LocostUSA.com

Hey guys (and gals too I guess...),

Some of you may remember that I built a gravity racer for the 2017 "adult" soapbox derby here in Portland. Things went well and I won it overall on my first try.

The Mk I on the way to victory in 2017:


I was then asked (on this very forum!), "Whatcha going to do to it now so that you're faster next year?"

At the time, I didn't know it but the answer was I was going to build a new one. I developed a very specific vision for the new one, to be called the Mk V, which I couldn't just modify the Mk I to achieve. So I built another, and although I didn't document it here, I did document it on this thread in another forum.

That build was also eminently successful. I won overall again in the Mk V. The Mk I was run to 3rd overall by a friend as well, so it was another very good showing for the Scuderia.

The Mk V on the way to victory in 2018:


I love the event. It's a blast. We will be on the hill again for 2019. I think the Mk V has the potential to go even faster and I would be hard pressed to build something else which might out run it. But I think I'm going to try. It will be difficult to put aside a car that is running within a sneeze of the track record which was set on a MUCH more favorable (HOTTER) day. But I think I am going to try. Why you ask? Read on.

At SEMA this fall, I chatted with someone who runs at Bonneville with a sidecar motorcycle and we had a conversation I just couldn't get out of my head. He asked me why I did a couple of things a certain way and then told me what he did and why for his decade of builds and going to the Flats, and what the results were from their wind tunnel testing. Sometime during that ~10 minute discussion, I realized I was going to be building a new car for this year.

I dug up some used go-kart running gear and acquired an old junked bike to put together a prototype chassis, adding in the front wheel of a pocket bike. This minimizes the height of the running gear underneath the bodywork. I think there's a bit more rolling resistance with smaller, wider, and stickier the kart tires, but I am hoping the smaller size turns into an aero advantage once at speed (>20mph or so). In switching to a single steered front wheel, it also simplifies/reduces the components out in the airstream as well.

My main concern is stability through the Learning Curve. I was pulling almost 1g laterally through there last year and I really don't want to have it flop over on me. The track and overall width will be similar, although narrower, but I am also thinking I will be able to keep it even lower overall than the Mk V as well. Dynamically, I don't think the corner cares if I have one wheel in the lead or in the trail position, as long as the height of the CG is low enough to keep some weight on the inside wheel. I would be curious if anyone has any evidence to the contrary. There was a lot of discussion when the Delta wing came out. I am not afraid to give the concept my own shot.

So, without further adoo, I introduce to you the working prototype for the Scuderia Kouba Mk VII:



It doesn't look like much right now but it will come around. The handlebars are on there just as placeholders, it will not be driven head first. I have the steering planned out regarding how to get it steered while laying down with my head at the stern. At this point the proof of concept indicates that it can be done, so I will be giving it a shot.

I have a new frame started which should be much more square and flat, and it will carry a wider track rear axle- it will be the go-kart front end with fixed tie rods, so that I have independently rotating rear wheels. I still need to figure out a few dimensions for it but it's definitely on its way. Watch this space for further updates.

Constructive comments and thoughts encouraged regarding the 1F2R configuration. That is the component of this build which breaks new ground for me. We clearly got the 2F1R to work well, I hope the single front wheel can apply the needed force to swing the front end around the corner without rolling me tangentially off the course.

I look forward immensely to this adventure!

Chris

Single-front-wheel vehicles are notoriously unstable in turns. An approximately 1-G turn is, I believe, extremely likely to deposit you on your head, which could be sub-optimal for your lap time.

As a demonstration (and for a really good belly laugh!), I refer you to https://www.youtube.com/watch?v=QQh56geU0X8

_________________
Scratch building, at continental-drift speed, a custom McSoreley-design framed, dual-Weber 45DCOE carburated, Zetec-engined, ridiculously fast money pit.

http://zetec7.webs.com/

I'm with zetec they pretty much outlawed sidecars driving both front wheels in bike side car racing (made everything else obsolete) I'm not sure its the same thing in gravity racers but I suspect Jeremy would say so.

I admit, I am skeptical regarding its cornering ability. The single thing making me go forward with the project is the rest of the fleet I have built is 3-wheeled and corners just fine. I am well aware of the Robin film and its roll-over talents. Looking at its layout, it's quite obvious as to why it turns turtle at the slightest hint of a corner. Clarkson is well off-center and very high off the ground, as is the motor. It is ideally constructed to be a roll over machine. Same can be said of the original 3-wheel ATV's, or the Harley or Goldwing trikes. Super high CG compared to the track width, super easy to roll over.

Think of a 3-wheeled Morgan: would it be any more or less stable if its driving direction was turned around? Physics would still apply the same force to its CG, introducing the same moment about its roll center, right? I've seen the Hamster flog one around pretty liberally (I think he has a thing for them) and it seemed to be under control.

Also, the Mk V is 22" tall at its tallest point. It was that tall because they are 20" tires and there's ~1.5" of ground clearance. The Mk VII has 10" tall tires, so it will only be as tall as I need to see over my own size 10.5 feet. The rear end I will be using is a bit wider than the one shown in the pic above- maybe not quite twice as wide, but close. I think it can work.

Based on the mechanics working out very well on the three other 3-wheel entries which have all been down the hill quite successfully (albeit in reverse), I am willing to give it a try.

I am also willing to admit that I may be wrong, but I'll never know if I don't try.

Absolutely true, my kinda thinking!

_________________
Perry

'If man built it, man can fix it'
"No one ever told me I couldn't do it."
"If you can't build it safe, don't build it."

Perry's Locost Super Che7enette Build
Perry's TBird Based 5.0L Super 7 L.S.O
Perry's S10 Super 7 The 3rd
Perry's 4th Build The Topolino 500 (Little Mouse) Altered
Perry's 5th Build the Super Slant 6 Super 7
Perry's Final Build the 1929 Mercedes Gazelle

We're missing a picture here?

_________________
***************
Geek49203 aka
Tim Wohlford
Louisville, KY
Hayes front, S10 +2 rear, Lalo body.

Physics applies equally, regardless of 2f/1r or 1f/2r. It's all about CG management...Not just vertically and laterally, but longitudinally as well. Keep your weight not only low and centered, but rearward too. If you were running the same tires all the way around, I'd probably start with a target for equal load on each tire. With the front tire being narrower contact (and harder compound?) It might help to move it back even further yet.

Also, as much as I love the TG Robin segment, they did things to the car to exaggerate it's tendencies.

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

The more I thought about it, this is the same conclusion I reached as well. It somehow doesn't feel too right though, or there will be some dynamic component to it having only one wheel doing the steering. Time will tell though.

I think there will be some benefit to keeping some weight on the front tire but definitely away from what I am calling the "roll centers"- a line drawn from the front contact patch to either of the rear ones. The further away the CG is from this, the more stable it will be.

I changed the link for the proto pic. I think it should work now.

Correct. Regardless of three wheels or four, connect the dots between the tires. As long as your dynamic center due to weight transfer stays inside that (3 or 4 sided) box, the car should stay shiny side up. The closer you get to the line, there closer you will be to drastically altering your view of the world.

I'm not seeing your prototype pic. Maybe try uploading directly to the forum?

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

The third picture of the proto type doesn't appear.

_________________
Perry

'If man built it, man can fix it'
"No one ever told me I couldn't do it."
"If you can't build it safe, don't build it."

Perry's Locost Super Che7enette Build
Perry's TBird Based 5.0L Super 7 L.S.O
Perry's S10 Super 7 The 3rd
Perry's 4th Build The Topolino 500 (Little Mouse) Altered
Perry's 5th Build the Super Slant 6 Super 7
Perry's Final Build the 1929 Mercedes Gazelle

Worked on the new car a bit this morning, getting the rear axle ready to attach to the new frame. Have it all laid out and aligned on the shop floor, just need to commit to a method of attachment. The rear axle is quite a bit wider than the live axle one from the prototype:



Frame members are just tacked together and the front fork is aligned and tacked in with two little scraps to hold it while I lock it in. Rear axle is just placed over the aft end of the frame. I need to figure out where the top rails of the chassis will be positioned and then start tacking them in as well, and then determine the wheelbase and weld in the rear axle.

From there I will do the steering system build out and then finish the brakes. After that it'll be time to make a body, so yeah, it's like I'm almost done already.

With that much caster/trail, ground clearance goes away quickly and steering effort greatly increases as you over center (no self centering steering once a little off center). I understand why you want the fork out of the line of sight. You could make a simple single sided arrangement as shown. Considering the wheel assembly is overkill for this, you may be able to omit one side as-is with a fabbed axle welded at 90 degrees into a tube upright with sphericals in single shear. I suggest you use a wheel chair wheel. You don't even need spherical bearings with careful alignment during welding. Consider uhmw hat bushings or separate the bush from the thrust washer. Fab sheet metal lock tabs for the single shear bolts.

The cycle wheel makes more sense to me if you wanted to keep the track narrow and build a simple leaning system to shift the cg inboard on turns. You'd sit higher to help shift the cg but could also have a shorter wb.

Build whatever you want.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

How about a leaning system?

_________________
mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.