Beefy disc brakes?

[swbluto]

I've noticed that bicycle disc brakes are designed to be light, so they consequently have minimized mass. This has the habit of minimizing heat capacity, though, which can run the risk of brake fade with fast heavy loads like that which might be associated with a high-power ebike.

So, are there appropriate disc brakes that can handle like moped type of braking but can be used on an ebike? What would be needed to fit moped disc brakes on a "regular bike"?

 

[liveforphysics]

I've noticed that bicycle disc brakes are designed to be light, so they consequently have minimized mass. This has the habit of minimizing heat capacity, though, which can run the risk of brake fade with fast heavy loads like that which might be associated with a high-power ebike.

So, are there appropriate disc brakes that can handle like moped type of braking but can be used on an ebike? What would be needed to fit moped disc brakes on a "regular bike"?

Brakes are something pretty easy to mount from anything to anything. I've faded the piss out of scooter brakes a number of times. I think dirtbike brakes are the way to go. The brembo's that come on KTM's feel fantastic. The whole package, lever, caliper, disk, etc fitted to a bicycle would be a brake package you would never fade on any bicycle.

Mounting it would involve a custom CNC adapter from bicycle hub disk mount pattern to dirtbike disk hub pattern, and a custom bracket to mount the caliper. Fairly simple work IMO.

Since only the front brake matters on a bike, you might find the cheapest method to roughly double braking thermal capacity would be buying one of the dual front disk hubs they put on the chopper style bikes for looks, but in this case it would actually be useful.

http://www.choppersus.com/store/product/813/Front-Hub---Dual-Disc-Black/

 

[Kurt]

Just a safety warning about fitting big powerful brakes to a MTB or similar. Make sure that your front wheel attaches to your forks with a through axle 20mm would be nice. The brake leverage on the axle can tear a quick R wheel right off the forks.

I also agree that normal bike brakes are a bit average. I put a set of avid disks on the front of my e bike after the first ride they were shuddering and glazed no matter what I do to break them in they seem to always glaze over very fast they just get to just hot and glaze over. My bike is slow 36v x5. I have tried it at 72v and the brakes were all but useless at that speed.

Kurt.

 

[Thud]

Having recently attempted this feat, I have some input....
There is a real issue with overall wdth in a typical bicycle set up. At 100mm (standard fron hub widths) I had spoke interfearance/clearance issues attempting to retro-fit a nissan brake system off a honda cr125 to a 20" bike rim. I looked at several Go kart calipers while searching out options.... I settled for twin rotors & the matching mechanicle calipers from Choppers usa.

I don't have any experiance with Hydrolic mountain bike systems. I have a real concern in performance riding senario's that boiling the brake fluid will render them usless in a short amount of time. (it still happens in motorcycle app's) so mechanical calipers for me for now. Need to fine some high performance pads now.

I should note also that my riding style uses brakes to their full potential.......I may be the only human to ever wear out front shoes on a honda spree.

 

[johnrobholmes]

I should note also that my riding style uses brakes to their full potential.......I may be the only human to ever wear out front shoes on a honda spree.

Another one here. Know where to get spree replacement parts? :lol:


Running a 203mm (bicycle) rotor on a 20" wheel seems to be working well for me, and I ride my brakes pretty damn hard. Nose wheelies are one of my favorite ways to stop. I do only weigh 160lbs though. Hayes Strokers on about all my bikes now. They are only two piston, but they are still very nice brakes and pretty cheap.

 

[curious]

I strongly recommend regenerative brakes over anything else for any direct drive hub motor e-bikes while using mechanical brake (whatever type) only as a backup. Installing a DIY proportional sensor on a generic brake lever is a 1hr job with basic tools. On-off switch type sensor should be even easier. Rear regen brake on my X5/Kelly has incredible power at high speed (250lb rider), very smooth action and no issues with pads alignment, glazing, wear etc. Energy recovery is not the key (although nice), but fade-proof braking is.

 

[katou]

My, but that sound interesting. Could you elaborate on the DIY proportional braking setup? I'm guessing that mod is only available to hubbies that support regen braking.

Very,.. curious.

Katou

 

[swbluto]

My, but that sound interesting. Could you elaborate on the DIY proportional braking setup? I'm guessing that mod is only available to hubbies that support regen braking.

Very,.. curious.

Katou

It's also available to "non-freewheeled" non-hub motors. I already implemented a plug braked on an RC motor, but it is way too powerful. I would think the wheel would "lock up" at speeds greater than 5 mph. (But it shouldn't lock up because the motor needs to turn in order to provide braking force. Hmmm... I wonder what it would do?)

Now it's making we wonder if I really need freewheeling. But, dang, I wanted to connect it to the pedals so of course I'll need freewheeling. Well, I could use a freewheeling pedal and than the motor would be coupled with the wheel. Or is it?

This is pretty confusing.

 

[curious]

My, but that sound interesting. Could you elaborate on the DIY proportional braking setup? I'm guessing that mod is only available to hubbies that support regen braking.
Katou

Here is how I modified the brake lever:
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=9950
There has been another thread recently how to add linear sensor to the brake lever, here is the link.
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=18134

I use Kelly kontroller wich has an input for proportional regen control. But even fixed regen (like in infineon controllers) can greatly reduce stress and wear on mechanical brakes, especially at high speed.

BTW I am not against a nice disk brake, but many issues using them on a heavy/fast bike go away if you augment it with regen braking.

 

[johnrobholmes]

If the motor did not freewheel, you could always remove the motor chain in an "emergency" when you only had pedal power.

 

[amberwolf]

I may be the only human to ever wear out front shoes on a honda spree.

The junked Spree I have uses band brakes...but it's from 85 or so. Can you use any parts from that? (probably not)

 

[liveforphysics]

I strongly recommend regenerative brakes over anything else for any direct drive hub motor e-bikes while using mechanical brake (whatever type) only as a backup. Installing a DIY proportional sensor on a generic brake lever is a 1hr job with basic tools. On-off switch type sensor should be even easier. Rear regen brake on my X5/Kelly has incredible power at high speed (250lb rider), very smooth action and no issues with pads alignment, glazing, wear etc. Energy recovery is not the key (although nice), but fade-proof braking is.

A rear brake is not really used in performance bike/motorcycle riding situations much at all though, unless it's just a quick stab to slide the tail a bit.

When you're riding hard, and braking hard, the rear tire is either not touching the ground, or just skimming across the ground with a couple lbs on it to act a bit like a rudder. I don't even have a functional rear brake on my GSXR-1000 at the moment, and I never even notice not having it, with the only exception being low-speed wheelie control is tougher.

But, for commuting, whatever slows you down and doesn't have any parts that wear out sounds like a winner. I can't see it being useful in a performance situation though.

 

[curious]

A rear brake is not really used in performance bike/motorcycle riding situations much at all though, unless it's just a quick stab to slide the tail a bit.

1. This is true for a normally balanced vehicle. In my case (packs mounted on the rack plus a heavy x5 hub, plus an occasional sixpack in a pannier bag) the friction in the rear is unusually high. If I lock the front wheel and apply full throttle, instead of burning the rear I slide the front. I have not been able to lock the rear with regen yet. As someone who has been riding relatively technical MTB singletrack in the past this is indeed a strange feel when you rear brake has more effect than the front one.

2. At high speed the problem is not the tire friction limit but brake overheating. I still remember a downhill ride somewhere in Crested Butte, CO when my front V-brake pads started burning (I am a heavy guy) and emitting thick white smoke for nearly a minute as I tried to find a safe run-off into the bushes (where I crashed safely with hundred cuts from thorns but nothing serious to the bones or the bike frame). Brake power dissipation rises as a product of V(speed) x F(braking force). When V is high the limiting factor shifts from tire friction limits to brake power dissipation limits.

3. Regen brake acts as a boosted brake, requiring very little force to modulate the brake action.

4. There is a psychological safety factor that works like this - with mechanical brake on a bicycle I sometimes avoid braking just to maintain momentum, especially when I am tired. With regen braking I know that about 60% of that energy is recycled so I brake when needed without hesitation.

5. There is very little change in brake feel over time as you go downhill, due to lack of any thermal / surface effects. Also braking action is not affected by dust, water and air temperature effects.

6. It is possible to design a true anti-lock regen brake (with custom controller firmware).

7. (forgot this one, editing in ) Brake pad wear / need for periodic adjustment is greatly reduced.

 

[liveforphysics]

All great points Curious. It sounds like a very good option in your application.

 

[amberwolf]

[If I lock the front wheel and apply full throttle, instead of burning the rear I slide the front. .

This is what happens with CrazyBike2 at 36V. Not sure yet with 48V and a properly aligned drivetrain.

6. It is possible to design a true anti-lock regen brake (with custom controller firmware)

It should also be possible to design a fully-locking-at-zero-RPM motor brake (no longer a regen brake, though) by using field coils rather than magnets, by locking the fields and armature windings to opposite polarities in a way that won't let the motor spin. Potentially a very high current situation, though.

 

[curious]

It should also be possible to design a fully-locking-at-zero-RPM motor brake

Why would you need one, perhaps for some advanced riding tricks ? You can short the phase wires and pretty much get this effect with any DD hub but generally it is much better to dissipate the power outside the hub, by either regenerating or dumping it into well-cooled dummy load.

With all my love towards regen braking, I still think that mechanical backup brake system should be good enough for an emergency stop from max speed with cold brakes. That on a >300lb e-bike is not a simple feat.

 

[amberwolf]

I'm not sure why I would want one; but the possibility sprang to mind. I'd rather have mechanical brakes for locking up the wheel should that be needed; just because there is a little less to go wrong with them.

I'm still working out getting the Fusin regen braking to work, as I have not yet gotten the freewheel fully disabled (still slips). Once I do, then I'll know a lot more about what I want out of regen or electrical braking.