Track bike conversion, with regen and torque based assist

[foijord]

Hi,
I'm thinking about the feasibility of converting my track bike to electric. Here's what I want to achieve:

- regen instead of rear brake (kicks in when back-pedalling)
- torque sleep, i.e. you can coast without resistance from the motor
- no throttle, automatic assist based on pedal torque

What do you guys think? is this feasible?

Cheers,
Frode

 

[aroundqube]

https://www.superpedestrian.com

 

[foijord]

https://www.superpedestrian.com

Cool, that checks all the boxes!
But I hate that the batteries are *in* the wheel. Just seems unnecessary to me. And my windows phone is not supported...
Also, I have a ton of 18650 laptop batteries that I would like to use so ideally I would buy a hub motor and a controller and build the pack myself.

So does such a controller exist? One that has sensors that can sense torque and can do regen effectively?

 

[dogman dan]

Hmm, you want to strap 20 pounds or so of weight on a track bike, and have it ride exactly like a track bike. (dd motors that do regen are heavy suckers)

I'm not sure if brakes are possible at all on the track bike, but I'd want a very light setup. That's a very small geared motor. Oops, there went regen. But maybe not if you open it, and do something to lock the clutch on the motor. Oops, there went coasting.

Then you can do a thun sensor/controller/cycleanalyst setup from Grin. Regen engaged by a push button on the bars. Screw the coasting, pedal lightly if you want to economize.

Not exactly what you wanted, but close. If you can put brakes on the bike, just put a small gear motor and pedal activated controller.

I think you need to choose regen, or coasting.

 

[foijord]

Hmm, you want to strap 20 pounds or so of weight on a track bike, and have it ride exactly like a track bike. (dd motors that do regen are heavy suckers)

I'm not sure if brakes are possible at all on the track bike, but I'd want a very light setup. That's a very small geared motor. Oops, there went regen. But maybe not if you open it, and do something to lock the clutch on the motor. Oops, there went coasting.

I thought that a geared motor would just turn when you coast, if you lock out the "clutch". Just like a DD motor? And perhaps there exists a controller that could do some kind of "torque sleep", like the Model S? Perhaps one could program something like that with an Arduino and some mosfets or something?

Then you can do a thun sensor/controller/cycleanalyst setup from Grin. Regen engaged by a push button on the bars. Screw the coasting, pedal lightly if you want to economize.

Not exactly what you wanted, but close. If you can put brakes on the bike, just put a small gear motor and pedal activated controller.

I think you need to choose regen, or coasting.

So a custom DIY solution is needed to achieve my goal. Not sure I'm competent enough to do something like this, but it seems like it ought to be so simple. Relatively speaking I mean.

 

[dogman dan]

Pardon my ignorance, so hard to keep up in this field.

I have never heard of torque sleep. But there is only one way it could be done with a direct drive motor, and that is to feed it enough power to eliminate the cogging. (motor acting like a generator when off, creating drag) 50w is generally plenty.

But the real drag, will be the weight of a typical dd motor. It just seems to me to be the wrong choice for a super light track bike.

I'm a notorious simpleton. KISS is my style. For a track bike, I'd just want to add at least one brake, and run a very light gear motor. And personally, a throttle. It will freewheel when you are in pedal only, and a twist gets you help when you need it. This setup is pretty much standard because it works well.

I know, I know, it will not be a fixie anymore. But the weight of one brake is nothing, when you just put an 8 pound motor, and 4 or 5 pound battery on the damn thing. It's still going to be fun to ride!

I'd look at 48v lawnmower and weed whacker batteries for a very small battery.

 

[foijord]

Pardon my ignorance, so hard to keep up in this field.

I have never heard of torque sleep. But there is only one way it could be done with a direct drive motor, and that is to feed it enough power to eliminate the cogging. (motor acting like a generator when off, creating drag) 50w is generally plenty.

I only know about torque sleep because the Model S recently got it through an OTA firmware update. So it's a thing, and perhaps more advanced than just feeding a little power to the motor since it took them a year to implement it (it's only really relevant for AWD cars which came out about a year ago). Anyhow, torque sleep is just a nice feature to have, it's not mandatory for me.

But the real drag, will be the weight of a typical dd motor. It just seems to me to be the wrong choice for a super light track bike.

I'm a notorious simpleton. KISS is my style. For a track bike, I'd just want to add at least one brake, and run a very light gear motor. And personally, a throttle. It will freewheel when you are in pedal only, and a twist gets you help when you need it. This setup is pretty much standard because it works well.

I'm not 100% sure, but I think this setup would be illegal in Norway and most of western Europe. I think you are required to pedal in order for the assist to be active.

I'm right with you on keeping it simple though, that's why I'm using a track bike in the first place. But I'm not running it as a fixie anymore. I did that for years, but got tired of it and wanted to give my knees a break. So i built a new rear wheel for it, with a Sturmey Archer 2-speed coaster brake hub. This setup is really cool, still no cabling, and still the clean look of a track bike but with gears and a brake! I also have installed a front brake of course. The bike wouldn't be legal without it, and I do want two independent brakes.

I guess I could start with adding a small geared hub motor and some kind of torque sensor for assist and forget about regen to begin with. The battery I would make out of 18650 laptop cells and probably carry in a backpack. So all I need is the small geared motor and a controller and some torque sensor thingies. The motor is easy to find, but I have no idea about which controller/sensor to get and how to install those on the bike.

 

[dogman dan]

Ahh, torque sleep likely something completely different in a car. They have gears, transmissions, one wheel in the air while 3 are digging, etc.

Having it legal, that's a novel idea for endless sphere. I think you will still be fairly happy with a single speed gear on a small rear gearmotor. Pedelec is easy, but good pedelec that uses a torque sensor costs a lot.

That much is technically easy, it's having the coasting ability combined with regen that's a bitch. I'd choose the coasting since you have a front brake.

You could front motor it, just to keep your rear gears, but with a motor, even a small low power one, one high gear can do all you need.

 

[foijord]

Ahh, torque sleep likely something completely different in a car. They have gears, transmissions, one wheel in the air while 3 are digging, etc.

I'm talking about the Tesla Model S, the awesome electric car. It has AWD through 2 motors, one driving the front axle, another one driving the rear. There's no gearbox like on other cars, just a reduction gear. So it's like a geared hub motor, without the freewheeling. The motor is engaged at all times (you need that to be able to reverse) The front motor has different gearing, more efficient in cruising speed. When you're cruising, the car will put the rear motor to "sleep" to minimise drag and only propel the car using the front motor. This is torque sleep and it saves energy. I figured an electric bike could do the same, it's all firmware in the controller right?

It might be naive, but I figured there would be an electrical engineer or two on this forum who could tell me if this is easy or hard to do. I'm a software engineer, and to me it sounds "easy". Easy for an electrical engineer at least, perhaps not for me. I mean, can't you just hook up e.g. an arduino to some mosfets and hall sensors and that would be enough to control a motor?

 

[John in CR]

You need one of those simple, light and slick auto-engage friction drive rigs. No regen but minimalist for a track bike.

 

[Drunkskunk]

The first problem is most track bikes are built too light to be strong enough to handle the extra weight and power of being motorized. even many road bikes are still built too flimsy. these bikes are designed to be only strong enough to survive human power used in the way they were designed, any extra material for added strength would add weight, and be counter to their purpose.

If you want a light weight ebike, start looking at touring bikes as a starting platform. They are built to handle the extra weight and will withstand the abuse of adding the equivalent of a second rider's worth of power.

Ebrakes aren't a reliable way to stop a bike. While they work awesome as a supplemental brake or "drag" brake, they are no good as a primary brake. You will also add a huge amount of weight to the bike by using a motor capable of regen braking. If you want to keep your bike light, stick with a small geared hub motor (Q85, Q100, Q100H, etc) and a conventional brake.

Torque sleep is just a marketing name Tesla uses for part of their power distribution profile. Its neat that they gave it a name, but few people are going to know what you're talking about unless you explain it. Yes, something similar can be done about the drag from the motor when not under power. In the ebike lexicon, it's called "Cogging". Nothing like the "Torque Sleep" exists because it isn't much of a problem, but you could design a circuit that detected the BEMF (back EMF) and applied enough power to result in a near neutral drag profile if you chose.

Most hub motors experience 10-15 watts worth of drag when unpowered at very fast pedal speeds. It feels roughly equivalent to riding with your tire 10lbs low. Even monster motors like I use on my monster bike have so little cogging that I can enjoy a long ride without much concern over the drag. Sure, I work a bit harder to ride, but then on any Ebike you will be carrying 20-40lbs more weight anyway.

The thing to remember is once you add all the components needed to power a bike, it's never going to handle like a non powered bike again. It will be heavier and the center of mass will be different. Compared to your lightweight track bike, even a well built Ebike will feel like a wallowing pig when ridden unpowered.
...... but then the power kicks in, and..