re: The Bent Zombie Tribrid Tadpole Trike (build phase)
I hope so silver! Yer so right about scale, height & speed vs perception, aviation illustrates that pretty drastically - 180mph inna Cessna 172 @ a coupla thousand feet > yawn, BUT 60mph in a MX ultralight spinnin' yer gear ofn the corn > OMGBBQCHICKENZ!!1! Brown Alert! Felt faster than any car I ever pounded on lol
With that thought in mind (or center of mass & stability... honest heh) I just spent the past two days fighting over just a few inches or even less, cutting, bending, moving & doin' it all over again - it's a tough battle & it's not over yet. In the previous pics it mighta looked kinda cool - but the fact is the front of the seat was just waaay too high & the back too low.
First step was to recruit a friend to help, putting the new seat on the floor they held up the back and raised & lowered it until we found a "neutral" riding position, one that was comfy & let me "see" all around w/o undue neck strain, then noting it's angle & height. Seat angle is the most important contributor to a recumbent's speed as it's the whole point after all - the lay-back design reducing frontal area (wind resistance) drastically... but that doesn't do me a danged bit o'good if all I can see is blue sky lol, I s'pose I could mirror the underside of my hat brim... naw
Armed w/some numbers at last, now came the
really hard part - cleaning out the ol' shop space so I could set up a table as a work area, which was no small task as I'm a bit of a pack rat & I had been grabbin' w/e was shiny with this project in mind. With the pile beaten into submission & the table set - I started cutting off all of the various mounts & tabs from the chassis & trimming down the excess w/a flap sander so I could set the parts back in place & get some real measurements. Interestingly, although I hadn't thought there was that much - I took about 10lbs of the frame when I did that & there's still one cross brace I gotta pull (weird, asymmetrical one in the back), but I busted my last cut-off wheel for the grinder so that'll hafta wait. Ofc I'll be adding weight back on again when I make my mounts *shrug*
I tried another three configurations before I realized I wasn't going to escape a basic truth - if wheelbase is X, component length & height Y, then center of mass will be Z - like it or not. So with some regret I decided that chopping the frame was inevitable - I needed another 4" no matter what. The catch was - where? I'd tried moving the engine so far back it stuck out, adding about 3" to the wheelbase and putting the jack shaft & pivot point for the rear suspension outside the chassis & I didn't like the repercussions at all. While the seat was
almost where I wanted it, it made mounting absolutely everything a nightmare... but the seat was so close... Chopping the beams under the motor gave me length but no more, so I decided to cut the front of the frame where the A arms mount as it's at an upward angle, lengthening those beams would raise spindle height as well, 4" in length added there gave me about a 1" rise, leaving the spindles still about 1" low, but that's easily fixed by mounting them to the top of the bars instead to the side.
Having already broken my last cut-off wheel for the grinder, WAY too impatient to wait till Monday to make the cuts, my trusty Dremel came to the rescue & the screaming death metal noises once again woke the house. Clamping a bit o'angle iron to the frame tubes I repositioned the amputated front end and gathered all of the bits & pieces together, a shift here, wiggle there & wow! Closer than it's ever been to a practical CG!
Now... it's a bit of a monster - the "ideal" wheelbase for a
racing tadpole is 30" W x 40" L, length ofc effects turning radius & width = high speed turn stability. Even uncut this chassis provided 30" W & 48" L - post cut I'm now at about 32" W x 51" L, a whopping 11" over ideal length - but only 3" over expected. Yet that length allowed me to drop the front of the seat almost a full 8" & puttin' my backside just about 13" off the ground, whereas w/the racing taddys yer just about 10" - close enough I figure. The length also provided much needed room for silly things like 1 & 1/2" clearance between the four stroke and the seat (needed for mounts & heat shielding, else hotpants lol) and room for exhaust & intake manifolds, room behind the seat for a fuel tank, room in front of the engine the batteries & ofc steering linkages... steering... yea...
About that - more math blarg. I'm not 100% confident regarding the stability of a single A arm at speed & under compression. In their current configuration & with 1 & 1/4" shock compression (actually 1" but 1/4" added for error margin), I get 3 & 1/2" vertical travel at the wheel but as they're single A arms and not doubles they don't travel straight up & down, it's more of a curve like this "(- -)" - which results in 2" of lateral tire "scrub" & negative camber under maximum impact load. Scrub is bad... but negative camber isn't always... so... I dunno, I figure I'm gonna hafta wait n'see. Converting to a double A arm really is pretty simple, but it does add just a touch of complexity & yet more weight and as everything else like Ackerman steering compensation, kingpin inclination & even travel and ground clearance is all lookin' so good, as supposedly 1" of shock compression & 2" of lateral scrub is within "acceptable" parameters
and as I'll be using shocks w/about 750lb load to test (want a stiff suspension, but that's prolly excessive) - I'm hoping it'll work out *crosses fingers*
So - after 2 days of battling for even just fractions of an inch here & there, it really doesn't
look much different, if anything it may look less "sporty" with the seat back higher - but I'm slowly managing to cram not one, not even two, but
three drives & all their systems into a space not much bigger than usually designated for just the one - me
Here's a coupla more pics heh, the stick in the front is for crankset tube length & approximate placement BTW;