8.5mph motors sunrise - how much at cost ?

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8.5mph motors sunrise - how much at cost ?

Postby expresso » 29 Jan 2021, 02:21

does anyone here have a sunrise quickie model chair and upgraded to the 8.5mph motors ?

if so - can you tell me how much you had to pay for them - - did you get them at cost or was charged retail ?

if anyone can tell me how much was paid ASAP tonight - - i need to know for sure so i can relay this info tomorrow when i will be discussing it with vendor etc, - long story - but if anyone paid for them - if you can tell me how much you paid -- in the US you can PM if you like

thanks
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 29 Jan 2021, 03:30

Just looked up on the sunrise site and the 8mph is actually cheaper than the 6mph, all 4 pole. Around 450 retail each approx cost to dealer will be approx a third less so 350 ish.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby expresso » 29 Jan 2021, 05:21

i did look it up - here in the US its more like $940 each - and yes the slower 6.5 is more by $40 each than the 8.5 mph

this is retail - but i need to know about any users here in the US who did a chair and upgraded to the faster motors - what price were they charged by there vendor - lets say - Numotion - i need to know the cost they paid to get them if anyone here did upgrade -

https://www.southwestmedical.com/replac ... -s636-s646

thats here in the US - UK maybe different pricing so not accurate enough - you may get them cheaper - than us here -

i would guess a dealer would get them for less than $1000 a pair easy - just looking for feed back from any user who paid for them and how much they were charged -
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 29 Jan 2021, 05:26

Less than 1K definitely!

For what its worth I bought some practically unused 8mph LINIX sunrise just like your ones on here for 320 a pair. Still boxed - looked new. Keep eyes open these things turn up! Obviously you would need to swap the hub for a 4 or 5 stud one from the old motors.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby elryko1992 » 29 Jan 2021, 21:00

I have a pair for sale brand new 8.5 mph like BM.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby expresso » 29 Jan 2021, 22:24

Burgerman wrote:Less than 1K definitely!

For what its worth I bought some practically unused 8mph LINIX sunrise just like your ones on here for 320 a pair. Still boxed - looked new. Keep eyes open these things turn up! Obviously you would need to swap the hub for a 4 or 5 stud one from the old motors.



strange that those are rated for 8mp and the others are rated for 8.5 mph - why did they do that or is that even true - it does show 8mph on those motors on the MWD chairs FWD - the RWD chairs 8.5
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 29 Jan 2021, 23:06

They were sold as 13kph, 8mph, 8.5mph all the same motor/gearbox. Depends on what local legislation or marketing department say.
What speed do they go? Depends on weight of user and chair, battery type and impedance state of charge, and what the voltage setting in the motor section is set to, type and overall diameter of drive wheel, etc.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 29 Jan 2021, 23:12

Heres a fun thing.

If you want to go faster, and no joke, buy some square powerful N52 or N50 neobdneum magnets Literally stick them with epoxy to the outside of the case in the same positions as the weak ferrite magnets inside your motors. Makes a huge difference.

Watch till end. Your chair will respond the same way. Lots faster. No loss of torque. A gain in fact.


youtu.be/9PfErFnXyt0
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Re: 8.5mph motors sunrise - how much at cost ?

Postby expresso » 29 Jan 2021, 23:26

send me the link to what i need to buy - just stick them on the motors ?
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Re: 8.5mph motors sunrise - how much at cost ?

Postby expresso » 29 Jan 2021, 23:38

would have to know where they are inside the motors first -
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 29 Jan 2021, 23:40

Pretty much.

You need to look inside and see where the magnets are though. Or "feel it" for the magnetism with a bit of steel outside through the casing.

Or you will be randomly guessing. And the got to be the right side up! Or you will make it slow and overheat. It actually increases efficiency if you do it correctly.

You use one magnet to find out which is the north south as ithey will repel or attract each other. Or safer to use a compass. Mark with black pen so you can see which is the same face. Stick them on magnetically and see if its faster. Do one side of the motor first. Then the other side of the motor. The chair will drive oddly and turn towards the slow side. Then do the opposite motor!

You could use these? Or any that you think are easier to get in there. Try to cover the whole magnet. Say 4 of these on each side of the motor can. https://www.ebay.co.uk/itm/5-x-Neodymiu ... 1195.m1851

The bigger the magnet, and the more of the magnet that you cover, the better it will work. The hobby motors I use in quadcopters etc are built with Neobdnium magnets and thats why they are so powerful.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby expresso » 29 Jan 2021, 23:49

that would be very cool if it did speed it up this way - stick them on color them black and thats it

i am sure your going to try it right ? when you do - and figure out the best way to do it - i will follow :thumbup:

alot of us have the same Linx motors that you have - dont you have any pictures of the inside of this motor ?
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 30 Jan 2021, 00:03

I did it already years ago while experimenting on an EMD 2 pole motor. It works.

I have not done it to a 4 pole motor yet. It will work exactly the same way. Some 4 pole motors seem to use 4 magnets. Some use 2. So I might need to get a compass out to see what is what! Or just experiment with a loose motor on the bench. They are all nickel plated so no need to paint black. Just epoxy on... Or let the magnet hold itself on! Or a blob of evo stick or other contact adhesive.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby expresso » 30 Jan 2021, 00:22

oh well - short lived
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 30 Jan 2021, 00:27

What do you mean short lived. The guy above is an idiot and I suspect a glove puppet of a guy I already deleted several times as he is nothing but a not very bright troll. So yes he will be short lived! And after 3 more posts ges gone.

Fitting rare earth stronger magnets internally improves efficiency and increases power and torque and free running RPM. But would increase cost enormously. We cant do that ourselves. But we can assist the existing magnets some by carefully positioning strong rare earth magnets externally. At little cost with some large gains. As many people have been doing for years.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby expresso » 30 Jan 2021, 01:19

BM if you figure it out where and how to add them to the Linx motors we have - and it works as intended - i will follow you doing it also

i cant experiment like you do - i wouldnt know where to start - with my luck it will kill them inside ? i rather do it after its proven and done and how etc, -

if you ever figure it out and do it - i love to hear the results - if it actually does work - this is the easiest way and cheapest to gain a bit more speed etc, as long as the chair acts the same and no damage to them inside -
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 30 Jan 2021, 02:24

I am not doing anything right now I am on my bed till this sore heals. Then I have millions of other things to catch up on!
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Re: 8.5mph motors sunrise - how much at cost ?

Postby expresso » 30 Jan 2021, 02:31

ok then - one of these days - hope your get well for the summer at least - enjoy the short 3 months we have - i cant wait -
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 30 Jan 2021, 02:41

Years ago I connected an f55 motor to the power supply on my bench. I set it to 6 volts. And unlimited amps. It ran at aroud 1/4 speed. I only had one big high power magnet. As I move it around the case it was easy to find the one spot that made the motor run faster. So its not hard to find the right spot. If I turn the magnet over, then the right spot is the opposite side of the motor.

To do a perfect job you would need to take apart and apply thin powerful flat magnets and "tile" the area that is outside of the magnet making sure the correct face N or S faces the motor. There are 4 magnets on a 4 pole motor I think from memory. But on many powerchairs there are only 2 still. So I dont get how they work! But with one strong magnet you should be able to find out. If you want to play!

You can see how it works on those two vids. But you do need them in the right place.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby expresso » 30 Jan 2021, 02:47

right you have to find the right spot and direction - its not something for me to do - but if it gets done and we find the right spot and direction etc, - since most of us use the same linx motors -

once done - alot of us can benefit and copy what you did knowing it will work and correctly placed - you have the knowledge so its easier for you to do -
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Yennek » 03 Feb 2021, 20:30

Don't want to be the party pooper here, but some of the statements earlier in the thread aren't exactly right. (And sorry in advance for the lengthy explanation.)

Using stronger magnets (or adding more magnets in the right), on a permanent magnet DC motor, gives essentially the same effect as gearing a motor lower (slower speed, more torque).  Using weaker magnets (or adding more magnets in the right spot "upside down"), gives essentially the same effect as gearing a motor higher (higher speed, less torque).

It might seem counter intuitive, but it's the physics. Math first, but physical example is further down the post.

The no load speed of a permanent magnet DC motor is defined as:

speed = Vt*Kv   -  Where Vt is the voltage at the terminals of the motor, and Kv is motor speed constant (usually in terms of rpm per volt)

Everyone here is obviously very familiar with this concept however, it is actually more useful to use the back EMF constant (Ke) in the calculation, where the back EMF constant is simply 1/Kv:

speed = Vt/Ke 

This still just applies to permanent magnet DC motors, but one can generalize it a bit to cover all DC motors.
speed = Vt/(Ka*phi)    -  Where Ka is the armature constant and phi is the magnetic flux from the field.

In a PMDC motor, phi is a constant (because it is made by the permanent magnets), so it is typically combined with Ka to give Ke (or Km), but on field wound DC motors, it is variable. Prior to fancy PWM schemes and such adjusting the field current (and thus the magnetic flux) was frequently a way one varied the speed of DC motors.  

Anyway, that equation shows the inverse relationship between speed and flux. Less flux = more speed.

However the torque equation for a PMDC motor is as follows:

torque = Kt*Ia    -  where Kt is the motor torque constant, this time in terms of newton metres per ampere (N·m/A), and Ia is the armature current.

This should be familiar with anyone working on the motor compensation on their chair. It also can be generalized for all DC motors.
torque = Ka*phi*Ia - Where phi is still the flux, Ia is still the armature current, and Ka interestingly enough is the same armature constant as above. (and thus Kt=Ke=1/Kv, wikipedia goes into details of that relationship in the "Motors Constants" article if one really cares.)

This shows a direct relationship between torque and flux. More flux = More torque.

And it makes sense that it has to work this way. Torque * Speed = Power. You can't just keep increasing the magnetic flux and get more power. At some point you would be drawing more power out then you are putting in, and you would have just invented a perpetual motion machine.

-------------------Start reading here if you don't want to bother with the math----------------------

Here's another way to look at this. If you take a motor just starting to turn, and simplify it down to just a stationary wire carrying current in a magnetic field. It gets some force exerted on it proportional to the strength of the magnetic field and the amount of current. This should make sense to everyone. Lots a torque, zero speed. More magnetic field gives more torque. More current, more torque too. 

Now consider the opposite extreme - a motor spinning at the no-load speed. This is a little harder to visualize. But imagine if the motor was spinning at the no-load speed because you were coasting down a hill - no battery hooked up to the motor (or resistors or anything else). At this point the motor would actually be acting as a generator. So if it was a 24V motor, it'd be putting out about 24V as a generator, but zero current (and thus zero power). It wouldn't slow down the chair because you aren't pulling any of the mechanical energy out as electrical energy. If you then hooked up a 24V battery to it, nothing would change. It would continue to be in balance. But say you made the hill a little bit steeper, now the motor (now acting as a generator) would be putting out 25V, and be charging the battery, and trying to slow the motor (this is regenerative braking). If you made the hill a little less steep, and the motor only generates 23V, then the battery would be pushing it along with just a little bit of energy. Makes sense so far? That voltage that the motor is generating? That's called the Back EMF.

Okay, now let's assume we are back on the slope where the motor was putting out 24V with no battery connected, and everything is the same except this time we put some weaker magnets in the motor. Actually let's make the Magnets exactly half as strong. If we do that the motor only puts out 12v as a generator. Makes sense right? Less magnetic flux, generator puts out less voltage. Great. 

Now let's hook that 24V battery back up to the motor. Well, now there is a 12V difference between the back EMF and the battery voltage. That battery will be pushing that motor pretty hard. How hard? Well, it will push it to nearly twice the original speed. Counter intuitive huh? Less magnetic flux gives a faster speed. 

But there are still good reasons to use neodymium magnets in some applications - for a given flux, they are both lighter and smaller than most other options. However, most neodymium magnets have a lower operating temperature than other types of magnets (about 80C). So one needs to ensure that they stay below that or they will loose their magnetism. All about choosing the right magnet for the application.

*Of course some simplifications were made in the information presented here. Some of the things ignored because they have a small contributing factor (such as the inherent drag on a "no-load" motor) do start to have a noticeable effect at extreme cases such as when the flux approaches zero or the flux approaches the saturation point of the armature core.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 03 Feb 2021, 21:02

Using stronger magnets (or adding more magnets in the right), on a permanent magnet DC motor, gives essentially the same effect as gearing a motor lower (slower speed, more torque). Using weaker magnets (or adding more magnets in the right spot "upside down"), gives essentially the same effect as gearing a motor higher (higher speed, less torque).

I disagree. Having tested this on my bench with smaller hobby motors. You gain a lot of rpm if driving a propellor. Because it increases torque. If free running you also gain a lot of RPM. That is easy to test too.
Stall torque was the same when limited to my bench power supply to 2A. But if set to a high non limiting figure stall torque also uncreses as you can no longer hold the shaft still with fingers!
It might seem counter intuitive, but it's the physics. Math first, but physical example is further down the post.
The no load speed of a permanent magnet DC motor is defined as:

speed = Vt*Kv - Where Vt is the voltage at the terminals of the motor, and Kv is motor speed constant (usually in terms of rpm per volt)
Everyone here is obviously very familiar with this concept however, it is actually more useful to use the back EMF constant (Ke) in the calculation, where the back EMF constant is simply 1/Kv:
speed = Vt/Ke

This still just applies to permanent magnet DC motors, but one can generalize it a bit to cover all DC motors.
speed = Vt/(Ka*phi) - Where Ka is the armature constant and phi is the magnetic flux from the field.

In a PMDC motor, phi is a constant (because it is made by the permanent magnets), so it is typically combined with Ka to give Ke (or Km), but on field wound DC motors, it is variable. Prior to fancy PWM schemes and such adjusting the field current (and thus the magnetic flux) was frequently a way one varied the speed of DC motors.
Anyway, that equation shows the inverse relationship between speed and flux. Less flux = more speed.
However the torque equation for a PMDC motor is as follows:
torque = Kt*Ia - where Kt is the motor torque constant, this time in terms of newton metres per ampere (N·m/A), and Ia is the armature current.

This should be familiar with anyone working on the motor compensation on their chair. It also can be generalized for all DC motors.
torque = Ka*phi*Ia - Where phi is still the flux, Ia is still the armature current, and Ka interestingly enough is the same armature constant as above. (and thus Kt=Ke=1/Kv, wikipedia goes into details of that relationship in the "Motors Constants" article if one really cares.)
This shows a direct relationship between torque and flux. More flux = More torque.

And it makes sense that it has to work this way. Torque * Speed = Power. You can't just keep increasing the magnetic flux and get more power. At some point you would be drawing more power out then you are putting in, and you would have just invented a perpetual motion machine.


But nobody claimed you were getting something for nothing. Current goes up! Across the board. My power supply shows this. And both torque and rpm definitely do increase! At least under load. Even when that load is just some motor bearings and gearbox A free running powerchair motor takes 5 to 7A. Due to windage/grease/bearings. And about 20A flat out on a road or pavement. So the extra magnets speed it up.



-------------------Start reading here if you don't want to bother with the math----------------------

Here's another way to look at this. If you take a motor just starting to turn, and simplify it down to just a stationary wire carrying current in a magnetic field. It gets some force exerted on it proportional to the strength of the magnetic field and the amount of current. This should make sense to everyone. Lots a torque, zero speed. More magnetic field gives more torque. More current, more torque too.


Agreed.
Now consider the opposite extreme - a motor spinning at the no-load speed. This is a little harder to visualize. But imagine if the motor was spinning at the no-load speed because you were coasting down a hill - no battery hooked up to the motor (or resistors or anything else). At this point the motor would actually be acting as a generator.


Agreed.

So if it was a 24V motor, it'd be putting out about 24V as a generator, but zero current (and thus zero power). It wouldn't slow down the chair because you aren't pulling any of the mechanical energy out as electrical energy. If you then hooked up a 24V battery to it, nothing would change. It would continue to be in balance.


True. But I was not refering to driving down a hill. But on the flat. That takes power. At full speed you will be moving at say 80% of the motors free running wheels off deck speed. Andas you say, adding stronger magnets is the same as a ower impedance motor. So now the thing draws more current and the motor goes 90% of the no load speed. Theres no time other than wnen running downhill that the motor load is zero. Typically you are using 150 to 200 watts.

But say you made the hill a little bit steeper, now the motor (now acting as a generator) would be putting out 25V, and be charging the battery, and trying to slow the motor (this is regenerative braking). If you made the hill a little less steep, and the motor only generates 23V, then the battery would be pushing it along with just a little bit of energy. Makes sense so far? That voltage that the motor is generating? That's called the Back EMF.


Absolute sense.

Okay, now let's assume we are back on the slope where the motor was putting out 24V with no battery connected, and everything is the same except this time we put some weaker magnets in the motor. Actually let's make the Magnets exactly half as strong. If we do that the motor only puts out 12v as a generator. Makes sense right? Less magnetic flux, generator puts out less voltage. Great.


I dont know why we are going downhill but OK we will carry on! No I dont think the motor will produce 12V it will produce the same 24V but behaves as a higher impedance motor. But not 100 percent sure.
Now let's hook that 24V battery back up to the motor. Well, now there is a 12V difference between the back EMF and the battery voltage. That battery will be pushing that motor pretty hard. How hard? Well, it will push it to nearly twice the original speed. Counter intuitive huh? Less magnetic flux gives a faster speed.

No. I disagree. The motor will make the same 24V (not sure) and behave as a higher impedance motor, and so will charge the battery less than with the strong magnets.
The magnetic feild doesent determine the open circuit voltage the armature rpm does I think. But it does under load.

When I swap out ferric magnets for rare earth magnets in my RC truck 550 motor for eg (I swapped the motor can over for a better one) I get more torque, and I get more speed. And I get a shorter run time so greater Amps. So that cannot be the case.

But there are still good reasons to use neodymium magnets in some applications - for a given flux, they are both lighter and smaller than most other options. However, most neodymium magnets have a lower operating temperature than other types of magnets (about 80C). So one needs to ensure that they stay below that or they will loose their magnetism. All about choosing the right magnet for the application.

My hobby motors get super hot. Its not really an issue. The motor coils and armature burn up long before the motors casing/magnets get super hot on a powerchair. The real reason is cost.

You may be right about them generating less volts with seaker magnets. I dont understand your formulas. When off this bed I will do some actual tests to find out for sure.

This is a 700 watt rated motor that I regularly run at 1200 watts or more. It turns at up to 54k rpms. And is loud. Its got brushless 2 turn Super low impedance. Runs at 120A and is 26mm diameter. Magnets? If sticking 1200 watts, 120A through these doesent mess up they magnets I dont think a powerchair motor would even tickle them.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 03 Feb 2021, 21:18

I understand that adding extra magnetic feild to reinforce the existing feild only increases torque. But torque is what propels the chair, turn the motor, drives a propeller through the air. So you will get more speed. I also understand that it may not be as fast when theres no load Such as deceleration and going dowhill. But those are the times we dont want to go faster! Anytime you are moving or accelerating or trying to get from A to B then a lower impedance motor or more magnetism is a help.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Yennek » 04 Feb 2021, 02:52

Burgerman wrote:
Yennek wrote:Using stronger magnets (or adding more magnets in the right), on a permanent magnet DC motor, gives essentially the same effect as gearing a motor lower (slower speed, more torque). Using weaker magnets (or adding more magnets in the right spot "upside down"), gives essentially the same effect as gearing a motor higher (higher speed, less torque).

I disagree. Having tested this on my bench with smaller hobby motors. You gain a lot of rpm if driving a propellor. Because it increases torque. If free running you also gain a lot of RPM. That is easy to test too.
Stall torque was the same when limited to my bench power supply to 2A. But if set to a high non limiting figure stall torque also uncreses as you can no longer hold the shaft still with fingers!

When measuring the stall torque, were you using a load cell? or some other quantitative measurement method.
Burgerman wrote:
Yennek wrote:And it makes sense that it has to work this way. Torque * Speed = Power. You can't just keep increasing the magnetic flux and get more power. At some point you would be drawing more power out then you are putting in, and you would have just invented a perpetual motion machine.

But nobody claimed you were getting something for nothing. Current goes up! Across the board. My power supply shows this.

If you were getting the same torque, of course your current went up. You changed the torque constant of the motor. You get less Nm of torque per Amp of current. Just like if you put in a higher ratio set of gears.

Burgerman wrote:And both torque and rpm definitely do increase! At least under load. Even when that load is just some motor bearings and gearbox A free running powerchair motor takes 5 to 7A. Due to windage/grease/bearings. And about 20A flat out on a road or pavement. So the extra magnets speed it up.
Yennek wrote:
-------------------Start reading here if you don't want to bother with the math----------------------

Here's another way to look at this. If you take a motor just starting to turn, and simplify it down to just a stationary wire carrying current in a magnetic field. It gets some force exerted on it proportional to the strength of the magnetic field and the amount of current. This should make sense to everyone. Lots a torque, zero speed. More magnetic field gives more torque. More current, more torque too.


Agreed.
Yennek wrote:Now consider the opposite extreme - a motor spinning at the no-load speed. This is a little harder to visualize. But imagine if the motor was spinning at the no-load speed because you were coasting down a hill - no battery hooked up to the motor (or resistors or anything else). At this point the motor would actually be acting as a generator.


Agreed.

Yennek wrote:So if it was a 24V motor, it'd be putting out about 24V as a generator, but zero current (and thus zero power). It wouldn't slow down the chair because you aren't pulling any of the mechanical energy out as electrical energy. If you then hooked up a 24V battery to it, nothing would change. It would continue to be in balance.


True. But I was not refering to driving down a hill. But on the flat.

Yes, but the example of going down the hill is to help with understanding the concept. Once the concept is understood, it is easier to apply to more non-intuitive situations.
Burgerman wrote:That takes power. At full speed you will be moving at say 80% of the motors free running wheels off deck speed. Andas you say, adding stronger magnets is the same as a ower impedance motor. So now the thing draws more current and the motor goes 90% of the no load speed. Theres no time other than wnen running downhill that the motor load is zero. Typically you are using 150 to 200 watts.

Yennek wrote:But say you made the hill a little bit steeper, now the motor (now acting as a generator) would be putting out 25V, and be charging the battery, and trying to slow the motor (this is regenerative braking). If you made the hill a little less steep, and the motor only generates 23V, then the battery would be pushing it along with just a little bit of energy. Makes sense so far? That voltage that the motor is generating? That's called the Back EMF.


Absolute sense.

Yennek wrote:Okay, now let's assume we are back on the slope where the motor was putting out 24V with no battery connected, and everything is the same except this time we put some weaker magnets in the motor. Actually let's make the Magnets exactly half as strong. If we do that the motor only puts out 12v as a generator. Makes sense right? Less magnetic flux, generator puts out less voltage. Great.


I dont know why we are going downhill but OK we will carry on! No I dont think the motor will produce 12V it will produce the same 24V but behaves as a higher impedance motor. But not 100 percent sure.

If you want to test this with your hobbie motors, you probably can. Hook two of them together mechanically (belt, gears, directly, whatever). On the input motor, give it some known voltage it such that you get a known repeatable RPM out (the motor will essentially be no load). Leave the output motor disconnected from everything except a voltmeter. Then play around with a magnet and identify that in one orientation the voltage increases, and in an opposite orientation, the voltage will decrease. If you note which orientation does which, and then disconnect the two motors and play around with the output motor, you'll find that the orientation that gave the lower voltage will give the higher speed.
Burgerman wrote:
Yennek wrote:Now let's hook that 24V battery back up to the motor. Well, now there is a 12V difference between the back EMF and the battery voltage. That battery will be pushing that motor pretty hard. How hard? Well, it will push it to nearly twice the original speed. Counter intuitive huh? Less magnetic flux gives a faster speed.

No. I disagree. The motor will make the same 24V (not sure) and behave as a higher impedance motor, and so will charge the battery less than with the strong magnets.
The magnetic feild doesent determine the open circuit voltage the armature rpm does I think. But it does under load.


They both do, but in the example I was holding the speed constant when disconnected. The equation for it is Vt = Ka*phi*speed (re-arranging the equation from earlier). Ever played with a generator(not alternator) from an old car (like 60's era VW?) with a separate mechanical voltage regulator? Obviously the speed will be all over the place, and so would the voltage. So what the regulator does, is it mechanically pulses the field coil on and off (like a pwm) using something that sort of resembles a relay. When the armature voltage drops below the desired value, it causes the relay to close, causing an increase in the field current (and increasing flux). This causes the armature voltage to increase, which causes the relay to open, field decreases, voltage decreases, cycle repeats.

Burgerman wrote:When I swap out ferric magnets for rare earth magnets in my RC truck 550 motor for eg (I swapped the motor can over for a better one) I get more torque, and I get more speed. And I get a shorter run time so greater Amps. So that cannot be the case.


Did you directly measure the torque produced at various speeds (especially zero speed)? Or is this visual observation? Remember if you change the magnets in a motor, you are changing the torque constant, so you can't just use the current (amps) to compare the torque between the two.

Burgerman wrote:
Yennek wrote:But there are still good reasons to use neodymium magnets in some applications - for a given flux, they are both lighter and smaller than most other options. However, most neodymium magnets have a lower operating temperature than other types of magnets (about 80C). So one needs to ensure that they stay below that or they will loose their magnetism. All about choosing the right magnet for the application.

My hobby motors get super hot. Its not really an issue. The motor coils and armature burn up long before the motors casing/magnets get super hot on a powerchair. The real reason is cost.

Hot is of course a relative term :) And admittedly my motors textbook is copyright 1997, so maybe those materials engineers improved the thermal performance in the past 25 years. And yes, cost is a reason not to use them if your application doesn't need them. A powerchair probably won't notice a difference in the weight. Size, well maybe? I could see if why one would want them if you had to cram a lot of them in a small space like on the Invacare style brushless motors.(Maybe they do use them? I've not ever had the chance to inspect a disassembled one up close.)
Burgerman wrote:You may be right about them generating less volts with seaker magnets. I dont understand your formulas. When off this bed I will do some actual tests to find out for sure.


I'd give you the name of the text book we used in my electromechanical energy conversion course, but I don't think it was written very clearly to start with. There's probably better out there. If I come across a good website I may pass it along too. And I totally hope you do some tests. Being in a lab, doing hands on, was my favorite part of school and is still a highlight when my job puts me back there.

Burgerman wrote:This is a 700 watt rated motor that I regularly run at 1200 watts or more. It turns at up to 54k rpms. And is loud. Its got brushless 2 turn Super low impedance. Runs at 120A and is 26mm diameter. Magnets? If sticking 1200 watts, 120A through these doesent mess up they magnets I dont think a powerchair motor would even tickle them.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 04 Feb 2021, 03:24

Torque measured by holding small motor shaft with fingers.
And torque measured by RC car ability to climb a slope at fixed angle an fixed volts, on a known angle. Speed(rpm) by watching the truck! And by sound. So a bit subjective but obvious enough. Will experiment more when I get off this damned bed. But your theory seems sound. But seems to go against what I see. Experiment needed...
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 04 Feb 2021, 03:27

Torque measured by holding small motor shaft with fingers.
And torque measured by RC car ability to climb a slope at fixed angle an fixed volts, on a known angle. Speed(rpm) by watching the truck! And by sound. So a bit subjective but obvious enough. Will experiment more when I get off this damned bed. But your theory seems sound. But seems to go against what I see. Experiment needed...

Of course torque is limited on ferric magnets because the feild coil strength overpowers them at some relatively low current or other. And that happens at a much higher level with the rare earth magnets in the small hobby motors and the truck 550 motors.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Yennek » 04 Feb 2021, 03:48

See if this plot helps a little bit. It should look pretty familiar, but each of the lines represents an otherwise identical motor, but with a different amount of field flux. Note that the armature current is shown on the left side, and it is different depending on the flux. And this is all at the same voltage.

So yes if you increase the flux to "red", yes you will have more Torque at say speed 0.9, and certainly more at say speed 1.5 (because green at that point has negative torque and would be a generator). But from stand still to about 0.75 the Green flux will have more torque. And of course the Green and especially the Red have more torque at a stand still.
Attachments
Torque Speed Flux (1).png
Torque Speed Flux Graph
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Yennek » 04 Feb 2021, 04:12

And if I'm remembering my lectures correctly, there is another neat property shown on that plot. If you notice, the area of the triangle made by each of those lines is the same (0.5 sq. units). That area will be the same for any motor with that amount of copper used in the windings, or strength of magnet. Whether 10 heavy wire wraps per coil, or 100 fine wire wraps per coil, if the amount of copper is the same, the area will be the same, it will just change the torque-current and voltage-speed relationships.

The logic behind this is that you only have to flow 1/10th the amount of current through the 100 wrap coil when compared to the 10 wrap coil to get the same torque, but you have 10x the resistance. But by using a more conductive material for wire, you can increase the area under the lines, and thus actually improve performance across the board. However, there aren't many metals less resistive than copper, and I don't think any are as cheap or easy to work with. Silver comes close on most points, except cost. And it is about 5-6% less resistive. If one could develop a room temperature super conductor, then that would basically eliminate the resistive losses in the motor. However you would still have the rotational losses, core losses etc.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Yennek » 04 Feb 2021, 04:25

Yennek wrote:... but you have 10x the resistance...


Logic error, should be 100x the resistance? because 10x length but also 1/10th wire cross section area. Hmmm.
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Re: 8.5mph motors sunrise - how much at cost ?

Postby Burgerman » 04 Feb 2021, 14:49

However when you consider that the motor is current limited by the controller, at the low end, and that unless you start going downhill, that you have friction and air to overcome and so are probably only ever at 80% max speed compared to an unloaded motor, adding a little extra magnetism to the outside can probably does give an improvement everywhere.
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