Engine Braking

[trapezeartist]

I raised this as one of my points on this other thread but it was too many questions at once, and most of it has fallen by the wayside now anyway.

So I thought I would address this one question again. My aim is to achieve a little bit of engine braking with the throttle closed, similar to a petrol bike. The Mecatecno I tried had this.

Having studied the information on konrad's website, I'm proposing to use the microswitch in the Domino throttle to feed about 1 volt into the PRB connector. I'll use the PRB/FRB Y-piece to actually make the connection at that end, meaning of course that the FRB won't work, but that doesn't matter. To get the 1 volt, I'm hoping to pick up 5 volts from the feed to the throttle (or maybe the lighting DC/DC converter) and use a converter like this https://www.amazon.co.uk/gp/product/B07DK6WN63/ref=pe_4074371_1338459331_em_1p_1_lm. Does that make sense, konrad?

If that's all OK, my only issue now is to understand the wiring colours. According to konrad's website, the main wires from the throttle are blue, white and black but I've got a connector marked T1 going into the throttle connector that has red, black and blue. The standard (non-EM) version of the throttle has blue, white and black, and the micro-switch wires are both green. However I've got a connector marked T2 that has white, brown and yellow.

If I ever manage to sort out the conundrum above, I also intend to add an on/off switch on the handlebars to switch the engine braking on and off.

Any thoughts?

 

[konrad]

I don't think it's in anyone's best interests for me to provide more information than what's already on my website.  It assumes a basic knowledge of electronics that is a prerequisite for making modifications to the bike.

But I really want to discourage anyone from using a DC/DC converter in that manner!  A DC/DC converter could potentially source sufficient voltage/current to damage the controller if it's improperly wired, improperly adjusted or just plain fails.

Stick with the potentiometer shown an the end of the Regen Experiments page: https://www.electricmotiontech.com/home/em-epure-race/regen-experiments#h.7lz2uhjj7x3c

The 2023 bike clearly has some wiring differences to my 2021 model that you will have to determine for yourself.

 

[trapezeartist]

15 hours ago, konrad said:

Stick with the potentiometer shown an the end of the Regen Experiments page: https://www.electricmotiontech.com/home/em-epure-race/regen-experiments#h.7lz2uhjj7x3c

I don't understand how that works. As I read it, the potentiometer replaces the PRB and plugs into the PRB/FRB connector on the main loom. So it's the equivalent of pulling on a little bit of PRB all the time. But whenever the PRB is applied, the throttle is disabled. That was why I was trying wire something through the micro-switch in the throttle.

[konrad]

The PRB does not emit 0 volts when it's off (more like 0.6V, from memory).  That, plus the fact that it's very difficult for your finger to apply only a tiny amount of PRB, probably gave you the wrong impression.  The threshold for the PRB to start affecting the throttle does not occur until about 1.1 volts.  (At least that's the behavior of the firmware in my 2021 controller.  Yours may be different.)

P.S. That T2 connector is where I guessed the throttle could be plug-in to obtain school maps. 

Edited April 25 by konrad

[trapezeartist]

On 4/25/2025 at 1:02 PM, konrad said:

The PRB does not emit 0 volts when it's off (more like 0.6V, from memory).  That, plus the fact that it's very difficult for your finger to apply only a tiny amount of PRB, probably gave you the wrong impression.  The threshold for the PRB to start affecting the throttle does not occur until about 1.1 volts.  (At least that's the behavior of the firmware in my 2021 controller.  Yours may be different.)

P.S. That T2 connector is where I guessed the throttle could be plug-in to obtain school maps. 

So somewhere between 0.6V and 1.1V is the sweet spot for engine braking. It seems like a very small window. Can it be controlled that accurately?

[konrad]

Yes.  The potentiometer shown on my website is called a trimmer, or trim pot.  It requites ~25 turns to go from one extreme to the other.  Also, you must measure the voltage when the trim pot is connect to the controller (because its input impedance will affect the reading).

 

[trapezeartist]

Thanks Konrad. I'm getting the idea now. I'm just struggling to find the right thing on Ebay now. Some are described as single-turn and others are multi-turn (presumably that's what I want) and most don't say. Also I need to find one with reasonably chunky terminals that will tolerate my somewhat clumsy soldering skills.

[trapezeartist]

I tried a quick-and-dirty experiment today to validate the theory. With the bike on a stand, I gradually applied more PRB while blipping the throttle. The first little bit did nothing (of course) but then I found a little spot where the throttle still worked but the motor slowed quickly on closed throttle. A little more movement and the throttle was disabled. So that little bit in the middle is what I need to use. I considered simply putting a cable tie on the PRB lever and while it worked in the garage, it's not a robust solution for riding. So I've jumped in and ordered a 10k potentiometer (I don't think it's a multi-turn, but hopefully that won't matter) and a JST connector so that I can wire it into the PRB/FRB Y-piece. Both items are pre-wired so I only have to identify the correct wires and solder the ends together. It will be a few weeks before it's done because the JST connector has to come direct from China.

[trapezeartist]

I had a brief ride with a cable tie holding the PRB lever in a bit. As near as I could get to the right spot appeared to provide some "engine braking" but it also put a dead zone into the throttle movement. One click more on the cable tie and there was about 90 degrees of throttle movement before anything happened. All this was done on a sloping field. I didn't venture into anything resembling a section. However the result was sufficiently encouraging to persuade me to go the next step with a potentiometer wired in. The parts have come so I'll be doing that over the next few days and then I'll go out for a little ride and decide whether I can live with dead zone.