DYI Recumbent Tandem

[flymeaway]

OK...so I need a challenge would really like to build a long distance capable recumbent tandem. So I'm going to build one from scratch. Just starting the project and expect it will take me through the winter to finish. The only design spec. I've settle on for certain is to use 3 eight foot sections of 1" ID EMT as the basic frame member. The bike will utilize the Bafang BBSHD mid-drive. Haven't decided on the voltage yet, nor the battery configuration, but I want to be able to ride the bike for an entire day and be able to cover any grade encountered without struggling. Will definitely include the Rohloff 500/14 tandem hub, with 26" wheels. For stability I'll be using the tadpole configuration. I'm hoping to be able to bring the cost of the bike in at less than $4,000.....we'll see!

Court J.

 

[flymeaway]

The basic frame member is done 4 lengths of 1" EMT MIG welded together, total out of pocket cost (plus my time welding $0.00) was $26.00. I tested the deflection in the center of an 8 foot span 200 lbs. equals .09375". This frame for it's small size (diameter) is very strong. Total weight of 8 foot length is 22 lbs.

The next step in the process will be building the rear wheel and front wheel frames.

Court J.

 

[flymeaway]

rear whee

OK....the basic structure to support the rear wheel is done. There is 1.5" of adjustment to tension the chain without using an idler arm. The wheel pictured is 700c which I had laying around. I used it to verify the accuracy of my machined parts. Everything is true and on center-line. The dropouts are Rohloff specific and cost me $50. On the finished bike the rear wheel will be 26". There's more to be done on the rear wheel support so the pictures don't show the final product, but the basic structure is there.

Court J.

 

[flymeaway]

Update...finished building the 26" wheels for the front. I also finished the spindles and mounted the wheels and brakes. Wheels have 3 degrees of positive camber and 12 degrees of positive caster. Caster is adjustable, Camber isn't. I also have the king pin angled at 10.5 degrees so the plane of the king pin intersects the tire contact patch. The spindle is also attached to the king pin at .375" behind the center line. I haven't attached the steering linkage yet, but you can see the rack and pinion that I'm going to use. This was the most complicated part of the build because it had to be precise and geometrically accurate. I'm very pleased with the result. I should be receiving the Stokers seat later this week. Once I locate the Stokers seat on the frame I can start to build the frame to hold the crank-set, locate the Captain's seat, locate the front axle relative to the Captain's seat and build the frame to hold the Bafang Mid-drive.

Happy with the progress.......

Court J.

 

[flymeaway]

The rack and pinion steering and wheel spindles are done. Worked out great, very positive control (no slop in the linkage), with built in design for "hands off" straight line wheel tracking. Couldn't be more please with the result. Also located the Stokers seat, but not quite sure of the height. It is 9" from the frame to the seat so I can always lower it. I want the stoker to sit about 4-5" above the Captain so the Stoker can see ahead without having to move their head to the side. Now that I have the Stoker located I can begin on the Stoker's crank set. I can also locate the Captain's seat.

Note......the front axle is adjustable so it can be moved on the rail. The final location is based on the Captain's seat.

Court J.

 

[flymeaway]

I finished the Stoker's crank-set and mount which allowed me to locate the Captain's seat. As you can see from the pictures it's a very simple efficient design. The transfer gear (red) is mounted to a freewheel so the Stoker can pedal independent of the Captain and vice-versa. Now that I Have the Captain's seat mounted I can locate the Bafang Mid-drive and mount it.

 

[George S.]

I finished the Stoker's crank-set and mount which allowed me to locate the Captain's seat. As you can see from the pictures it's a very simple efficient design. The transfer gear (red) is mounted to a freewheel so the Stoker can pedal independent of the Captain and vice-versa. Now that I Have the Captain's seat mounted I can locate the Bafang Mid-drive and mount it.

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Nice! I don't know enough to dream about doing that.

You said something about a problem with a battery pack? Seems like there are BMS issues out there. Hope you got it resolved. Given the shipping problems, not what I want to hear.

Hope you get this bike done for the that great New England Winter riding season.

Really, it's beautiful!

 

[flymeaway]

You said something about a problem with a battery pack? Seems like there are BMS issues out there.

Yes, I have never had a battery issue until about 1 month ago. My commuter, the Titanium 48V 750W mid-drive would power up but as soon as I began to pedal then immediate shut down. Fortunately I had already ordered a 52V shark pack for the tandem so I swapped out the batteries and everything works fine. Haven't taken the Shark pack apart yet to trouble shoot but it's either the BMS or a cell. I did have over 3,000 miles on the bike before the problem.....I guess my "luck" just ran out.

"Hope you get this bike done for the that great New England Winter riding season."

That would be very nice, but it's looking less likely!

Court J.

 

[flymeaway]

Update.....

Ordered the Rohloff 500/14 last Thursday (from Germany) arrived yesterday. The dealer is absolutely incredible. This is my 3rd Rohloff and they ship and arrive faster then buying stuff in the states!!!! To boot, his price is excellent. I purchased the recommended rim Ryde Andra 30 which I have never used in a wheel build......WOW everything written about this rim is true. The rim is a bit on the heavy side, but, and it's a big BUT!!, if you want a finished wheel that is extremely strong, durable, and trues up perfectly while building, this is the rim. From now on any 26" wheels I build will be Ryde Andra 30's. The max spoke tension is 1200N which is at the upper limit of what I feel is reasonable. I used 238mm Sapim Race spokes and tightened the wheel to just under 1200N, the spokes are very tight but because the rim is directional drilled when you look at the spoke it is perfectly straight from nipple to J bend. The spoke head is seated exactly in the drilled countersunk hole and the nipple is seated squarely in the rim. I'm more confident that this wheel will not break spokes then any other rim/hub combo I've built and to date, I haven't had any broken spokes on wheels I've built.. You can see the staggered directional drilling on the rim in one of the pictures, beautiful!!!!!!

I had an issue with the steering bar on the bike which has forced me to redesign the steering and steering link. No matter what I did I wasn't happy with the interference of the steering bar with my knees while pedaling....live and learn. Should have some updated pictures in a week or so.

Having a lot of fun building this tandem and already dreaming of building a recumbent single next year.......

Court J.

 

[dm nelson]

Update.....

Ordered the Rohloff 500/14 last Thursday (from Germany) arrived yesterday. The dealer is absolutely incredible. This is my 3rd Rohloff and they ship and arrive faster then buying stuff in the states!!!! To boot, his price is excellent. I purchased the recommended rim Ryde Andra 30 which I have never used in a wheel build......WOW everything written about this rim is true. The rim is a bit on the heavy side, but, and it's a big BUT!!, if you want a finished wheel that is extremely strong, durable, and trues up perfectly while building, this is the rim. From now on any 26" wheels I build will be Ryde Andra 30's.

Impressive project! Wonderful to have the documentation on the fine parts & workmanship involved. Has me thinking about someday putting a mid hub on my old breezer uptown with a shimano nexus 8 hub. Best wishes for ease and success with the final tandem project!

 

[flymeaway]

with a shimano nexus 8 hub

The tadpole tandem will be my 3rd installed Rohloff and now that I have ridden the other two bikes through the summer I can honestly say that any ebike I design and build or convert will have an IGH hub. I'm done with traditional cassettes, and all the inherent maintenance issues that are eliminated with the IGH. Of course the decision to use an IGH really locks me into mid-drives....

 

[flymeaway]

Update........

I completely redesigned the steering mechanism because no matter what I tried I was unable to get appropriate clearance for my knees when pedaling on the original design. Because the rack and pinion requires a full 270 degrees of rotation from centered to either stop I had to used a gear reduction system 4/1 ratio to reduce the required steering arm deflection to 65%. I'm satisfied with the result. Because of the spindle geometry and the rack and pinion the steering works like a car. It will hold a setting until it is returned to zero (straight) and the wheels will try to remain in a straight configuration until the steering arm is moved. This should help a lot to avoid "bump steering". Next up is mount the Andra 30 and Rohloff wheel and finalize the drive train.

Court J.

 

[JohnT]

Very cool build! Rack and pinion is unusual on a tadpole, isn't it? Glad to hear you're designing with bumpsteer in mind. I hope the chain is precise enough. Looking forward to seeing it develop!

 

[flymeaway]

Rack and pinion is unusual on a tadpole, isn't it?

I suppose it is. It is substantially more precise then the usual steering linkage. Combine the precision of the rack and pinion with 3% of camber, 10.5% of kingpin inclination and 12% caster and the steering is very accurate and stable. The steering arm support is adjustable so chain tension is adjustable. I am able to set the chain so the control arm is perpendicular at wheels straight. Road conditions don't affect the track and the steering holds the setting even when the control arm pressure is released. It's a very stable system. Working on the chain drive line and installing the rear wheel with Rohloff IGH. Should have an update in a week or so.

Court J.

 

[George S.]

I swapped out the batteries and everything works fine. Haven't taken the Shark pack apart yet to trouble shoot but it's either the BMS or a cell. I did have over 3,000 miles on the bike before the problem.....I guess my "luck" just ran out.

Court,

What's weird is that I bought one of those Ebay LiFePo packs that you mentioned in the earlier builds. (I mostly started by just copying you.) It's been 18 months and I've used it steadily on one of the bikes I ride. I ran the battery down, by mistake, and figured out some things about the pack. The LVC does work, around 33 volts on my 36 volt pack. I figured maybe I stressed the battery. I did a charge and discharge cycle with a watt meter. The battery is supposed to hold about 540 watt hours. I'll be darned if, after 18 months, it's right there still. I've kept it charged, mostly, and run it down maybe 80% a lot, but this sort of amazes me. I didn't expect this from a $260 pack.

Was wondering where your Chinese LiFePos have ended up? It's tough, because the packs are big and heavy and that's not convenient. But the older chemistry does seem to work pretty well.

The new bike, with the rack and pinion steering. Wow. That's DIY at a whole different level. Having a more stable platform, and one that can be streamlined somewhat, gives it potential. I'd put big flashing lights on the back, in traffic, but that's not such a big deal anymore.

Hope it all works out and that it pushes ebikes a little farther out. Very inspirational.

 

[flymeaway]

Was wondering where your Chinese LiFePos have ended up?

They're still functioning.....the bike with the most charge cycles is the Cafe" Latte'. 48V 750W BBS02. That was the bike I converted in the Spring of 2015. I rode it as my primary commuter in 2015 and when I switched to the converted Titanium this May it became my wife's primary bike. Until then she was mostly riding the original Elite 36V 500W bike. The batteries are still going strong and even though I don't keep track of charge cycles the 48V pack must be somewhere north of 400. But they are heavy bricks!

Court J.

PS...yeah the rack and pinion steering is probably overkill but it does make an exceptionally stable steering system.

 

[flymeaway]

Update....

Mechanically the bike is essentially done. Time to add controls and electric components. The chain drive line came out better then expected, very clean and efficient. The one unexpected issue was handlebar real estate, because of the orientation, vertical as opposed to horizontal, I've decided to mount everything but the brakes on other brackets. you can see the LCD and On/Off, plus, minus switch mounted in front of the front axle. The Rohloff shift will be mounted to a bar coming off the left side of the seat post. I did take her for a quick spin in the parking lot, manually setting the Rohloff to gear 6....yahooooooo!!!! Handles like a dream, tracks straight as an arrow, very stable and extremely easy and positive to steer, should have built this bike a few years ago!!!!!

Court J.

 

[George S.]

Beautiful bike. Maybe you will start something. Congratulations.

 

[Hugh]

Wow, you've just raised the level of homemade to a whole new status, beautiful job

 

[Captain Slow]

Wow!!!!! How many people could build this????? Very few could even come close.