Thorn Expedition TANDEM with BBS02 750W? Anyone??

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brightonebikes   1 µW

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Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by brightonebikes » Feb 01 2016 12:51pm

Hi,
I'm after a little help if anyone can please.
I have Bafang BBS units on several bikes and am considering the possibilities of fitting one to a tandem, a Thorn Expedition Tandem from 2001 with the S&S coupling.
Does anybody have any experience with tandem transmissions and Bafang mid-drives?
Any help, pointers, photos, illustrations etc. greatly appreciated.
Many thanks
Darren

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Leebolectric   1 kW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by Leebolectric » Feb 01 2016 1:04pm

front rider "could use a bafang BBsHD...but individual frame clearances are up to you to determine.
It may also be light on power for two people and a heavy bike.

a lightning rods, or Tangent kit would be better suited in terms of power.

the rear riders cranks would be the issue...a bafang would not mount there due to the dual sided chainrings needed.

I have similar plans, but much higher powered with a tangent kit. ;)
Screen Shot 2016-01-25 at 7.14.13 AM.png
2015 Intense Tracer275 with Tangent Ascent inside triangle https://endless-sphere.com/forums/viewt ... 28&t=75045
2010 Turner 5Spot with BaffangHD https://endless-sphere.com/forums/viewt ... 28&t=75569
2009 KHS Velvet 6" with BafangHD (see above thread^)
2015 SantaCruz Bantam with TEMPORARY Cyclone https://endless-sphere.com/forums/viewt ... 28&t=76131

brightonebikes   1 µW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by brightonebikes » Feb 01 2016 4:48pm

Thanks for your ideas, much appreciated.
I'm thinking a BBSHD could be the best option all things considered and fits budget.
I need to do more research on chain arrangements for tandems.
Cheers
Darren

Xray   100 mW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by Xray » Feb 04 2016 6:18am

Why couldn't you use the mid drive in the stoker's position? I'm considering doing this on a tandem trike. Seems like you could use a left side square taper tandem crank in place of the normal left Bafang crank arm. Then still use the idler chain in the normal position. Or, for that matter, change the captain's crank to a normal crank and run your idler chain on the right. Not speaking from experience here, just trying to figure it out myself.

BigBird   100 mW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by BigBird » Feb 04 2016 10:29am

I was considering this a while back and also wanted true torque sensing. I came up with the following complicated solution but never implemented it. (Got a Bionx D500 system instead).

E-Tandem with Bafang BB02 Mid Drive, THUN Torque Sensing BB & Triple Crank+

I THINK I have come up with a way to have all the features I want on my E-Tandem?
Comments/Critiques/Suggestions WELCOME!

BACKGROUND - I have a single new Haibike with the FABULOUS new Bosch 350 Watt system with seamless Torque Sensing Pedal Assist which I LOVE and which provides 50 hilly miles of significant silent assist from the 36V 11AH battery. I am trying to get similar performance for our Tandem. We are reasonably fit and will always be pedaling but are 71 and 70 years old and no longer able to keep up with our younger biking friends on the longer hillier rides.

Proposed E-Tandem Configuration
1) Starting Tandem = 1984 Santana Arriva steel frame with traditional left side captain-to-stoker timing chain and right side stoker triple crank driving a 7 speed freewheel and 27" wheels. Bottom brackets are both 68MM with an eccentric adjuster on the front/captain position.
2) Replace stoker rear bottom bracket with 120MM Thun Torque Sensing bottom bracket which reads torque applied on the left side crank.
3) Rotate the front/captain bottom bracket eccentric to get the thin side positioned forward and down so that the critical thickness of the total bottom bracket is no more than the ~12MM distance between the Bafang bottom bracket and the Bafang motor case.
4) Remove the front/captain bottom bracket and install the Bafang BB02 with 46T chain ring in the standard manner. It will not go quite all the way in due to the eccentric but is designed to work on a 73MM bottom bracket as well so should be OK with the inability to go in the last few MMs.
5) Replace the left crank arm of the Bafang BB02 with the original Tandem left front/captain crank arm that has the left side captain-to-stoker timing chain ring still installed.
6) ADD a right side captain-to-stoker set up that will allow the Bafang BB02 46T chain ring to connect to the RIGHT side of the rear/stoker triple crank. See this article for how to do this - http://www.bikexprt.com/bicycle/tancrank.htm. In summary this will be done by ADDING a 4th outer right side chain ring to the rear stoker triple crank. This will fit between the largest original outer chain wheel and the right crank arm and will be enough smaller than the 52T existing largest chain ring to avoid interference between the added timing chain and the original rear drive chain.
7) THE ADDED 4TH STOKER/REAR RING WILL HAVE 48 TEETH = 2 MORE TEETH THAN THE 46T DRIVE ON THE Bafang BB02. Thus, the Bafang drive chain wheel will ALWAYS be at a slightly ~4% higher RPM than the front crank arms. Thus, the Bafang motor and drive chain wheels will be "freewheeling" (not engaged with the front crank arms). This will allow ALL of the front/captain human pedaling torque to go through the original LEFT side captain-to-stoker timing chain and into the left side of the Thun rear bottom bracket. The left pedal effort from the rear/stoker will also be applied to this left end of the Thun. Thus the Thun will sense 3/4 of the total human torque. This Thun torque signal will be routed to a Cycle Analyst which will be programmed to have the Bafang motor provide 50%, 100% or 200% assist and this will be routed by the right side Bafang to rear/stoker added chain.
8) Add chain tensioners to the bottom of both the original left side and added right side timing chains. This is necessary because the front bottom bracket eccentric cannot be used with the Bafang BB02 (and the 2 parallel chains would require different adjustments anyway).

HELP! - IS this going to work? And if now why not and how can it be made to work?

BOM:
Triple chain ring bolts = Harris
Bafang Chainring Adapter
Chainwheels?
Chain
Motor
Thun
Extra long Cables
Cycle Analyst
2 Chain Tensioners
Battery?

Positives:
Quieter
27" Wheels = no Brake issues

Negatives:
Need 2 Chain Tensioners
Stress on original drive train
Complexity

brightonebikes   1 µW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by brightonebikes » Feb 04 2016 4:49pm

Thank you, this is just the sort of stuff I was hoping.
I'm in the process of processing it.... it's likely I may have questions!

Xray   100 mW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by Xray » Feb 05 2016 12:13am

Yeah, that first illustration is what I would use if I was working with a regular tandem. If I can figure out how to re-position the idlers on my recumbent, I will use it for sure.

BikeFiver   1 mW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by BikeFiver » Feb 12 2016 10:36pm

We have been really pleased with our Rans Screamer with BBSO2 750 W.
GreenLightening R.jpg
GreenLightening R.jpg (56.59 KiB) Viewed 2184 times
We have found the power to be plenty. We use the 2 power level when in the 5 power setting. We only use the PAS never the throttle. We cruise level at 20-24 mph and any downhill is 25-29 in 54x11 gear. Max so far 38mph. We have a 50 mile range using 80% of the 17A/hr 50volt Em3ev battery. I think it was sold as 16.5A/hr but tested at 17.5 by Paul. Thanks Paul!
Dropout R.jpg
Dropout R.jpg (73.28 KiB) Viewed 2184 times
This is a key component. The rear wheel needed extra support to keep it in the dropouts. I machined these for both sides. Two peddlers and BBSO2 is way to much on quick release to hold. I know because the maiden voyage was interrupted by having to reseat the wheel 4 times.
Battery Box.jpg
Battery Box.jpg (74.85 KiB) Viewed 2184 times
This is where the battery rides. The right side is fixed to the bike, the left unbolts to remove the battery. Paul fixed me up with the 6ft of power cord to go from the BBSO2 to here. EM3EV will get my business because of that kind of support. I also bought some extensions for the brake and monitor leads just in case.
Bottom Bracket.jpg
Bottom Bracket.jpg (82.47 KiB) Viewed 2184 times
Here's where the neat part happens. Because this is a tandem, the stokers BB has the derailleur and is not effected by the BBSO2 replacement. You add an outside, slightly smaller 52 chainring with racing triple bolts and you move your drive line to the right side. Thanks for the info Harris Cycles. The bolts are getting hard to find but they are out there. I initially used the optional 52 t BBSO2 chainring but I have just changed to a Drop Stop 52t front chainring with 130 adapter to the BBSO2 as I still occasionally throw a chain. I can't tell if it is thrown from the front or rear chainring. We will see if this helps.

Why is this neat? The captain can ease/freewheel the BBSO2 after tapping the brake to kill the power, shift while under peddle or stoker power only, and use all the normal 24 gear range. 54x11 to 24x34 on this bike. Great efficiency and no loss of top or granny gear. If you don't have electric power you must have granny gears for any tough hills as there is NO STANDING up hills with a recumbent bike. Just sit and spin!

This Screamer makes this chain drive line switch easy as the chain idlers are ambidextrous and mount to either side. It should be just as easy on a delta frame as there are no idlers to worry about.

As for the 1000 Watt motor, we find any speed above 27mph to become annoying for sustained periods due to wind noise and buffeting as well as the hyper attention to road required to avoid debris and holes.

Here's my question. Concerning PAS only. We only use the 2 setting out of 5 levels, does that have any relation to power used when set at Paul's "stock" settings? Or is it just setting the cadence at which power is weaned off?

Kent

Xray   100 mW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by Xray » Feb 13 2016 2:33am

That is a beautiful setup on your Screamer! I have thought about setting our tandem up like this but with this setup I couldn't use the throttle easily. The stoker would have to be pedaling whenever the throttle was engaged. Due to age and injuries catching up with us, we want to be able to be on motor power only at times. It would be nice to keep the triple though. I have thought about using an IPS system where the drivetrain would run through a freewheel at the stoker's crank. What is your battery box made of?It looks great on there, very finished.

WoodlandHills   10 kW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by WoodlandHills » Feb 13 2016 1:54pm

The Power Assist is a simple throttle lock that is turned on by moving the pedals. There are actually 9 levels in the software, but depending upon your display as few as three are accessible. In all cases you will have level 1: the lowest and level 9 the highest. If you have a 5 position PAS you will have levels 1,3,5,7 and 9; if you have a three position display you have levels 1,5 and 9. Some display models will let you change the number of PAS settings via the hidden menus in the display. To change the power levels of the various PAS settings and their associated speed limits you will need a programming cable from Luna and a Windows computer as these are not acessible from the display.

The Bafang drives have no cadence sensor and no torque sensor, there is a pedal movement sensor and a wheel speed sensor only. It does not know how fast nor how hard you are pedaling, just that the pedals are moving......

Warren   100 kW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by Warren » Feb 13 2016 3:48pm

BikeFiver,

"This is a key component. The rear wheel needed extra support to keep it in the dropouts."

I will bet you a beer that your quick release skewer is like the one up top, which uses soft plastic as the cam follower surface.

http://bikebro.com/Images/e2/quick_releases.gif

As an old bike mechanic, I will tell you these should be banned as unsafe garbage.

BikeFiver   1 mW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by BikeFiver » Feb 13 2016 8:15pm

Left Dropout.jpg
Left Dropout.jpg (81.23 KiB) Viewed 2106 times
Here's the left dropout with new skewer. The old quick release was of quality steel but worn. I think the prior owner was having issues with movement as well. The movement cost the bike some metal and the quick release no longer had any sharp edges to grip the bike. Nowhere for the skewer to go now.

The battery box I bent from galvanized 20 ga steel. Alas, the box was too wide for the chain to clear, so I made lemonade by cutting it in half, bending in the edge 1/2 in on each half and adding the bolts which makes it much more functional. I have since added a galvanized top cover and padding all around.

The power is not used to eliminate the exercise but to smooth out the hills and increase the range of our adventures. We both peddle constantly, but really appreciate coming over the top of the hills at 15 mph and the constant breeze it provides in the deep south summer.

Our long, rolling hill route is 46.38 miles and was completed in 2hr 4m 58sec for a 22.3 mph moving average and max speed 35.2 mph. The BBSO2 showed one bar remaining on the battery. 50V Battery charged to 90%.

This shows the route with elevation and speed etc. https://connect.garmin.com/modern/activity/947372342

Thanks for the info on the PAS and power levels!

Kent

Warren   100 kW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by Warren » Feb 14 2016 11:08am

With the arrival of "lawyer lips" on front forks, manufacturers were able to switch to cheap skewers. Once those cheap skewers became ubiquitous, some OEMs went to machined spot faces in the rear dropouts.

http://wpc.6e94.edgecastcdn.net/806E94/ ... dl_3D1.jpg

Not an awful idea, even when using quality skewers. It occurred to me that you could do something similar with your aluminum blocks, eliminating the need for a wrench to fix flats.

Xray   100 mW

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Re: Thorn Expedition TANDEM with BBS02 750W? Anyone??

Post by Xray » Feb 14 2016 12:08pm

We have the same rear drum brake on our tandem with a 48 spoke 20" wheel. I'm thinking of changing to a solid axle for strength.

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