Cheap Sachs XR1 upgrade

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qwerkus   100 W

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Cheap Sachs XR1 upgrade

Post by qwerkus » May 12 2019 12:38pm

As mentioned in other threads, I moved to a very hilly region. We live on the slope of a 1400m (4593.176ft) mountain with 2 kids, so basically every commute is either rushing down or crawling up. I built a couple of ebikes for the city we lived in before, but they were no match for the new place. So I build a new one based on a corratec frame using a bbs02 only to discover that this motor is way too weak to carry serious weights (200Kg) uphill: after trying different options (long john,long tail) I found out that a bike + trailer is the most flexible option, especially with the kids, but also a quite heavy one. So to haul my stuff, I don't need a racing speed system, but one with very high torque. A good option would be a powered trailer, and in the long term (next year) this is my plan. But for this summer, I have to stick with the trailers we already own, without motors. So I went out looking for a better solution, when I found a super cheap 2nd hand Sachs XR1 ebike.
a.jpg
b.jpg
Sachs is a german builder specialized into mopeds that used to build quality bikes. This one is a rather cheap model from 2009 running a stock bafang geared motor with a chinese controller. Surprisingly enough, it's still working after 10 years! The original battery is now very weak, yet still strong enough to carry me over 10miles home! None of the parts seem to be upper class, especially the super cheap suntour fork, yet this bike comes with some nice features. For once, it has tektro hydraulic disc brakes with integraded sensors, which will certainly find some use. Than the frame comes with a 85-90mm square space behind the seatpost to accomodate the controller and the battery, which effectively increases its wheelbase and makes it more stable. And finally it comes with wide chainstays which can accommodate up to 27.5x2.5" tyres, while most bikes from that generation would be limited to 2". The frame itself is very light despite the nearly 2" oversized downtube, and the welds are quite clean. Perhaps too light, since the rear part doesn't make a sturdy impression. Yet sachs felt confident enough in its aluminium dropouts to ditch torque arms completely...

Anyway - my first plan was to cut out the controller box and build a larger battery which would power a bbs02 or a bbshd. Than, as mentioned, I realized the first one would be to weak, and found it impossible to get an aluminium profile of the right dimensions to fit the space behind the seatpost. Also, I figured some sort of regen would be very welcome when riding downhill - so no bbshd after all.

Than I investigated a 2wd solution, which would still be the simplest solution up to date, using a regen capable hub combined with a small front hub motor, or an unused tsdz2 mid drive which I happen to have in my garage. The best hub for this setup would be the GMAC from ebikes.ca, which comes with a locked clutch to allow for regen even with a geared hub motor. Unfortunately, this thing is expensive! And quite heavy on top of it.

So figured that with 4.1+3.8KG of additional weight, I could do better, and started pondering about direct drive mid motors. So here is the current plan:
c.jpg
The sachs bike comes with a controller box directly welded onto the frame. Since it has to support the weight of the battery, it's quite sturdy, and could become handy as a mounting base for a custom mid drive motor. Without any modification, there would be max 85mm diameter available behind the seatpost; with some grinding and cutting, 100-105mm should be possible, which opens up the question of which motor to use. A C80100 from alienpower would be a perfect fit, but I'm affraid this motor would be too weak. 100mm would probably be better, but apart from the revolt models - which are super expensive - I don't know any good ones.

The battery would have to move into the frame, and since there are no bottle mounting holes (!) a triangle bag from luna or em3ev will have to do. I never used one of those, but it seems to be the simplest option, on top of offering plenty of space.
triangle_bag.jpg
triangle_bag.jpg (28.67 KiB) Viewed 393 times
Now the obvious problem with this kind of setup is how to mount the second drive train. #219 Kart pieces seem readily available, and quite cheap, yet you still have to find a way to moun the large rear sprocket. I spend a couple of weeks tinkering with the issue, and figured that it could be done with a 3sp or an 8sp IGH. God I love those. Super simple to maintain, and the alfine 8 is really a nice piece of mechanics for a decent price.

The 3sp hub fom shimano is the hub that offers the widest space between the rotor disc and the left hub flange (around 25mm). On top of that, all centerlock disc rotors come with some sort of aluminium spider, which means you get a quality aluminium adapter for free, where you can mount the disc rotor on one side, and the chainring adapter on the other.
free_adapters.jpg
Using a second adapter together with some spacers,it should be possible to go around the hydraulic caliper and mount a large (at least 110t) #219 chainring concentric to the disc brake,without interference. This would allow for a left side drive train + disc brake setup.
3sphubadapter.jpg
Now this would require a custom chainring to be lasered somewhere, on top of an adapter disc. Also,it's only possible with a shimano inter3 hub,as those are the only ones with enough room on the left side for the bypass adapter. Unfortunately,3 speed is not nearly enough if you want to keep up with the motor speed.5 would be a min; 8 even better.

So I looked for a way to mount a second drivetrain on an alfine 8 hub, and found out the there is actually just enough room on the right side, between the hub flange and the sprocket, to mount a spider and a larger #219 sprocket. An easy way to do this would be either to drill 9 or 18x M3 holes in the hub flange to attach the spider, or laser a 3.5mm flang adapter, which could be bolted to the existing spokes holes together with a spider, and fitted with new spoke holes of a larger diameter to mount the spokes (kindoff a flange-diameter-increase-adapter), like this:
8sphubadapter.jpg
8sphubadapter.jpg (40.81 KiB) Viewed 406 times
Either one hub + adapter should work, but I'd really like to go for the 8sp version, even though the thought of 2 chains running side by side with 2 different speeds doesn't sound very secure.

The final problem - apart from finding the right motor - would be the optimal reduction. A 2 step reduction,using a 1:2 or 1:3 5MGT belt transmission, and a 12T to 96T #219 chain would certainly fit the said torque requirements, but it would also increase costs, weight and drag significantly, hence a single stage 1:10 reduction would be my preference. Using a 11T motor sprocket and a 110T rear chainring, it *should* fit into the frame,but I'm not sure it would provide enough torque. Any thoughts on that ?

So much for today;I try to keep this thread alive until the completion of the bike. My time frame is around 2 months.

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Re: Cheap Sachs XR1 upgrade

Post by ElectricGod » May 14 2019 1:39am

Gear hubs are generally weak. If you look at any of the Shimano products, they don't recommend them for MTB use as they are not strong enough for human power in that use. Running a motor to the gear hub in the back wheel would easily be 3-10x more powerful than a typical human. It wouldn't last long.

I have a Shimano alpine from 2010 or so. The planetary and sun gears are fine. The shifting components are thin bits of metal that have to hold the power going down the chain. These small shifting components are what usually break. Sure enough...in my gear hub, that's exactly what gave out.

If you can keep the RPM's to the gear hub high, then it doesn't suffer as much stress as it does at the very low RPM's of a bike wheel. In a scenario where the gear hub is running at a few hundred RPM's, the stress on the shifting pawls is greatly reduced. The gear hub can't be installed in the wheel to keep the RPM's high. More RPM's the better.

If you want a strong gear hub, expect to pay $1200 for it and get a Rohlhoff.

A C80100 at 80kv is pretty ideal for this size motor for EV use. Get above that and the motors eRPM gets too high for typical motor controllers. Too low of a kv and the copper per phase tends to be too thin. Of course if you like to mod stuff, rewinding is a great way to beef up the wattage of the motor. The C80100 from the factory has no holding power at the shaft to bell union. You'll need to reinforce this union to make the motor reliable for regular use...like this.

Image

Revolt Pro and E motors are a better option than anything from Alien Power. An RV-100-pro or E will already have a key in the shaft to bell union so while not ideal, it's lots better than the C80100. Of course I want my motors to last long term so I still reinforce the bell to shaft union. Revolt motors don't have a motor base included and Revolt refuses to make something generic. Making a base is pretty much the only option. I've done that for all my Revolt motors. If you got one, I could make you a base.

Image

The Revolt Regular motors can be pretty good, but they need a LOT of modding to get past their piss poor aspects. I've jumped down Revolts throats multiple times about how shitty certain aspects of the Regular motors are and they refuse to fix anything about them. Even if those fixes would cost them nothing, they won't fix anything on this product line. If you want a motor that's going to be solid out of the box, avoid the Revolt Regular motors. My 120-regular after loads of modding is pretty good, but the 100-regular is probably going to need a rewind to get it usable.

The RV-100 series are all potentially significantly stronger than the C80100. The stator and magnet ring are larger in the Revolt motors. AKA 100mm vs 80mm.

Gearing is king...
You can take a motor strong enough for running a skate board and gear it far enough from 1:1 and it will run your cargo bike...just not very quickly. At some point you want a motor that can get you a decent amount of speed and torque. A 4kw outrunner such as the C80100 geared low enough to get you 30mph will produce a lot of torque. I run mine at the point where I'm getting good torque and 45mph at 66v. It's fine for pushing me around, but for hauling a good bit more weight, I'd gear it lower and lose 10mph top speed. Depending on your expectations, a C80100 will get your cargo bike moving just fine. Personally I'd go for the 100-pro or E.

That brings us to the next item. You will be able to run a 100-pro on a PV 12 fet controller. The E will need an 18 fet.

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Re: Cheap Sachs XR1 upgrade

Post by qwerkus » May 14 2019 3:25am

Thanks for the awesome reply EG. As mentioned, my plan is to use the IGH-grears for human power only, while (somehow) mounting a 219 chainring directly onto the hub shell, in a direct drive setup. Only that config would give me regen,on top of sparing the rather weak IGH gears.

Reading your extensive take on the AP C80100 vs Revolt motors,I think I will go with the AP C80100. The Revolt 1000 Regular would be the only one fitting into the frame, the E and Pro version beeing 5mm too large (diameter), and also quite long. So even if the RV 100 Regular would probably be stronger than the AP C80100, I don't have the time or the money for extensive modding.

Does anyone know the stock torque constant of the AP C80100 ? My plan would be to run it at 1500 to 2000W, with a 1:10 reduction. With a top speed of around 45-46km/h (28mph) on a 27.5" wheel, this means roughly 3500rpm at the motor, so I'd require a low 70 to 80kv version. With a 2 Stage reduction, I could squeeze a 1:24 reduction in, and use the stock 130kv motor, but than again, that seems just too much custom modding to be realistic with my budget.

Second question is cooling: would a C80100 @2000W stay cool enough to use the stock air ventilation, or would it require an additional fan ? The motor itself is already quite long, so with a fan,it won't fit into the frame anymore.

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Re: Cheap Sachs XR1 upgrade

Post by ElectricGod » May 14 2019 12:33pm

qwerkus wrote:
May 14 2019 3:25am
Thanks for the awesome reply EG. As mentioned, my plan is to use the IGH-grears for human power only, while (somehow) mounting a 219 chainring directly onto the hub shell, in a direct drive setup. Only that config would give me regen,on top of sparing the rather weak IGH gears.

Reading your extensive take on the AP C80100 vs Revolt motors,I think I will go with the AP C80100. The Revolt 1000 Regular would be the only one fitting into the frame, the E and Pro version beeing 5mm too large (diameter), and also quite long. So even if the RV 100 Regular would probably be stronger than the AP C80100, I don't have the time or the money for extensive modding.

Does anyone know the stock torque constant of the AP C80100 ? My plan would be to run it at 1500 to 2000W, with a 1:10 reduction. With a top speed of around 45-46km/h (28mph) on a 27.5" wheel, this means roughly 3500rpm at the motor, so I'd require a low 70 to 80kv version. With a 2 Stage reduction, I could squeeze a 1:24 reduction in, and use the stock 130kv motor, but than again, that seems just too much custom modding to be realistic with my budget.

Second question is cooling: would a C80100 @2000W stay cool enough to use the stock air ventilation, or would it require an additional fan ? The motor itself is already quite long, so with a fan,it won't fit into the frame anymore.
I run my C80100 at 5kw without any added cooling.

Since you are driving a bike wheel, you will need 2 stage gearing. The specific gear ratio is dependent on wheel circumference, motor RPM at whatever your pack voltage is and the desired speed you want.

I always want regen so direct drive to the wheel is important to get that.

I don't know how your back wheel works. Some gear clusters are mounted via freewheel threads. If that's your set up and you know you can live with just a couple of speeds, there's sprocket mounting options that can use those threads. If your brake rotor mounts with a 6 bolt pattern, that can do double duty and mount a sprocket and the brake rotor. The brake position will need some rework to make both fit, but it can be done.

An option is a custom hub made by LightningRods. He makes a hub that takes a standard gear cluster on the right side that threads onto freewheel threads. On the brake side, it has 2 sets of 6 bolt pattern. One is inset further than the other for mounting a sprocket.

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Re: Cheap Sachs XR1 upgrade

Post by qwerkus » May 14 2019 1:28pm

ElectricGod wrote:
May 14 2019 12:33pm
An option is a custom hub made by LightningRods. He makes a hub that takes a standard gear cluster on the right side that threads onto freewheel threads. On the brake side, it has 2 sets of 6 bolt pattern. One is inset further than the other for mounting a sprocket.
That sounds interesting,though I never read about this hub before. Also not listed on his website Do you have a pic ?
I asked LR for some help to build a kit for this bike, but he replied that he's super busy. Not sure if he would have time to machine hub for me.

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Re: Cheap Sachs XR1 upgrade

Post by ElectricGod » May 14 2019 5:50pm

Compact gearing...

I forgot about these planetary gear sets used for industrial stuff. They are quite compact, all metal construction and come in a lot of ratios. This can get your gearing done for you in a fully enclosed package. All you need to work out is connecting the motor to the gear set and the gear set to the wheel.

Nema 34 is plenty strong for your uses. You could probably go to the next size down too since it will be spinning pretty fast and be OK. Look around for these units on ebay and you will find a lot of ratios.

https://www.ebay.com/itm/5-1-Nema34-Pla ... 3643528495

With the right planet set, your motor sprocket could be 15-17T and the wheel sprocket 70-80T. This would keep the over all sprocket sizes small and easier to implement.

Large sprockets tend to be noisier than smaller ones. I have a 117T sprocket. Despite the chain line being dead straight, it acts like a speaker cone and amplifies every little sound in the drive train.

If you do get one of these planet sets, consider draining out the oil. Who knows what they have in them from China. Get a high teflon content, thin oil. Something like is used in the Rohlhoff hubs will work great in here and reduce frictional losses from oil viscosity a lot.

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Re: Cheap Sachs XR1 upgrade

Post by ElectricGod » May 14 2019 8:23pm

qwerkus wrote:
May 14 2019 1:28pm
That sounds interesting,though I never read about this hub before. Also not listed on his website Do you have a pic ?
I asked LR for some help to build a kit for this bike, but he replied that he's super busy. Not sure if he would have time to machine hub for me.
You can see the LR hub in this listing.

http://lightning-rods10.mybigcommerce.c ... -and-140r/

In the recommended parts list is this "165mm billet 6061 wheel hub with 4140 chrome moly axle"

It's the part shown in the last 2 images from that listing. It's not included in the kit. You have to order it separately.

I searched his site and he doesn't list it for some reason, but that's Michael Backus for you. His site hasn't seen an update in quite a few years.

He works with a local machinist who does good work, but orders take a good while to get done.

You don't really need this part as you can work out mounting a sprocket and rotor on the same 6 bolts, but this is a better option.

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Re: Cheap Sachs XR1 upgrade

Post by qwerkus » May 15 2019 8:38am

ElectricGod wrote:
May 14 2019 8:23pm
In the recommended parts list is this "165mm billet 6061 wheel hub with 4140 chrome moly axle"
Thanks. I knew about the qulbix hub; sadly only for fatbikes. LR was kind enough to reply to my inquiry with another link: http://www.damgood.com/cycle.html
This one fits into 135mm dropouts, but the price is ... steep!

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Re: Cheap Sachs XR1 upgrade

Post by ElectricGod » May 15 2019 10:21am

qwerkus wrote:
May 15 2019 8:38am
ElectricGod wrote:
May 14 2019 8:23pm
In the recommended parts list is this "165mm billet 6061 wheel hub with 4140 chrome moly axle"
Thanks. I knew about the qulbix hub; sadly only for fatbikes. LR was kind enough to reply to my inquiry with another link: http://www.damgood.com/cycle.html
This one fits into 135mm dropouts, but the price is ... steep!
LR originally said he was making his hub for various sized drop-outs. I wonder what changed?
Regardless of who you get these custom hubs from, they won't be cheap. This is a limited production, specialty item and they will be fairly expensive as a result. It's not the materials involved, just the production and labor costs that are expensive. Parts like this would be made on a CNC mill and lathe, but only get cheap if they are made by the thousands and they never are more than 10 or 20 at a time.

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Re: Cheap Sachs XR1 upgrade

Post by Grantmac » May 16 2019 10:57am

I'd take a look at the QS1000 mid drive motor. It's 110mm OD but you can likely mount it ahead of the bottom bracket. Then run a first stage reduction to the left side crank before a second stage to the rear. For a commuter possibly run regen instead of a rear brake and just bolt a sprocket directly to the rotor mount.

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Re: Cheap Sachs XR1 upgrade

Post by qwerkus » May 16 2019 1:52pm

Grantmac wrote:
May 16 2019 10:57am
I'd take a look at the QS1000 mid drive motor. It's 110mm OD but you can likely mount it ahead of the bottom bracket. Then run a first stage reduction to the left side crank before a second stage to the rear. For a commuter possibly run regen instead of a rear brake and just bolt a sprocket directly to the rotor mount.
You mean this one:

Image

I checked it out some time ago, indeed very large. I wonder how ppl manage to fit 174mm between the pedals ??? About your suggestion: not sure it would be wise to drop the rear brake completely. Any real life feedback here would be welcome. After all, I'm planing to haul sizable weights with this bike; if it suddenly becomes impossible to stop while rushing downhill, I m going to be in a lot of troubles. I read that some controller allow reverse torque for strong braking, but this uses power, and I'm not sure the chain would survive it.

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Re: Cheap Sachs XR1 upgrade

Post by Grantmac » May 16 2019 2:08pm

That's the one, similar overall length but less diameter to the Cyclone with its included gearbox.

It should perform well with a 12:1 or so reduction.

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Re: Cheap Sachs XR1 upgrade

Post by qwerkus » May 16 2019 3:01pm

Update: no double chain right

I did some tests today, and had to realize that a dual right chain setup is not possible on this frame, at least not with 2.4" tyres. There is between 16 and 19mm of space between the tire and the bike chain, when mounting the dished nexus sprocket outwards. Knowing that a #219 chain is around 12mm wide, there is just not enough room left on either side of the chain to avoid rubbing on the tire, or worse, hit the bike chain. So back to square one: how to fit a brake into a dual chain setup.

Since bypassing the disc caliper is the main issue with a left side drive, I'm considering switching to a roller or drum brake. Those are narrower than a disc brake, and still good enough to stop a rear wheel (at least I hope so) with the right lever. I have a pair of roller brake, and am not convinced by them, especially the additional drag. But how about a large drum brake ?

Sram / SA makes a 5sp IGH with a large 90mm drum brake:

Image

5 sp is really the minimum if I still want to pedal, but could work out. Only real drawback I can see is the weight: 2.4Kg!
The left flange seems large enough to allow for some drilling, and bolting a 219" sprocket.

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Re: Cheap Sachs XR1 upgrade

Post by Grantmac » May 16 2019 5:08pm

Does it have to be an IGH and could you perhaps spread the drop outs?

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Re: Cheap Sachs XR1 upgrade

Post by ElectricGod » May 16 2019 6:33pm

You forgot the other drawback...can't hold the power of a motor much larger than 300 watts.
Sturmey isn't known for strong gear hubs.
In town road use, light people power only!
Last edited by ElectricGod on May 16 2019 8:20pm, edited 1 time in total.

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Re: Cheap Sachs XR1 upgrade

Post by Chalo » May 16 2019 6:46pm

ElectricGod wrote:
May 16 2019 6:33pm
You forgot the other drawback...can't hold the power of a motor much larger than 300 watts.
Sturmey isn't known for strong gear hubs.
Road use, light people power only!
You can put practically any amount if wattage through a gearhub, as long as you don't exceed the maximum input torque. In practical terms, this means you may not be able to use it in a full sized wheel if you want to turn the power way up. But as a jackshaft, no problem.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Cheap Sachs XR1 upgrade

Post by ElectricGod » May 16 2019 8:21pm

Chalo wrote:
May 16 2019 6:46pm
ElectricGod wrote:
May 16 2019 6:33pm
You forgot the other drawback...can't hold the power of a motor much larger than 300 watts.
Sturmey isn't known for strong gear hubs.
Road use, light people power only!
You can put practically any amount if wattage through a gearhub, as long as you don't exceed the maximum input torque. In practical terms, this means you may not be able to use it in a full sized wheel if you want to turn the power way up. But as a jackshaft, no problem.
You are right and I already said that, but he wants to use it in the bike wheel so no bueno.

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Re: Cheap Sachs XR1 upgrade

Post by Grantmac » May 16 2019 10:32pm

He's not looking to drive through the IGH gears, he wants to drive the shell.

Personally I'd just get a different frame with v-brakes and bolt a sprocket directly to where the disc would go. A 135mm rear doesn't offer much room.

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Re: Cheap Sachs XR1 upgrade

Post by qwerkus » May 17 2019 4:21am

Grantmac wrote:
May 16 2019 10:32pm
He's not looking to drive through the IGH gears, he wants to drive the shell.

Personally I'd just get a different frame with v-brakes and bolt a sprocket directly to where the disc would go. A 135mm rear doesn't offer much room.
True that. Though 2hand frames with room for a custom mid drive, the battery, with canti bosses and chainstay large enough to accomodate 2.4+ tyres are not very common where I live. I was lucky to find the sachs for a good price. And now that I invested into this bike, I'd rather go with a 2wd option as mentioned in the first post than ditch the frame alltogether.

I'm not set on IGH - just love the low maintenance. The problem really boils down to finding a 135mm hub with a disc mount, which has around 25mm between the disc mount and the left flange. This way you can easily bypass the caliper. I figured out that on many cheap geared hub motors, the manufacturer choose narrow flange distances like the infamous cute q100:

Image

I'd really hate having to buy a new hub motor just to take out its motor in order to have a hub with large flanges. So there are possible options, but none of them seem ideal:

Option 1: Shimano 3sp hub disc brake
Pros: Lightweight, sturdy, flange offset from the left large enough to mount a sprocket
Cons: Only 3sp = impossible to keep up with the motor, designing a caliper bypass is a real pain

Option 2: SA 5sp hub with drum brake

Pros: Compact, flange large enough to bolt a disc, 5sp IGH
Cons: HEAVY, not much space between the left flang and the integrated torque arm, torque arm could interfere with my frame due to the rear kick stand mount, drum brake overheating during long downhills

Option 3: Any small gear hub motor with a narrow flange gap
Pros: Caliper bypass simpler because of the large flange diameter, most hub flanges are overbuilt so drilling is not a problem
Cons: Probably weight (though I have no idea how much a hub shell without motor weights), derailleur required (I could live with it), requires a custom axle+bearing mod and finally: requires a motor!

Discarded options so far:
1- Regen only - no rear brake; reason for discarding this option: dangerous when racing downhill with cargo
2- Right drive dual chain; reason for discarding: interference with tyre and/or pedal chain
3- Buy a new frame with canti bosses; reason for discarding: either time consuming search or expensive

Fallback option:
2wd with GMAC 10T rear and Tsdz2 mid. Main drawbacks: WEIGHT, complexity, GMAC price.

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Re: Cheap Sachs XR1 upgrade

Post by qwerkus » May 19 2019 10:31am

New Plan: IGH Jagshaft aka the Brompton Problem

Upon witnessing the difficulty of squeezing 2x chains + 1 brake disc into 135mm without rubbing or other interferences, it seems that a single chain would solve many issues. But since I want regen, the only way to do that would be to use an IGH as a cheap crank-gear alternative, and a handy jag-shaft between the motor and the rear wheel. Here is a rough layout of the design:
transmission.jpg
There are many difficulties with this setup, but should it work, it would prove very neat. Only one chain to tension when removing the wheel. Shorter chains = less weight. Also,I could do everything (besides the primary motor reduction for which I need a 15mm 5mgt belt) with cheap 1/8 bmx chains instead of the expensive #219 Kart pieces. Cool looks! Main drawback in terms of design efficiency: the pedaling energy goes through 2x chains and 1x IGH before reaching the wheel,which means more losses. Not ideal knowing that human pedal power is already a scarce ressource...

The first an main difficulty of this setup is figuring out a humane gear ratio. On a normal bike, you'd have a 1:2.1 ratio between the crank and the IGH, maybe 1:1.8 if you're lazy as I am. Yet in order to have usable secondary motor reduction between the IGH shell and the rear wheel, you'd need a huge 1:6 or 1:5 ratio between the crank and the IGH to be able to keep up with the motor speed though the IGH gears. This is very similar to driving a super small wheel with pedals, like on a Brompton bike - hence the name of this setup!

There are a couple of solutions to do that. The simplest would be a very large chainwheel on the crank, but the smallest cog shimano IGH would accept are 16T and 17T for Sturmey Archer. This would translate into a 70t+ chainring, which is super expensive and not practical for obvious reasons.

I figured that an easier way to do it would be to choose an IGH with a large overall ratio, and use half of it to multiply the crank input. So let's do some simple math to check if it's possible.

The target speed of my setup is 40-45km/h with a 2.4x27.5 tyre. Given the tyre's elasticity, I'm using 700*pi as cirumference value. So 45km/h <=> 45*1000000 / [(702*pi)*60] = 341RPM
This needs to be reduced to around 85RPM at the crank level, which require a ratio of 1:4 or 400% for the highest gear

Using a shimano alfine 8 with an overall ratio of 307% and setting the 1st gear at the lowest, we can reach the target ratio by using a 3:1 ratio between the crank and the IGH gears, and than a 1:2.25 ratio between the IGH shell and the rear wheel. Not much for the motor, but something to work with. Using the lowest available 16T cog, this translates into a 48T chainring which is a medium size.

Moving to a larger 55t chainring (largest one I could find for a good price), we can reach a 3.44:1 entry ratio and hence a 1:2.58 output ratio.

If we switch to an Alfine 11 IGH which has an overall range of 409%, using the same 55T large chainring at the crank level and a 16t IGH cog, we can reach an output ratio of 1:3.44 between the IGH shell and the rear wheel, which starts to be useful as a secondary motor reduction. Even better would be a smaller cog; I've read about 14t alfine cog mods in some dark brompton forum topics,but I doubt this is possible without interfering with the gear selection mechanism.

Of course, those considerations are all based on the top gear. The output ratio between the IGH shell and the rear wheel effectively limits the range of useful gears. Using the previously mentioned numbers, I calculated that only the 4 top gears of the Alfine 8 would be effective, and the 6 top gears of the alfine 11. All other gears are just too low to add significant traction at a human cadence.

Conclusion: using an Alfine 11 IGH, the setup could be doable. On the positive side: people seem to dislike them for some reason,which makes them cheap on ebay.

The next issue would be mounting the IGH (somehow): Those things are quite large, 135mm from nut to nut, and 186mm axle length. I'd need to fit this behind the seatpost so as to not interfere with the pedaling leg. Not sure if you could trim it a little bit. An alternative would be the Sturmey Archer x-rf8 IGH which comes in a version with 120mm only OLD (over locknut dimension). Also,it seems SA managed to push the ratio to 325% which beats the alfine 8, but doesn't come close to the alfine 11. The main drawback would be the 17T cog, which translates into an even larger chainring (now we're talking 60T) and realiability: I did some googling, and there is very little feedback about those new hubs, yet enough to conclude they are no nearly as polished a shimano hubs.

NB: I'm leaving the rohloff hub purposely out of this, as it's price is wayyyy out of my league - even second hand.

An finally, I'd need some sort of fixed gear rear wheel. This problem appears to be more tricky than initially thought, as nearly all fixie hubs have thread-on flanges,which would loosen during regen braking. The best I could find is this dual side 6 bolt hub:

Image

But it's expensive, 110mm only and more annoyingly 15 or 20mm Through Axle, while I need a standart M10 or 3/8 bolt on plain axle.
Last edited by qwerkus on May 21 2019 9:43am, edited 2 times in total.

qwerkus   100 W

100 W
Posts: 267
Joined: Jul 22 2017 4:00am

Re: Cheap Sachs XR1 upgrade

Post by qwerkus » May 20 2019 12:06pm

I tried fitting a cardboard model of the setup today, and figured that:
1 - 150mm behind the seatpost, which is the minium to fit an IGH as jagshaft, is very uncomfortable. Just too wide.
2 - 100mm IGH jagshaft + 80mm motor + holder / brackets / space does not fit into this frame, at least not where I wanted to.

This whole things is getting very frustrating, and I'm seriously considering the MAC + middrive or MAC + frontdrive option. Also,seeing how much the price for bbshd have dropped in europe, I might just slap one of those in. The hd would certainly haul any cargo I have, but not allow for regen. But after seeing how hot things get when trying to brake 200Kg of load downhill, I'm not so convinced by regen anymore. I'm affraid I'd burn anything but a very large DD hub in no time, and frankly why would I use a motor that heavy, when the same weight could be used to increase the battery size, which would increase range much more than 10 to 15% regen.

qwerkus   100 W

100 W
Posts: 267
Joined: Jul 22 2017 4:00am

Re: Cheap Sachs XR1 upgrade

Post by qwerkus » May 22 2019 4:50pm

Quick update: I found a place where you can get quality #214 T6 7075al cut to custom size. A 120T cost around 100€. Not exactly cheap,but if it saves me the troubles of a primary stage reduction, it's definitely not that expensive. Together with a 11T motor sprocket, I could nearly reach a 1:11 reduction,or a 1:12 with a 12T sprocket which should be slightly more quiet. 295mm diameter though! Half the size of the rear wheel!

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