Two chains on triple crankset? Gonna rub or not?

Hi, just one question regarding use of 2 chains (one from crankset to rear wheel, and one from motor to crankset), the one from motor is going to be permamently on the biggest sprocket, is the other chain going to rub when on the middle sprocket or they will have enough clearance? Can't check it myself yet as parts are still in post. No freewheel on crankset (I want to use Shimano M371 crankset).
Thanks in advance

You realize that you will be forced to predal with the motor if you don’t have a freewheel crank? That can be painful when your feet slip off the pedals.

Anyway, you can use a narrow enough chain to avoid rubbing. Derailers setting might be a frequent concern though.

On triples I've done this with, there's generally enough clearance if chainlines are straight. You'd have to test it on your crankset.

If you have bolt-on chainrings, you could add spacers between the two rings you want ot shift between, and the one iwth the motor chain, if you don't have clearance.

If the chain for hte motor goes up vertically, there may not be clearance for the derailer itself, though. The chain may have to come from below, behind, or in front of the cranks.

I looked up that M371 crankset , and it is a old fashioned squared tapered crankset, ( it uses a square taper matting surface with the BB )
So
You can order a freewheel crankset that others use on their mid-drives,
There are the square tapered cranksets
or
Some people use the i-s-i-s type of BB's / Cranksets that are a little lighter , and are said to have a much better mating surface than square taper,
and they reportedly, do not come loose as much as the square taper ones.
Others here can tell where they bought theirs as I have not yet owned a mid-drive.

Thanks guys for very helpful replies. At this time I'm planing to go without freewheel, because I want to use mid drive as an assistance only, when climbing. So I will be pedalling at the same time. I have SPD pedals so my feet rather stay there unless I don't want lol. To be honest I want to try to keep the cost to minimum for now, will see how it works and then I may upgrade it. Unfortunately my canondale has that square taper crank and I'll keep it as is for now. I'm going to mount the motor in front of the crankset, so it should be fine with front derailleur. And that shimano crankset has sprockets welded together, so I can't add washers to increase distance between the two. I'll start with bit narrower chain for motor and will see... Thanks again

Just to add something, maybe it could be one of the cheapest mid drive conversions lol, with 36V 350W motor and 36V 10Ah battery. Along with controller, throttle, watt and amp meter, freewheel sprocket for motor- £180 Made some diy brake switches for hydraulic disc brakes too.
I'm going to use 10s lipo (4s and 6s in series), with 10C cont discharge it's 100A, but controller won't pull more than 20A anyway. Have these lipos from rc planes I used to fly, but that pair hasn't been used much and all cells are in similar, almost new condition (had maybe 5 full cycles). I'll be using lipo cell monitor, so they won't discharge below 3.5V per cel.
These batteries still show up at hobbyking website with discount prices, I grabbed them two for less than £80 from UK warehouse (Multistar brand). On fixed wing, 4s 8Ah was enough for over 90 minutes of continuous flight, with peak current sometimes even 35A.
After some time, if it's going to work well, I'll get/make li ion pack with minimum 20Ah capacity.

If you have to you can replace the right crank and chainrings to something that does allow spacers, if you find it necessary.


BTW, I made a really cheap middrive with a powerchair motor on CrazyBike2; info about that is in the first part of that thread (in my signature), before I changed it to hubmotors due to frame flex problems causing chain derailments. I didn't use a freewheel either, and it caused a number of problems over the time I used it; could've had a broken leg once if the problem had continued farther than it did (caught pantseam in chain).

I have a plan for doing it with freewheeling cranks later, probably on one of my trike designs.

@amberwolf, I never ride while wearing long trousers, only shorts or shorts on top of lycra leg warmers, and shoelaces are secured under velcro straps on my shoes, so there's nothing to be caught by chain/sprocket.
I also thought about getting A4 acrylic sheet (3mm?), and making chain guard from it (cut to shape and bend using heat), it would cover motor sprocket and at least top part of the chain, almost touching crankset chainwheel with ~2mm clearance to crankset chain guard.
My friend is engineer in the factory and has well equipped workshop in there, and he said he can make me mounting bracket from aluminium plate to my design.
And btw bicycle I want to convert is Canondale Trail 5.

Will there be a freewheel on the motor end? Otherwise you'll be spinning the motor full-time when pedaling which might defeat the purpose of just having it for a hill boost if it's dragging on the flats...
Edit.. Just saw freewheel in the parts list

And this is totally not a knock against mid drives, but if you're a normal full time cleats and Lycra rider (I'm part time), be mentally prepared for how loud a mid drive is... It throws some off that are used to quiet rolling road bike. The constant clicking of the motor freewheel is there or the the motor/chain noise.. which again isn't an issue for lots of people.

@Voltron thanks for input, actually I wouldn't call myself lycra rider lol, I feel more comfortable in shorts, only when it's cold/wet I wear those leg warmers. It also helps when wearing knee leg guards (long ones). I don't use my bike for commuting, I put it on towbar mounted bike rack and take it to different places. There's plenty flat trails around, but there are steep hills too, and that is my main reason to have mid drive assistance. I prefer riding off roads, country lanes, trails, I use roads only if there's no other way. There are Tamar Trails, Dartmoor National Park, Camel Trail and lots of others places that are less than hour away (in a car). I'm aware of mid drive noise and I'm ok with it Nonetheless I thought about hub drive too and I don't throw that option away, but first want to try mid drive.

I'm having a hard time telling from the pictures if individual chainrings can be swapped out on the M371 but it looks like they can't. My gut feeling is that you're gonna miss not having access from the big ring to the wheel. An old 10 speed crank set might do you better. You'd only have 1x7/8/9/whatever but if you get the kind with bolt on chainrings you can experiment with different sizes/gear ratios to dial in something you like.

@fourbanger thanks for reply. I'm still trying to match all necessary pieces to have complete freewheeling crankset, but I don't want to spend half of what it all cost me till now. Tartybikes sell threaded crank arms but they're not cheap and with length >170mm they have only isis type- that would mean I'd have to replace BB for isis (have square taper atm, another cost). Looked at Lunacycles and Sickbikeparts, they have cheap crank arms, but postage from US is more than crank arms themselves. SJS cycles in UK sells cranks with freewheel and spider for chainwheels, although this seems to be the most expensive option of them all (even ordering them from US and getting flanged freewheel separately would still be cheaper, but I would need sprocket with freewheel' pcd or spider that fits).
Also I've tried local machining shop, to have thread made on crank arm (one I have on my bike, there's plenty material to reduce and thread it for freewheel), but they said they can't do it.
I found die with size 1.37 x 24 tpi, but it costs £30, and still would have to precisely trim OD before threading. Actually I could upgrade my diy plotter to 3rd axis and use it as cnc table
You're right about M371 crankset, it has welded together sprockets.
So after all looks like getting freewheeling crankset is not possible unless I spend ~£70 on it. However your suggestion about getting crankset with bolt on sprockets could be the best and the cheapest solution for now.

I've been thinking about that freewheeling crankset and I have another question. This crankset from sjs cycles has 104mm pcd, and triplet on my bike, although it's one piece triplet, has 104 pcd too. What if I take that off and bolt it onto crankset from sjs cycles and add 4th chainring, let say 36T (motor will have 12T sprocket, I want 3:1 ratio) on the outside of the spider (closest to crank arm)? I suppose it would need few more mm spacing, as spider looks too thin to achieve clearance betwen two chains, but it should be doable. That would let me use all 3 chainrings on crankset, while 4th one would be motor driven. I know I could put all 4 chainrings on the "inside" of freewheel, but then chainline would move towards bb, and bb spindle could be too short for that...

Well for what it's worth. I'm still in the process of building my first ebike, but it sounds like we have a very similar idea of what we want to accomplish. Depending on what kind of motor you're using, there may be the option of driving the LEFT side of the BB with another crankset.

The caveat the is that you WILL have to pedal when you engage the motor. That's basically what I'm up to.

What motor are you using, anyway?

Cost to a minimum is a good idea. I just looked at buying a 36T Cyclone gear from Luna and they are dirt cheap at $10usd but shipping to Canada is $25, same goes for CycloneTW website - So I need to splash more shit into my order to make it worth my while. But they got them crank freewheels too! Just something to think of if you require a crank freewheel.

MrNotEnglish said:

Thanks guys for very helpful replies. At this time I'm planing to go without freewheel, because I want to use mid drive as an assistance only, when climbing. So I will be pedalling at the same time. I have SPD pedals so my feet rather stay there unless I don't want lol. To be honest I want to try to keep the cost to minimum for now, will see how it works and then I may upgrade it. Unfortunately my canondale has that square taper crank and I'll keep it as is for now. I'm going to mount the motor in front of the crankset, so it should be fine with front derailleur. And that shimano crankset has sprockets welded together, so I can't add washers to increase distance between the two. I'll start with bit narrower chain for motor and will see... Thanks again

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You won't need or want the lowest part of your gear range once you have motor assist. So there's no reason to plan for 4 chainrings.

If there is a problem with two separate chains rubbing, you can add spacers to either the motor chainring or your pedal drive chainrings to move them apart slightly. Alternately, you can use a tandem crank on the left side, like Stokemonkey, to apply motor power. That leaves your normal front shifting unaffected.

fourbanger said:

What motor are you using, anyway?

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I've ordered dirt cheap, MY1016Z3 36V 350W geared brushed motor for £52 shipped from AliExpress, and 12T freewheel sprocket for £15.

fourbanger said:

Depending on what kind of motor you're using, there may be the option of driving the LEFT side of the BB with another crankset.

Click to expand...

Chalo said:

Alternately, you can use a tandem crank on the left side, like Stokemonkey, to apply motor power. That leaves your normal front shifting unaffected.

Click to expand...

I thought about adding chainring crank on the left side, but I'd need different freewheel for the motor or chainring, and going this way, even if I decide to get freewheeling crankset, it wouldn't do its purpose (spindle would transfer motor power from left chainring to rignt chainset), so I'd have to pedal with the motor anyway. Only way to get it sorted, would be getting opposite freewheel for the motor that would have to be on the right side and putting normal crank arm back on the left side. And all this would generate unnecessary costs..

Chalo said:

You won't need or want the lowest part of your gear range once you have motor assist. So there's no reason to plan for 4 chainrings.

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Actually I think there is reason for 4 chainrings, in my case. My intention is to have motor as assistance only, and if I change my plan about route and wish to ride longer, I still want to use the smallest chainring on hill climbs, in case of empty battery of course. As I wrote earlier I prefer off roads and sometimes hills can be very steep.

But I appreciate your ideas and suggestions

I am currently working on a spreadsheet for gearing. Its setup for my motor gear of 16T, the two crank gears have both 44T then to the rear cassette which is currently only on one gear of 22T. I will do a screenshot of where I am at now and add it here the formula is quite easy to understand, which is also on the spreadsheet.

On a mid drive you cant play around with the motor simulator unless you know what to do. Justin explained it well in the motor sim thread. Basically you put into the sim an effective wheel diameter based on what all your gears are.

Equation is at B22
or wheel size x (motor to crank gear x motor gear) x (crank gear that goes to the rear x rear gear)

Please note at A30 you cant use a freehweel gear on the motor when using the motor as a mid drive. I used whats called a brake disc mount cog then rotate the motor around and reverse the direction of the motor. There is a fixie item you can buy where the fixed gear threads onto freewheel threads then a reverse thread locker ring goes on. Perhaps that is not even needed because of the crank freewheel action, but it could still unthread off.

View attachment 1






I am currently working on another spreedsheet, where I use the motor sim and input different effective wheel diameter on an extreme case of 20% grade and seeing what the info states. It seems that nothing below a certain effective wheel diameter is necessary.



ewd of 10" seems to be a good comprimise unless you got a very long 20% slope. For my needs, I have one slope that is 21% for a 100-150m or so.

So, sorry, that first spreadsheet is used to calculate the wheel diameter to be used in the ebikes.ca simulator for mid drive motors?

Is that right?

Hey Lads, I've run into little problem.. Motor and freewheel sprocket from China arrived today, it looks like motor is about 2-3 mm wider than space between cranks. More precisely left crank arm has no clearance to turn around IF I'd like to mount the motor less than 15cm from BB on underside of frame. However it's fine if I mount the motor higher on the frame (towards front fork). But this option doesn't look nice with motor in the middle of the frame. Do I need to replace existing bb (some japan brand, 122mm, shimano cups) for one with longer spindle (132mm)? Would this make big difference for crank-derailleur chain line? Btw seems to be just that round button part of motor back cover, on which crank arm catches on.
Also, do you have any ideas how to mount my1016z3 motor on the frame without properly machined bracket? My friend has gone on holiday for almost 4 weeks, don't want to wait that long for him to make me one.
Thanks

Sick Bike Parts has a 132mm cartridge bottom bracket that's reasonably priced and seems to be of decent quality.

If you have any intention of using four chainrings as you suggested before, you'll probably need some extra chainline width anyway.

Thanks Chalo, for now I plan freewheel on the motor shaft only and 3 chainrings in total. I'll probably get that freewheeling crankset but for now I'm costs. And I think I found the way around that wide motor, I'm going to buy 175mm left crank arm only with needed offset. And it doesn't come from abroad, whereas postage from sick bike parts is weight dependent, and almost as much as parts, when I was looking at those.
Hopefully I will begin my build on Thursday

fourbanger said:

So, sorry, that first spreadsheet is used to calculate the wheel diameter to be used in the ebikes.ca simulator for mid drive motors?

Is that right?

Click to expand...

No, the first spreadsheet is to get an idea of the effective wheel diameter with different gears from the motor gear, to the two crank gears to the rear wheel gears. You can see how on line 41 it goes from 11.556 for hill climbing ability all the way up to 37.818" in effective wheel diameter, which is a useless that will never be used, that being the 11T on the rear wheel, but also the 12T if your rear gear has that. The 13T gear on the rear can be used but I found not much gains provided. Surely the 15T would be used for cruising flat ground and going fast.

Then I use that to input into the motor simulator at ebikes.ca and put in all the parameters. In my case, I have a 23.5% grade on a pathway thats 150m in length. I also have a few other 15% and 18% much shorter.

A high rpm/volt aka KV means a low turn count motor, spins faster for given battery voltage. Has larger winding diameter and can take more amps, perfect for a direct drive motor that is mounted as a mid drive. For my needs though, I'd require a shorter axle that would have to be custom machined so my feet dont hit the 150mm axle length, and order in a Cyclone BB and crank, which costs more money, so my project is cancelled. It would be a wicked ass setup though. Ultra silent with a Sinewave Controller and a controller that can punch out huge amps for atmospheric power, yet still have 26" wheels. Cant hide the motor much when its mounted above the crank.




but I've converted back to rear hub motor.

MrNotEnglish said:

Thanks Chalo, for now I plan freewheel on the motor shaft only and 3 chainrings in total. I'll probably get that freewheeling crankset but for now I'm costs. And I think I found the way around that wide motor, I'm going to buy 175mm left crank arm only with needed offset. And it doesn't come from abroad, whereas postage from sick bike parts is weight dependent, and almost as much as parts, when I was looking at those.
Hopefully I will begin my build on Thursday

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Freewheel on motor aint gunna work I tried that on mine and it just doesnt work. You either have to have a FIXED gear on the motor and whatever normal crank then your pedals will always turn, or have a freewheel on the crank, and if you want it to last then do not skimp on it and go for the heavy duty model.

How freewheel on the motor not gonna work? It's purpose is that I don't turn motor shaft when it's off, while pedaling, especially cos it's geared motor and harder to spin by shaft. I know I could do that by using freewheel on the crankset and add 2nd freewheel on the crankset so I don't have to pedal with motor. But if motor has one freewheel, then would need just one for crankset.