Kids 20” e-bike conversion questions norco storm

[Mwmx54]

Hi, I am looking for advice on what motor and battery to use for a kids e-bike conversion? I have twin 8yr old asthmatic girls that love mountain biking, but can’t go more than a few minutes up any slight inclines without getting severely winded. They have 20” norco storms which have removable bb’s, but I’ve also noticed they make 20” hub drive motors. I’d really like the bike to peddle assist as opposed to thumb throttle, and a tourque sensor would be preferred over cadence? I think it’s a called? that only detects peddling, but I understand they are not as readily available. So if anyone has any recommendations on a small lightweight motor and battery that would be awesome. I have been looking at the 250w 20” hub drive rear wheels with cassettes, and the smaller Bafang 250w mid drive, (but I think it has the same footprint or close to the bigger motors) but I’m not sure I’d be able to swing it up out of the way very far. Has anyone built a small bike like this?
Thanks

 

[amberwolf]

What specific riding conditions do you have that must be overcome? Slope and length of hills, weight of bike+rider, winds, road surface type, etc., speed required up the hills, are needed to figure out the power (watts) necessary to do the job.

Once the power is known, then a system with enough power to do the job can be found, that will run at the right speed to not overheat while doing it.

Then the amount of range (time or distance) that the assist is required can be used to find out how many Watt-hours of battery are required to do this job.

One of the best ways to do this is via the simulators at ebikes.ca, but there is a learning curve to using it; we can help with that but only if you provide sufficient info.

My guess is a 250w hubmotor that's wound for a low enough speed would probably work fine, paired with a low-power controller to match, but if you have steep enough hills or headwinds on them, it might not be enough to keep from straining the riders.



For control systems, the Cycle Analyst v3 can use a cadence or torque sensor to generate a throttle signal to run any "dumb" throttle-only controller.

I use this to control the speed of my SB Cruiser heavy-cargo trike via pedal cadence--the faster I pedal, the faster it goes. (I could have the cadence control torque or power, but for my setup speed works fine).


Pretty much all presently-available controllers with "cadence" sensors don't actually use them for cadence control, and dont' even bother coutning how fast you're pedalling--they simply detect that you are or aren't pedalling, and turn the system on full or off, at whatever assist level is chosen.

So the CA is the only option I know of besides DIY to make a cadence-controlled system. (there are projects here on ES to use a small MCU to read a cadence sensor and create a throttle signal based on that, but they're not nearly as versatile as the CA is, and you'd have to build them and program them).

There are some controllers out there that are designed to work with certain Erider torque sensors directly, and there are several options if you're willing to futz with programming and setting up a controller with open-source firmware and whatnot (KT and Lishui, etc).

 

[docw009]

If you want torque sensing, then it's the TongSheng TSZ2B which cost me $260 shipped from PSWpower last year, They can run on 36V or 48V. Maybe 36V would be OK,. The weight is around 8 lbs, I believe.

The problem is your kids might not be able to pound the pedals hard enough to activate the TSDZ2B torque sensor. My wife cannot. I'm not so strong either. A few smart hobbyists wrote their own firmware to address that issue. It's free, but really gave my head a whirl to install and implement. The result though is I've been able to set my wife's bike up so she can ride it. Ditto for my bike.

What the firmware does is ease up on the pressure needed to run the motor. It even allows cadence operation. It does make for a buit of tuning, which might be tricky with kids, sinec you can;t ride it and get the same results. What I thought would work for my wife didn't. Took a few days of test rides.

One problem is that on a 20" frame, your mid drive motor hangs pretty low. Might hit a rock or root. The TSDZ2B kits come with throttle, but they can be left off

I doubt I could do a 20" hubmotor/wheel and electronics for $260 these days, and I have done four of them in the past. I suggest a rear hub motor if you do it. Front motors can break forks if poorly installed. In my case, I bought bare motors and put them into 20" rims, four times.. That's about $200. ELectronics is about $80-100. In general, I believe you'll find a hubmotor more responsive/stronger than a TSDZ2 mid drive, but they can be kept pretty mild mannered, if you buythe right controllers.

Neither kit will need much battery to power a 8 year old on a bike. Go for small batteries and keep the weight down. Not much room on a 20" frame for a battery anyway. Probably go with a rear rack and a small battery in a bag.

A small kit with a 10-12A controller will likely run on an appropriately sized 40V-52V tool battery, If you can get them for a good price, I think they're better and safer than your tyoical small ebike battery.





.

 

[Mwmx54]

I do quite a bit of 3d printing, which for me means quite a bit of coding custom firmware to modify the printer, and I really hate it, as I’m not any good at it, but I can if I have to, nothing hurts my brain more than tinkering with firmware, so I think the ca v3 could be a good option, I will probably try just using a cadence sensor and seeing how it goes first. As for rider and terrain, they’re under 50 lbs and the bikes are very light also, We live on a mountain in Utah, so a lot of hills, but many trails are well used and not terrible to ride even on an analog bike(unless you have asthma). Basically you can ride pretty easy hills, or extreme rocky steep hills(they’ll be on the easier). They really just need a little extra power, not so much speed, maybe 10-15mph max, and about 1-2 hours of riding, of which half would be going down hill.

 

[Mwmx54]

The tongsheng would be perfect, I can make minor firmware changes, if I have to, but because of the way it mounts I think it would hang too low. Do you have any pics of yours mounted? Did you mount it hanging straight down, it looks like it has to, in order to use the clamping bracket right? And which display did you use?

 

[amberwolf]

Without actual slopes/etc I couldn't tell you what power is needed, so I could only still give you the same guess for a hubmotor system.

(middrives can be lower power because they use the gearing of the pedal drivetrain to convert speed of the motor into torque, just like for the pedals, so if the rider is shifting correclty and the system is geared correctly for the usage, they can be more efficient. If hte rider isn't shifting or the gearing is wrong, they can actually run worse than a hubmotor that *is* setup correctly.)

The speed you want to go up the hills is important, along with the loading, becuase the motor has to be able to reach that speed (or else it won't assist at that speed) *but* the system shouldn't be loaded down heavily when run at a much lower speed than it's max, or it may overheat after enough time doing that.

So, when picking a hubmotor for this, pick one that has it's max speed in the wheel size you want to use that is close or the same as the max speed you want to go up the hills. It doesn't matter if it can reach the speed you ride on the flats, because you don't need help there, just on the hills, right?

If using a geared hubmotor, almsot all of them have a freewheel in them that disengages the motor when riding faster than the motor runs, so it doesn't drag against the pedalling in those cases (while a DD hubmotor would drag some).


If picking a middrive motor, make sure the system is geared for the pedalling to be "easy" in the gears used for the heaviest loads, because it makes it better for the rider *and* the motor.

 

[E-HP]

Hi, I am looking for advice on what motor and battery to use for a kids e-bike conversion? I have twin 8yr old asthmatic girls that love mountain biking, but can’t go more than a few minutes up any slight inclines without getting severely winded. They have 20” norco storms which have removable bb’s, but I’ve also noticed they make 20” hub drive motors. I’d really like the bike to peddle assist as opposed to thumb throttle, and a tourque sensor would be preferred over cadence? I think it’s a called? that only detects peddling, but I understand they are not as readily available. So if anyone has any recommendations on a small lightweight motor and battery that would be awesome. I have been looking at the 250w 20” hub drive rear wheels with cassettes, and the smaller Bafang 250w mid drive, (but I think it has the same footprint or close to the bigger motors) but I’m not sure I’d be able to swing it up out of the way very far. Has anyone built a small bike like this?
Thanks`

Which model do they have? Single speed, 6 speed? If you want a hub motor, you should verify that the dropout width is ~135mm. If they are the single speed version, it may be difficult to find a hub that will fit (assuming the width is narrower on the single speed). A front hub would work in most cases if the rear isn't wide enough.

The TSDZ2 is a good option as long as your girls are good about remembering to downshift before they come to a stop. If you go that route, then make sure you have chainstay clearance for the front chainring, since some of the models have a smaller 30T chainring, and it's hard to tell what the maximum size the frame can accommodate. I think the smallest chainring for the TSDZ2 is 34T.

 

[Mwmx54]

very interesting, it sounds like quite a bit goes into picking a motor, I didn’t expect that, but I will do more research, they have geared versions of the norco storm, but they keep them in 1st gear almost always as they have a hard time moving the shifter, next year they will probably be strong enough though, I swapped on of them for thumb shifter but they can still barely push that, and even with gloves twisting the grip shift takes more effort than they can muster while pedaling. I’m leaning towards hub drive now, mainly for the clearance under the bike unless there is a mid drive that could swing up enough, but even then 42t is the smallest front sprocket I can for them, and stock they came with 30t, so that alone would lose some clearance. The dropouts are 135mm. This is the bikes they have 2021 Norco Storm 2.3 - Specs, Reviews, Images - Mountain Bike Database however they were only $200 when I snagged them.

 

[nicobie]

I think a geared hubmoter controlled by a cycle analyst would work best for you. Go to grin's website and read up on what Justin has to say. It will answer most if not all your questions. I believe he sell kits with everything needed to convert to an ebike. It's not the cheapest way to get an ebike, but it is by far the best.

 

[E-HP]

...they have geared versions of the norco storm,...
...The dropouts are 135mm...

Battery placement could be a challenge. What's the minimum distance between the front tire and the frame downtube?

 

[offGridDownUnder]

but can’t go more than a few minutes up any slight inclines without getting severely winded.

A calibration question, please.

Is there also a limit for them when pedaling on flats? If yes, then that speaks against 'only' pedal-assist as they may not be able to maintain the pedalling when they are in the outback and want to come home.

 

[amberwolf]

but even then 42t is the smallest front sprocket I can for them, and stock they came with 30t, so that alone would lose some clearance. T

Sounds like you probably need to change the front sprocket back to the original, since a smaller one would make it easier for them to pedal up a hill without having to change gears in the back; the top speed will be proportionally slower but it will help them out.

If you haven't actually changed the sprocket out, you might look into doing it to an even smaller "granny ring" sized one, or changing the rear cluster for one with a much larger low gear.

 

[Mwmx54]

Thanks for more info everyone, I’ve spent weeks researching, but having real advice is much better.
What is “grins” website? I’m unfamiliar with that name.
Also, about the sprocket size, I was saying the bikes came with, and currently have 30t sprockets, the motor I was referencing is only available with 42t as the smallest I could find.

 

[amberwolf]

Home page

Grin Technologies

ebikes.ca

 

[marty]

8yr old

8yr old + bicycle = dangerous
8yr old + bicycle + motor = more dangerous

I know this because I used to be 8 years old.

can’t go more than a few minutes up any slight inclines without getting severely winded.

Severely winded is what happens when you exercise. Exercise is good. Keep doing it. Drink water.

they keep them in 1st gear almost always as they have a hard time moving the shifter, next year they will probably be strong enough though, I swapped on of them for thumb shifter but they can still barely push that, and even with gloves twisting the grip shift takes more effort than they can muster while pedaling.

If their hands can not operate shifters? Most likely hands are not strong enough to operate brake levers. Nothing good happens when a bicycle don't stop. Small slow single speed bicycle with foot brake is better for small children.

When I was 8, one of my friends had one leg. I asked why his leg was cut off below the knee? Bicycle accident. Fast moving bicycle. Slow moving truck. Truck ran over his leg. He had a fake leg made from wood, metal, and leather. I am older then plastic.

they keep them in 1st gear almost always as they have a hard time moving the shifter

Hill are why bicycles have gears. Small gear in front, big gear in back is the way to get up a steep hill. Walking bike up a hill is the way to go if you are not racing.

Good way to teach children about how the gears work might be a bike repair stand. Bike repair stand is the most wonderful tool for bicycle maintenance. Lubricate and adjust everything that moves. I like motor oil on the chain. Check tire air pressure.

Give children tools and lubricants so they can maintain their own bicycles.

Basically you can ride pretty easy hills, or extreme rocky steep hills(they’ll be on the easier). They really just need a little extra power, not so much speed, maybe 10-15mph max,

If you [Dad / Mom] are riding with the children? You just need to go a little slower. Or forget the bicycles and walk.

 

[E-HP]

Thanks for more info everyone, I’ve spent weeks researching, but having real advice is much better.
What is “grins” website? I’m unfamiliar with that name.
Also, about the sprocket size, I was saying the bikes came with, and currently have 30t sprockets, the motor I was referencing is only available with 42t as the smallest I could find.

Another route you could go in is to keep it very simple. My twins were premees, so had all of the associated ailments including asthma, which they eventually grew out of around middle school. A simple route would be to provide some assistance without creating a crutch. They may have difficulty breathing, but that doesn't mean their legs can't function like any other 8 year old.

The simple route would be to go with a low power setup, like the 250W motor you were thinking about, but only using a push button instead of a throttle or pedal assist, that they just push when they need help. 250W even at full throttle is pretty gentle, and you could add a potentiometer to adjust the assistance provided when pressing the button, but I don't think it will be necessary. The torque sensing bottom bracket and any other bells and whistles may be what you want, but not necessarily what a kid needs. They'll probably have more fun having a "turbo" button, rather than caring about how seamlessly assistance is provided using a torque sensing PAS, with very little power under it's control.

 

[E-HP]

If you [Dad / Mom] are riding with the children? You just need to go a little slower. Or forget the bicycles and walk.

It's new world. A lot fewer young kids out riding on their own, and most are with their parents. I've recently started seeing a lot more kids on ebikes, riding with their parents. They are surprisingly responsible, more than the ones on pedal bikes, staying on the right side of the path, in their lane, and stopping to wait for their parents at intersections. The parents seem to be responsible as well, teaching their kids good habits. The pedal bike kids tend to be all over the trail, and a lot of the time I just come to a complete stop to wait for them to pass by.

 

[aredridel]

Severely winded is what happens when you exercise. Exercise is good. Keep doing it. Drink water.

Please don't say this about asthma. That's exactly wrong. Winded as in "need more air because your circulatory system is still improving" is one thing, Winded as in "need more air because your lungs are closing up and you literally can't move air" is entirely different.

 

[Mwmx54]

8yr old + bicycle = dangerous
8yr old + bicycle + motor = more dangerous

I know this because I used to be 8 years old.


Severely winded is what happens when you exercise. Exercise is good. Keep doing it. Drink water.


If their hands can not operate shifters? Most likely hands are not strong enough to operate brake levers. Nothing good happens when a bicycle don't stop. Small slow single speed bicycle with foot brake is better for small children.

When I was 8, one of my friends had one leg. I asked why his leg was cut off below the knee? Bicycle accident. Fast moving bicycle. Slow moving truck. Truck ran over his leg. He had a fake leg made from wood, metal, and leather. I am older then plastic.


Hill are why bicycles have gears. Small gear in front, big gear in back is the way to get up a steep hill. Walking bike up a hill is the way to go if you are not racing.

Good way to teach children about how the gears work might be a bike repair stand. Bike repair stand is the most wonderful tool for bicycle maintenance. Lubricate and adjust everything that moves. I like motor oil on the chain. Check tire air pressure.

Give children tools and lubricants so they can maintain their own bicycles.


If you [Dad / Mom] are riding with the children? You just need to go a little slower. Or forget the bicycles and walk.

Please don’t have kids. Mine can handle their own just fine, they’ve been riding dirtbikes since they were 2.5 years old as well as peddle bikes, but unfortunately there is no land near our home that is open to dirtbikes anymore, and it’s not always easy to load everything up where it is legal. I’d rather my kids be outside enjoying the outdoors than glued to a screen like most others, and if that means they occasionally get hurt, then that’s how it goes, and hopefully they learn something from it. And not to be rude, but your comment wasn’t needed or asked for, I don’t need any advice from someone like you about how to raise my kids. And the world doesn’t need more coddled children addicted to screens and too afraid to go outside.