Can you add PAS to a throttle-only kit

[richj8990]

I'm trying to do a mid-drive conversion on a carbon frame. That means the Bafang / Tongsheng kits probably will not fit. I can always try CYC later but for now I'm trying to do the conversion for closer to $500 than $1000 (and I already have the Hailong II battery). For now, although the CYC kits look fantastic, I'll hold off on buying one and try something else.

Some of the Chinese stuff is reasonably priced at $250-400, and of course who knows if it will really work or not, but one thing that I really need is PAS for climbing technical singletrack. To give you an example, L-Faster builds a 750W mid-drive that's basically a Bafang BSS02 clone but the motor is too close to the crank axle so it probably will not fit over the bottom of the carbon downtube. They also have 350W and 250W mid-drive kits, but only with throttle.

I find that really dumb. If someone is on pavement, they don't even need a mid-drive kit, they just do an easy hub drive conversion and ride all day long on pavement with a throttle. Offroad is not the same at all as pavement. With a dirtbike, there is enough torque to power up hills with a throttle only, but as you offroaders know, e-bikes are not dirtbikes, and you still have to pedal and turn the handlebars very, very precisely up steep singletrack with obstacles. PAS in that case is 100% needed for a constant amount of wattage; maybe you will need to change cassette gears once in a while up the hill; otherwise you have consistent watts going through the rear wheel while you do what you normally do on an acoustic bike: pedal and turn according to what the terrain gives you, second by second, minute by minute. A throttle up techy singletrack would be a joke. You'd be spinning out all over the place. And ending up looking for the 'walk' function on the display.

So here's the general question: if the male/female pins are correct, can someone shop around for a display that provides PAS, hook up the PAS sensor to the inside left crank and controller, hook up the display to the controller, and one way or another (either automatically or through programming in the display) generate PAS with what came as a throttle-only kit? I tried to do with with an E-bikeling SW900 display / controller and Bafang front-hub, and PAS didn't work (throttle did work). The Bafang front hub can only take a KT-LCD3 display for PAS. One of the reasons I'm typing this today is that my KT display is dying again for a 2nd time, so I'll need to switch back temporarily to the SW900 that's been sitting in the garage for a few years. The SW900 doesn't have a lot of programming options like the KT does and that's probably why it cannot do PAS. But, for example if someone bought a throttle-only kit, and the KT display had compatible pins to that kit's controller, could they use the KT display and buy a PAS sensor, again with compatible male/female pins? Or is that question too generalized and if so, what specific examples are there for 'generating' PAS with a relatively universal display? Lastly I want to emphasize that I already have a front hub drive and will be ADDING a mid-drive to a different bike. Two ebikes not one. So really the question is for both hub and mid-drives: can you 'add' PAS to a throttle-only kit, hub- or mid-drive.

 

[amberwolf]

If a controller (throttle-only) doesn't directly support a PAS sensor, there's no way to just plug one in and have it work. The software in the controller would need to support it (know how to read the signal coming out of it and respond appropriately).

If the controller's software and hardware support PAS but they just didn't install a plug for it (haven't seen this happen yet, but it could) then you could install a compatible plug for the PAS sensor you want to use and assuming that PAS sensor's signal is one that controller understands, it would then work normally.

Same for adding a throttle (for PAS-only controllers).

Note that there are several kinds of PAS sensors, even just counting the cadence types, and not going into torque sensors. See the ebikes.ca info page on PAS stuff for some details on these.


For any controller with a throttle input you can use the Cycle Analyst v3 from Grin Tech ebikes.ca to add PAS (cadence or torque sensor or both) to it. For this, the PAS and throttle (and ebrake, etc) all now connect to the CA's inputs, and the CA's output (throttle, the only output it has) connects to the controller's throttle input.

Any display you use on the controller still connects as and does whatever it did before, the CA does not replace that.

Displays are not generally intercompatible between controllers, so using a display that didnt' come with a controller, especially if it's a different brand display than the controller came with, probably will not work. They dont' speak the same language, or the data is in different formats, etc. Because it is just an electronic switch, then if the voltage and wiring is compatible the display's power button will usually still turn on the controller, but there is no information exchange between them when incompatible.

Displays generally don't do anything other than display information sent by the controllers, and send data from keypresses to the controller, as well as have a settings menu and storage onboard, so they can tell the controller at powerup what settings the user chose during setup that are different from defaults (for those controllers that don't store the settings in their own memory when powered off). They don't generally interpret sensor data (like brakes, throttle, PAS, etc., that job is generally done by the controller.

 

[E-HP]

I think cadence based PAS on technical off road is like suicide. It's too hard to control and can be unpredictable and actuate at the worst times. A torque sensing PAS would be better, since it just amplifies your pedal pressure, so more predictable. It takes a lot of practice to manage a hall based throttle, but it can be done, which is what I prefer off road.

As far as adding PAS to a controller, the Cycle Analyst can add that functionality for both cadence and torque based PAS. I believe the KT displays and controllers, when flashed with open source firmware, can also support torque based PAS. As far as mid drives go, Bafang won't support torque based PAS, but Tongsheng and CYC do.

BTW, displays are brand specific, so if you get a KT display, just get a KT controller with PAS. You won't be able to use it with a generic throttle only controller. With a KT controller, it will be cadence PAS by default, unless you flash the display.

 

[richj8990]

I think cadence based PAS on technical off road is like suicide. It's too hard to control and can be unpredictable and actuate at the worst times.

I don't think cadence-based PAS is really what you think it is. If you pedal at 30 rpm and are in PAS 2 with 250W, it stays at 250W +/- 10% for as long as you pedal and are in PAS 2. If you pedal at 100 RPM and are in PAS 2 with 250W, it also stays at 250W +/- 10%. It has a specific wattage per PAS level regardless of how fast or slow you pedal, as long as the cadence is above about 20-30 RPM. All you do is actuate it with 1/4 turn or so of the pedals, and that's it, it's off and going. There is no proportinality to cadence like there is for torque sensing. The faster or harder you pedal, the more human watts are added but 0 extra electrical watts are added. Trust me I've used a non-torque based PAS cadence for years and that's how it works; it's on/off.

Also, up hills it produces constant power; you can shift up or down if needed when the trail gets steeper or more flat. Or just put it into a different PAS as long as the driven wheel doesn't spin a lot. With a throttle, you need to hold it constant with a hand twist or thumb; both of those types are a big issue holding the throttle constant when you are going over obstacles. You need to concentrate 100% on how your tires and pedals clear obstacles and not on holding the watts constant, let alone having one hand distracted from keeping the steering straight. Lastly, if you are going up something like pavement, even a geared hub drive will start bogging down under throttle if the pavement gets a bit steeper or you are going up more than a couple hundred feet. That does not happen with PAS; as long as you have enough battery you can climb thousands of feet up all day long with PAS and a geared hub drive. I've done it, you don't even get tired and more importantly, the motor doesn't get tired like a direct drive or throttle only would. A throttle only geared hub drive begins to behave like a direct drive on steeper hills --- it gets tired. PAS negates that motor fatigue because it provides (at least between 300-600W) consistency for the motor below its peak output. Even a mid-drive motor can burnout if they are putting it in boost mode (PAS 3) all the time up hills.

I see all of these videos on how guys juice up their hub drive bikes, or install a mid-drive and...then they go out on flat pavement or gravel to 'show' how great their ebike is. Please. That's not even a real test. A $500 Walmart E-Bike can do that!!! The real test is at the bottom of at least a 400 foot hill, go up singletrack (or neglected, overgrown doubletrack that used to be a fire road decades ago), have it be between a 10-20% uphill grade, with plenty of rocks and erosion ruts, and then (and only then) you will really see how well your e-bike climbs. That's the real test, not these guys throttling on a flat surface and bragging about it. Try a 13% grade with 4-6 inch obstacles, with tight turns and off-camber sections, and then see if you can throttle that. PAS on a geared hub can do it. I know because I've done it.

On Strava, I never look at the E-bike downhills, only the uphills. I've made several uphill segments to see how a geared hub drive with PAS stacks up against what I assume is 100% other mid-drives, at least 90% mid-drives I'm sure, especially now in 2023. Now this is not to 'win' some uphill race, it's just for analytics. The higher-end mid-drive eMTBs are getting very, very popular in my area, and the stats for my hub drive used to be better until recently because there are way more mid-drive e-bikes out there than there were a few years ago.

5% grade, 9/17
7% grade, 4/8
8% grade, 5/84 (a lot of uphill switchbacks = front hub can swing around them faster)
9% grade, 5/9
10% grade, 65/109
12% grade, 53/63 (this is VERY technical)
13% grade, 2/4


Above numbers mean a 500W geared hub drive with PAS up hills can hold its own against the lower-powered 250W mid-drives they sell today as complete $4000-8000 bikes. Why? A 500W nominal geared hub drive has around 50 Nm peak torque, which is about the same as the 40-60 Nm peak torque of a nominal 250W mid-drive. You need PAS to keep that torque constant up hills. The only real advantage of a mid-drive is that you can do more complete mountain biking with it, as in modern frame that's not QR, tubeless tires, better performance down hills, etc. If I was not waiting in the mail for a mid-drive, I'd really try to fix my hub drive PAS problem more than I am doing now.

A torque sensing PAS would be better, since it just amplifies your pedal pressure, so more predictable. It takes a lot of practice to manage a hall based throttle, but it can be done, which is what I prefer off road.

As far as adding PAS to a controller, the Cycle Analyst can add that functionality for both cadence and torque based PAS. I believe the KT displays and controllers, when flashed with open source firmware, can also support torque based PAS. As far as mid drives go, Bafang won't support torque based PAS, but Tongsheng and CYC do.

BTW, displays are brand specific, so if you get a KT display, just get a KT controller with PAS. You won't be able to use it with a generic throttle only controller. With a KT controller, it will be cadence PAS by default, unless you flash the display.

I had two KT controllers, 48W 17-30A nominal ones; the original Bafang front hub kit came with a KT-LCD3 display and controller, a no-name throttle, and it worked with no display manipulation. Switched from twist to thumb with an aftermarket throttle and it also worked fine. Throttle works even better now with an E-Bikeling 36/48V display and controller, BUT the PAS does not. So in my experience throttles are much more generic than PAS, hence the question in the subject line for this thread. Mid-drive kit with PAS is coming so I'll live with throttle only on the hub drive.

 

[E-HP]

I use cadence based PAS now with RPM ramping. It's cadence based (increase in cadence can be set to increase or decrease assistance). I like it that way since when I downshift, my cadence goes up, and the ramping automatically adds more power for the hill I may be climbing. Works great. The danger is in what you are describing, where the motor dumps a fixed amount of power, when you don't want it to. Hubs climb fast, mid drives can climb slow, and that's where the advantage is, not in the ability to climb itself. I climb 20%-25% offroad with a hub, but can't do it slower than 15 mph for a mile, but can go slower (5mph) than that for short periods, so I can do a technical climb at a slow speed, using throttle, but not for long period.

I know a guy that died two years ago on his ebike. Technical uphill climb. I've ridden there several times. I'm guessing the bike applied or continued to apply power when he wasn't expecting it, when he flew off the cliff; mainly because it's almost happened to me a few times. Now I just shut off PAS at the trail head.

 

[amberwolf]

I don't think cadence-based PAS is really what you think it is.

Cadence-based PAS operation depends on the specific controller design.

So what you see with yours isn't what everyone will see, as theirs may operate differently.

Almost all of them don't actually care what cadence you pedal at, and only detect that you *are* pedalling, and then provide the full assist of whatever level you've chosen in the display.

For "torque simulation" type controllers that will provide a certain amount of power or current, but for most controllers it will simply provide a certain "speed" (simply a specific amount of throttle, or % of PWM of battery voltage to the motor). (all the PAS controllers I've had so far are the latter type, and are difficult to safely ride in traffic as there is insufficient control without using the throttle instead)

So for your specific controller and chosen settings, you get the behavior you see and posted. Other systems will be different than that.

Using the Cycle Analyst v3, you can actually get assist based on the speed at which you are pedalling (your cadence), modified by however you choose to set the CA up.

This is how I use it on the SB Cruiser, so I use the pedals to control the motor assist directly and proportionally, exactly as if I was pedalling without motor power.

I could also use a torque sensor, but for almost all situations I don't need one, the true-cadence-based assist works fine.

(it would *not* work for me if I only had the type of cadence-sensor PAS that almost all controllers use where they only detect that I *am* pedalling and I had to choose specific assist levels to do specific things or keep changing assist levels to match traffic speeds, etc--I would have to use a throttle instead for those types of systems to safely ride in my situations).