Controlling the ESA front fork on R1200 RS 2016 independently of BMW’s two in-built Road or Dynamic settings.

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First, I’m going to address the why.
I have a Wilbers Nivomat rear shock – equipped with spring rate and damping to suit me – it is excellent, [see here] . Installing that shock means that the ESA function on the front only allows it to work in Road mode, this isn’t a problem the majority of the time, but when going as fast as I dare on Alpine hairpins (which got footpegs on road), with and without luggage, it’s noticeably unsettled when transitioning between heavy braking and getting back on throttle – it just needs to be firmer.

Two, I’m retired now and wanted a project I could spend time on to learn something technical, keeping my brain active and maybe benefit my motorcycling life.

I spent many hours googling about BMW’s ESA system, how it works and what options there are to tune it. There was very little out there, certainly not a full explanation.

This thread https://www.r1200rforum.com/threads/help-needed-tight-forks.61652/ was the most informative and kind of my starting point, and the table of values in the 6th post proved to be a useful heads up and match what I was later to see. So that started me down the route of discovering what Pulse Width Modulation (PWM) was all about, had no idea before doing this. So, I read a few 101s on PWM and got a basic understanding of about it.

Having got a basics, I realised that to move forward I had to be able to ‘see’ what signals the bike was sending the front-fork. I bought a handheld oscilloscope for £120, [this one from Amazon] (I got a great deal looking at the price now)

It took me some hours to understand how to work with the Oscilloscope (my son helped me with this, he has occasions to use one in his job) and I’m still far from proficient.

To access the ESA signal, I needed to tap into those control wires – so rather than cut the bike’s loom, I tracked down the appropriate connector part numbers, and found a set for sale on ebay Werbung: https://www.ebay.co.uk/itm/257191284787

I bought two sets, and these matched the male and female of the two way connector that connects the left front fork to the bikes wiring loom – the mated connector in question is clipped to the left side of the radiator expansion/filler tank behind the steering head. Here's its location (Yellow Arrow), Red arrow is the other half that now links the bikes loom to the dummy load (cover this later)
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Using the connectors’ own pre-wired tails, I joined a pair of bought connectors to make a short cable to plug-in between the bike’s connectors, this cable had exposed copper so I could attach the oscilloscope probes.

Now, I could have done this analysis on my bike but would only have got one set of results (for Road), but I happen to have a second R1200 RS in the garage (that’s another story), that’s done 61,000miles and has the original ESA suspension front and rear. I took the newly assembled lead and plugged it into this bike, got it running, and set the suspension to Road, connected the oscilloscope and took a picture of the output display, then set it to Dynamic and took a picture of the display.

Here are those pictures of the oscilloscope display, Road followed by Dynamic.

In Road mode the pulse width is covering 3.5 to 4 graduations
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Dynamics mode the pulse width is covering no more than 3 graduations
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I did some calculations based on these and determined that in Road mode the voltage is allowed through for 30% of the cycle, and in Dynamic it was on for 23% of the cycle – this was encouraging as it matched the numbers in the table in the thread linked above. The other values I took away were the Cycle frequency, approx 2Khz, and that the peak voltage was in the 12 to 14 voltage range (which makes sense on a 12volt bike with an alternator kicking out 14.4volts).

At this point I knew what I had to recreate to control the ESA independently. I then start to investigate what was out there to do this, I spoke to a motorcycling friend, who has a PHD in radar electronics and a creates his own (ham) Radios, and he assured me it would be simple enough and to check out Amazon.

Firstly, [I bought one of these for £7 from amazon]

And whilst it showed I was on the right track, I could not get the potentiometer to be granular enough to move the duty cycle by 1% at a time, nor could I get it to produce a stable wave below 35% duty cycle and neither could I tune it to a suitable cycle frequency (although I understand this isn’t critical). Oh and I hasten to add, I wasn’t connecting this to either bike at this point, no, no, too worried I might burn something out, so I was working with a fairly large 12v brushless computer fan and a 12v 20 LED array (both that I had laying around in the shed), these operated as the ‘load’, i.e. they substituted as the ESA unit in the fork leg.

I did a bit more research and found this [small format PWM controller] for £13 from amazon

With that I was able to replicate the bike’s Road and Dynamic ESA signal exactly. Another advantage was that when powered up this PWM controller uses the settings that were in place when it was powered down, something the other unit didn’t do, happy days.

Now I need a switched 12~14volt supply from the bike to power this unit so it could produce the 12v modulated output. I took the ignition switched feed from the BMW accessory output (on the right side below and external to the seats), attached this to the input on the PWM controller, V+ V-

I then wired the OUT- and OUT+ to the appropriate BMW connecter (as sourced above) and plugged this into the ESA front fork.
Powered up the bike and got a warning on the dash!

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We’ll return to that in a moment, but with the bike running and moving the duty cycle between 30% and 23% and pumping the front suspension up and down against the front brake, I could feel a difference, hurrah. I then experimented with lower duty cycles, at about 15% the front-end locks up, like it does when the ignition is off. I also tried going a bit higher 30 to 40% and sure enough things got softer still. I’m not comfortable with running it much above 35% as this might impact the ESA unit’s life.

Now to return to that ESA warning light on the dash. I fully expected that to be present, so I’d already done some figuring out from the current and voltages involved and determined that the bike was expecting to see a load somewhere between 2 and 5 Ohms depending on the voltages of 12 to 14.

I measure the resistance, via the connector, that the ESA unit in the fork had, it was showing 2 Ohms, but someone had warned me resistances this lower are notoriously difficult to measure accurately with cheap multi-meters (my new oscilloscope doubles as one) but I was at least in the ball park with my calculations.

I also knew from the calculations and other things I’ve read that the Wattage involved was going to be in the order of 20 to 30watts.

I sourced a selection of [100W metal cased resistors] (100Watts as this gave a good operating safety margin). From this selection I knew I could make various values from 1 to 6 Ohmns in 0.33 Ohm steps. As it was my first choice of a 3 Ohm, got the fault to disappear, I did try 2 and 4 Ohm and the warning returned, so 3 Ohm it is.

I jury rigged all this together and went for a ride. It worked, and I could tell a difference between 20% duty cycle and 30%.

The buttons are around 7mm in diameter but are slightly raised on the control panel, so although I have to look to ensure I’m pressing the correct one, I can operate them with winter gloves on. With summer gloves I don’t have to look as I can just about feel them. One press on the + or – “DUTY/N” buttons changes the duty cycle by plus or minus 1%.

Having done the proof of concept, I now needed to make it operational, i.e. figure out how to mount the controller on the bike and waterproof it.

I found a [small cast alloy box] that I hoped I could fit the PWM in, it was a tight fit on the depth, but I managed it by trimming the bottom of the controller. I cut and filed a hole in the lid to fit the controller in. I then cleaned and sprayed the box a silver colour that almost matches the rest of the silver/greys on the bike. I used numerous beads of silicon sealant around each opening to seal them. I also drilled two holes, one for the power cable in and one for the modulated output signal. I passed the cables through and sealed these with silicone too.

I decided the best place to mount my controller was in the original BMW sat-nav location, i.e. on the top yoke / triple clamp (having moved my sat nave above the dash on month one of ownership). I dug out the original mounts from a box in the shed, inverted them, and drilled two holes in each and in the bottom of the box and bolted it in place (also sealing these bolts, inside and out).

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Originally I mount the resistor on the metal frame above the radiator, close to the steering damper mount on the frame – thinking it would be in a cold air stream – but it got too hot and (oddly) drop in resistance and caused the ESA fault to display, so it is now mounted on the plastic ‘bars’ under the fairing panels you remove to access the head lamps, and it hasn’t faulted since (400 miles in), it does get too hot to touch, but not so hot as to melted plastic cable ties or impacted the 'bar' - two of the straps around the resistor are metal cable ties but I just cannot get these tight enough to fully secure it so have a plastic one as well.

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I have found that for me under most conditions a duty cycle of 27% works, and only on rougher roads with bad road repairs do I set it to 30~33%.

If the PWM control unit fails, I can plug the original connectors back together and go back to Road mode only.

Was it necessary? Not really. But I have enjoyed working it out and installing it, and it is providing me some control that I’m genuinely utilising, I will be riding it in the lower range (down to 23%) this summer when I head back to the hairpins of the Italian Alps, where last year I found Road mode lacking.

I'm willing to answer any questions (other than why) but I may take a few days or weeks to respond as I'm away riding a lot in the coming months.

JasonQ

I was shocked at the improvement of a Tractive fork cartridge on my 2023 R1250RS . Its also a alum body vs steel OEM , and over 1 pound lighter. Your research is great.

Zitat von JasonQ im Beitrag #1

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I'm willing to answer any questions (other than why) but I may take a few days or weeks to respond as I'm away riding a lot in the coming months.

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Does that work with the ESA for or only the basic fork? re: Tractive fork cartridge

An update: since the end of July I have covered 7,700 miles around Europe in two separate trips. The second was down to the mountain and valley roads of the Italy Slovenian border (amazing place) and little further west in the Stelvio region.

The control unit has worked amazingly well. Whereas last year I was consistently scraping the foot pegs (both left and right) on every run through a series of bends, this year, on multiple runs on those the exact same bends, the pegs stayed off the tarmac. So well pleased with that.

The control unit has proven reliable in temperatures from 4C to 38C (and that temperature ranged was hit on the same day in Switzerland!).