP and RBR went with negative scrub radius on their 2017 F1 cars.
I was thinking about running a EB410 Tekno as a 2wd on carpet when I get back to racing, but the large scrub radius of using a slim 2wd front rim put me off the idea...

Seeing cornering shots of some (most) cars always shocks me especially the rear wheel camber. This shot is fairly typical I'd say. It looks terrible..

Ps Other image is a Predator. Very long bottom arms (longest ever?), shorter top, low roll centre migration.
30Tooth and stanleyw808 like this.

Last edited by AntH3000; 01-23-2018 at 02:26 PM.
AntH3000 is offline  
Old 01-23-2018, 02:21 PM
  #75  
Suspended
iTrader: (1)
 
Join Date: Oct 2017
Posts: 781
Trader Rating: 1 (100%+)
Default

Originally Posted by fredswain
I saw your "3.99" as you called it. Your mod to move the rear shocks ahead of the rear arms was already a conversion kit that X-Factory had offered for a while. Yours did look more factory by using the Associated bulkhead though as opposed to a carbon fiber spacer and long standoffs. It was pretty obvious that this would be a feature on the 4.0. My mid motor Durango ran shocks in front of the arms with a 3 gear setup 5 years ago. It didn't have a laydown gearbox though. I built a mid motor RC10 30 years ago that also had the shocks in front of the rear arms. It's a nice setup on modern high grip tracks but on true off-road dirt it's nearly useless. Design around the conditions though and use what works best.
Yeah, and the XFactory kit keeps all the weight of the shock tower behind the rear axle, not to mention it adds more weight up high. Even the 4.0 keeps the tower behind the shocks, which means my rear tower, wing mounts and wing is further forward than even a 22 4.0

I have 108g of ballast added to my car to make it to the 1540g weight where I like my car. That 108g is behind the motor under the gear box. I can change my weight bias by quite a bit. With a couple small setup changes and the right tires I know my car would be very good on a loose dirt track. When the track is not really high grip my car is very predictable a little bit beyond the limit. I've developed my car around high grip clay tracks, but the concept of mass centralization is going to produce a car that is easy to drive to the limit, no matter the available grip.
urnotevenwrg2 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.