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PAS system

Old 10-26-19, 12:36 PM
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PreacherG
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PAS system

I'm a newbie.

Please explain the PAS system. It seems some only operate when you pedal, others work without pedaling. Some sync with pedal rate, others do not. I do not know enough about this to ask a more intelligent question, so please help me learn.
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Old 10-26-19, 02:22 PM
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PAS = pedal assist system. All require pedaling to activate the motor. The other option is a throttle.
Some are RPM activated (speed of the wheel activates motor).
Some have torque sensors (torque sensor in bottom bracket, rear hub or ???) that activate the motor.
Some have both.
Some have both plus a speed sensor (system uses both of above plus a sensor for the speed of the bike to determine level of assist).
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Old 10-26-19, 03:51 PM
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Two styles: (1) speed and (2) torque.

The speed system provides more motor assist the faster you pedal, common on cheaper ebikes and lower end conversions.

The torque system provides more motor assist the harder you pedal. This the big feature of the TSDZ2 mid drive conversion.

The torque sensor system is always in the bottom bracket, because it has to sense how hard the rider is pedalling. It can't do that at the hub because of gearing and the motor drive (unless it is a front wheel drive motor). There are torque sensing bottom brackets available and controllers that will interface with them and standard motor control units.
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Old 10-26-19, 10:20 PM
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Just FYI, BionX (if not others) had the torque sensor in the rear hub.
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Old 10-27-19, 11:56 AM
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There's various other torque sensing systems that measure chain tension or dropout deformation, too.

(And, IIRC, the power split systems that NexxtDrive and Revonte are developing can effectively calculate torque through their speed regulation methods - using Toyota terminology, they know how much power MG1 is pulling off of the rider to maintain a certain crank speed, they know how fast the rider is spinning the cranks, and they know the fixed torque split of rider input power to MG1 and to the output, allowing them to trivially calculate input torque (as long as, at least in the NexxtDrive version, the rider input isn't exceeding the output speed, if that happens rider torque bypasses the power split system and goes straight to the output - but then you know rider torque is high enough that you've maxed the system out).)
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Old 10-27-19, 05:59 PM
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I have a DAS-Kit 500 watt rear hub drive with 6 PAS settings. It only detects that you are turning the pedals. Each settings 1-6 will propel you to a certain speed if the pedals are turning. For example 1 = 10mph, 2 = 12, 3 = 14, etc.... If you are riding with a group going 13mph, then you could put it on 2 and pedal a little harder. Or you could put it on 3 and pedal intermittently so that it stays around 13mph. Basically the PAS setting sets your target speed. A setting of 6 doesn't produce any more acceleration than a setting of 1. It also includes a throttle so that no pedaling is required.

I also have a mid drive mountain bike with a Bosch motor. It doesn't have any settings that work like the PAS above. It uses torque and cadence in different ways depending the assist setting.
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Old 10-27-19, 07:30 PM
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Mid Drives normally use speed plus cadence (pedal rpm) to determine what gear you are in so that power at the wheel can be stable.

My rear hub drive Bafang kit seems to change the controller power based on pedal assist level setting 1-5 as pedaling slower or faster does not seem to affect the power. There is no speed sensor visible not probably required as motor rpm will match speed directly.
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Old 10-28-19, 04:12 AM
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Originally Posted by fly135 View Post
I also have a mid drive mountain bike with a Bosch motor. It doesn't have any settings that work like the PAS above. It uses torque and cadence in different ways depending the assist setting.
AFAIK, most of the OEM-oriented systems (Bosch, Shimano, Brose, Yamaha, and I believe Panasonic) have each mode mapped to a certain percentage of input power (with the exception of Bosch's eMTB mode, which applies a curve to the assistance), and some systems also consider angle (that is, when climbing a hill some systems increase the PAS percentage).
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Old 10-28-19, 09:13 AM
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Originally Posted by bhtooefr View Post
AFAIK, most of the OEM-oriented systems (Bosch, Shimano, Brose, Yamaha, and I believe Panasonic) have each mode mapped to a certain percentage of input power (with the exception of Bosch's eMTB mode, which applies a curve to the assistance), and some systems also consider angle (that is, when climbing a hill some systems increase the PAS percentage).
That sounds right. My DAS-Kit hub drive seems to be either on or off at the same power depending on speed and PAS setting when you start/stop pedaling up until you get close to the top speed of that setting. Then it seems to taper the power off. So the acceleration from stop is always the same no matter what PAS level. If you actually want to change the amount of power, you need to go into a password protected menu and change the power output of the motor.

I tend to use my Bosch mid drive in almost exclusively EMTB mode because it feels the most like riding a regular bike.
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Old 10-28-19, 09:15 AM
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Hi Preach, you really have to try them out with a test ride. Even within a category, the feel is different. Probably less so with a torque sensor, but there is a whole range of behavior in the cadence systems and some are designed quite poorly

Experience with the bad cadence system probably has caused many ebikers to swear by the torque sensor system, but there are some decent cadence systems.
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Old 10-28-19, 10:24 AM
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+1^^^ My BBS02-equipped bike has an RPM sensor and I ride it almost exclusively instead of a Haibike with Yamaha system (RPM, torque and speed sensors) since it's more fun (for me).
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Old 10-28-19, 02:34 PM
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I made it to our only local bike store today and rode a Trex mid motor PAS with 9 speed derailleur and hyd discs. First bike ride in 25 years!! Starting without power then turning it on worked well for me. You could really feel the motor kink in! Stopping with hyd disc was very fast and smooth!! Derailleur with paddle shifters is a HUGE improvement over what was sold back in the day!

After reading your great information and talking to the sales rep, please see if I got this right.

Fact Check
PAS only works if you are pedaling at least a little.
PAS settings set the max speed without much pedal power.
Brake cutoff is not needed with PAS because motor goes off when you quit pedaling**********????
No throttle on a basic PAS system.
Systems with a throttle will provide power without pedaling**********
Today's derailleur systems shift smoothly without missing gears, are reliable, need little maintenance, and the chain stays on**********? (Compared to back in the dark ages)
Disc brakes (vs rim calipers) are really needed for an e bike

Thanks so much for your great information and help educating me in this great hobby!
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Old 10-28-19, 07:38 PM
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You need brake cut-off with PAS.
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Old 10-28-19, 09:00 PM
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Thanks Mikey. That's why I made the list! This forum is GREAT!
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Old 10-29-19, 06:05 AM
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Some of the OEM PAS systems don't have it - my Gazelle with a Bosch system and Magura HS22 hydraulic rim brakes doesn't. (IIRC Magura does offer an add-on in-line switch for their hydraulic systems, but cut-off switches are apparently only legally required for S-Pedelecs (in the US, we'd call this Class 3, although I don't think there's a legal requirement for Class 3 to have them), and there, you want discs anyway.)

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Old 10-30-19, 11:39 AM
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If I begin to descend or approach a corner, I touch the brake for a split second just to switch off assistance. Obviously I still pedal. It makes no sense to ride without pedalling, especially as I have regen charging, but I don't want to use battery if I don't need to. Also, it's second nature to turn a pedal occasionally during braking, even if this is just to lift a pedal out the way of an inside kerb etc. I do not want the motor triggering under such circumstances. I expect the omission of brake cut-out would be annoying!
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Old 10-30-19, 03:25 PM
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Yeah, with a cadence-sensing PAS, I would hate not having cutouts, but in practice, with a torque-sensing PAS, it's perfectly fine (you can spin the pedals with no torque and get no power).
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Old 10-30-19, 07:21 PM
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Sounds to me it is about time the manufacturers started providing a bit more information about how their system works . I did not think about the safety issue of the PAS activating halfway round the corner.
Somehow I have never yet noticed any wobbly moments and am pretty sure my PAS has no cut out.
Bafang kit system, with rear hub.
At least I know what questions to ask, thanks for all this feedback.
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