trike design questions

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Ratfink1962

Ratfink1962

Joined
Oct 6, 2008
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Location
Haysville, Kansas
It looks like I will be building a gravity racer for the upcoming Gravity Shootout hosted by the Coasters http://locojoe.com/coasters/uploads/coasters_posters_and_fliers/2009_Gravity_Racer_Flyer_big.jpg

So my idea is to build a three wheel contraption using two skinny road style 10 speed wheels and a single wheel with a coaster brake.

Im in the process of trying to finalize my design and im not sure which way to go, My goal is to build something stable and fast. Im torn between having two front wheels and a single rear, or two rear wheels and a single front. The rules are pretty simple, it must steer and have a brake.

Any advantages or disadvantages to running one design over the other? Steering on the front axle or rear?

Im leaning towards the two front (fixed) wheels and a steerable rear wheel, but wanted some input before I proceed. Would this way be stable enough? steerable without having it become to squirrely?

I dont have a whole lotta time to get it done which means I need to keep it simple.
 
I would keep a 2 wheel contraption if possible. A trike of any form is inherently unstable.
 
ive got a trike built gravity racer stashed in my attic that im gonna have to bring out so i can hopefully make it out to the race in wichita. but man its like a 4hr drive for me!!! :( my gravity racer has two 12inch axleless wheels up front, and a 20inch out back. its hard to explain i guess ill just have to drag it out sometime soon for a pic. ACTUALLY.......check this link out. http://viewmorepics.myspace.com/index.c ... ID=1540488 this picture is me and my gravity racer I BUILT OUTTA 2x4's!!! this is kind of a backwards trike i guess...its heavy and HUGE but it freakin flies!!! ive ben clocked by the local police doing 47mph on three consecutive runs on the same hill.

Easy E
 
the only problem i forsee with a rear steer trike, is that any slight turn is gonna want to whip the back end around. but who knows! i really wanna do this gravity race now that ive watched the video but theres a car/bike show that weekend that the spokesmen might be a part of... decisions decisions. you kansas boys should come to blue valley park and race with fast eddie and i where theres turns and huge hills!! good luck with the build ratfink

Easy E
 
Elvis is in the building!

lol, there are plenty of car shows... you'll have tons more fun screaming down the hill.

To get back on topic, I think the stability will be ok If I can figure out the perfect pivot point for the rear steerable wheel. Maybe build in some steering stops to limit the travel since I should only need small adjustments to keep it going straight down the hill.

I thought about a 2 wheel contraption, but im still liking the challenge of making a trike.
 
Ok so I have decided to build it with two wheels out front and one in back.

I will also build in a slight "caster" by mounting it on a slight forward angle which should also help keep it going somewhat straight...I hope... LOL

I think I have the brake figured out, steering... not so much. Thats something Ill have to figure out once the frame is done and the wheel is mounted.

I will have some pics maybe soon.


Elvis.. I forgot to ask, but Im assuming your steering is accomplished by the center pivot on the two front wheels? at speed did it feel stable, or twitchy and hard to control? And 47 mph is plenty fast!!
 
ill do my best at trying to explain how the steering works on mine. inbetween the 2x4s that are the frame, up front, the is a 4x4block with a hole in the center of it. ive got a really long bolt that runs through it all with washers where they need to be and a lock nut on the end of course.i pivots on that center bolt. as for stability, i had too many washers in it when i tested it so it kinda rocked ever so slightly, and when i got it up to speed, which i know had to have been WAY faster than 47mph, at least it felt like it, it was a little hard to control, kinda like a gyro-scope type thing but still maintained and functioned top notch.

if you still are looking for a brake setup, heres what i did. i dont have any pics of it though. i just used a 20inch bmx fork mounted horizontally with the front brake from the bike still attached, then i ran a brake cable and lever underneath the pegs in the back so i used my foot for a brake. very cool and very functional.

hope some of this makes sense and is somewhat helpful to you. post some pics of your progress once ya start buildin!

Easy E
 
Thanks for the info, and yes it helps.

My brake idea is pretty simple. Im using the rear wheel off of a kids 16" stingray. The tire is a 16x3 which is probably more than wide enough to handle the braking load. The brake itself is the original coaster brake on the 16" wheel, I will fab up a cable hooked to a length of bike chain to make it functional.

Ive already got the rear part of the frame ready along with the pivot point, pics coming soon!
 
i have found that using bigger wheels is better, it might take just a hair longer to get up to speed, but you will achieve higher speeds. and also skinnier tires. if i did it all over again, id use a 26x1 3/8 tire in the back and some 20s up front. a friend of mine has a gravity racer that is built exactly like mine but he used 12inch wheels for all three wheels. we have the exact same design except for the wheels aspect and i smoked him every time. just some food for thought for ya

Easy E
 
my gravity trike for the atlanta soapbox derby.

it worked great. straight hill.
no crashes.

one thing i am changing for next year - add more weight.
3032367819_fc7d88af56_b.jpg
 
Elvis, yes I am using 26x1 3/8 wheels/tires for the two front wheels, the rear is only a 16" because thats all I had laying around. I will probably end up washing out the old grease and going with something lighter in weight to help it spin.


Blink... thats friggin cool! love the sawblades!
 
Well Ive got the basic frame laid out, tacked and awaiting the attachment of the rear wheel/steering assembly, I was gonna do that tonight but ran out of time.

After that Ill move to the front, and build up a front axle since I did end up getting a couple of road bike wheels.

aka_locojoe said:
Nice to see progress. I'm anxious to see where this goes.
Click to expand...

It probably wont be pretty, but it should roll down the hill... I hope :lol:
 
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