Build Concept

[Smurf]

Hello all,

I've been fooling around on Google SketchUp, and I think I found something reasonable and quite fun. TRex style, using practically any 750cc or higher motorcycle, custom 2" tube cage, and possibly 600cc or larger ATV front suspension.

Steering wheel, gas and brake pedals, and hand-shifted with clutch on the shifter by your thigh.

http://www.youtube.com/watch?v=wLK5_y3kL_g

Any thoughts or input would be greatly appreciated. Cage too strong, or some weak spots? Any ideas for entry/exit? Perhaps use thin metal bar framing with sheetmetal cover for a lift-off body? I thought to put sheetmetal under and over the tube horizontally on the floor, with expanding foam between the layers.

Am I correct in thinking this should be somewhat easy to register with Motor Vehicle, because it'll be based on a motorcycle with a VIN plate?

Thanks for viewing!

 

[jdmkid]

thats cool. sorta like a t rex. drop in a gsxr and you have a fast *** buggy.

 

[Smurf]

Yeah, like a TRex, but 1/30th of the price :biggrinjester:

 

[OzFab]

Great concept. I have one observation: I noticed your tie rods are in front of the kingpin, IMO, you will be better off with rear facing steering arms

 

[Smurf]

Thanks Fab. And yes, the tierods are in front of the kingpin. It's not a permanent thing, more of a space issue. I was thinking the pedals would be about 1' forward of the bottom of the windshield, the next crosspipe. That would give me almost 4' from back-of-butt to toes for legroom. Still haven't figured out what to borrow the steering box from, perhaps a smaller dune buggy box off eBay? Or just Pittman-arm?

Cutting the end angles on tube will be difficult, do you guys think square tubing would work? Is 2" round tube overkill? It's drawn as 2" OD, 1.75" ID.

 

[Acavet]

Square tubing is easier to work with but its not as strong as round tubing and it weights 3 times as much.

Sandrails are made of 1 1/2" tubing and take a hell of a beating. 2" would be way overkill for a project like this.

This thing as an excessive amount of bracing to begin with, if your intent is to just drive it on the street.

 

[Smurf]

Shrunk it down from 2" to 1.5" tubing. This is with blue glass for body panels, with the instrument panel and Jegs seat. Still haven't figured out the entry/exit, I'm thinking the roof bar should be a pivot, so you can raise the leftside glass and roof up and to the right. I think the body cage would be strong enough, the roof wouldn't need to be boxed solid..?

 

[Smurf]

The way it's set up now, the blue cage is 141 total feet of 1.5" tubing. Google says 1.5"OD, 14ga wall tube is 1.25 pounds per foot.. Gives me ~176 pounds of frame. Uh oh lol

 

[OzFab]

Square tubing is easier to work with but its not as strong as round tubing and it weights 3 times as much.

Square tubing of the same size & wall thickness as round tubing weighs slightly more

Sandrails are made of 1 1/2" tubing and take a hell of a beating. 2" would be way overkill for a project like this.

It's better to use larger, thin wall material than smaller, thickwall.
Smaller, thickwall tube is much heavier than larger, thinwall tube. If you want to use 2" then 1/4" wall thickness is overkill; 1/8 wall thickness will be plenty.

This thing as an excessive amount of bracing to begin with, if your intent is to just drive it on the street.

You can never have too much bracing. Bracing not only strengthens the frame, it also protects the occupant from impacts. IMO, there's not enough bracing in the base frame.

Having said that, I would reverse the side bracing so that they all meet in the centre so, instead of a diamond shape you end up with an X shape. At the moment, the centre has no impact support

The way it's set up now, the blue cage is 141 total feet of 1.5" tubing. Google says 1.5"OD, 14ga wall tube is 1.25 pounds per foot.. Gives me ~176 pounds of frame. Uh oh lol

Ask yourself, how much does the donor bike weigh?

 

[TheWingnut]

I think it looks kool and has a good setup, but ive dealt with soemthing liek this in the past and it can be very unstable.

When i was younger, me and my frined baught a sooter-like thing that had two wheels in the front and on in the back, and when i turned it, pressure would shift very fast and would almost throw you off.

If you are planning on picking up a lot of speed then you might not want to turn a whole lot with this, because pressure shifts very fast with these if your not careful.

 

[Acavet]

I gave you the wrong info in my original post, round tubing weights about 23% less than comparable sized square tubing. You really don't need 2"round tubing that would really be overkill.

Contrary to Fabromans post you don't need a frame that weight almost 200 lbs for something that small. It is over built for your stated usage. The locost lotus uses 1" square tubing, box ladder frame, it seats 2 uses a full size car engine and trans and is under 100lbs.

Take a look at this street rail, its powered by a V6 with over 200 hp has a wheel base over 110" and is built of a combination of 1 1/2" and 1" tubing.

You just dont need anything that radical for that short of wheelbase and a motorcycle engine. Your going to have more strenght just by virtue of having a shorter overall wheelbase and lenght.

 

[Smurf]

My main purposes with this vehicle would be cheap transportation that is different and fun. Realizing two wheels are more economical than four, but I don't trust being on two wheels around these Suburban Assault Vehicles, I figured three wheels is the way to go. Typically, it wouldn't go above 45mph. If I feel it's strong enough, perhaps some straight-line highway speeds.

That said, tipping is an issue on many trikes. I'm currently working to bring the entire cockpit and engine assembly about 12" forward, putting more weight on the front two wheels. And speaking of weight, 176 pounds wouldn't be too much for a 750cc to push around town, and a 1000cc should get it going real good.

How about 1.5"x1/4" tube? Should be a reasonable compromise of strength and weight? And I'm thinking that I should keep the motorcycle's frame in the design, using the fork mount to secure it to the back of the seat area. Then use tube sticking out the backend to secure the bike near the bike's center of gravity. I believe this would be a lot less aligning, precise fabricating, etc.

 

[Acavet]

1.5 tubing is going to be more than enough for your intended usage. Because of the short wheelbase you could probably even get away with 1" tubing.

Your not talking about trying to use 1/4 thick tubing are you? Your referring to the cross braces? If so then your going to need at least 3/4".

Your not going to need all that cross bracing in the area of the passenger compartment. You could eliminate the upper bar and two diagonals that meet in the center. It would make entry/exit much easier too.

 

[fowler]

I wouldn't be taking out any bracing
I wouldn't trust that V6 road rail
It looks like a well aimed kick would bend it
Let along a side hit by a speeding hatchback

By buggy uses 1 1/2 tubing for the roll cage
2 inch box for the basic frame rails
And 1 inch box for bracing
It can withstand end over end rollover
So 1 1/2 is good size

Don't forget the lotus was designed by highly qualified engineers useing state of the art computer program's over a few years
A bloke in his back shed should overbuilt

 

[Smurf]

Well, seems we have two conflicting schools of thought on tubing sizes lol. Before you posted this morning Fab, I was already doing another sketch using various sizes. The core length and front suspension supports are 2" (red), the cockpit area is 1.5" (orange), and the smaller bracing stuff is 1" (green). That's also an early version of the body that would be going over it in the background.

With this update, I made the roof 18" wide, while the cockpit walls remained 36" apart. This should make entry/exit a breeze, while also allowing "gullwing" covering later, if I should desire.

I will be reworking the front suspension soon, as my a-arms were almost 2' long.

 

[OzFab]

Personally, I would use 2" between the suspension supports, 1.5" for the top & front of the roll cage connected to the base frame so the cabin is "self contained" (if that makes sense)

... but, that's just me

 

[Acavet]

There is a reason that there are thousands of tube frame sand rails using 1 1/2 tubing, because it works.

If you think that a piece of tubing between you and a side impact from another vehicle is going to protect you, you have no clue about the dynamics of impact. Protection is about crumple zones and the dissipation of energy it is not about a piece of 1 1/2 tubing you are going to hit with your body with nearly the same force as if you hit the other cars bumper.

This is a picture of a frame that I built many years ago for a single seat street legal car. Its made of 1 1/2 square tubing. I wouldn't build anything this heavy today, its just not needed.

Here is a picture of a single seat race car frame built with 1" tubing. If its strong enough to race, its strong enough for the street.

Box style frames are incredibly strong and don't require nearly as much material as ladder style frames to maintain the same rigidity.

 

[OzFab]

If you think that a piece of tubing between you and a side impact from another vehicle is going to protect you, you have no clue about the dynamics of impact.

I need to ask, who is that directed at?

 

[Smurf]

With this vehicle using a motorcycle on the back, I would think having plenty of bracing on the back of the cockpit would be beneficial. I've done probably four different frame versions since posting this thread, each trying different methods, and I assume eventually one will just look "right".

"his is a picture of a frame that I built many years ago for a single seat street legal car. Its made of 1 1/2 square tubing."

Then again, the main reason I've been leaning towards the 2F1R trike is because four-wheel homemade vehicles are reportedly a pain to register. I like the sleek teardrop shape of a 2F1R, but if getting the paper pushers to approve a four-wheel idea were easier I might be drawing those.

 

[Smurf]

http://www.youtube.com/watch?v=GacdWNtB_D0

Another version. This one is only 6' long from bumper to back, which saves me 2' of overall length. The 'sidepods' would obviously need some aero work.

The main frame is 2", all other tubing is 1"