Dahon 26" Folding bike - Is it safe to install a hub motor?

[User6969]

I want to convert my 20 year old 26" Dahon Matrix folding bike into an ebike because i can take folding bikes the train for free.
I ordered a 140€ 1000W hub motor kit from aliexpress. The 135mm rear hub spacing seems to fit. I plan to put the battery and controller in a double bike bag on the bike porter. And maybe buy bigger disk brakes and thicker tires if needed.
I read here that i definitley buy need torque arms. But what torque arms i should get? Are the cheapest ones from ebay enough and is it possible to mount them on this frame? The frame is made of Aluminium 7005.

 

[neptronix]

Don't buy cheap torque arms unless you're okay with trashing the frame. Especially if you are using regen.
A millimeter of slop is too much.

ebikes.ca's torque arms are the only ones i recommend.
If you stick to stock power, then you can get away with one of these:
V7 Regen Torque Arm 14mm

 

[User6969]

Don't buy cheap torque arms unless you're okay with trashing the frame. Especially if you are using regen.
A millimeter of slop is too much.

ebikes.ca's torque arms are the only ones i recommend.
If you stick to stock power, then you can get away with one of these:
V7 Regen Torque Arm 14mm

I dont really care too much about the frame, but i ofc dont want to risk falling off and geting injured.
i can do without regen breaking but it would be nice to be able to use 2000W too with a VESC controller. Should i get the V6 maybe?

And is there a cheaper option? The bike was only 200€ years ago, ebike kit 140€ and i even got a 500Wh used battery for only 40€, it feels wrong to pay so much + 37$ shipping for a bit of metal now

 

[neptronix]

There are cheaper options, but they don't work as well ( almost always have ~1mm of slop ) and sometimes require some fabrication to make work.
The advantage of these is that they completely eliminate any slop in the axle connection interface.
A single one might work up to 1500w. I can't guarantee 2000w.

Could be cheaper to get them from grintech.eu:
Torque Arms - Ebike Parts - Shop

I like VESCs a lot. Big fan of the spintend brand because you get a good quality VESC at a middle price that way

 

[amberwolf]

it feels wrong to pay so much + 37$ shipping for a bit of metal now

A well-engineered and manufactured bit of metal, compared to the cheap ones that simply don't do the required job.

The problem with choosing based solely on cost is that you aren't picking based on suitability for purpose. Some cheaper things still do the complete job required. Most don't.


Also, in the case of products from ebikes.ca the money doesn't just pay for the metal, it pays for the research and testing that produced it, and funds further such research and testing to produce useful and usable parts that are suitable for their purposes.

Many of the cheap TAs are clones of early versions of ebikes.ca designs, but less-well-manufactured and often of poorly-chosen materials inappropriate to the purpose.

 

[E-HP]

Dahon 26” Folding bike - Is it safe to install a hub motor

Nope, not with cheap crappy torque arms. Keep it as is, or save your money until you can convert the bike properly.

And is there a cheaper option? The bike was only 200€ years ago, ebike kit 140€ and i even got a 500Wh used battery for only 40€, it feels wrong to pay so much + 37$ shipping for a bit of metal now

Are you ok with the wheel coming off at 25mph?

 

[gromike]

If you were to get your hands on a Grin V7 torque arm you wouldn't question the cost.
But do your conversion however you want. If it doesn't work, please post pictures .

 

[offGridDownUnder]

I ordered a 140€ 1000W hub motor kit from aliexpress

You didn't bother to provide a link to or a photo of the motor, but people are suggesting the v7 Grin Torque arm - so I'll assume the motor you have bought uses an axle with flats on it to prevent the axle rotating. This will then be a 12mm or 14mm axle with flats cut so that the distance is 10mm across the flat - which roughly corresponds to the standard width of a fork or rear dropout.

Very few actual frames come with precise 10mm openings, and that the frame is 7005 means it is easily damaged. That alloy is strong, but not extremely hard or resistant to point loads.

The problem is that if there is any play in the match between the axle and the dropout, you will (not might) machine the frame slot leading to failure. With a 1000w motor, this is guaranteed. If there isn't any play, you're going to have a hard time getting the wheel in and out of the frame to change the tires, and you'll wear the distance wider just by doing this.

The Dahon is a nice frame - what you paid for it does not change this. People are telling you to use the v7 clamping torque arm to save you money - the price of buying another Dahon-level quality frame. There is no quick-fix, and no work-around.

These people are trying to help you. Pry your thinking away from the idea of spending less on what is needed and instead focus on saving the investment you already have. If you go cheap, you will pay later on this.

When the motor-dropout contact does fail, your motor will wind itself up and rip the cables out - so you'll lose both frame and motor. You may be able to use a 250w motor with axle flats in a steel or very strong alumin(i)um dropout with just C-washers and no torque arm - a 1000w motor will damage your dropout in time without a torque arm.

 

[E-HP]

But do your conversion however you want. If it doesn't work, please post pictures .

I don’t think we need more pics, since a lot of people try cheaping out on torque arms. If you’ve seen one, you’ve seen em all.

I’m guessing since Germany has public/subsidized healthcare, it may be worth taking a chance, since theirs no out of pocket for the ER stay.

 

[offGridDownUnder]

... and a detail. If you do choose the Grin v7, then when you are clamping the inner part to the motor shaft, take the time to only turn each of the two screws 1/2 turn before switching to turn the other. Yes, it's a bit tedious, but you'll only be doing this once, and if the insert turns a little aside, it can wedge in the housing and you'll think you've reached full torque on the screws before the insert actually seats solidly on the axle.

After using one on my Shengyi SX2, I wrote into Grin support suggesting they mention this in their directions. Justin replied that he thought this would be obvious to most people - I guess he doesn't read all the posts here. He may have added this by now.

 

[E-HP]

and i even got a 500Wh used battery for only 40€, it feels wrong to pay so much

Don’t ever charge that battery indoors and don’t leave it unattended. Sounds like your willing to cheap out on the most important components when to comes to safety, but don’t forget the safety of others who you may also put at risk.

 

[rafalg]

1 or 2kW of power seems plenty, not something that you can just slap cheaply on any bike.

 

[docw009]

I guess you ordered something that looks like these kit. They offer an inexpensive way to get a fast ebike. The main tradeoff is weight. Too heavy for my tastes since I use my bikes for recreation. I suppose that if I were using it as an appliance to get to work, I wouldn't care,

The second is legality in your locale. I thought Germany would look at this as a "faster "S-Pedelecs" (up to 45 km/h) are considered mopeds, mandating a driver's license, a mandatory helmet, insurance, a license plate, and use on regular roads"

With the size of the motor, it's obvious you exceed 250W. Good luck with the legal stuff. Good luck with the torque arm too. Crank the axle nuts down with a torque wrench too. WHat are people using? 35-40 nm?

 

[User6969]

Could be cheaper to get them from grintech.eu:
Torque Arms - Ebike Parts - Shop

I like VESCs a lot. Big fan of the spintend brand because you get a good quality VESC at a middle price that way

Thanks, Grintech is only 10€ shipping for me.
Speaking of cheaping out, i can get the Makerbase VESC 75200 200A from Aliexpress for 88€. Spinted i could only get 100A for that price, i guess it would have less thermal headroom.

Don’t ever charge that battery indoors and don’t leave it unattended. Sounds like your willing to cheap out on the most important components when to comes to safety, but don’t forget the safety of others who you may also put at risk.

Yea i am already charging this battery attended only. But not because of the battery itself, its made of high quality Samsung cells but because i replaced the locked BMS with a small chinese one that fits the housing.
If i get a VESC i will later also get a bigger battery with a Daly BMS or something. But ill try to do it as cheap as possible xD

I don’t think we need more pics, since a lot of people try cheaping out on torque arms. If you’ve seen one, you’ve seen em all.

I’m guessing since Germany has public/subsidized healthcare, it may be worth taking a chance, since theirs no out of pocket for the ER stay.
View attachment 377366 View attachment 377370

View attachment 377369

Thats scary. The first pic looks like its the ebay torque arm and it could be the same hub motor i bought. I wonder what happened there, did the screw loosen because the torque arm wasnt tight enough?

I guess you ordered something that looks like these kit. They offer an inexpensive way to get a fast ebike. The main tradeoff is weight. Too heavy for my tastes since I use my bikes for recreation. I suppose that if I were using it as an appliance to get to work, I wouldn't care,

The second is legality in your locale. I thought Germany would look at this as a "faster "S-Pedelecs" (up to 45 km/h) are considered mopeds, mandating a driver's license, a mandatory helmet, insurance, a license plate, and use on regular roads"

With the size of the motor, it's obvious you exceed 250W. Good luck with the legal stuff. Good luck with the torque arm too. Crank the axle nuts down with a torque wrench too. WHat are people using? 35-40 nm?

View attachment 377387

Yes its this kind of kit. These motors all look the same to me. I hope they are the same quality internally too, i saw someone even used his with 5000W/80A.

This guy also made his own torque arm with a drill and angle grinder. I could do that too, just dont know how safe it would be in the end.

Any e-bike/pederlec here can have unlimited power legally, as long as its rated 250W continuous and has a 25 km/h limit. And the motor has to work only when pedaling. I can hardcode those limits in an open source STM32 ESC firmware. So at a legal assesment they cannot even say i could change the limits while riding. And off road i can use a different controller or flash the firmware.
I dont think the motor size is a problem legally, because there are commercial pederlecs with big motors too, they are just limited to 250W continuous by the controller.

But I agree this motor is very visible and a problem for police. At least its DD so it should be silent with a good controller.
I can still return it. Is there a smaller cheap DD hub motor i can also use at up to 2KW?

Very few actual frames come with precise 10mm openings, and that the frame is 7005 means it is easily damaged. That alloy is strong, but not extremely hard or resistant to point loads.

The problem is that if there is any play in the match between the axle and the dropout, you will (not might) machine the frame slot leading to failure. With a 1000w motor, this is guaranteed. If there isn't any play, you're going to have a hard time getting the wheel in and out of the frame to change the tires, and you'll wear the distance wider just by doing this.

The Dahon is a nice frame - what you paid for it does not change this. People are telling you to use the v7 clamping torque arm to save you money - the price of buying another Dahon-level quality frame. There is no quick-fix, and no work-around.

Im glad no one has said anything against the frame yet.

Lets say i buy 2 V7 torque arms, what speed and Watts would you trust the frame to support?
Is it any worse than a modern Cube hardtrail MTB frame for example?

 

[neptronix]

This is not a particularly strong frame but i've seen worse.

It'd probably handle 3kw just fine, the real limit is top speed. The ride might get too rickety above ~50kph because of the folding mechanism causing the frame to oscillate. Or maybe it's okay.

I think if you are in the 2kw club and also use regen, this is a reasonable point when you need to think about 2 torque arms.

 

[docw009]

I made probably a half dozen torque plates, using drill press for the 10mm hole, and a file to elongate it. I also used a sawzall and angle grinder to shape the plate. Tedious work, but nothing else on my plate during a long cold northern winter, Actually made more, but many were ruined when I misplaced the location of the mounting holes.

Probably their main contribution was to provide more clamping surface on the frame.

 

[neptronix]

I've made and bought torque plates but once i used a clamping torque arm, i would never go back.
Even if that TA is so tight that you have to hammer it on, the clamping torque arm is still tighter than that.

 

[amberwolf]

After using one on my Shengyi SX2, I wrote into Grin support suggesting they mention this in their directions. Justin replied that he thought this would be obvious to most people - I guess he doesn't read all the posts here. He may have added this by now.

Unfortunately most people assume that things are obvious to others; I learned the problems with this back in the late 80s / early 90s when Honewell CFSG went to the JIT (just in time) assembly approach, and began laying off thousands of people, and we had to write the manuals on how to do the assembly and testing, step by step, with literally every single step and every single move, so that literally anyone could sit down at the bench and do the work without any training (so they could then lay all of us off and replace us with much much cheaper workers, and not have to worry about them causing airplanes to crash from their zero experience in building and testing these things).

It is one reason I post so much detail on some occasions (and used to do so much more often), pointing out things that might seem obvious but often are not.

 

[99t4]

Even if that TA is so tight that you have to hammer it on, the clamping torque arm is still tighter than that.

Excellent point there.

OP: Judging from your posts you are a true Bargain Hunter and very proud of the Bargain Hunter prices you have paid for your components so far. Good for you! But realize that the TA has a very specific job to do-- to reinforce an extremely weak interface between a narrow round axle (that has been slightly flattened out) and a thin weak slotted dropout. Very poor engineering decision that has become an industry standard, mainly out of inertia and traditional cultural practices that apparently value incessant replication of existing techniques with emphasis on lowest price over improving towards better mechanical methods and materials.

For a good outcome, you may have to purchase a non-Bargain Hunter price TA for your project. The good news is you can transfer this quality TA to another bike when the time comes.

 

[User6969]

Just a quick update, the kit arrived and fit the frame, I only had to file the dropouts a bit.
With the stock 1000W controller and 15S battery it goes 50 km/h. I definitely need more acceleration though and better brakes.
I alreadyd ordered the Makerbase VESC 75200, and parts to make a 16s5p 21700 battery with 80A cont.

I also found a german bike shop that sells cheap CNC torque arms and ordered 2.

Zubehör - ElectricRide-Shop

electricride.de

For testing I used the cheap ebay torque arm, it was super loose originally as expected. But I flattened it with a hammer to make the opening smaller.

Sadly my 1000W motor seems to be a bit different from other ones, it has the motor cables coming through the end of the axle and not coming out in the middle.
I want to install a temp sensor so i know how much power i can push. I guess i could also upgrade the motor wires while im doing that, but idk what motor cables to buy.
Does anyone have experience / is there any thread on upgrading the cables on such a motor and how thick they should be?

 

[99t4]

I guess i could also upgrade the motor wires while im doing that, but idk what motor cables to buy.
Does anyone have experience / is there any thread on upgrading the cables on such a motor and how thick they should be?

What is your reason for upgrading the motor wires? Are they overheating? Might not be necessary to do all that extra work.

 

[amberwolf]

I want to install a temp sensor so i know how much power i can push. I guess i could also upgrade the motor wires while im doing that, but idk what motor cables to buy.
Does anyone have experience / is there any thread on upgrading the cables on such a motor and how thick they should be?

Depends on what phase currents you're going to demand thru them.

What gauge are the wires now, and what current do you need them to handle? (if your controller doesn't specify phase current, just tell us battery current, and you can typically guesstimate PC by multiplying that by 1.5x or so).


12g is pretty typical for the average medium-power hubmotor. It's unlikely you would need more than that unless you're really pulling a lot of phase amps and overheating the wires already in there.

 

[Papa]

I want to convert my 20 year old 26" Dahon Matrix folding bike into an ebike because i can take folding bikes the train for free.

Why the heavy-weight 1-2kW power plant (and 6+kg battery) on a lightweight aluminum "folder"?.... especially since it needs folding for rail transport?

Just seems far more prudent to me to slap-on a 250W lightweight hub motor on the folder, W/minimal battery for rail transport,... then save your kW muscle motor for a more suitable (used?) steel frame... and reserve it for legal off-road.

 

[User6969]

What is your reason for upgrading the motor wires? Are they overheating? Might not be necessary to do all that extra work.

To have more headroom for increasing the current. Idk yet how much i need but I think 60A would be nice. As much as i can do safely, without risking the frame falling apart, backflipping, melting the wires or melting the motor (which i guess takes longer to overheat, thats why i want to install the temp sensor). My controller and battery will be able to do up to 200A Peak 80A continuous.

Depends on what phase currents you're going to demand thru them.

What gauge are the wires now, and what current do you need them to handle? (if your controller doesn't specify phase current, just tell us battery current, and you can typically guesstimate PC by multiplying that by 1.5x or so).


12g is pretty typical for the average medium-power hubmotor. It's unlikely you would need more than that unless you're really pulling a lot of phase amps and overheating the wires already in there.

Around 14 awg i think.
I read that its ok to use a smaller wire through the axle if its connected to a bigger wire right at the end of the axle so it can transfer the heat. But how small is ok?
I also need to add 1-2 extra wires for the temp sensor. Or repurpose the hall sensor wires and use the VESC HFI.

Why the heavy-weight 1-2kW power plant (and 6+kg battery) on a lightweight aluminum "folder"?.... especially since it needs folding for rail transport?

Just seems far more prudent to me to slap-on a 250W lightweight hub motor on the folder, W/minimal battery for rail transport,... then save your kW muscle motor for a more suitable (used?) steel frame... and reserve it for legal off-road.

You are probably right but id like to avoid having one more bike to take care of.
Currently I dont really mind the weight, i already took it on the train. And im putting the battery in a bike bag/ pannier so i can take it out if needed.

I didnt buy a smaller motor because I heard they are very loud and have plastic gears that break. Now i found one guy getting good power from MXUS XF15R which is only $90.00 and much smaller. But idk if its worth. A couple kg less, less visible. But more audible.