Recumbent Series Drivetrain

[rhitee05]

After a lot of putzing around and scratching my head, I've decided to scrap putting the Cyclone motor onto my Trek bike. I'm not very happy with the configuration and wasn't really able to get the gearing ratios right. I don't want to make major modifications to the bike, so time for a new approach.

The new plan is to build a recumbent frame from wood and parts of donor frames. The drive train will be designed with the Cyclone in mind. I expect it will take me a while to complete, but this should end up being a much better solution.

The drivetrain I have in mind is a serial setup using a jackshaft to combine pedal and motor power. I don't think this is especially original, but seems like the best setup for a dedicated electric-assist bike. I have a couple of details in mind which I haven't seen discussed here before that I think will help make this an effective solution.

Here's the basic setup. The pedals will use the standard triple chainring from the donor bike and the rear wheel will also keep it's cluster. I've pondered a few options for the jackshaft. Either a rear hub or a bottom bracket could be made to work and all the parts are out there. Both would require mods, though, and might need some specialized parts which are hard to find and/or expensive. I think it makes more sense to build the jackshaft around a standard shaft. Sickbikeparts sells freewheel adapters which fit a 5/8" shaft and would work quite well. I can also find a variety of sprockets from McMaster-Carr and other sources.

The jackshaft will have 3 sprockets: pedal input, motor input, and output. Using separate sprockets for each is a little more complicated, but gives me a lot of freedom to choose the proper ratios. The pedal input sprocket will be mounted in a freewheel using the Sickbikeparts adapter. The other two sprockets will be fixed-mount directly to the shaft. I'm hoping that since the freewheel will only see the pedal torque, I can get away with using one of the less-expensive freewheels rather than the White Industries version. Also, using the triple chainring in front will give me different ratios between the pedal and motor speeds. I can set it up so the largest ring is a leisurely cadence for when I don't feel like pedaling much and the middle ring is a faster cadence for more pedal power. The smallest ring would end up not really being used with the motor (too fast!), but will provide a pedal-only "granny gear" so I can get up some of the hills around here if need be.

The actual configuration will depend on how the donor bike(s) are set up, but here's an example of how it would work. A typical MTB might have a 24/34/44 crank with say 32-13 rear cluster (or something close). I'd like to use relatively small sprockets on the jackshaft, so I'll choose a 14T freewheel as the pedal input and a 20T sprocket as the output. That gives a total ratio of 44/14*20/13 = 4.84 in high gear and 24/14*20/32 = 1.07 in low gear. My nominal top speed goal is 30 MPH, which works out to about 400 RPM at the wheel assuming a 26" MTB wheel. So that would be a pedal cadence of about 82 RPM in top gear.

The Cyclone motor has a top speed of about 3000 RPM at 24V, which is about 314 RPM after the gearbox. That works out so I want about a 16T sprocket as the motor input to match the top speed and cadence. I think I would eventually like to upgrade to 10s batteries, but then I can just change the sprocket to get the right ratios without messing up anything else. Convenient! This setup gives motor-to-wheel ratios from 0.55 to 1.35 which gives me almost a 2.5:1 range.

I think this seems like a good approach, but I'm definitely interested if there are any suggestions, particularly about the jackshaft. I don't really have any fabrication ability, so a cost-effective way to use off-the-shelf components is necessary. Use of scavenged standard components is even better.

 

[StudEbiker]

The jackshaft you describe is the same configuration I am going with on my Bike E build. I decided to go with 1/2" shaft though instead of 5/8". 5/8" just seemed WAY too overkill for the application. Of course the problem is that 1/2" shaft freewheel adapters are hard to come by. I got mine from FFR Trikes, but expect to spend sum bux if you go that route. If you look at my build thread you will see how I came up with a nice simple 1/2" adapter for the fixed cog that uses a 1/2" collar lock inside a bottom bearing cup. If you have access to an angle grinder and a welder, this is a very simple and effective solution which ends up being smaller and lighter than the FFR Trikes version (not to mention MUCH cheaper!) :wink:

 

[spinningmagnets]

Matt may still have a few 1/2-inch shaft to freewheel adapters left, PM him.

 

[amberwolf]

I'm still working out exactly what I am going to do on my in-progress build, but it will have basically the same power paths as yours. ATM I have a jackshaft made for me by Thud for a BB shell, with a FW-threaded adapter on the left side and open shaft on the right, to which I'd need to mount whatever adapter to chainrings I end up needing (I'll ahve to make that part).

I have considered using an IGH as the jackshaft, in such a way as to give me 3 speeds of motor shifting, and then using a single-speed rear wheel or another IGH in the rear wheel, no rear derailer/cassette (to simplify chainlines/growth/etc on the rear swingarm). I just havent' worked out a suitable way to separately input pedal and motor power to the IGH without combining them prior to entry to it.

 

[rhitee05]

Matt may still have a few 1/2-inch shaft to freewheel adapters left, PM him.

Thanks for the tip. I'll have to remember that when I get a little closer to actually putting bits together. I expect this build will be a slow process...

I have considered using an IGH as the jackshaft, in such a way as to give me 3 speeds of motor shifting, and then using a single-speed rear wheel or another IGH in the rear wheel, no rear derailer/cassette (to simplify chainlines/growth/etc on the rear swingarm). I just havent' worked out a suitable way to separately input pedal and motor power to the IGH without combining them prior to entry to it.

That would work well if there was a way to put two independent freewheels onto the IGH. Not sure if that's even possible, or what sort of adapter would be required to make it work. I guess you could do it using a 2nd jackshaft to combine before driving the IGH... but then you might as well put the IGH in the wheel where it belongs! You could definitely do a variant of this using an 3-speed IGH in the rear instead of the cluster. The 3-speed would give a little less gearing range (I think 16:9 for a typical 3-speed, vs about 2.3:1 for a wide-range cluster), but it would still be totally workable.

For myself, my priorities are 1) parts I can scavenge, 2) common off-the-shelf parts, and 3) stuff I can make work with very simple mods. Anything that requires machining, welding, or any sort of skilled fabrication is way, way down the list. There's a reason I became an EE not an ME!

 

[amberwolf]

I'm pretty sure it's not possible to put even one normal FW on the IGHs I have here (old 3-speed SA, Sachs, and Shimano) without building an adapter, assuming there's even enough axle length.

Buuuut...if you use an IGH without an internal FW (or disable it, if possible), and if you put the FW on the motor end of it's chain, and use FW cranks, you could put one input sprocket on each of the spoke flanges, and take drive off of the original input sprocket (which also conveniently would easily line up with a rear wheel's input sprocket).

If the chainline is long enough/routed such as to warrant an idler from your cranks, and the idler would be farther forward than the motor, you could put a FW on a jackshaft at that point, made from a simple rear hub in a set of dropouts. Drive from the pedal chain to a SS FW threaded onto the hub, and drive out of that via a sprocket on the hub's flange back to the IGH's flange sprocket.

If you decided you needed a wide speed range on the pedals, for very low gearing for hills and such without motor assist, and also a high gear for high speed motoring while still applying significant pedal power, you could use a multispeed cassette on that hub/jackshaft above, and either a shifter for it or just manually move the chain from one to another, with a slide-able guide to keep the chain directed to the right one.

Of course, all that depends on the IGH not having a FW or being able to disable it.

Assuming it has one and you can't, then you could mount it via the spoke flanges to the bike frame, still take drive off of the original input sprocket, and now provide input via the axle, with motor input on one side and pedals on the other. This would require something as a pivot in the shifter chain as it exits the axle, so that the rotating chain is converted to non-rotating whatever for the bike to pull. Shouldn't be that hard to come up with using existing parts from a hardware store; I have a partial idea but not enough to draw it up yet using existing parts. Making or getting the adapter from the axle to a FW thread should be simple enough, in theory.



As for a simple jackshaft to just combine the two power sources into one and feed it back to the rear wheel, that's easy (meant to stick this in the original post I made here, and forgot).

Take a regular rear hub with threads for FW, mount it normally by it's axle in dropouts or clamps attached to the bike frame.

Thread on the first SS FW, then thread a left-side BB cup into that, then thread on the second SS FW.

Take a small sprocket off of a multispeed cassette, one that has holes machined in it, and line these up with at least a few of the spoke holes in that hub's spoke flange (on either side, but probably easier on right side to get chain to rear wheel). Drill out those spoke holes to the size of bolt that will fit thru both flange and sprocket as tightly as possible, then bolt the sprocket to the flange.

It's likely the smallest sprocket you can fit on the flange with boltholes in it will be larger than the SS FW sprockets, so you may have to compensate for this in your motor output sprocket size, and your front chainring size(s), to get the same gearing as if the jackshaft was 1:1 instead.






FWIW, the reason I am trying to think of ways to keep the IGH out of the rear wheel is because I've had enough situations where broken spokes on one trip but needing to do another trip the same day or early the next, with insufficient work-on-bike time to fix the wheel, required I just swap the wheel out, on CrazyBike2. If I can make this possible on the new bike, I don't have to worry about finding enough spokes of the right size to keep on hand for lacing up the IGH at least twice, plus some spares, and/or keeping at least two IGH laced wheels around (one on bike, one as spare).

Also, because if I can use the IGH as the jackshaft, it solves one more problem.

 

[rhitee05]

I understand your desire to keep the IGH out of the rear wheel for easy swappability. There are definitely a lot of possible combinations of stock and semi-stock bike parts that could be used to put together a jackshaft, with or without gearing.

I don't think I need a geared jackshaft for my purposes. I'm quite happy keeping the rear cluster, and with a 32-14 cluster I'd get a 2.3:1 range. That's enough to stay in the efficient band of the Cyclone motor from just under 10 MPH to top speed of 30 MPH, so I don't need any more gearing than that. I understand the appeal of an IGH, though, nice and clean with simple chainlines.

One appeal of just using a simple shaft and adapters to make the jackshaft is that I could easily swap the pedal chain to the left side. Not sure if that's what I'd like to do or not, but it's nice to have the option without requiring specialized left-hand freewheels or such.

 

[rhitee05]

A slightly OT idea came to me a while back as I was pondering this project, I'll put it up here for discussion and possible inspiration to others.

One type of CVT transmission works by using two cone-shaped pulleys flipped 180-deg relative to each other with a belt that moves lengthwise. It occurred to me that something similar could be done using a rear hub as a jackshaft. Keep the normal cluster on the rear wheel - 7 spd, 8 spd, whatever. Get a matching hub and cluster to use as a jackshaft, except reverse the sprocket order. I think this should be possible, at least for a cluster with individual splined sprockets and possibly with slight modification. The tricky part would be rigging the shift mechanism for the jackshaft cluster. I suspect that a 2nd rear derailleur would work if you removed the tensioning arm. As a kludge you could just use two separate shifters, but it would be better to rig a cable splitter so both would move together.

The result would obviously have discrete gears and not be a CVT, but it would have substantially greater gear range. A typical cluster has a 2:1 or maybe 2.3:1 ratio. Putting two back-to-back would give you a 4:1 or 5.3:1 ratio. That's a wide enough range to have both respectable top speed and a usable granny gear.

I seems so simple I feel like there has to be something I'm missing. Can anyone see a reason this wouldn't work? Although, I suppose it's not really any different than getting a wider ratio with the back cluster and front triple, so maybe this isn't as original or useful as I thought!

 

[Powdersummit]

Have a look at the phaser gearbox. It is exactly what you are describing.

http://www.nosmokemtb.it/UK_phaser.html

It sounds like a really nice setup with a wide gear ratio in a compact form factor. you also have the advantage of keeping the chain in a straight line for better efficiency.

Carl

 

[amberwolf]

One type of CVT transmission works by using two cone-shaped pulleys flipped 180-deg relative to each other with a belt that moves lengthwise. It occurred to me that something similar could be done using a rear hub as a jackshaft. Keep the normal cluster on the rear wheel - 7 spd, 8 spd, whatever. Get a matching hub and cluster to use as a jackshaft, except reverse the sprocket order. I think this should be possible, at least for a cluster with individual splined sprockets and possibly with slight modification. The tricky part would be rigging the shift mechanism for the jackshaft cluster.

Naeem (numberonebikeslover) made one like this, in his original bike build thread.

I don't recall how well it worked out in the end, but it did work.

 

[rhitee05]

Well, whaddya know. Not such a crazy idea after all, I suppose.

It did occur to me after I posted that you could still use this setup to achieve a wider range of ratios than a regular triple setup. If you have a really extreme cluster like a 34-11 (not sure that's a standard one, but you should be able to make one easily enough), you could get almost a 9.6:1 range. That would be quite impressive. Perhaps worthy of more consideration...

 

[amberwolf]

34-11 is a common enough one on 8 or 9 gear clusters (I think that's what's on the broken-frame Specialized that someone abandoned here).

 

[rhitee05]

Probably the ticket for this would be to start with maybe an 8-speed cluster. Based on the really sketchy motor data plots online, the efficient range of the Cyclone motor is roughly 2000-3000 RPM. Thus, if adjacent gears have a 1.5:1 ratio or less, I can always choose a gear to keep me near peak efficiency. Based on this, 4 speeds gets me a 3.4:1 range, 5 speeds gets me 5.1:1, 6 speeds gets me 7.6:1, 7 speeds gets me 11.4:1.

So, if I start with an 8-speed cluster, I can rejigger it to place the 6 sprockets I want to use in the outer 6 places, either a small sprocket or a spacer in the 7th space, and then use the innermost space for the input/output sprockets. It would be pretty easy to choose the drive ratios to keep within the desired range.

Figuring the pedal input to the scheme is a little more difficult. A sprocket could be attached to the hub body, but the freewheel is in the wrong direction. I could disable the freewheel, but that would require either freewheel cranks or yet ANOTHER jackshaft. Hmmmm...