Regen Experiments

Progressive Regenerative Braking

I'll begin by saying that, in my opinion, the only need for regenerative braking is to increase a vehicle's range.  The mechanical brakes work just fine for retarding forward motion.  However, that opinion may not be shared by everyone.  Cindy loves variable regen braking as she feels it gives her much finer control than the rear brake offers.

Control of regenerative braking can be divided into two categories: Vehicles that have a mechanical clutch and those that don't. I developed regen braking for the latter class of vehicles and described it fully in the EM 5.7 section.  Vehicles with mechanical clutches offer new challenges and opportunities.  The ePure Race is such a vehicle.

EM's optional solution is shown below.  It's called “PRB R” and mounts in place of the clutch master cylinder reservoir cover and plugs directly into the SiliXcon controller.  It is EM's P/N TC01Q-60403-00-00 with a US retail price of $279.  This actually seems like a reasonable price to me – especially compared to the cost of some EM parts.

It does seem like an elegant solution, but far from optimal for trials riding.  I imagine transitioning your “clutch finger” to the PRB lever and back would not be smooth.

Performance Metrics

How can we evaluate the effectiveness of regen braking?  The intangible “optimal feel” is important, and likely differs greatly among users.  But riding time/distance is not intangible.  The Cycle Analyst has been a valuable tool in helping quantify my intuition.  Prior to having any data, I guesstimated that as much as a 10% additional range could be achieved on the EM 5.7 via regeneration.  Maybe so, but it's not likely for my riding.  Based on data from the Cycle Analyst over a few rides in a single location, 5% would be a more achievable goal.  That number is the proportion of regen Wh versus driving Wh.  But just because you put “X” Wh into the battery does not mean you will get the full “X” Wh back out.  Based on the battery charge/discharge testing I conducted earlier, I would estimate the process is about 88% efficient (e.g., it took 1828 Wh to charge the battery, but only 1610 Wh came back out).

Push Button Regen

The prior owner of my bike had wired a regen push button near the left handgrip.  It routed +5 volts directly into the controller's analog regen input. Pressing the button produces maximum regeneration (which still seemed fairly weak to me).  In retrospect, this was actually a pretty good solution.  But I wanted to get a feeling for any advantages variable regen could offer.

Difficulties Bleeding

Unfortunately, I found it very difficult to bleed the rear brake!  There was a lot of air in the system when I first attempted to take a pressure measurement.  At first, I could only generate 30 psi.  More bleeding, then 50 psi.  More bleeding and finally in excess of 100 psi.  At 50 psi there is a minor drag on the wheel, but you can easily turn it by hand.

None of my usual tricks for bleeding worked.  I backfilled the system by injecting brake fluid into the bleed nipple.  I used a Mity-Vac to suck brake fluid through in the usual direction.  Of course, I tried manual bleeding (while elevating and tapping on various parts of the system while doing so).  Because the brake hose is routed through the swingarm, it's not worth the trouble of removing the swingarm in order to elevate different parts of the system during bleeding.  I had the same trouble with the 5.7 (which has the same rear brake hose routing).  Because the 5.7 had lain on its side returning from Texas, there was zero rear brake when we got it home.  I had to literally hang the rear of the bike from the ceiling in order to get all the air out.  I'll probably have to do the same with the ePure.  I can't really blame EM for this since it is a Sherco swingarm.

Signal Conditioning

I expect to have some analog signal conditioning electronics (just an op-amp hopefully) between the pressure transducer and the controller's PRB input.

Ideally, pressing on the brake pedal will initially produce regen braking with no or minimal mechanical braking.

I'm hoping that some combination of pressure transducer full-scale range, post-signal amplification/limiting, and air in the brake system will give me the feel I want.  A cheap Chinese eBay product may be useful here.  I have a hydraulic ABS attachment for motorcycle brakes on order.

Unfortunately, I don't expect to be able to field test a prototype before the weather turns.  Some lab experimentation will be necessary anyway.

Encouraging Initial Results

The weather was favorable for some driveway testing - although I had to rush a bit to get everything ready (was in the middle of a tire swap).  Unfortunately, my Chinese ABS reservoir got delivered to the wrong buyer, so I won't be trying that anytime soon.  Not sure how long it will take to get a replacement.

My first test in the driveway was using a rock-hard pair of Jitsie / GoldFren 173 brake pads.  I originally bought these for my OSSAs, but they were completely unusable.  I considered throwing them away numerous times but figured they might be good for something someday.  That day has not yet come.

I thought the hard pads might work because I wanted the regen to do most of the initial deceleration.  Between the hard pads and having air in the system, the stopping power was insufficient.  I did however see up to 25% regen on the Cycle Analyst with those pads.

Subsequent testing with the stock pads yielded only about 10% regen and the stopping power is almost good enough (there was still air in the system).  Other numbers from the Cycle Analyst: Maximum driving current 45A.  Maximum regen current -13.2A.  Peak speed of 13.6 mph, an average speed of 5.3 mph.  Total distance 0.81 miles and 41 Wh/mile.

I'm encouraged by these preliminary results.  My biggest fear was that I would lose the ability to simultaneously use the rear brake and throttle.  I sometimes play one against the other in very tight, very slow speed turns.  After a certain level of regen (command voltage) is reached, the SiliXcon controller no longer takes input from the throttle.  I tested that a lot in my driveway and had no difficulty.  Because of the ePure's mechanical clutch and its precise throttle, it's easy to achieve very slow, very smooth low-speed turning and I had no need to simultaneously drag the rear brake.

Chinese ABS Module

A replacement ABS module finally arrived.  I mentioned this item briefly in the 5.7 section on the design evolution of my electronic clutch.  At that time, I had assumed it worked something akin to a hydraulic accumulator and would introduce some “sponginess” into the feel of the brake system.  Nope.  It's actually a pressure-limiting valve as discussed below.  I'm not sure if it (or something like it) will be useful or not.  No instructions accompanied the unit.  I had assumed the gold “knob” was an adjustment.  Wrong again.  It's just a cap - the setscrew it fits onto can be used to provide some preload to the spring.  But the O-ring is the only seal and the gold cap needs to bear against it.  So if there is any adjustment, it's quite limited. 

I had used a 100 psi transducer for a variety of reasons even though I assumed the pressure could be well above that.  The $14 Chinese sensor was rated for a burst pressure of 600 psi.  I now realize the failure pressure is considerably below the burst pressure.  Several things were learned:

1. It is very difficult to bleed the rear brake with the pressure transducer as installed.

2. The presence of the transducer makes removing the rear wheel more difficult and I could see it being damaged in a crash.

3. A much higher-pressure transducer will be required, plus some signal conditioning electronics to make this design work.

4. If the transducer does mechanically fail, you will have zero rear brake. 

I have ordered a 1000-psi transducer and will build some signal conditioning electronics to produce a 5-volt output at the appropriate pressure (which would have to be determined).   I'll report back on this topic as progress is made.

Fixed Automatic Regen

In the meantime, I have configured a potentiometer as a voltage divider to provide a constant fixed voltage into the PRB input.   I adjusted the potentiometer to provide 1.0 volts.  This produces an automatic regen whenever the throttle is closed.  It provides “engine braking” that's not quite as powerful as a typical 2T trials bike in 3rd gear.  I like the familiar feeling it provides but do not expect it to extend the bike's range.   In fact, the Cycle Analyst showed only 0.2% regen (equivalent to 0.2% more range) during a 39-minute test ride.  Although the Cycle Analyst calculates this number, I checked it against other values it provided of -0.0151 Ah during regen versus 5.40 Ah during driving.