Saturday, April 28, 2007

Pictures Finally!

I rode around the cemetery near my house yesterday. It's a great place to ride with no traffic to speak of and very quiet neighbors. It's fairly level and the road winds around a lot. I rode for about a half hour, averaged 10 mph so it was a nice leisurely test ride.

The recumbent seems about ready to tear down for sanding and paint. I didn't find any new issues. The boom is much stiffer. The seat feels fine, although I think I'll make new covers for the finished bike to fix the extra grommet problem. The speedometer mount works great. I decided to leave the handlebars alone.



Tuesday, April 24, 2007

Riding My Recumbent Bike Again

I took a ride yesterday after making the last set of changes to my bike project.

The seat is pretty comfortable, and I don't slip down anymore. I think I've conquered that challenge.

The front boom is a lot stiffer now, and while riding it, I didn't really notice any flex, although I have to admit I forgot to watch for it while riding.

I made a better place to mount the sensor for the speedometer, and attached a bracket to the frame to hold the display at the bottom of the steering riser (between my thighs when I look down). I discovered the magnet that attaches to a spoke and whips past the sensor, was a loose so it wasn't registering when the bike was going above about 5 mph. I tightened it during a mid-ride garage stop. Also during the stop, I realigned the back wheel which I installed crooked two days ago (how embarrassing).

After a couple more trips around the block, I decided the bike handles much better with the new front dropouts (and the rear wheel straightened out). It's a little floppy at very slow speeds (below about 4 mph), but feels smooth, predictable and solid at higher speeds. I would like to have a little more tiller in the handlebars, though. Tiller is the distance from the centerline of the steering tube, back to your hands. Maybe I'll reverse the gooseneck or try another handlebar.

The front brake position still looks fine even though the tire sits 1/2" further forward than before. In fact, it might even line up better. Go figure.

I'll take some pictures tomorrow - I promise. I'm finally getting closer to a finished bike! It's been about a year since I started.



Sunday, April 15, 2007

Gears and Other Interesting Numbers

I used the Gear Inch & Shift Pattern Calculator just to crunch some numbers. Don't get the idea that I'm obessed with this whole gear ratio thing - I mean it's just a bike. Who really cares what the gear ratios are and how many shift combinations copy each other? What matters is whether the bike is fun and ridable or not. Anyway, just in case years from now someone else is deciding whether to build a bike and they're surfing the web for ideas and numbers and copying pictures to a special folder like I did... here are some more numbers.

My chain rings have 28, 39 and 50 teeth. The gear cluster on the back wheel has 14, 16, 18, 21, 24, 28 teeth. My rear wheel diameter is 26.5", so my gear-inch range is 26.5 to 94.64".
If you're not familiar with gear-inches, that means in low gear my wheel would feel like a 26.5" diameter wheel if the pedals were attached directly to the wheel (like a unicycle). In high gear it would feel like a 94" diameter wheel. The really useful numbers that come out of this is that at 50 pedal strokes per minute, in low gear, I would go 3.94MPH, and in high gear at 70 strokes per minute I would go 19.71. Those are pretty reasonable numbers -a good hill climbing torque, but a good downhill high gear with a few gears in between.

Whl Dia: 26.50 inches
Chainring: 28/39/50

Cluster: 14-16-18-21-24-28

1> 28x28 = 26.50"
2> 28x24 = 30.92"
3> 28x21 = 35.33"
4> 39x28 = 36.91"
5> 28x18 = 41.22"
6> 39x24 = 43.06"
7> 28x16 = 46.38"
8> 50x28 = 47.32"
9> 39x21 = 49.21"
10> 28x14 = 53.00"
11> 50x24 = 55.21"
12> 39x18 = 57.42"
13> 50x21 = 63.10"
14> 39x16 = 64.59"
15> 50x18 = 73.61"
16> 39x14 = 73.82"
17> 50x16 = 82.81"
18> 50x14 = 94.64"

I think I could probably do without the middle (39) chainring if I were starting from scratch. The lowest range and the highest range overlap. But - it's just a bike, and what difference does a 6 ounce gear make when I carry way to many extra pounds myself. I read somewhere that the cheapest, bestest, most cost efficient way to make your bike lighter is to lose a couple pounds.

And still more numbers if anyone cares:
Seat bottom to crank angle = 8 degrees above horizontal
Seat back to crank angle = 112 degrees
hip joint to crank = 34"
crank bearing center is 1" lower than hip joint (drops 1.75 degrees)
X-seam = 40.5"



Saturday, April 14, 2007

New Fork Dropouts

The new dropouts are on the fork. I'm going to fix my seat before I take a test ride. That should be about it for major changes, so I'm getting closer to a paint job and a finished bike. It would be nice to have it done by summer, but that's probably wishful thinking. It all depends on how much time I can put in.



Saturday, April 07, 2007

Forks for the Bike

I realized it's been a while since I posted a picture of the whole bike when I tried to describe to my Mom what it looks like. This picture shows things pretty well, but it still had the old seat. I haven't modified the new one yet - I'm working on the fork right now. Today I cut the new dropouts for mounting the front tire on the fork. I'm adding a little tab to the front side so I can mount a fender. I think I'll need to move the brake forward a smidge to match the new tire position, but I'll wait and see for that.

"...just wing it and see what happens."

The garage door broke a spring Friday. Luckily it happened when my wife was coming home after picking up #1 kid from school instead of when she was leaving to go. The guys who installed it 6 years ago came right out and fixed it.



Sunday, April 01, 2007

Some Calculations

Center of Gravity Calculations:
Weight / Arm / Moment
Front Whl 138.5 / 9 / 1246.5
Rear Whl 169.5 / 50.5 / 8559.75
Total Wt 308.0 / - / 9806.25
CG= 31.84"
Estimated CG height: ~ 31" from the ground (just above belt).

Ok, so here's how I did it. (I know the guys at work are snickering now, because this is a normal function of our job, so if this is old news, just bear with me - some of my friends would actually find this interesting.) I hung a string from the front side of the crank bearing bracket (bb) with a pointer tied on the end. This became my datum point. I measured the distance from where it hit the floor to the center of the contact patches for the front and rear tires. 9" and 50.5" respectively. I set the rear tire on a block the same height as my bathroom scale, and set the scale under the front tire. Then I sat on the bike, and recorded the 138.5# weight. I swapped the wood block and the scale and weighed the rear wheel - 169.5#.

Then I multiplied the weight on the front wheel (138.5 pounds) by the arm (9 inches) to get a moment of 1246.5. I did the same for the rear, then added the two moments (1246.6+8559.75). To find the center of gravity, I divided the total moment (9806.25) by the total weight (308.0 pounds) for a CG of 31.84 inches (31.84" aft of the front side of the crank bearing). That puts it just about 1 inch forward of the bottom of the vertical tube below the seat. It also means I have 55% of the weight on the rear wheel, and 45% on the front, which should feel fairly stable.

Now the actual measuring was a lot more difficult than it sounds here. My scale is digital, and you have to tap it then wait until it zeroes (about 8 seconds), then within the next 5 seconds step on and hold perfectly still while it reads the strain. Using this scale to weigh a bike was almost impossible. I had to get everything centered and ready, straddle the bike, squeeze the brakes so I wouldn't roll off, tap the scale with the wheel and hold it up until it said 0.0. Then at just the right time, I had to set the wheel down in the right spot, sit down, get my feet on the pedals, steady myself against the wall without supporting any weight, and hold perfectly still until the scale gave a reading - but I couldn't lean to see the display so I had to just guess at the time.

Using these numbers, I went to the steering calculator (actually it's called the Trail Calculator since that's what it figures out) and plugged in my numbers. My theoretical trail (ideal amount of trail) calculated out to 1.5". My actual trail calculated to 2". Adding another 1/2" of rake to my forks would bring my trail right on target.

So today, I built a jig to hold my fork and locate the new drop outs. I drilled some holes into the center block and inserted pins where the axle is currently, then I cut some 1/2" thick spacers I can insert under the block after I cut off the old dropouts.

Another productive weekend.