Pedal Assist

[joe duerr]

Does anyone know where I can find out how pedal assist actually works. I have tried Google. My pedal assist has five magnets in a circle that pass a sensor. The magnets will only work in one direction and all the magnets are positioned the same north pole on one side and south pole on the other side. The speed that the magnets pass the sensor adjusts the speed of the motor. Logic says that if I put 5 more magnets in the same circle positioned north and south the same as the others all spaced equal that the sensor would think the wheel is going twice as fast. The opposite is true and I can't figure why?

 

[pxpaulx]

The basic pedal assist you've got simply recognizes the movement of the pedals. It isn't sensing speed or anything more than the movement of the pedals to engage the pedal assist - the amount of power being applied would be based on the level of assist selected via the controls on the bike.

 

[joe duerr]

The basic pedal assist you've got simply recognizes the movement of the pedals. It isn't sensing speed or anything more than the movement of the pedals to engage the pedal assist - the amount of power being applied would be based on the level of assist selected via the controls on the bike.

It is NOT just recognizing the movement of the panels, It IS sensing speed because the faster the pedals are turned the faster the motor goes. The tests I am running there are no pedals I am just spinning the magnets past the sensor. The faster the magnets are rotated the faster the motor goes. I NEED the question I asked answered and that is does anyone know where I can find out any information on HOW it actually works. What is the sensor sensing? Why does it only work in one direction and why do more magnets not increase the speed. I am looking for information on the science behind HOW they work.

 

[Ravi Kempaiah]

The basic pedal assist you've got simply recognizes the movement of the pedals. It isn't sensing speed or anything more than the movement of the pedals to engage the pedal assist - the amount of power being applied would be based on the level of assist selected via the controls on the bike.

Here you go: http://www.ebikeschool.com/pedal-assist-systems-pas-vs-hand-throttles/

 

[pxpaulx]

Thanks for the link @Ravi Kempaiah . @joe duerr No need to be snarky. Maybe you'll find an answer over at endless sphere, a lot more technical knowledge well be found at that forum with the diy crowd. Mostly end users of pre made/manufactured bikes around these parts.

 

[joe duerr]

Here you go: http://www.ebikeschool.com/pedal-assist-systems-pas-vs-hand-throttles/

Sorry if I came across snarky but I tried to explain in detail that I was looking for anywhere I could find information on how what I am using works. I thank you for the time you spent to give me that link. I am new to this forum and have no idea where to look for the data. I would be interested in the "diy" crowd if that is more technical. How do I find that? This quote is from that link "The most common type of pedal assist system comprises a ring of magnets mounted on the pedal crank and a sensor fixed to the bottom bracket. As the pedal crank turns, the sensor reads the rate of pedaling. The faster the pedal cadence, the faster the controller will make the motor to spin." This is the system I have. I do not have the system that senses torque. It senses the speed of the 5 magnets on a ring that pass a sensor. First of all I am doing this all on a test bench. The wheel/motor, controller, pedal assist and battery are all on a test bench. What I am looking for is the science behind exactly what it is sensing because... there are 5 magnets in a circle that all pass the same sensor which is mounted in a fixed position. The faster I turn the magnets the faster the wheel turns which is exactly what it is supposed to do. If I turn it backwards the wheel does not move which is exactly what it is supposed to do. If put the disk with the magnets on backwards then the faster I turn the disk (backwards) the faster the wheel turns which is exactly what it is supposed to do. So the sensor is detecting the north/south side of the magnets. The problem I have is that logic would tell you that instead of five magnets on the disk you put ten equally spaced magnets on the same circle going past the same sensor that the sensor would think that the wheel is turning twice the speed that it actually is because instead of five magnets passing the sensor on a single turn there would be ten magnets passing the sensor on a single turn. The problem is that is not the case. With 10 magnets on the disk the wheel barley turns and jerks on and off. The quote from the article was the only information I could find on Google on how it works which sadly doesn't tell me anything that I need to know. Why is the spacing of the magnets critical and how does the north/south side of the magnet interface with the sensor. What is the sensor actually detecting.

 

[pxpaulx]

I wonder if the magnets aren't wired to the controller, where the rotations are tracked by the controller's programming to appropriately adjust the speed? Although if that were the case, adding magnets theoretically wouldn't do anything (which it sounds like is not the case). I do definitely recommend you check out endless-sphere.com which is a forum for all things electric vehicle related, and is a much more diy crowd, as well as being significantly more active (and larger) than this forum (mainly due to a broader scope). Endless-sphere isn't just diy as in building things from kits, it is much more the tinkering and truly building things from the ground up type of forum, I would guess you'll find your answers there if they are out there to be found!

 

[opimax]

logical thought...maybe. The magnets are now closer together . The control thinks it will (for sake of ez math) 2 sec for the next magnet but since it is 1/2 as close, it takes only 1 sec for the next magnetic surge the bike thinks it is going twice as fast so additional unexpected magnets would decrease speed or power

 

[tinasdude]

Thanks for the link Ravi. Think it addresses hub motors

 

[harryS]

With more magnets, the magnetic fields are probably overlapping and the sensor never really sees it collapse, so it cannot tell when a magnet has crossed the sensor. If you redid the spacing for six magnets, it would probably work. Maybe 8 could work.

Put a voltmeter on the sensor output and it should bounce between o and 4-5 volts as a magnet crosses the sensor. Verify which level is reached when a magnet is on the sensor. I would guess 0 volts and it goes high when the magnet is removed, Anyway, if additional magnets don't allow the voltage to change, then the overlapping field was the cause.

 

[Ann M.]

Your controller has to be programmed or matched to sense the additional magnets; a controller designed to read a 5 magnet PTS will not react properly with a 10 or 12 magnet PTS

 

[joe duerr]

I designed a wheel with 10 magnets that have the same spacing as the 5 magnet disk and it works great. I get twice the speed for every rotation of the pedals.
Thank you all for all the input. It works with my controller exactly as the 5 magnet disk did but doubles the speed of the motor. Works out you can put as many magnets in a circle as you want but the distance between the magnets is critical. The disk I put them in is 4.6" diameter, made it out of epoxy glass, glued the magnets in and painted the whole thing to match the bike. I mounted the sensor (without the ring) on the frame. I will post some images when I get a chance.

 

[harryS]

Smart, Joe. Bigger wheel for the same magnet spacing. Your intuition was right!

 

[vincent]

hey joe,

was just wondering about this myself for my cemoto

is this still working well?

and how did you move the sensor out further?

if you have some pics of before and after that would be great

last question did you try to find bigger disc online , like ebay etc

would you be interested in building another disc for me to purchase?

 

[joe duerr]

A picture of the disc I made is at this link. It is on the first page. The disc is the red circle on the pedals.
The battery and controller are in the small box on the rack. I did not put a throttle on this bike but I did put a speedometer/odometer on.
I don't like wires so for the speedometer I ran the wires into the handlebar through the neck and out the hole just above the wheel.
I need the odometer to test my ultra light 27.2 Ah batteries vs my 18 Ah batteries.
https://www.facebook.com/joe.duerr.5

 

[vincent]

thanks joe, your bike looks great, you did some serious work on that project


will see if i can find someone willing to mod this for me at some point
pas seems a little weak on this bike and a little more power would be good

how much increase in power did you get with the 4.6 disc?


last nite i emailed a company that sells the disc on ebay, they replied that yes if i add magnets it will make the motor go faster but i need the same size disc
sounds like they dont know what they are talking about


if i can find a shop in phx that builds electric bikes- think there are some, will see what they can do

lots of discs on ebay that show several empty holes, wondering if on that type you can buy a bigger disc and move the magnets around where you want
or buy some more magnets and glue them in and pop out the other ones
they all had to be ordered from china

 

[joe duerr]

thanks joe, your bike looks great, you did some serious work on that project


will see if i can find someone willing to mod this for me at some point
pas seems a little weak on this bike and a little more power would be good

how much increase in power did you get with the 4.6 disc?


last nite i emailed a company that sells the disc on ebay, they replied that yes if i add magnets it will make the motor go faster but i need the same size disc
sounds like they dont know what they are talking about


if i can find a shop in phx that builds electric bikes- think there are some, will see what they can do

lots of discs on ebay that show several empty holes, wondering if on that type you can buy a bigger disc and move the magnets around where you want
or buy some more magnets and glue them in and pop out the other ones
they all had to be ordered from china

The power increase doubled. It is 24 speed and in the highest gear ratio (slowest pedal rotation) it goes.
It really is no longer pedal assist it is speed control because there is no effort to the pedal. Same size disc more magnets does NOT work.
Tried it. The 5 magnet disc I had had five extra holes centered so I put magnets in them, made sure north and south were correct and it didn't work.
If you make a larger disc to add more magnets you have to also move the Hall sensor to where the magnets are.
You can make a disc out of anything that is not magnetic. I used epoxy glass because I had easy access to it and it is rigid.
You can use wood, plastic or even aluminum.
Measure the distance between the magnets and maintain that distance and you can put as many as you like on a disc.
Where are you located?
https://www.facebook.com/joe.duerr.5

 

[ebikernz]

The power increase doubled. It is 24 speed and in the highest gear ratio (slowest pedal rotation) it goes.
It really is no longer pedal assist it is speed control because there is no effort to the pedal. Same size disc more magnets does NOT work.
Tried it. The 5 magnet disc I had had five extra holes centered so I put magnets in them, made sure north and south were correct and it didn't work.
If you make a larger disc to add more magnets you have to also move the Hall sensor to where the magnets are.
You can make a disc out of anything that is not magnetic. I used epoxy glass because I had easy access to it and it is rigid.
You can use wood, plastic or even aluminum.
Measure the distance between the magnets and maintain that distance and you can put as many as you like on a disc.
Where are you located?
https://www.facebook.com/joe.duerr.5

Great post Joe! I recently acquired an older 6 speed pedalec with a rear hub motor and also noticed the magnetic sensor on the crank and curiosity via Google has led me to your post.
You've clearly asked questions and have described the dilemma which I myself have stumbled upon and now with some helpful advice from fellow members you've managed to modify your ride to gain some added power. Well done mate!
Question..Am I correct in saying that the maximum attainable speed is not actually any higher but you use less energy to get there or is there still some level of assistance even when pedaling flat out in the highest gear? I'm thinking that at some point the speed via mechanical rotation exceeds the electrical hub rotation speed!
Just wanna go faster!