Planning a Tadpole

[Kinky6]

Hi, I'm new to the board, and already did sort of an intro over in the General Chat forum on Southerners on this board. I'm interested in building a trike, but at over 300# and with bad knees, I can't handle something low-slung. With that in mind, I want something that will be easy to stand up out of, and yet will be stable with a higher center of gravity.

I'm thinking that a tadpole trike with a seat height about the same as a normal chair (18") might be the ticket. Maybe something like Tony Davis' trike (http://www.atomiczombie.com/gallery/...vis/trike2.htm (http://www.atomiczombie.com/gallery/tonydavis/trike2.htm)) with under seat steering and full suspension - both front forks and rear wheel frame would work for me. I tried out a Sun EZ-3 up in ATL the other day. I liked the seat height, and the seat itself, but just wasn't wild about the steering feel. So, I've bought a couple of cheap mountain bikes from pawn shops and thrift stores, next up will be a set of Street Fox plans.

I will use a rear section from a cheap 26" mountain bike for the rear suspension, maybe a 21 or 24 speed bike, and a front suspension like Ed Evans' trike (http://www.atomiczombie.com/gallery/edevans/oldblue.htm), but with the seat dropped down in between the three wheels. I'd like to use a matching pair of forks that already have the mount for the disc calipers so that a later upgrade will be easy, but I haven't settled on a front wheel size yet.

I like the seat designs that Timmy has on his page, (http://bellsouthpwp2.net/k/a/karlet/Seats.htm) but I've already bought something very close to that; I got a new seat from a Sun EZ-3 off of eBay last week.

Question for discussion: front track width vs. typical door frame width? I gather that a lot of these trikes have a front track width around 33-35", yet a typical door is only 30-32" wide. Are we talking garage storage only?
Just wondering what some of you guys have done.


That's all that I've got for now. Later, Kinky6 :cool:

[TheKid]

You could make the trike as wide or as narrow as you need by simply lengthening or shortening the crossmember. If you want the trike to fit through a 30" doorway, the total width of the crossmember should be 20", which will give a total width of 29-29 1/2". The excess axle length on the outside of the front wheels should be cut off. With the trike that narrow, you may want to keep the seat height to a maximum of 16" for stability.

[gbbwolf]

I bought the streetfox plans,the deltawolf, the kyoto, and the streetfighter.

Just to read them all and figure out what I wanted.
Here is my opinion.

With the streetfox my problem was doing the caster and camber for my first build, also I think it does not tend to be built for a stout gentlemen.

I am 6ft7 355 pounds.

When you get too high in the saddle the center of gravity around corners is going to throw you for a loop.

I had my delta on 2 wheels.

The 14mm axles In my opinion are also going to be a factor with the amount of weight you are putting on them.

StreetFighter in my opinion has almost the same problems for gentlemen our size.

The kyoto I think might be ok but putting my 355 on one side if I am riding alone might present a whole new set of problems.

Deltawolf design is simple with 26 inch wheels in back, wider hubs,
1.5 inch square 14 guage tubing.

With slight modifications to brad's plans which I explained somewhat in my gbbwolf post's.

I raised it higher off the ground and wider in the rear for my broad shoulders.

This thing is a tank.

I rode it for about 17 miles this evening.
I hit 18th gear on some hills.
Which in my opinion is pretty dang fast.
Other than a little noise from a non-greased pillow block bearing,near the end of my ride it was PERFECT.

I also saw you are thinking of using 2 bmx bikes for the front wheels forks and all.
Big Problem even though my delta-wolf is built like a TANK, I don't think you want it steering like A SHERMAN TANK.

My freind built one like you are describing It rides like a tank.
He got the plans off of ebay I have the pic here.http://forum.atomiczombie.com/attachment.php?attachmentid=166&stc=1&d=1216100297

Do what you want but I think you will be sad when you ride it and it turns like a grocery cart with 4 flat rusted wheels.

If the LoadRunner had been out when I built my wolf I think I would have built it first.

But after my long ride today, and the stares yells and honks, and cool trike comment's I doubt it now.

Just my .06 cents.

Nelson

[TheKid]

The tadpole pictured rides like a tank because the steering geometry is far from ideal. There's no caster angle whatsoever, nor is there anywhere near center point steering. It looks like there's 3 or more inches of trail. A better example of using forks on the front end of a tadpole is in the AZ Builders Gallery. In the Trikes and Quads section, go to the bottom and check out Terry's Trike. It's doesn't have true center point steering, but I guarantee you it handles a whole lot better than the trike you pictured.
That said, you're right about instability. I originally built my tadpole with a 28" track, and a seat height of 20". I lowered the seat 2", but there was still some instability. It was almost eliminated when I lowered it to 16". At high speeds, (Over 20 mph.) it was a little shaky, but I rarely go that fast unless I'm riding in a park. When my hip and knees started getting worse, I made the trike much wider and raised the seat. In order to be able to ride pain free, the BB must be at least 7" below the seat. I also used shorter cranks, which helped a lot. So now I have a tadpole that's not so fast, but it rides great. The steering was always quick and responsive due to the center point steering and correct Ackerman, and more important, 1/8" of toe-in. A slight bit of toe-in improves handling quite a bit over straight ahead wheels. On quads and tadpoles, the steering geometry is even more important than on a bike. It's more like a car than a bike.
If you need a trike, Kinky, I agree that a delta for larger individuals is probably the better choice, but even then, if you raise the seat, the rear must also be made proportionately wider to help prevent instability. The DW calls for a rear crossmember if I remember correctly, 6 inches wider than your shoulders. Add 7 inches to that, and that's your total width. However, if you're going to raise the seat and not fit between the wheels, you could go slightly narrower. Using 20" rear wheels may also help, especially with bad knees. The gearing will be lower, the center of gravity will be inherenly 3 " lower than 26" wheels, and the wheels are actually stronger than 26" wheels. I'd also look into shortening the cranks to 140 - 150 mm which will help your knees immensely. If you get aluminum cranks, it's not so hard to shorten them, but the taps aren't cheap. There's a builder that sells shortened cranks named John Stonich. His site is listed in this thread:

http://forum.atomiczombie.com/showthread.php?t=311

[Kinky6]

Thanks for the feedback, like I said, I'm still in the planning stages, and am looking at a lot of design elements for one of these.

I hope the guy who built that green trike has moved past that to something more ridable. "The tadpole pictured rides like a tank because the steering geometry is far from ideal. There's no caster angle whatsoever, nor is there anywhere near center point steering." No kidding, it looks like it was designed as a retirement project by the guy who designed the Tatra automobile. And he's selling the plans on eBay?

What I'm wanting to do is to use the head tube and forks for both front wheels, along with the same rake or steering angle as on the donor bike. While using the front suspension parts may make the design more complex, I want it to remain as simple as possible at the same time.

Later, Kinky6 :cool:

[AtomicZombie]

Besides the green trike having go-cart steering (like two wheels at the end of a board), it has one really dangerous aspect - the force placed on the top fork bearing hardware. The top fork bearing hardware is not designed to be under any stress at all, and in that design most of the riders weight is pushed up against the top fork bearing. When those tiny threads give out, it will be face plant, pole vault city!

Brad

[TheKid]

You'll need to set the head tube angle front to rear to get 1/4" - 1/2" of trail. Your method won't give you center point steering, but you will have suspension. I had a PVC quad that was set up in a similar fashion, but without suspension. Before the PVC warped, there was a small amount of wheel scrub due to a lack of center point steering, but it wasn't bad enough to worry about. The quad couldn't go faster than 12 mph, so I don't know if wheel scrub would have been an issue at higher speeds.
I didn't notice that go cart steering. Lots of research went into that design. It must have taken 5 or 6 minutes.

[Kinky6]

I guess that since I'm new to this stuff, I'm not understanding what "center point steering" is. :confused: On the center of the vehicle's long axis? This would make sense for a bicycle or a motor cycle. On that green "kludge-cycle" this becomes two wheels turning in an arc around the steering axis.

On the Street Fox and the Street Fighter cycle car, there are two wheels that steer in parallel with each other (more or less, accounting for ackerman and toe-in adjustments) while their steering axis is just a little bit inboard of the wheels' centerline.

On the Tony Davis trike, and the Ed Evans trike, the two front wheels steer in parallel with each other, while both have their steering axis running through the centerline (or centerpoint) of the wheel. This set-up looks like the most reasonable path to incorporating front suspension while reusing easily available bicycle componants.

While I know that re engineering bikes or trikes ain't rocket science, it just seems that I'm not understanding something in the lingo.

Thanks, Kinky6. :cool:

[robertwb70]

If I'm not mistaken center point steering IS steering with Ackerman included.

[AtomicZombie]

Center point means that the wheel pivots on its axis where it hits the ground....

http://moodle.student.cnwl.ac.uk/moodledata_shared/CDX%20eTextbook/dswmedia/images/scrubradius.jpg (http://moodle.student.cnwl.ac.uk/moodledata_shared/CDX%20eTextbook/dswmedia/images/scrubradius.jpg)

This way, there is very little bump steer and friction.

Ackermann steering allows the inner wheel to turn more into the corner, as it has to travel less distance than the outer wheel...

http://www.cauc.co.uk/joomla/images/stories/ackermann_new.jpg (http://www.cauc.co.uk/joomla/images/stories/ackermann_new.jpg)

This way, there is no wheel drag or skidding.

I hate to mention the green jack-knife trike, as I honestly think it is lethal, but it has neither center point, Ackermann, or any way to add brakes front wheels.

Even those plastic kid's sidewalk cars have center point and Ackermann steering.

Brad

[robertwb70]

So center point is similar to trail but on the same axis as the camber (perpendicular to trail we usually talk about). Sounds like fun to get all those angles lined up right at the same time.

[TheKid]

It's not that difficult. Just take your time and tack everything in place until you're sure its right.