Chopper Recumbent
 
Chopper/Bobber
Recumbent E-Bike
Design, Musing and Frame Building

A project by Warren Beauchamp

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9/23/2010
I've been seeing some of the new-ish chopper bikes, with swoopy tubing and fat tires, and the look is starting to grow on me. Time to design a recumbent version. I am told that this is not really a chopper because the fork is not long and raked out. Thom Ollinger says it's a bobber.

The bike would have a triple clamp front suspension, and remote steering on top of the "tank" bar.

Oh, it will probably have electric assist too. I like fast bikes and it will probably be heavy and slow without the e-assist. 

After several design iterations, here's my concept. 72" wheelbase!

So, you might ask, how are you going to bend those sexy curves in that thin wall tubing? To bend the tubes you need a "roll bender". These can be quite expensive. The Pro Tools roll bender is $1200 with one die included. That's a manual bender. Powered ones are crazy expensive.

I recently found the Harbor Freight roll bender - $160, includes 1 inch , 1 1/2 inch and 2 inch dies. Yes it's an el-cheapo Chinese tool, but reviews are positive. Because it includes a 1" die, I'll probably go with 1" tubing. Because I already know this bike will be heavy, I may part from the chrome moly steel, and use something more easily bent like HiTen (Hi Tensile) steel instead.

10/04/2010
I talked to Garrie Hill about the type of tubing to use, and he thinks I should use 2" aluminum tubing and bond it all together with spiffy CF lugs. 

10/14/2010
Garrie made a test part for me. Here it is in the Vaccum bag. Before putting on the CF, the aluminum tube was waxed to allow the tube to be removed later.

After the part was cured, it was removed from the vacuum bag, and the CF was cut down the center line.
The lug could then easily be removed. The trick is to the finish the ragged ends of the lug to cut them off straight, or to make a really slick pattern.
11/05/2010
This bike will have really huge 26" tires like:
  • Surly Endomorph 26" x 3.7" tire - 60 PSI - $120 ea! (with Large Marge rims)
  • Kenda Flame 26" x 3" tire - 40 psi - $30 ea
  • Maxxis Hookwork 26" x 2.4" tire  65PSI - $30 ea (with 32 hole Sun double track rims)
  • CST Cyclops 26" x 2.45" tire - $14
  • Schwalbe Fat Frank 26 x 2..45" tire - 55psi - $40 ea

The Surly tires would be cool, but are too spendy for me, so I'll go for the Hookworms.

More superwide tires/wheels at choppersus.com
 

11/10/2010
I drew up the scale drawing. It keeps looking better. 72" wheelbase!
 

This drawing was later used to make the prettier computerized drawing at the top of the page.

Other iterations: One   Two   Three   Four
 

Here's a chopper from the China bike expo.
2/1/2011
Here's a nice looking chopper frame from http://www.bicycledesigner.com that looks a lot like the frame I want to built, and it only costs about $150. It would work well with 26" wheels and a recumbent seat. An additional BB could be added higher up on the frame for me of a recumbent pedaling position.

Unfortunately, with only about a 55" wheelbase, it's much too small for me.

10/15/2011
I thought I found a frame at chopperus.com that would work again. This one is bigger and I like how it looks better, but it's too small again.
Here's a bit more refining of the frame shape. Now I'm thinking to drop the recumbent pretense because it really is a chopper that would be for cruising, and just go with a springer seat
10/20/2011
More refining. I changed it to use regular handlebars, lowered the BB, and changed the middle tube. Now there is more room for batteries and motors and stuff.

I decided to use steel tubing so I can braze it together.

 

10/22/2011
Here's what I would look like on the choppersus frame. Probably I would fit if I put the seat up high, but then I may as well be riding a mountain bike.
Here's my riding position on the proposed bike to scale. Yes, that is a big bike.
10/29/2011
I finally broke down and bought a tubing roller from Harbor Freight tools. It seems relatively well made. I also bought the stand.  It's a little wobbly, and yes it would work best if bolted to the floor, but I am going to bolt it to some 2x4s to spread out the load instead.

It has dies for 1/2", 1", 1.5" and 2". I am planning on building this bike using 1.5" tubing, so that works for me.

Here is a short section of 1.5" x .035" 4130 tubing that I rolled. 6" of tubing on each end will be lost. The section in the center is the minimum radius bend that I will need for this bike, so I guess this will work for me. It takes a lot of muscle power to roll the tube back and forth, but that's ok I need the exercise. The tube had a small groove in it at this large angle but otherwise the bend looks great.

Next steps are to make a full sized drawing and order some tubing.

11/06/2011
I ordered 25 feet of 1.5" x .035 wall 4130 steel tubing from Aircraft Spruce. They will ship lengths up to 8 ft via UPS. I ordered 5 ft lengths.

I finished the full sized drawing and started rolling tubing. Here's the down tube. It turned out very nice.

The drawing isn't high enough contrast on the brown paper to show up on the camera, so you can't see that the final drawing is just a bit different than the last drawing above.

I rolled a couple more tubes. The bottom tube with the compound curve does have a couple artifacts where the bend transitions. It only takes about 20 minutes to bend each tube.
11/07/2011
Finished bending tubes. Now comes the hard part, putting it together. Here are the tubes all mocked up.

Next step is to obtain the head tube and bottom bracket, and to gather the frame fixtures. That shiny thing below the frame is a 36" steel ruler. Yes, there are parts that need to be cut off still...

Thinking about some rear suspension. I like this design, very compact.
11/16/2011
Another rear suspension revision.

This bike will probably get the wheels and electric motor from my MTB e-commuter.

11/20/2011
I received the head tube and bottom bracket, so it's time to start putting the frame together. I started with attaching the head down tube to the head tube and worked from there.

Here's the tubing notcher I used to fish mouth the tubes.

I used my homemade frame jig to align each tube while I tack brazed it and it turned out pretty well. The fork is just hanging on the frame in this picture.

Next step is to build the rear stays and the suspension pivot.

11/23/2011
I mounted the front suspension fork last night. This is a nice fork that I picked up in a fleabay auction, but it was made before MTB disk brakes were standardized. It does have disk brake mounting tabs but I'll need to make an adapter to be able to mount a standard disk brake. In addition, the disk brake on my current disk brake front wheel barely clears the fork tube, and the brake rotor mounting bolts have hard interference. The only option I can think of it to machine several millimeters off of the disk rotor mount on the hub.

I got a good suggestion from lowracer builder Rick Gritters. He said to use a sturmey-archer XFD hub brake. A little research shows that this brake has about the same stopping power as a disk brake, so that works for me. re-lacing the wheel with a new hub will be less work than getting the disk brake to work.

11/27/2011
Here's the frame with the front fork mounted, sitting in the frame jig to ensure everthing is straight before I complete the brazing on the head tube and the joint that will be drilled out for the rear pivot.
Here's the rear suspension pivot shell, bearings, axle, and the clamp stock that will be used to fasten the axle to the rear stays. I was able to source all of the tubing from my box of tubing cutoffs, and the bearings were left over from an aborted project I was contemplating several years ago.

I have often joked that my hobby is making big pieces of metal into smaller ones, fortunately some of those smaller pieces do end up getting used.

I fully brazed the joint and then used a fairly standard bi-metal hole saw to cut a hole in the joint of the chrome moly tubing. It's important to take your time and use plenty of cutting oil to prevent dulling the hole saw teeth.

The frame was clamped in place on my drill press, and I used a level to ensure that the frame was perfectly perpendicular to the drill press.

After spending a lot of time attempting to make sure the pivot shell was straight using the frame jig, a small square, a micrometer, and my eyeball, I tack brazed the shell into the frame.

Probably not perfect but for using rudimentary tools in a cold garage it's fine.

Here's the bearing and axle in the frame.
12/04/2011
Here's a Tubing Roller demonstration video of me rolling the rear stays for the bobber.
I put the bike back in the jig, and cut the rear stay tubes to fit between the pivot bearings and the Surly dropouts.

It was very difficult to ensure everything was straight with all the curved tubes. I'm not too concerned about perfection, but it would be really nice if the wheels were straight with the frame. Even with a frame jig this is difficult.

I brazed the chain stay tubes to the dropouts. 
12/05/2011
I carefully measured and measured and measured again before drilling the hole in the chain stay for the pivot tube clamp. I put it all together in the jig and a small miracle occurred. It all slid together. I tack brazed the tube clamp into place. In this picture you can see the axle sticking out of the tube clamp. I will slit the chain stay on the bottom and braze a clamp in place which should hold the axle firmly.

Next I need to take it all out of the jig, put wheels back on it and eyeball it to make sure the wheels will be straight. The bike is going to be really low. Now I'll be able to see whether the suspension or the frame bottoms out first.

I ordered a  Y shaped shock from ChainReactionCycles.com after seeing a recommendation. It was a good price and free shipping from jolly old England. Let's hope it gets here soon.

12/06/2011
I took the bike out of the jig and stuck some wheels on it to see how far off the rear swingarm was. Hrrm. I need to hack off one of the rear dropouts and take about 1/4" (5mm) out to make it straight. Oh well, that's why I just tack it together until the frame is all completed.

12/09/2011
Much grinding and re-brazing later, the rear suspension is fixed so the wheel now points straight, as near as I can tell...

12/10/2011
Here's the cushy Planet Bike seat I bought from Gaerlen. Mounting it will be much easier than a recumbent seat. The tube I am holding will clamp to the tube behind it.
Here's the shock I purchased from ChainReactionCycles.com. After checking out how the shock will deflect I decided that a complex design as in the two drawings above is not needed.
12/18/2011
I finished seat mount bracket and made the front shock mount. By using the split tube clamp design it is fully adjustable. Also a nice shot of my nicely organized workbench. Hey, I'm using that stuff!
I have just enough 1.5" tubing left to build massive stays. These really would not need to be this big but I think it looks better than a smaller diameter tube. I'll use .5" tube to triangulate from the rear shock mount down to the lower stay.
Here's what I'm using for the shock bearing. The socket shoulder screw fits into the brass bearing which fits into a couple concentric tubes. I had to hand machine (file) a bit off the outside of the outer tube to allow it to fit in the shock properly.
Here's the bearing in the shock.
12/19/2011
I now have a rolling chassis. Because I used such beefy chain stays I will not need a huge amount of triangulation in the rear subframe. The BMC "600 watt" hub motor fits nicely in the rear.

I need to do a bunch of  tweaking, finish brazing the tacked joints, and cap the tube ends before working on the bottom bracket and handlebars.

I'm still waiting on spokes to lace the drum brake into the front wheel.

12/22/2011
I finished brazing the frame tubes, did some tweaking, etc. Also I added handlebars and the bottom bracket shell. It's beginning to look like a bike.

The handlebars are 7/8 X .058" 6061-T6 aluminum, and I bent them with a 3/4" conduit bender. This works nice as long as you want to make a 5" radius bend. The handlebars are very wide and long, but they are in a comfortable position. I'll use these until I actually get a chance to ride the bike. I may end up doing a remote steering as it would be much more compact and I wouldn't have to deal with the "tiller effect".

The suspension seems to work well. Bouncing on the seat both the front and rear suspension have a bit of bounce but not too much.

12/23/2011
I rebuilt the front wheel with the Sturmey-Archer disk brake and fabricated a clamp to hold the brake torque arm in place.

I have received some feedback saying that the front fork is a bit steep. It does look that way, but I measured and it has 2.5" of trail which is as designed. I rolled it down the driveway and it seemed to handle ok at that speed.

12/25/2011
I liberated some more parts off of the MTB e-bike. I wanted to get the front brake working today but I trashed the cable, so I settled on just taking a picture of me on the bike in the garage.

I was thinking the big handlebars would work out, but now I'm having second thoughts. They are really big. That top tube is too perfectly place as the mount for remote steering.

Merry Christmas!

1/3/2012
Thinking about the bike stand. This will integrate with the rear suspension pivot and fold up to put relatively inconspicuous. A bolt on the back side of the pictured slot acts as a stop to keep the gear in up or down position.

1/7/2012
After much cutting, brazing, grinding, and brushing, the tubes in the rear sub-frame are now capped. Yes they still need some cleanup, I am far from a perfect brazer.

Before reassembling the bike, I need to add a small gusset tube between the upper and lower stays and add the mounting post for the chain guide pulleys.

1/10/2012
I added the mounting posts for the chain guide pulleys, finished brazing the BB mounts and capped another tube, then started to re-assemble the bike. I want to ride it before doing any more brazing!

Note that the power side chain is pulled down to the suspension pivot by  the idler to eliminate pedal induced suspension hop.

1/14/2012
I added the chain, derailleur and back brake, then decided that  I needed to remove the back wheel again, which is a pain. It would be so much easier if the bike would stand on its own. Time to build the bike stand. Here it's shown with  the bike stand legs in the down position.

I ordered a bag of JST-SM connectors from ebikes.ca to use to extend the connectors for the e-bike throttle, Cycle Analyst, and the hall sensors in the rear hub motor.

1/15/2012
Brazed on some braze-ons for the rear derailleur cable and cut the slots and tapped the pivot tube to make the bike stand stay in one place. The fenders I ordered from choppersus.com should arrive tomorrow.

 

Page 2 - Electric, Tweaking and Paint.

 

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