BBSHD on tandem?

[kiltedcelt]

The way that most tandem drivetrains are laid out, whether it actually has a shifter at the middle/stoker position or is a chain that runs directly to a geared hub - if you stick a BBSHD on the front of the bike (captain's position), then does the chainring tooth count on the motor even matter when figuring out gear inches? If the BBSHD is just running to the chainring setup in the middle of the bike, and from there back to a cassette with derailleur, is the only chainring that matters in determining highest/lowest gear and top speed the one in the middle at the stoker position? Logically it would seem so, but I'm wondering since most of the time you see Bafang mid-drives running directly to a rear wheel, does introducing this intermediate crankset/chainrings like on a tandem mess up anything related to power transmission? I guess the alternative is simply to make sure that whatever gearing you want is based on what is installed on the motor and simply duplicate the tooth count on the chainrings on the stoker crankset.

 

[john61ct]

Every gearing point "counts".

Just a question of where you want to make changes up or down.

Anyone ever take advantage of a tandem to put in two midrives?

To me seems the perfect platform for a long-longtail cargo conversion. . .

 

[markz]

Anyone ever take advantage of a tandem to put in two midrives?

Whatever gives ya more power, the better!

 

[amberwolf]

There are a number of BBSxx systems on tandems threads, if any of the info is useful:
https://endless-sphere.com/forums/search.php?keywords=bbs*+tandem&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

 

[kiltedcelt]

Thanks for the link - there was some interesting information on there. I was also able to get some input from folks over on a recumbent riders forum as well. The nice thing about a tandem and designing this frame from scratch is that theoretically I can incorporate a 2x crankset which will give better gear range than a standard mid-drive usually allows for. Where things will get complex is tying everything together and still keeping a free-wheeling crankset for the stoker. The freewheel in the stoker position is not only necessary for my wife to be able to pedal at a different cadence or rest, but also when the trike is set up in cargo mode so that I don't have to build something specifically to cover a set of spinning cranks nestled in the forward portion of the cargo bed. With freewheeling cranks I can probably 3D print some kind of removable clamp to hold the cranks in whatever position works best to interfere the least with the cargo bed.

 

[Balmorhea]

On a traditional tandem, the cranks are linked and synchronized by a chain that always has the same size rings at each end. This chain runs on the left when a front derailleur is to be used.

Are you placing the BBSHD as a jackshaft, on a third bottom bracket? Because otherwise, one or the other of you will be running at the same RPM as the BBSHD. It's not obvious how you'd implement a front derailleur in this scheme, either.

 

[kauaicycler]

Here's how Justin did a bbshd install on a tandem. This video is about upgrading the bbshd to a phaserunner but the donor bike is a tandem.

[youtube]fsRwVHwCCog[/youtube]

 

[kiltedcelt]

Balmorhea - the BBSHD is on the front bottom bracket (captain's position), and there will be a freewheeling crankset in the stoker position, and I will likely see if I can engineer a way to make that also a 2x. The freewheel crankset I bought is from Sick Bike Parts and from what I gather they're *mostly* 2-4 stroke motor kits, but they carry a heavy duty freewheel that is designed to mate with a drive side crank arm. They have specific spiders that allow attachment of various chainrings as well as cogs that would deliver power from whatever type of motor - e-bike, 2-stroke engine, etc. I was pretty sure I knew how this worked, but when I actually received the crankset/freewheel combo yesterday I was able to confirm it. Basically just a big freewheel that you can bolt chainrings to. It means the stoker can coast or pedal at whatever cadence independent of what the captain's cadence is. Additionally, even if I shift gears and the stoker is still pedaling, the shift cut-off switch will cut power to the motor so that the captain doesn't have to signal for the stoker to stop pedaling during gear changes. Of course stopping pedaling during gear changes would be necessary if I used an Alfine hub, but instead I'm using an 11-46 cassette in the back. I think I will be able to hack up a traditional 2x or 3x crankset to make something I'm then able to bolt to the inside of the crankest freewheel. The outside chainring will accept power from the BBSHD, and then the inner two will transmit it to the rear cassette with the ability to have great gear range with the 2x derailleur as well.

 

[Balmorhea]

Freewheeling cranks are always a maintenance problem, because existing freewheel mechanisms aren't designed to carry chain tension while ratcheting (rather, only when locked up and transmitting drive torque). You're in the uncommon situation of having both the captain's pedal power and motor power being stacked up and the resulting chain tension fed through a freewheel that's ratcheting. That freewheel will fail early and ugly.

I think it will be difficult to reconcile shiftable double chainrings on the rear bottom bracket, with a fixed normal chainline from BBSHD. Maybe use one of the more outward offset rings (like Lekkie 36t) to carry the front timing chain. If that set of rings is smaller in size than the ring in the middle position, it and the timing chain might stay out of the way of the front derailleur.

 

[kiltedcelt]

Not sure why this particular freewheel mechanism would be more likely to fail. Sick Bike Parts does offer two versions of freewheels for the crankset and I bought the heavier duty version. Also, according to their description it's made for them by White Industries who pretty much know how to make durable hubs. As long as I can build this tandem up in about a month and then flog it pretty hard for the next 5 months I'll be able to return it under warranty if it blows up and then research some other option. There is at least one two-wheel tandem company that makes a freewheeling option that has a separate freewheel built into the frame, and some recumbent tandems also offer the same similar freewheeling crankset for the stoker, but without the extra hub/chain option that the one tandem company has. I guess we'll find out how well this will hold up.

 

[Balmorhea]

Not sure why this particular freewheel mechanism would be more likely to fail. Sick Bike Parts does offer two versions of freewheels for the crankset and I bought the heavier duty version.

The problem is that the "heavy duty" front freewheel only has one bearing in it. The cheaper one has two rows of bearings, but they're loose crappy ones that aren't intended to carry any load while turning.

Either way is fine when the freewheel is used normally-- if there's only chain tension at times when the freewheel is locked up and not rotating. But if you apply a lot of chain tension (from motor power plus your pedal power) to a freewheel that's rotating (because the stoker isn't pedaling), that freewheel will crap out quickly. It's not designed to do that.

When it takes itself apart, you won't be able to pedal home from either seat. It's a show stopper. It's not an easy field repair, even if you carry an extra $85 freewheel with you. You'll need a crank extractor and a freewheel spline tool with a long handle, and you might need to put the crank in a vise.

 

[markz]

I thought White Industries made a freewheeling crank, but I couldnt find anything beyond normal crank sets. No market for fw crank.
"White Industries MR30 Crankset – 1x or 2x and Low Gear Options"
https://gravelcyclist.com/bicycle-tech/review-white-industries-mr30-crankset-1x-or-2x-and-low-gear-options/

Luna Cycle does some fw stuff "in-house" aka next door at a machining shop
(as far as I am aware, Eric did speak of it in one of his video's)
Here is their "in-house" fw crank, $175
https://lunacycle.com/luna-tick-crankset-for-mid-drives/

Heavy duty Luna Tick freewheel designed to take massive power (now 50 percent quieter than older version)

More of the same old same old
https://gngebike.com/freewheel-crank

Here is an interesting read, freewheeling cranks were sold at one time with no relation to ebikes.
https://bikeretrogrouch.blogspot.com/2016/01/here-we-go-again-freewheeling-cranks.html

The French company HxR has just introduced a new product they call Easy Shift.

he Easy Shift crank is made for the latest 1x11 "Enduro" MTB drivetrains. Like the old Shimano FFS, it has a freewheeling mechanism built into the crank, but it is paired up with a true fixed-gear 11-speed rear hub. No "friction freewheel" here - so don't get anything caught in the chain, 'cause you'll lose it. Granted, that's the case with any fixed-gear drivetrain, but just sayin'.

The Easy Shift crank and bottom bracket alone are listed at about €450. Adding a chainring, the fixed-gear 11-speed hub, and the bash-guard/chain-guide takes the price up to €995.

 

[kiltedcelt]

So if I understand correctly, this freewheel is designed to allow the cranks (rider) to coast when the motor is putting power through the chainring connected to the drive sprockets (cassette), on the rear wheel. What you're saying is that in effect with the captain pedaling and simultaneously dumping extra watts from the BBSHD into this freewheel which is in turn spinning the rear wheel - it'll be sitting there making that ratcheting sound when the stoker is coasting. So you're saying that unloaded spinning will destroy the freewheel? I guess if it's simply spinning at coasting speed with no load that's pretty normal for a freewheel, but you're saying spinning it a lot without the pawls engaged is what's going to eat it up sooner rather than later. I'm trying to figure out this is different than say something like a DaVinci tandem with "Independent Coasting System"

http://www.davincitandems.com/drivetrain-info/

Although the DaVinci does use two single-speed freewheels, but on the non-drive side, so more like a traditional tandem with a timing chain on the non-drive side. I was researching this and found an article on the Sheldon Brown site about several different ways to set up a tandem drivetrain, some of which allow for a free-wheeling stoker position.

https://www.sheldonbrown.com/tancrank.html

The last option on the page - the Front Crossover Drive - looks like it might be a viable alternative for my trike. I run the BBSHD directly to the rear cassette, and I build a freewheeling crankset for the stoker that will run up to the BBSHD on the non-drive side. I replace the non-drive side BBSHD crankarm with a non-drive side tandem timing crank arm. The problem I see with that is that the stoker can coast, but if they continue to pedal, then they'll be driving the chainring on the non-drive side of the BBSHD and thus will be preventing the captain from coasting while also keeping the motor running.

Seems like a better option is to try to do something similar to the DaVinci IPS. Maybe rather than two freewheels on the non-drive side like they show, I put my White Industries freewheel on the right side and a single speed freewheel on the left side connected to the stoker cranks. Basically doing something similar to the DaVinci but trying to keep the chains that are driving everything mostly on the right side. The trike is going to have 170mm spacing in the rear to accommodate 26x4.0 tires so we're already going to have a wide, fat-bike style of Q-factor, so I can always build stuff in such a way that if I have to stack freewheels up on the right side or something maybe I can make that work as well. I do still want to figure out some way to still have an intermediate 2x crankset between the BBSHD and the rear wheel to be able to get a bit more gear range though. At least since I'm building it all from scratch I can place whatever combination of chainrings/bottom brackets/freewheels/cranksets wherever will work best to achieve the main goals which are: 1. coasting/different pedal cadence for stoker and 2. 2x gearing with BBSHD. Any input you can offer is appreciated.

 

[kiltedcelt]

markz - thanks for reminding me of that Luna Tick crankset. That came up somewhere in all the ciphering I've been doing over the last several days but I might have dismissed it either due to maybe being out of stock, only one color choice available right now, or possibly cost. Although, if it will do what I want in terms of allowing the stoker to coast and will be a much tougher option than the Sick Bike Parts FW cranks then it would probably be worth the significant price bump. Although just looking at it I wonder if I'd be able to bolt on an extra chainring to allow me to make it a 2x. Since it runs a 1/8 chain to the motor and a 3/32 chain to the cassette, I could always run that 3/32 chain to the inner ring of a 3x and use the two outer rings to be the 2x that I want to run to the rear cassette. I'm going to have to bust out the Fusion 360 to start drawing this all up to try to keep it straight in my head while I figure this all out. Then again, maybe I'm just being ridiculous and I won't even NEED a 2x drivetrain. After all, wide-range 1x cassettes were designed to make mountain bike drivetrains more simplified while eliminating the shifting of a 2x or 3x system, eliminating the gear overlaps and keeping the same percentage of gear range. I ended up buying the MicroShift 9 speed wide range system that is based around an 11-46 cassette, but I could've just as easily gone for the (I think), 11 speed 11-50 cassette. Just a bit more expensive. Chains I think were the deciding factor behind going with MicroShift Advent 9 speed. Start going to 10 and 11 speed and there's a big price bump in the cost of the chains. This is easily going to require 6 chains to span the distance between all the various gear configurations.

 

[markz]

FW crank is not made to handle the kind of power a mid drive system spits out. The pawls inside the fw bearings cant handle the power over a long period of time, add to that the expansion and contraction of heat and cold weather, water and salt.

How it Works: The motor spins the chain attached to a 44T crank gear, that 44T crank gear is directly attached to a 42T crank gear via the crankset. That 42T has a chain wrapping around that goes to the rear gears. If you did not have a fw, your pedals would be moving every time you twist the throttle. FW the gears can move and your pedals do not. You dont want your pedals to be "fixed" to that spinning, be like a fixed gear bicycle where there is no freewheeling. Uncool in my books!
Having 3 gears on the crankset, would enable you to shift the front derailleur between two crank gears.

If the chain breaks, or rear derailleur gets smashed or whatever it is.... you will be doing the walk of shame.

 

[markz]

The so called Heavy Duty fw bearing from Sick Bike Parts will last longer then the normal one. I've read stories here on ES that the HD fw fails easy enough if enough power is applied to it, not sure if they had a 3 or 4kw cyclone, bbshd or whatever. Search ES and find out. I will see what I can pull up.

Interesting find
https://endless-sphere.com/forums/viewtopic.php?f=28&t=29649&p=428048&hilit=freewheel+crank+fail#p428048

Some random find from an ES post.
http://www.electricscooterparts.com/freewheelclutches.html

Failed stock
https://endless-sphere.com/forums/viewtopic.php?f=28&t=68028&p=1302715&hilit=freewheel+sick+bike+parts+pawls#p1302715
https://endless-sphere.com/forums/viewtopic.php?f=28&t=34407&p=499718&hilit=freewheel+sick+bike+parts+pawls#p499718

https://endless-sphere.com/forums/viewtopic.php?f=28&t=69867&p=1203851&hilit=freewheel+sick+bike+parts+pawls#p1203851

The [Sick Bike Parts heavy duty] motor freehub insides scattered on the road at the top of the last hill -- some 600 miles of use before failure on this one.

 

[Balmorhea]

So if I understand correctly, this freewheel is designed to allow the cranks (rider) to coast when the motor is putting power through the chainring connected to the drive sprockets (cassette), on the rear wheel.

That's how SickBikeParts used it, but it's absolutely not how it was designed to work. The "heavy duty" freewheel is a White Industries bicycle freewheel, custom manufactured with a bolt flange instead of teeth. But it's a bicycle freewheel. That means it's only designed to have torque/force on it when it's locked up, not when it's overrunning.

The locked pawls form one row of support, and the bearing forms the second row of support. When it's rotating, there's no second row to support a chain load on the freewheel. It trashes the bearing.

If you use the other, cheaper kind of freewheel, there are two rows of bearings that support each other. But they're lousy small low-precision bearings that were not intended to carry any load at all. So when you do rotate them under load, they deteriorate very quickly.

You can't make a bicycle freewheel reliable to transmit drive forces while ratcheting. It would be possible to design and manufacture a freewheel that is good for that, but so far there isn't one.

 

[amberwolf]

Is that why some designs that need a freewheel use a sprag clutch (or roller clutch) instead?

 

[Balmorhea]

Is that why some designs that need a freewheel use a sprag clutch (or roller clutch) instead?

Even a CSK clutch/bearing needs to be paired with another bearing to withstand drive loads. Whatever you use as the one-way clutch, there must be two rows of bearings that can support the full chain tension.

 

[kiltedcelt]

Balmorhea - It sounds like from what you're saying, even the more robust version of the free-wheeling crankset manufactured and sold by Luna (the Luna Tick), will also end up failing in this application because again, even it is probably not engineered to freewheel for long periods with no load on it. The main point of trying to have a free-wheeling crankset for the stoker was so my wife specifically could pedal at a different cadence than me. Also, since this tandem is going to be convertible to cargo hauling, that would mean that when it's in cargo mode with the cargo deck installed and rear seat removed, the stoker cranks would continue to spin with the captain's cranks/BBSHD which is to be mounted in the front position. Of course if the stoker cranks were freewheeling they wouldn't spin during cargo mode, just freewheel which apparently leads to bearing/hub guts destruction. I get how freewheeling cranks are able to work on a NON e-assist tandem. It doesn't really matter much in that case because the power output through that freewheeling system is lower and there is no goofy use-case where you're riding a tandem around with no stoker for an extended period of time with the stoker cranks freewheeling away. Seems to me like there's really no other way to set this up to still have the BBSHD as well as independent pedaling or independent coasting. Might just be that it has to have the most traditional type of tandem drivetrain where both cranksets are linking and moving in unison.

 

[amberwolf]

The main point of trying to have a free-wheeling crankset for the stoker was so my wife specifically could pedal at a different cadence than me.

Wouldn't a different size chainring for her be a better solution, that more closely matches her cadence? And allow her to contribute to the power propelling the bike?

A freewheeling crank just lets her spin the cranks, but she would not be able to input anything, there would be no load on them for her to push against unless she matches the speed.

 

[Balmorhea]

The thing that will reconcile the problems is for the front crank and the rear crank to feed independently into a jackshaft, which in turn drives the wheel. The easy ways to implement this scheme wouldn't allow independent shifting, but they'd allow a fixed ratio of front and rear RPM, and they'd allow independent freewheeling.

Imagine two left side chains-- front on a wide chainline, and rear on a narrow chainline-- driving a jackshaft through two side-by-side left hand freewheels. On the right side of the jackshaft, there's a double or triple chainring setup and a front derailleur. None of the three freewheels in the system (two LH freewheels on the jackshaft and one on the right side of the rear wheel) is under tension when it's ratcheting.

Does this make sense?

 

[kiltedcelt]

I wonder if somehow I'm over-thinking all of this. I wonder if something like the e-assist on this DaVinci tandem might work in my application. It *looks* like the stoker crankset is using a left side freewheel, so it has the same kind of jackshaft system like you're describing. I just wondering though, if there's no stoker, then doesn't the motor/captain still spin the left-side freewheel on that jackshaft which means with it just being forced to spin with no pawl engagement then it just ends up burning up anyway?

http://www.davincitandems.com/tandem-models/ebike/

 

[kiltedcelt]

Problem solved! I contacted Todd at da Vinci Designs, explained what I'm trying to do (basically creating the same kind of drivetrain as is on the Tailwinds tandem), and he will be putting together an entire jackshaft assembly with bottom bracket shell, left side freewheel, etc, and selling it to me as an entire unit configured to match the basics of my design. I'll be able to shift a 2x and also have the BBSHD driving the whole assembly pretty much the same as you see with the Tailwinds tandem. In discussing with him my requirement of the fat bike rear wheel and chainline to go around the 4.0 tire, plus the fact that BBSHD is spaced for a 68-73mm BB, he will likely configure my assembly so the BBSHD timing chain runs to the inside and the 2x chainrings will be on the outside - basically opposite of how the Tailwinds is configured. It's certainly a more pricey option than any freewheel crank setup like the Sick Bike Parts or Luna Tick, but I'm far more confident that folks who are making tandems including e-assist models *and* incorporating the ability for the captain and stoker to coast independently that I'm getting an assembly that will work for my application. Of course I'm going to get cornholed with the restocking fee to send back the stuff from SBP that I don't need, but that just means I'll never spend money with them again.

 

[Balmorhea]

Cool. Be sure to use one of the deep dish chainrings, like the stock steel one or better, the Luna Eclipse 42t or 48t. The deeper the ring, the more room you’ll have to implement the front shifting mechanism.