motor to make "digital drive" feasible?

[kylerlaird]

I made a tiny bike for my daughter who refuses to learn to ride. (Don't get me started.) She has amazingly strong legs, as demonstrated on her fat-tire trike, but I pulled the pedals off of this bike. My goal was to make an electric version of her Strider, which is way too small now. I want to keep it simple for her.

This bike is run by a 60V Dewalt battery and Flipsky 75100. The thumb throttle is a speed control. It only goes up to a brisk walk. I ride it up and down the hill here at the house. It maintains the speed remarkably well with me on it. I've even taken it for a ride through the woods. It can barely make it up one of the hills.

This is a fairly large motor on a small wheel. I'm pumping way too much current through it. Torque is marginal.

I have been working toward "digital drive" for other bikes so this has been an interesting experiment for me. It's hard for me to imagine these direct drive motors ever being sufficient for solely powering a bike. Gearing is the obvious answer. Geared motors tend to be low-powered, though.

My dream motor:

1. loads of torque - sufficient to pull an adult up a steep hill with 27" wheels, >100Nm?
2. medium speed - top out at 15-20 MPH
3. clutchless
4. 10mm round axle/side cable exit/decent torque arm system

Does such a motor exist? I recently bought a Citycoco-style hub motor for a mini-bike. It's rated 2000W/60V. I haven't seen much torque from it yet, but I just started working on it. It's huge/heavy. Is that where "digital drive" is headed?

 

[amberwolf]

What exactly do you mean by "digital drive"? (it's usually used to refer to on/off only control, without any form of modulation)

What is your specific definition of "steep hill" (actual slope, and actual speed and weight, make a huge difference in power / torque requirements, and in what any specific system can do).



Regarding hubmotors, they're used in plenty of "high-torque" applications, but it requires the proper motor with sufficient battery and controller capability to supply the current necessary to the motor to overcome the load on it.

For example, myMy SB Cruiser heavy-cargo trike used two mismatched hubmotors and controllers to climb (at 20mph) whatever the slope is on Cave Creek Road and on 7th street from Dunlap on up to the top of the hill where The Pointe is, here in Phoenix.

North Mountain Village · Phoenix, AZ

Phoenix, AZ

www.google.com

I'd guess at the time I did that that the total weight with me and the extra battery and other stuff I carried with me was over 400lbs. On flat roads I've hauled an upright piano, and various similarly-heavy dog food and/or grocery loads, with and without the trailer, though braking considerations means I am usually under 15mph for those hauls.

There are various other builds here on ES with much higher torque capability (like Doctorbass pulling a schoolbus).

So if you aren't getting enough torque out of the motor, it's either not wound for the job it's doing (usually overheating), or it's not being fed enough current for the job (usually not overheating).


Depending on the variety of riding situations you need it to work efficiently under, a middrive that runs thru a shiftable drivetrain could be much more efficient and better at the job than a hubmotor (which can only be "geared" for one situation).


The only available hubmotors I know of with a round axle and proper torque arm built in instead of trying to use flatted axles for torque are the Grin ebikes.ca GMAC, and the various Heinzmann motors. GMAC is clutchless, don't know what's available from Heinzmann these days.

 

[99t4]

I made a tiny bike for my daughter who refuses to learn to ride. (Don't get me started.)

While we bike enthusiasts don't like to admit it, you may have to conceed defeat at some point. I have one niece that refuses to bike, even as all the other kids and adults are having a great time on our biking adventures. I usually can get the kids to try anything, but for her it was always a struggle to get her to ride. Set her up with a nice bike, arranged fun rides, etc. To her credit, she did at least try it. But it remained a struggle. Eventually we all gave up, preferring to maintain civil relationships.

 

[kylerlaird]

While we bike enthusiasts don't like to admit it, you may have to conceed defeat at some point. I have one niece that refuses to bike, even as all the other kids and adults are having a great time on our biking adventures. I usually can get the kids to try anything, but for her it was always a struggle to get her to ride. Set her up with a nice bike, arranged fun rides, etc. To her credit, she did at least try it. But it remained a struggle. Eventually we all gave up, preferring to maintain civil relationships.

I'm not ready to concede. She really enjoys cycling. She asked for her fat tire bike to become a trike so I did it. The rear is so wide that she has to leave it in high gear. She still rides it like a beast. I'm tempted to electrify one of the trikes for her but I want her to be comfortable on two wheels first. (She won't try much because of something her sisters said. It doesn't take much.)

 

[nicobie]

Put a motor on her bike and watch her drift! Her sisters will be in envy.

 

[neptronix]

Couple things:

I have been working toward "digital drive" for other bikes so this has been an interesting experiment for me. It's hard for me to imagine these direct drive motors ever being sufficient for solely powering a bike. Gearing is the obvious answer. Geared motors tend to be low-powered, though.

I've been on this forum since 2010 and this is the first time i've heard the term 'digital drive'. All electric bicycles are digitally driven already.. soo... explain yourself

My dream motor:

1. loads of torque - sufficient to pull an adult up a steep hill with 27" wheels, >100Nm?
2. medium speed - top out at 15-20 MPH
3. clutchless
4. 10mm round axle/side cable exit/decent torque arm system

27" wheels make your requirement slightly more difficult than usual ( the larger the diameter, the harder a hub will have to work, the smaller the wheel, the more power can be output by a given hub ).

How steep of a hill? and how long?

There's a variety of direct drive motors ranging from 250w-5000w that fit 10mm axles. The only one that is round ( and also has a built in torque arm ) is:
Grin Rear All-Axle Hub Build

( this would be a good motor and fits your specifications as long as this hill isn't a mountain )

I recently bought a Citycoco-style hub motor for a mini-bike. It's rated 2000W/60V. I haven't seen much torque from it yet, but I just started working on it. It's huge/heavy. Is that where "digital drive" is headed?

View attachment 343678

FYI, i would not run more than ~500w on this configuration. Front suspension forks are famous for shearing in half with front motors when running at even lower power. Front fork dropouts are also typically much more flimsy compared to the rear dropouts. You also need torque arms. I hope you are not running really high power on this.

 

[4πr^2]

I made a tiny bike for my daughter who refuses to learn to ride. (Don't get me started.)

Get her a bike with training wheels and sneak out every week or so and raise them up an eighth inch. In a few months she will be 2-wheeling and not even know it.

 

[99t4]

I'm not ready to concede. She really enjoys cycling.

Sorry, looks like I misunderstood. I saw the word "refuse" in your OP and that reminded me of my niece's attitude.

 

[kylerlaird]

Get her a bike with training wheels and sneak out every week or so and raise them up an eighth inch. In a few months she will be 2-wheeling and not even know it.

I tried ordering ordering these "adult stabilizers" but it's apparently a scam site. Just got my PayPal refund.

Bike USA Adult Stabilizer Wheel Kit – Agouveia

 

[kylerlaird]

Sorry, looks like I misunderstood. I saw the word "refuse" in your OP and that reminded me of my niece's attitude.

Yup, the refusal is just about balancing. At the slightest wobble she jumps off. And we're on grass.

I did have a little breakthrough. I was riding the e-balance bike around while she was on the trampoline with friends. She jumped on and we rode together for a bit, even controlling the throttle. It was great to get her on the bike but it was far from comfortable for me. I ordered a banana seat to try to make it more feasible (and cool!). It has been weeks but it's scheduled to arrive today.

https://www.amazon.com/gp/product/B000AO7H4S

I'm hoping that once she gets the feel of balancing with with me, I can jump off and use the sissy bar like a training handle.

Amazon.com

 

[Chalo]

For my part, I think handing a >100 nm motor to a weenie kid who won't even try two wheeled riding is inviting a traumatic whoopsie that may drive her away from e-bikes permanently. Bikes with less than half as much torque, and wheels that are half again as large in diameter, work fine for full sized adults. You can always find a staircase/spillway/cliff that will fight your motor to a standstill. That alone should not govern how much torque is appropriate on a kid's bike or scooter.

 

[4πr^2]

I tried ordering ordering these "adult stabilizers" but it's apparently a scam site. Just got my PayPal refund.

Bike USA Adult Stabilizer Wheel Kit – Agouveia

Dang - sorry to hear you got scammed, but sounds like paypal is making it right. Looks like those sell for about $149 in a 'reputable' market such as ebay (lol).

Bike USA Inc Refurbished Original Adult Stabilizer Wheels Kit 789264329644 | eBay

The Bike USA Original Stabilizer Wheel kit is designed to balance your bike and let you ride! This training wheel kit is perfect for individuals who have trouble balancing a two-wheel bicycle without any assistance.

www.ebay.com

Those are pretty big, obviously for adult sized bike. But given the kid-sized bikes you show, you might be able to get away with much smaller/cheaper models. Looks like quite a selection for kids bikes around the 12-20" range. But you'd also need to get around the rear derailleur, etc if they are going on that Zukka.

But definitely look for models with a wide range of adjustability. (ideally long slots) If the set has a short range or has discreet / widely spaced steps, it would force a noticeable jump in spacing and drop in stability... that might foil this scheme!

bike training wheels for sale | eBay

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