Dahon Folder Grin Kit Conversion

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Aaronrob222   10 µW

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Dahon Folder Grin Kit Conversion

Post by Aaronrob222 » Nov 27 2021 2:30pm

Earlier this year, I fell in love with the electric Citi bikes in New York that are based around PAS actuated 250-350W motors and 36V batteries. I've ridden in the city for 5-6 years but stopped after work-from-home became permanent. These Citi bikes just totally reinvigorated my love for cycling but, alas, are rarely available and are sporadically charged when they are.

After about a month and a half of obsessive research, I took the plunge on one of the Grin "Ready-to-Roll" kits for my folding bike. Before this decision, my choices had been floating around 3 categories of kits:

1. Genteel grampa kits: Leeds. These 8Fun hub kits were my first choice for ease of installation, cost, and name brand cells in their batteries. Cons:the 250 watt motors that drew in me are likely to start feeling underpowered in my hilly part of Manhattan. Leeds' conversion philosophy centers around staying in their ecosystem and not asking too many questions about componentry. Upgrading or branching out would be hard. The Australian company Dillinger had interesting kits but their options for 20 inch wheels were lacking.

2. All of the Bafang BBHD or BBS02 mid-drive kits floating around the internet. Cons: I may try my hand at mid-drive in the future but, outside of Luna, the sourcing for these kits are kinda murky. Ultimately, the Q factor of the cranks--that they "stick out" further horizontally--would be tricky for my low sitting folder on fast turns. I still want to ride my bike like a bike!

3. Grin hub motor kits. That they have an actual 75mm front hub motor, Crystalyte SAW20, first drew me in. I currently really like how my bike handles and don't want to radically change much, so the Crstyalye is basically the only hub option. The rear, alloy dropouts of my bike is 130mm, so I didn't want to chance trying to spread out for the standard 135mmm motor hubs. I've used low panniers on my front 20" wheel and when it's weighted down, it really beautiful cancels out the "twitchiness" of Dahon forks. I expect that the front hub will have the same effect.

Bikes, parts, and components:
  • Dahon Vigor all aluminum folding bike.
    D86C656F-C350-4910-876B-3B53E2A625EA_1_105_c.jpeg
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  • Crystalye SAW20 direct drive front hub motor laced to narrowish 19mm inner diameter wheels
    f_SAW20.jpeg
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  • 1.5 inch Scwhalbe Marathon tire in front to puncture protection, 1.75 inch more subtle Schwalbe Road Cruiser in the back. I had these on hand. I typically use narrower, slick tires and any type of traction feels like molasses to me but addressing flats with a wheel that is attached at 3 places and bolted to torque will not be like my current quick release set up.
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  • Two Grin torque arms for both sides of my aluminum fork. My conclusion has been that with proper use of torque arms, my riding style (never really much over 15mph), and the relatively low power of this motor, the alloy fork won't be much of an issue. I plan on keeping a close eye on it in any case.
  • Touring-grade 20 inch rear rack (made by Tern) and 300mmx35mm DiN rails for mounting the battery cradle onto the rack. I've seen others mount dolphin/Hailong downtube batteries to Dahon frames but I feel anxious about mounting an 11lb battery this close to the hinge of the fold.
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  • 36V 26.5 Ah batter and Z9 Baserunner both chosen because that was the biggest battery the kit can come with! These are already expensive, so I just picked the one that would last longest in terms of single trips and charging cycles. https://ebikes.ca/shop/electric-bicycle ... ttery.html[/url]
    B3626LiM-DT
    Actual Weight (kg) 5.18
    Dimensions (L x W x H, mm) 370x89x137
    Frame Mount
    Nominal Voltage 36 Volt (10s)
    Full Charge Voltage 42.0
    Capacity (Amp-Hours) 26.5
    Cell Type Panasonic NCR18650GA 10S x 8P
    Internal Resistance (Ohms) 0.06
    b3626lim-dt.jpeg
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For now, throttle only. I ordered a 24 pin PAS but will not install that immediately as stop-and-go-traffic isn't so kind here. I also ordered a set of e-brakes that are compatible with my regular long-pull levers and V brakes but I'm not sure if I'll install those from the get-go.

Aside from anxiously waiting for the rest of my kit to arrive (the battery itself was basically teleported to my apartment in a few days but the rest is currently moving across the continent) and pouring over the CA manual, any tips for preparing for this build?

Looking forwarding to posting my progress and pictures. Many thanks for all the contributors to this forum. I've really learned a lot from the generosity of this community. I hope to post what I learn about converting low weight folding bikes, particularly for those who lack space and require something lighter than commercial folding ebikes offer. (There are 4 flights of stairs to my tiny apartment and I have the physique of a university administrator, not a bodybuilder, lol...).
Last edited by Aaronrob222 on Nov 28 2021 7:15am, edited 1 time in total.

99t4   10 kW

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Re: Dahon Folder Grin Kit Conversion

Post by 99t4 » Nov 27 2021 11:37pm

Can't go wrong with the largest battery. :thumb: 11 lbs. for 954Wh is not bad. The main thing is that you will be able to avoid the extremes of full charges and deep discharges, which should help battery longevity immensely.

Do you have to store it all in your 4th floor apt.? No elevator? Better add up all the weight and see if you are up to the hauling it all up and down the stairs every day. Actually I can't see where you could improve it in the weight dept. Baserunner small and light, small hubmotor, etc.

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Re: Dahon Folder Grin Kit Conversion

Post by john61ct » Nov 28 2021 2:18am

Link to your battery source?

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Aaronrob222   10 µW

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Re: Dahon Folder Grin Kit Conversion

Post by Aaronrob222 » Nov 28 2021 7:13am

john61ct wrote:
Nov 28 2021 2:18am
Link to your battery source?
Updated in the OP. https://ebikes.ca/shop/electric-bicycle ... ttery.html
B3626LiM-DT
Actual Weight (kg) 5.18
Dimensions (L x W x H, mm) 370x89x137
Frame Mount
Nominal Voltage 36 Volt (10s)
Full Charge Voltage 42.0
Capacity (Amp-Hours) 26.5
Cell Type Panasonic NCR18650GA 10S x 8P
Internal Resistance (Ohms) 0.06
99t4 wrote:
Nov 27 2021 11:37pm
Do you have to store it all in your 4th floor apt.? No elevator? Better add up all the weight and see if you are up to the hauling it all up and down the stairs every day. Actually I can't see where you could improve it in the weight dept. Baserunner small and light, small hubmotor, etc.
No elevator, narrow stairwell, 3 locked doors between my 155lb self (again, not a bodybuilder) and my home at the end of the commute. It looks like (and is) a hassle, but I've tested how it will work according to the anticipated weight below by bungy-cording my wife's dumb bells to my current bike and... walking down and up the stairs.
bike weight.png
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By putting a small folded towel on my shoulder (I always used to carry one anyway!) and hoisting the bike up and placing the saddle nose over my shoulder, it's actually quite evenly distributed over my body. The trip down is relatively easy. The trip up... I can tolerate discomfort in short bursts!

I'm not sure how casually one can remove these types of batteries (Hailong etc) from their cradles. I do anticipate removing the battery to charge and if it's simple enough, I'll toss it in a back pack before my assent.

And I already own this bike, but there ARE folding bikes that are cheaper, equal weight, and accomodate both a conventional 100mm front hub and 135mm rear hub. An ideal candidate would be a DownTube Nova https://www.downtube.com/downtube-nova- ... ding-bike/ This bike in particular has the benefit of having a steel fork that's disc compatible to boot.

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Re: Dahon Folder Grin Kit Conversion

Post by 99t4 » Nov 28 2021 3:25pm

Aaronrob222 wrote:
Nov 28 2021 7:13am
I'm not sure how casually one can remove these types of batteries (Hailong etc) from their cradles. I do anticipate removing the battery to charge and if it's simple enough, I'll toss it in a back pack before my assent.
Easily slides forward after unlocking. Bit more force required initially to disengage the connection.

That could help, having more of the weight strapped close to your body instead of cantilevered out on the end of the frame swinging from your shoulder. Might make the descent more sure-footed as well. :wink:

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Re: Dahon Folder Grin Kit Conversion

Post by john61ct » Nov 28 2021 3:44pm


A towel is just about the most massively useful thing an interstellar hitchhiker can carry. Partly because it has great practical value. You can wrap it around you for warmth as you bound across the cold moons of Jaglan Beta; you can lie on it on the brilliant marble-sanded beaches of Santraginus V, inhaling the heady sea vapours; you can sleep under it beneath the stars which shine so redly on the desert world of Kakrafoon; use it to sail a miniraft down the slow heavy River Moth; wet it for use in hand-to-hand combat; wrap it around your head to ward off noxious fumes or avoid the gaze of the Ravenous Bugblatter Beast of Traal (a mind-bogglingly stupid animal, it assumes that if you can't see it, it can't see you — daft as a brush, but very very ravenous); you can wave your towel in emergencies as a distress signal, and of course you can dry yourself off with it if it still seems to be clean enough.


More importantly, a towel has immense psychological value. For some reason, if a strag discovers that a hitchhiker has his towel with him, he will automatically assume that he is also in possession of a toothbrush, washcloth, soap, tin of biscuits, flask, compass, map, ball of string, gnat spray, wet-weather gear, space suit etc., etc. Furthermore, the strag will then happily lend the hitchhiker any of these or a dozen other items that the hitchhiker might accidentally have "lost." What the strag will think is that any man who can hitch the length and breadth of the Galaxy, rough it, slum it, struggle against terrible odds, win through and still knows where his towel is, is clearly a man to be reckoned with.
Hence a phrase which has passed into hitch hiking slang, as in "Hey, you sass that hoopy Ford Prefect? There's a frood who really knows where his towel is."

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Aaronrob222   10 µW

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Re: Dahon Folder Grin Kit Conversion

Post by Aaronrob222 » Dec 21 2021 11:40am

UPDATE!

So, my project was stalled after USPS "delivered" all of my kit minus the battery to the wrong address. Grin was on the cusp of replacing my order when I got a knock on my door from the super across the street--my package had been sitting in his stairwell for 3 weeks... opened, rifled through, but otherwise totally intact.

Almost immediately I installed the kit without much trouble and my first short ride was exhilarating. Best of all, despite not moving forward with any of my weight-saving plans, the five flights back to my apartment were... not so bad! I ended up installing the battery on the frame itself and I believe it offers much better leverage with the saddle nose on my shoulder than jimmying the battery to a rear rack. I'm much more of a short-burst type of exercise guy, so this suites me very well.

One stumbling block, however: in my later haste to fit the torque arms, anti-"lawyer lip" washers, and axle nuts onto the axle, I overtorqued the nuts (this manifested in the bolt getting tighter, tighter, tighter, and then... looser). Lots of examination revealed that it is only the nuts themselves that are stripped--perhaps Grin smartly chose a nut somewhat softer than the axle.

Seeking to replace the 10mm M12x1.25 nuts, I found some 8mm "locking" version with an integrated nylon washer. The result now is that both nut and torque arms fit perfectly flush (I ended up filing down the lawyer lips and tossing the washers). My question: does the use of a shorter axle nut defy ebike? The old nut had 5 threads whereas the new one has 3.
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Other than that, aside from installing the front tire on backwards and likely going overboard on zip-tie cable management, I'm extremely psyched. Looking forward to doing a deeper dive with the Cycle Analyst.

Below is the somewhat finished product + custom towel rack :wink:
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Re: Dahon Folder Grin Kit Conversion

Post by SlowCo » Dec 21 2021 3:45pm

I would try to find full threaded nuts so the clamping force is divided over more threads.
And the axle seems to not be completely centered in the drop outs of the front fork?



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Re: Dahon Folder Grin Kit Conversion

Post by 99t4 » Dec 21 2021 5:23pm

Nylox nut is a wonderful invention, but is really not appropriate for an axle nut. Better to find a replacement similar to what was supplied (more threads). Did Grin not supply a split lockwasher? That should go directly under the axle nut for best nut retention potential.

Can you post a photo clearly showing the axle setting in the dropout? i.e., head-on photo of the end of the axle setting in the dropout, without the nut, washer, or TA? Then we could see if the axle is fully seated.

The axle almost certainly has 10mm flats (industry standard) but could be 14mm diameter which is good for axle strength but may require round-filing the dropout for greater depth, so the axle is more fully captured in the dropout.

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Aaronrob222   10 µW

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Re: Dahon Folder Grin Kit Conversion

Post by Aaronrob222 » Dec 23 2021 3:27pm

Many thanks for the replies, 99t4 and SlowCo. I ended up ordering another pair of nuts directly from Grin (I needed to get a communication cable to the controller and CA anyway).
SlowCo wrote:
Dec 21 2021 3:45pm
I would try to find full threaded nuts so the clamping force is divided over more threads.
And the axle seems to not be completely centered in the drop outs of the front fork?
I saw this as I was uploading the photo. I tightened up without putting my weight on the forks for a photograph but it typically sits essentially flush. See below for how the axle sits in the dropouts.
99t4 wrote:
Dec 21 2021 5:23pm
Nylox nut is a wonderful invention, but is really not appropriate for an axle nut. Better to find a replacement similar to what was supplied (more threads). Did Grin not supply a split lockwasher? That should go directly under the axle nut for best nut retention potential.
No split washer was supplied but there is an axle washer. Grin's technical help suggested that their axle washer and nut alone should suffice but checking the torque of the nuts often would be required. There are major pot holes on my commute, though. I'd really like to use two torque arms.

Left and right dead-on:
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Visually, there is a less than 1mm gap on the left side at certain angles. Is that worth filing?

The axle nut, torque washer, and torque arm - 18mm
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Length of exposed axle is 15mm, 3mm shorter
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What is the rationale for avoiding shorter nuts if the axle space cannot fully accomodate longer ones? I figure I gain 1-2 threads per side by using the full sized bolts--perhaps that's more significant than I realize.

Regarding Nylox, do these types of nuts present a specific disadvantage for this use case (like nuts with nylon inserts are typically weaker / designed for lower torque connections?) Or, is it just that they don't provide any real "locking" benefits in the context of ebike axles? I don't have any illusions that they're providing a ton of locking power but I do appreciate that they stabilize the nut when I'm tightening it--it's just nice having the nut not move at all once I start to tighten things up. And I was pleased that the nut was basically flush when everything was torqued to spec--having the nut extend past the axle was anxiety inducing, which is maybe not so warranted.

Lastly, while reading around on this topic, it seems like motor manufacturers are often stingy with axle length. Does it really save that much money to use shorter axles given the importance of torque arms? Maybe the comparatively tiny DIY community using beefy torque arms doesn't warrant lengthening OEM axles?

Anyway, my gratitude to those providing advice and direction here. I look forward to writing more about my experience in case it's helpful to others looking into Dahon and these Grin kits in particular.

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Re: Dahon Folder Grin Kit Conversion

Post by SlowCo » Dec 23 2021 3:53pm

Aaronrob222 wrote:
Dec 23 2021 3:27pm
See below for how the axle sits in the dropouts.

You can see that the center of the axle is below the center of the dropout.
Although the axle flats are equal, the diameter of the hub motor axle is larger than the diameter of the normal wheel hub axle. Therefor the hub motor axle can not be seated high enough in the dropouts. If you have a round file you can gently file the top of the dropout to get the radius matching and a little higher. Just 2mm would do the job.


10 to 14 mm axle diameter.jpg
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Re: Dahon Folder Grin Kit Conversion

Post by 99t4 » Dec 23 2021 11:23pm

Aaronrob222 wrote:
Dec 23 2021 3:27pm
No split washer was supplied but there is an axle washer. Grin's technical help suggested that their axle washer and nut alone should suffice but checking the torque of the nuts often would be required.
Grin is generally reliable and trustworthy. I would follow their recommendation on this. You could request their axle nut torque spec (guessing 40-50 ft-lbs?) and borrow a torque wrench to check this, to see if you are wildly under- or over-tightening the axle nuts. Helpful if you lack mechanics experience ("feel") in this area. (Torque to spec with the tq. wrench, then, using your regular wrench, try to tighten it a hair more. Several times. Remember what this felt like so next time you can approximate the same force without needing the tq. wrench.)

Judging from your previous photo of the deformed original axle nut, you over-tightened it by a good amount. :wink:
Aaronrob222 wrote:
Dec 23 2021 3:27pm
Visually, there is a less than 1mm gap on the left side at certain angles. Is that worth filing?
Looks like the fork dropouts are adequately capturing the entire axle diameter with room to spare. Not worth filing, esp. if you don't have experience in this, as another recent poster got himself into trouble from filing his dropout to aggressively and created stress risers that had to be welded over.
Aaronrob222 wrote:
Dec 23 2021 3:27pm
What is the rationale for avoiding shorter nuts if the axle space cannot fully accomodate longer ones? I figure I gain 1-2 threads per side by using the full sized bolts--perhaps that's more significant than I realize.
Want to accomodate max. number of threads with common axle nut size. Using thin nuts risks damaging the threads before reaching the desired torque. (There's not enough "meat" there.) Think wheel lugnuts on a car. Don't you think the auto manufactures would use thinner (cheaper) nuts there if they could get away with it? No, they're thicker than usual for that size. Even so, they still get damaged by Walmart tire jockeys over-enthusiastic use of their zip guns.

Also must take into account there's "missing" axle threads (~40%?) because of the flats machined into it.
Aaronrob222 wrote:
Dec 23 2021 3:27pm
Regarding Nylox, do these types of nuts present a specific disadvantage for this use case (like nuts with nylon inserts are typically weaker / designed for lower torque connections?) Or, is it just that they don't provide any real "locking" benefits in the context of ebike axles?
Disadvantage in this case, yes. Limited real estate on the axle threads there to generate sufficient clamping force. The thickness of the plastic insert is taking up valuable space that in this case would be better off as steel, which would better able to support the high torque for the higher clamping forces required of an axle nut. Nylox better used in lower torque applications.
Aaronrob222 wrote:
Dec 23 2021 3:27pm
Lastly, while reading around on this topic, it seems like motor manufacturers are often stingy with axle length. Does it really save that much money to use shorter axles given the importance of torque arms? Maybe the comparatively tiny DIY community using beefy torque arms doesn't warrant lengthening OEM axles?
IM(and others)HO, the motor mfgrs are continually dropping the ball by skimping on axle length, wire thickness, and (most importantly) not offering a built-in TA solution beyond the standard not-so-effective axle flat solution.
[/quote]

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Chalo   100 GW

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Re: Dahon Folder Grin Kit Conversion

Post by Chalo » Dec 24 2021 1:46am

Three full, good condition threads engaged between like materials will hold all the tension that a fastener's torque spec provides. But you don't have full threads to work with. The axle has interrupted threads, so to get full strength you need more of them engaged. The more the better, really

Nylock nuts are not a problem per se; but the plastic grommet takes up room that could otherwise have steel threads in it. The interrupted axle thread will brutalize the locking portion and quickly render it ineffective anyway.

The axle nuts that came with my Crystalyte motor a million years ago were very soft, with loose fitting threads and faces that weren't quite perpendicular. I stripped them despite trying to be very careful. I replaced them with automotive wheel lug nuts which worked fine. I now buy flanged nuts on eBay to replace damaged, crusty, or weirdly shaped security nuts on hub motors. M12x1.25 and M14x1.50 are the most common sizes in my limited observation.
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: Dahon Folder Grin Kit Conversion

Post by docw009 » Jan 25 2022 9:02am

In hindsight, a rear motor combined with a 5speed or 6 speed freewheel might have solved your 130 mm concerns. I converted a Schwinn Loop for my wife. It has an integrated luggage rack, which makes the rear dropouts very stiff. There was no way I wanted to put any force on them. Even though it measured 135 mm, I couldn't get my Q100H with a 7 speed to fit.

Fortunately the Aikema100 and Q!00H motors have a removeable two piece bushing . I used my trusty sawzall to "machine" it down by 5mm. Then I found a 6 speed Shimano in my junkbox and it dropped in. It's a 250W motor, but I still installed torque arms on both sides.
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Re: Dahon Folder Grin Kit Conversion

Post by docw009 » Jan 25 2022 9:47am

I am glad the community got you away from those Nyloc nuts. They sell flanged M12-1.25 nuts on amazon, ebay, and at Lowes though. I think it is frustrating when the motor doesn't have enough axle to cover the threads.If it just manages to cover the last thread, I think that will suffice.

As far as torque, I always did my hubmotors by what felt right, having worked on cars for years. Last year, I found my torque wrench, clicker type. I've not found a spec in writing for the 10x12 axles yet. I've decided that 30nm or 22-24 ft-lbs is about right, In any case, that's higher than what I was doing by hand when I started retorquing my bikes.

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