Regenerative Braking, is it this easy!?

4

420b

100 W
Joined
Aug 13, 2018
Messages
126
So on my 500w China DD Hub motor (which I recently found to be more like a 1000w+ motor), I recently have been experimenting with the brake cable and shorting different 5v pads to ground. So there is this one pin called A3 and when I short it to ground the motor just stops like the brakes were applied. I’m pretty sure this is regen braking. This kit keeps making my day!

 
eee291 said:
Yes, yes it is!

Just make sure the torque arms are up to the task.
Click to expand...

YAY! Took her for a ride old school, only pedaling, and we got back .1 volts! I have noticed there is like a half second delay in applying the regen brake. That’s probably due to my controller, but I guess you can’t win them all...

About the torque, isn’t it the same amount and direction of torque being applied as when I brake physically? Meaning if my brakes work fine and my wheel hasn’t fallen off yet (steel frame, old but not a cheapo) I should be good?
 
No.. It's totally different. The brakes are grabbing the wheel, but not twisting the axle. With Regen the axle keeps rocking back and forth every time it alternates between going and braking... It loosens things up in a hurry.
 
420b said:
About the torque, isn’t it the same amount and direction of torque being applied as when I brake physically? Meaning if my brakes work fine and my wheel hasn’t fallen off yet (steel frame, old but not a cheapo) I should be good?
Click to expand...
Nope. The torque from conventional brakes is applied to the rim; this torque is applied to the axle.

What a lot of people find is that their bike works just fine with EV forward and mechanical brakes because the first time you accelerate, the axle tries to "cam out," hits the limits of the dropouts and just stays there. (As long as there's not too much torque.) The next time you accelerate it's already at its limits.

But with regen, when you accelerate, it torques and hits the limits of the dropouts, then when you brake it torques in the other direction and hits the other limits of the dropouts. Do that enough (rotating it a tiny amount back and forth each time) and the nuts loosen. If you neglect to tighten the nuts eventually the axle cams out and spins (and/or falls out, rips up the wiring, jams the chain etc.)

Sometimes you can get away with just making the nuts super tight, but especially with higher powers (accel OR braking) you need a torque arm to keep the twisting under control.
 
Thanks for the explanation folks. Here is my axle. image hosting services It’s not aluminum (99% sure) and it looks pretty tough. That said, I’d like to get some torque arms to make sure the worst doesn’t happen. There isn’t much of an online market for torque arms for bikes, so what would you guys recommend?
 
There are a gazillion ideas here: https://endless-sphere.com/forums/viewtopic.php?t=26444&start=15

The approach I (and many others) took should work pretty well with your dropouts. Just make sure that you make the hole for the axle nice and snug fitting. the tighter the fit, the better. And use two. One on each side.

https://endless-sphere.com/forums/viewtopic.php?f=2&t=26444&start=175#p1315521
 
wturber said:
There are a gazillion ideas here: https://endless-sphere.com/forums/viewtopic.php?t=26444&start=15

The approach I (and many others) took should work pretty well with your dropouts. Just make sure that you make the hole for the axle nice and snug fitting. the tighter the fit, the better. And use two. One on each side.

https://endless-sphere.com/forums/viewtopic.php?f=2&t=26444&start=175#p1315521
Click to expand...
Those look clean. What tool did you use to make the hole for the axle?
 
All I had to do was solder the EBS pads together on my 1000w controller. It's funny because the controller I've got is tiny compared to a lot of these bigger "1000W" controllers on ebay... like half the size. Super easy and I have a steel fork without and torque arms right now. No issues (legs crossed). Your controller looks similar in size to mine, how many FETS is it? Congrats on the regen! This is a brake lifesaver
 
Philaphlous said:
All I had to do was solder the EBS pads together on my 1000w controller. It's funny because the controller I've got is tiny compared to a lot of these bigger "1000W" controllers on ebay... like half the size. Super easy and I have a steel fork without and torque arms right now. No issues (legs crossed). Your controller looks similar in size to mine, how many FETS is it? Congrats on the regen! This is a brake lifesaver
Click to expand...

I got 12 FETs on mine. The only problem is that the regen braking is actually taking a second to activate, making it really bad at sudden stops. Did you ever have this experience?
 
420b said:
Those look clean. What tool did you use to make the hole for the axle?
Click to expand...

I forget exactly. A drill press for sure. I think I drilled two holes and removes the remainder and got the final shape with hand files. I may have used a coping saw with a metal blade for some sections. The outside shape was done with a hand held electric grinder and hand files. Of couse, I sanded things as well before painting.
 
420b said:
The only problem is that the regen braking is actually taking a second to activate, making it really bad at sudden stops. Did you ever have this experience?
Click to expand...

Regen braking works best once you become accustomed to the speeds and distances in order to minimize the use of your mechanical brakes (and minimize their maintenance) as well as maximize energy recovered through regen. Make some torque arms (I always recommend clamping type when using regen) or learn the hard way with in the best case deformed dropouts and/or motor axle. At such a tiny radius your talking about thousands of pounds of force rocking back and forth in your dropout, so over time something will give.
 
John in CR said:
420b said:
The only problem is that the regen braking is actually taking a second to activate, making it really bad at sudden stops. Did you ever have this experience?
Click to expand...

Regen braking works best once you become accustomed to the speeds and distances in order to minimize the use of your mechanical brakes (and minimize their maintenance) as well as maximize energy recovered through regen. Make some torque arms (I always recommend clamping type when using regen) or learn the hard way with in the best case deformed dropouts and/or motor axle. At such a tiny radius your talking about thousands of pounds of force rocking back and forth in your dropout, so over time something will give.
Click to expand...

But my regen actually takes like 1 second to kick in. Like when I’m rolling slow and I activate it I don’t hear the whine or feel the resistance until 1 second later, sometimes more, sometimes less. I’d like to upload a video in a bit to showcase the issue.
 
Regen delay is from the controller. Different controllers will have a shorter delay or none. Some that are programmable might have this delay as an option that can be set. Some controllers have variable regen, that can be controlled with a throttle. All programmable controllers that I know can be set to automatically regen on throttle release, that is acting like compression on a gas engine.

In every case, regen is not constant. When the difference between controller voltage settings and battery state of charge is little, regen can’t be powerful, but as the battery voltage gets lower the regen does kick better. Variable regen does give it a better functionality, by giving you control of regen braking, making it better able to replace your brakes. Good brakes are always more precise and efficient than regen though. You will never achieve a shorter braking distance with regen than with good brakes but, both combined together can improve your braking distance in some slippery conditions.
 
One of my goals for my bike is torque arms so that's in the works...

I do have the second delay or whatever. I'm very used to it and I prepare for the drag essentially when I'm braking... I actually kinda like it. Allows me to ease into braking more...
 
Hehe... In this thread "Search found 0 matches: pad"... While yer saving a few percentages in battery capacity... yer saving huge in brake pad wear. :wink:
 
billvon said:
420b said:
About the torque, isn’t it the same amount and direction of torque being applied as when I brake physically? Meaning if my brakes work fine and my wheel hasn’t fallen off yet (steel frame, old but not a cheapo) I should be good?
Click to expand...
Nope. The torque from conventional brakes is applied to the rim; this torque is applied to the axle.
Click to expand...

I think it's more that with conventional rim/disc brakes, the torque from the wheel is applied to the frame (where the brakes are mounted), so the axel sees limited stress from braking.

With regen, the torque from the wheel is applied directly to the axle, which causes it it shift in the drop out.
 
lionman said:
I think it's more that with conventional rim/disc brakes, the torque from the wheel is applied to the frame (where the brakes are mounted), so the axel sees limited stress from braking.
Click to expand...
Right. Torque can only be applied _between_ two places (for example, a car's driveshaft and its motor/transmission mounts.)

On a bike, all rear wheel torque ends up affecting the rear wheel, so it's all measured with respect to the axle. With rim brakes, it is applied far away from the axle (about 12 inches) so the force for a given torque (in foot-pounds) between wheel and frame is low. With disk brakes, it is applied closer to the axle (about 4 inches) so the force between wheel and frame is 3x higher for a given torque. With regen the force is applied to the axle itself. On a 1/2" axle that means you have 1/4" of distance between axle centerline and frame contact point, so force is 48x higher than the rim brake requires. Which is a lot for that small dropout to handle.
 
I disabled the regen, the controller logic sucks. Basically, at high speeds it does low regen (which I like), but then when you slow down it RELEASES regen for a literal second, then enabled a high regen which locks you up. The issue is mainly the release of regen when slowing which caught me off guard the first few times and almost got me into a wreck. Not to mention the lack of braking modularity that you have with my form of regen, because it’s either on or off, no in between.
 
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