how long to learn??????
halfway through building a LWB lowrider, bum about 13" from ground
Got the chassis rolling today so jury rigged some steering, set up the seat (no brakes, gears etc) and had No1 son trial push me round the garden.
Wobbled every where and Promptly fell off burnt chest on still hot handlebar weld
after about 5-6 goes I could at least stay on (usually) but It felt very insecure.
My sense of balance is reasonable, I can surf, windsurf, cycle, iceskate, skateboard, etc.
I hope I'm correct in assuming it gets easier once pedalling because being pushed adds some weird stresses. (I'm trying to kid my self thats why I fell off )
almost wet myself laughing
The best bit? Loved the seating position, just plywood at present but soooooo comfy.
Hope I can get it wired, I think this is going to be a blast.
It would help to know some details. What is your steerer angle, rake, seatback angle? Tiller? Better yet, got a pic? My experience in giving test rides is that by the second lap around the parking lot, most riders are noticeably more stable and can restart themselves with only minor awkwardness. With homebuilts, though, all bets are off. Putting something together based on aesthetics sometimes results in, um, non-optimal handling parameters.
Hmmmmm, non-optimal handling charicteristics, I like that.
Originally Posted by BlazingPedals
It definately felt that alright. In my defence I have never ridden any kind of recumbent before but have ridden many ultra radical chopper motorcycles with no problems, even with chronic fork flop from phenominal rake angles.
Steering angle - 62 degrees
trail - 2.5 inches
Forks are old straight BMX
Length between axels 76 inches
Front wheel = 20 inches
Rear wheel = 26 inches
Angle between seat pad and back is 115 degrees
Front of seat is angled up at 10 degrees.
So I guess I'm leaning back at approx 35 degrees from vertical. (This is optimal for my broken back comfort)
It will have OSS with track rods but the test roll had tiller steering (definately didnt like that)
In the (terrible) photo -
The steering test was the blue square tube tacked to the bmx bars with a mountain bike handlebar tacked to the driver end to give some semblance of control
the crank is level with the bottom of my butt. The chain is on the large ring just to check clearance, the steering head will fit approx where the wooden block is supporting the seat front.
The photo isnt reversed - the drive chain is on the left crossing through under the seat via a jack shaft to a 15 speed mountain bike setup. Still have to make the LHS front deraileur
The seat back has not been cut to size or shaped yet.
Total cost to date - about $20:00 (for consumables only) everything else is from discarded bikes.
Time output about 3 weekends
Lessons learnt so far -
seat must move forwards approx 2 more inches
Front wheel bearings have too much play so must adjust before next test
Forget a tiller and get the final steering sorted.
With my 320 lbs on board the boom/spine flexes a fair amount (suspension????) but there is design room available to triangulate it. (I was attempting to keep it as minimalistic as poss.)
Last edited by savarin; 12-24-04 at 07:05 PM.
Reason: attatchment didnt attatch
Hmm, that might be a good question for an experienced builder, which is NOT me. To me, two and a half inches sounds like not enough rake for such a slack steerer angle. You might need more rake. Without enough rake, there would be too much trail, which would make the bike handle sluggishly; and tiller would make it even harder to balance at low speeds. One other thing I notice is that the front and rear tires don't appear to be in the same plane. Is that just the angle of the picture, or do you need to straighten it?
The seat is fairly upright, and the seat is certainly low enough. So those two things shouldn't be problems.
Sorry I'm not being more help.
Hey! everything is of help, no worries.
Originally Posted by BlazingPedals
The wheels are in line its just the photo.
The fact that I now have to move the seat forewards will allow more layback if I feel its worthwhile.
The 2.5" trail seems to be the average for most two wheelers of "normal" construction so I thought that would be a fair starting point. Maybe I should rake it out further but that would also produce more fork flop I believe.
Details in your pix are a bit vague but if the diameter of the (monotube?) frame is
same as regular bike, you run the risk of having a sudden frame failure on some
random bounce. Look at the frames on the Rans site (www.rans.com I believe),
at Easy Racers/Tour Easy and the Rotator Pursuit: www.rotatorrecumbent.com
for variances. Monotube should probably be beefed upto 1.25 or 1.375 if you
want to continue single tube at that weight. My learning curve with a Pursuit
was 200+ miles before the wobble got to be reasonable. Ride it on a big flat parking
lot first. Steve
Originally Posted by sch
200+ miles, ouch! thats a a learning curve all right.
Theres hope for me yet.
The main tube is 40mm x 1.5mm, ( 1.57"x 0.06) heavy but this is the first prototype so I dont want to spend big yet.
I will put off the parking lot for a bit as I hate gravel rash
I've re-measured and the actual trail is 3.52 inches which according the the trail calculators should give a "normal" feel to the steering.
Added chains today, if it was a mountain bike then they were set in the middle of the low range. (no method of shifting yet) Moved the seat foreward 2". still tiller steering though.
Actually rode out the garage, down the entranceway and up and down the street.
Got fast enough that brakes would have been nice.
Left hand turns are easier (just like in speed skating, surfing etc)
I can now start from a standstill but a low speed turn is not an option yet though.
This is sooooooo much fun.
a big fat 56 year old with a stupid grin plastered over his face.
The steel pursuit monotube is probably about the same. Mine is Ti, the first version of which was
made with 1.75" tubing, but several weld failures at the cutout where the BB barrel was welded into
the monotube led to a recall and substituting 2.125" tubing for the monotube. This still provides
some vertical bounce but MUCH less than before and the lateral stiffness at the front is much higher.
I used to be able to deflect the frame sideways by pushing on the pedal but not since the upgrade
was done. Stiffness in a monotube is directly related to tube diameter, and not as much affected
by wall thickness. If you can find some chromoly in 1.75 by say 0.04 or so you might find that even
better. Frame weight is not a problem at your present weight. One other thing: study the mid drive
on the Pursuit. It is accomplished by welding a tube perpendicular to the monotube and threading it
to standard axle thread (10mmx1.0mm) and cantilevering a 6spd cassette mounted on bearings so that
it freewheels both directions and having a inboard cog (17t on mine) to drive the rear cassette which
is a standard Ultegra 9spd. The mid cassette is 12-32T, no front der, front CW is IIRC 42T. Net is
a drive range ratio of > 7:1 and with 54 gears you have no large gaps from one gear to the next.
I have come to appreciate the low seat height, 15". Unfortunately, in my experience the LWB with
relaxed angles on the front and reduced front wheel loading, it takes less for the front wheel to slide
out and hence to fall. Since you are only 15" up, the fall is benign, a bit of road rash on the hip. You learn to keep an eagle eye for sand, gravel, thick paint strips on damp roads and recently clay mud
on the edge of the road. I ride mine 2-4kmi per year, and use it about half the time when I ride.
I'm in the process of also building a type of lowrider recumbent. My seat will only be about18 inches of the ground. First check for wheel flop, if you don't know what that is, stand by the bike move the handlebars fron side to side watching to see if the front of your bike rises and lowers. If it does then the head angle isn't right. If you are useing regular bike forks you could try bending the forks for more rake, which will reduce wheel flop. ( Go to recycledrecumbents.com) ADC shows how to bend you forks and so much more all for free. Hope this helps Rogermo
Originally Posted by rogermo
Having built many "choppers" in the late 70's I always found that fork flop was a function of too much rake. In fact my last chopper built in 83 had a very radical fork rake angle and suffered from an excessive amount of flop. (still easily ridable but no chance of hands off)
A standard wedgie also has fork flop albeit only about 3/16". It seems to me that the only way to get rid of fork flop is to have zero trail, ie the tire contact patch being directly under the steering axis so that when the wheel turned the contact patch remains under the steering axis. or with a 90 degree head angle, then any form of trail would produce the famous supermarket trolly shimmy.
The function of fork rake angles (as opposed to steering head angles) is to move the "trail" closer to the steering axis
It is my understanding that "trail" is the "magic" dimension, too little and the bike is a "lively" steerer, too much and its a "slow" steerer.
I am considering removing the front hangers and welding a set on with a series of slots to check this out.
Yesterday we experimented with the height of the handlebars and found that having the hands level with the shoulders gave a far more positive and secure feeling. Interesting but I would not like to do many miles in that position.
Its the reduced front wheel loading that lets it slip in the gravel. Our CofG is low down but sits in the rear third approx so letting the very light front contact bounce (more like weight off in skiing) and skip. (I think)
Originally Posted by sch
I'm not an engineer and only have seat of the pants experience so If I am wrong here please let me know.
I also think Rog had it backwards. My pursuit flops a lot, but the steering is not a problem once
you are under way. Problem only at rest, where if you let go the bars, the slightest angle will
cause the front wheel to flop over. My turn radius low speed is about 1.5 lanes in the road for
180* turn. Your approach to the rake adjustment sounds like it might allow a dial in. Only problem is
sorting out what is due to lack of experience on the bike versus what is due to the rake change. My
first 20-30 miles were like I was 6yrs old back on training wheels, all over the place. One other aspect
to a very few bents, the Pursuit among them: the ability to pull back on the bars a little to increase
torque going up hills. Most bents with a vertical or near vertical steering column allow NO pull back
on the bars, in fact best control is achieved with the lightest touch. In my tryout phase I rode a
couple of SWB and was very wobbly when I gripped the bar like I do on the DF (regular) bike, when
I steered with just fingers laying over the top of the bar, the ride smoothed out nicely. Reason was
I was pulling on the bars with mild variances in the tension in either arm and the bike responded to
the little assymmetries by wobbling back and forth. The Pursuit tolerates a firm grip. The Rans
V2 is another bike that allows a bit of pullback on the bar. Shoulder height would be a little high for
me, mine are about 5" below shoulder height. A friend referred to "ape hangers", took me a bit to
figure out what he was referring to but you would know about that. Bent riders tend to call such
the "superman position" as opposed to "chipmunk" position where the elbows are more flexed and
the bar is closer to the chest, like many Rans SWBs. Steve
I'm only going to play with the trail once I feel confident.
Originally Posted by sch
I think its pretty much in the right spot for the time being.
I'm amazed after the garden experience how quick I started to feel "reasonably" confident and pulled a few figure 8's. Like your bent it took me about 1.5 lane widths to do so.
My youngest son jumped straight on and was off with the wind.
when I rode it back into the garage and went up the sharp easment with a huge bounce it was remarkably stable. Nice feeling.