torque Values

[ThomasKaeding]

[size=200][size=150]Good Morning everyone,
My name is Thomas and I am new to the forum Very cool forum. You guys have most definenitly taken it to a new leval. I have my first question.
How is the torque of a brushed motor established or figured out? I have been reading about the BM3 and am trying to establish a baseline at a given voltage and amperage. Thank you and Hello again to everyone.
Thomas[/size][/size]

[Burgerman]

Hi. You need to know the motor manufacturers specs. Without those you can only really generalize. or compare.

If efficiency is about the same, you can guess approximately that:
A 4 pole will have a higher stall current than the controller allows and so is limited to the same peak level. So at stall, voltage makes no difference. As a 24v battery, or 48v battery will both be reduced at the controllers output to the same pulse-width. Or voltage. To limit current to the same motor value.

And that a 4mph motor will have double the torque of an 8mph motor at the same current limit. The driving current will be halved in most situations. And a 48v battery will double peak rpm giving you the lost speed back, for free!

[ThomasKaeding]

Thank you for the reply. I'm in the very early stages of sourcing brushless hub motors controlled by a Roboteq controller and powered by a LifePO4 battery pack and inputs will be via an Apem joystick. I'm following your lead Burgerman. It's going to be a significant task for sure. The motors have been difficult due to the very "sparse" information available out of Asia. I'm truely takeing the monumental task 1 step at a time. So essentially I am trying to establish a (minimum torque) for a 4 Wheel Dr. outdoor chair.
Thomas

[ThomasKaeding]

Thank you for the reply. I'm in the very early stages of sourcing brushless hub motors controlled by a Roboteq controller and powered by a LifePO4 battery pack and inputs will be via an Apem joystick. I'm following your lead Burgerman. It's going to be a significant task for sure. The motors have been difficult due to the very "sparse" information available out of Asia. I'm truely takeing the monumental task 1 step at a time. So essentially I am trying to establish a (minimum torque) for a 4 Wheel Dr. outdoor chair.
Thomas

[Burgerman]

If this is for a powerchair Chinese hub motors wont work well for a bunch of complex reasons.

[ThomasKaeding]

I am beginning to see that. Rpm's that are published in the specs are much too high, I can't get input amperage to run by the guys at Roboteq I can't even speak to an engineer other than to tell me "cost per unit and shipping". This is the primary reason that I am taking this very slow and joined this forum. I have a budget but I am not going to haphazardly waste my customers money. Any this is the primary reason that I am taking this very slow and joined this forum. I have a budget but I am not going to haphazardly waste my customers money. Any sources/ideas for Hub motors for this application I am all ears.

[Burgerman]

You need a different "type" of brushless motor that has much less cogging, more starting torque etc. And that uses some quite involved controller to do so. The alternative is to do as will on this forum does. He has some custom made motors to his spec, and uses belt or chain drive.

For the direct drive, gearless brushless, right now theres only one viable option. And its relatively cheap!

Read the first half dozen posts here. viewtopic.php?f=2&t=6628

[shirley_hkg]

BEWARE !

Controller with TrueTrack feature , like INVACARE , is not a good candidate for 4WD .

They tend to act on each others at turns . That costs huge currents .

[Burgerman]

Dont think he is doing 4x4?

Even if he does that doesn't work well anyway, with any motors, as it takes way too much power to skid steer on good grippy surfaces. Requires huge power to turn properly that EVs dont really have.

[ThomasKaeding]

I am very very appreciative of the incredible level of expertise that you guys share with me. But I kind of got a little bit away from my initial question and that was how many foot pounds/NM does the BM3 motor produce at a maximum safe level

[Burgerman]

No actual figure. So couldn't say.

At what Amps though? The 8.5mph ones are usually paired with 120A controllers. At that level they give about the same as a 6mph motor on an 80 Amp controller should you be able to find any actual figures. I am using a 150A controller, usually set to limit current at 130A and at 45 volts, this level of current isn't only possible at stall, as it would be with a 24V system, but right up to half speed, or about 8mph.

So acceleration can be rather brisk... Unlike a 24V system where max current falls away as speed increases from stall onwards, it remains constant. And so peak torque is constant and doesn't drop up to any normal speeds. So you need to make sure that this is adequately controlled by setting up your acceleration rates, and motor load compensation, and max current limits with care to be sure not to damage the motors or flip the chair.

[ThomasKaeding]

Well, I found a brushless motor that has a torque spec of 120 NM at 48 V and 55 A. Basically I am trying to establish what is too small or to low for a power chair. The Robotech HBL 2300 series operate at 60 V and 75 A max.

[ThomasKaeding]

The company that manufactures this brushless motor has a series of motors that go to 400 mm torque of course much higher amperage . Trying to establish what is over Spec'ing the motor and what is under Spec'ing the motor

[Burgerman]

Well I use a 15 degree ramp at the pub. That looks very steep. Total weight 48 stone with lead bricks and 20 stone occupant. A quick beer mat calculation shows I need about 15 stone of thrust at each wheel to steer, control properly and go up. And I can quite easily. Although its probably wrong... You need a 50 percent reserve/headroom to steer?

That then requires 210lb of "thrust" per wheel. That wheel is 14.4 inches diameter. So if the wheel was 24 inch diameter (12 inch radius) we would need around 210ft/lb torque. Fortunately its not! So we only need just over half of that. So 130ft/lb would be ball park. Nm I dont know... But google says 176? But thats rough... Its also only at stall, if motor impedance is high, and maybe at speed if its low.

And your 400nm torque is limited by the controller amps. So don't let low impedance fool you you WANT that because otherwise a turn, at say 25% pulse-width or less will do nothing... And it wont zero steer. You need impedance low enough that it draws a LOT of amps with a small stick movement. Remember that turn RATE will be typically 35% pulsewidth at FULL stick, and it may take 100A to initialise a turn on the spot. I doubt you will find any hub motor with enough smoothness at really slow speeds, and enough torque at low pulsewidth and adequate torque. Although 48V gives you a better chance.

[ThomasKaeding]

Wow, thank you Blurgerman. I have a lot to consider and a lot to think about. One step at a time. Thank you again sir

[Burgerman]

Consider this as it will really hurt your brain.

If stall current is limited by the controller software at 100A as it often is (or should be) the only thing that changes is pulse-width.
Lets say the motors natural Amps at 24V stalled is 100A. And to keep it simple full speed is 10mph.
Under Stall condition, with these motors, pulsewidth will be at max or 100% and the controller will not be limiting it.

If the chair does 10mph at 100% pulsewidth, and you suddenly gun it, the it follows then that the acceleration rate falls away in linear fashion, until a friction-less top speed is achieved at zero Amps. (we are in a vacuum!) This happens because of the generator affect of the motor. As speed increases the motors voltage rises to match the battery.

Now consider this...
To have a sensible (zero speed) turn on the spot mix rate you will only want about 1mph on each drive wheel in each direction or your legs will fly off the footplate! So that means you set that turn speed (turn rate) parameter in the controller software/programming low.. 1 mph per motor is 10% of your 24V or 10% pulse-width, 2.4V. So you push the stick FULLY sideways on say a carpet, or grass, and nothing happens. Because thats means just 10A to each motor... Watch this. This is a clamp meter. Hooked over ONE motor wire. http://www.wheelchairdriver.com/gopro/motoramps.mp4

As you can see, 10A isn't going to get you far when turning!!! The reason that it gets 100A here INITIALLY, is because there are some current sensors inside the controller. They look at motor current, and ADD pulswidth! A positive feedback system. Its a bit of computer code called Load Compensation. Usually entered in mOhms in the software settings. So thats what causes it to jump from 10A to 100A! Its helping you behind the scenes. Once friction is overcome, amps then drop back to your 10% before your chair spins out of control.

Now, increasing voltage, or lowering impedance helps. Or using some kind of counting in a brushless controller, to determine position helps. And thats what the Invacare motors/controller does. Hence the TT or True Trac name...

You are in for a very steep learning period! Its easy on the face of it... But its not!

[ex-Gooserider]

Somebody, I think it was WoodyGB, posted a spreadsheet that did a lot of the motor calculations for you, I think it was originally developed for the electric bike folks, but it seemed useful to the degree that I played with it... Not sure if it does anything with brushless motors or not, but it should be able to give you values for the brushed motors....

ex-Gooserider

[faico_26]

Consider this as it will really hurt your brain.

If stall current is limited by the controller software at 100A as it often is (or should be) the only thing that changes is pulse-width.
Lets say the motors natural Amps at 24V stalled is 100A. And to keep it simple full speed is 10mph.
Under Stall condition, with these motors, pulsewidth will be at max or 100% and the controller will not be limiting it.

If the chair does 10mph at 100% pulsewidth, and you suddenly gun it, the it follows then that the acceleration rate falls away in linear fashion, until a friction-less top speed is achieved at zero Amps. (we are in a vacuum!) This happens because of the generator affect of the motor. As speed increases the motors voltage rises to match the battery.

Now consider this...
To have a sensible (zero speed) turn on the spot mix rate you will only want about 1mph on each drive wheel in each direction or your legs will fly off the footplate! So that means you set that turn speed (turn rate) parameter in the controller software/programming low.. 1 mph per motor is 10% of your 24V or 10% pulse-width, 2.4V. So you push the stick FULLY sideways on say a carpet, or grass, and nothing happens. Because thats means just 10A to each motor... Watch this. This is a clamp meter. Hooked over ONE motor wire. http://www.wheelchairdriver.com/gopro/motoramps.mp4

As you can see, 10A isn't going to get you far when turning!!! The reason that it gets 100A here INITIALLY, is because there are some current sensors inside the controller. They look at motor current, and ADD pulswidth! A positive feedback system. Its a bit of computer code called Load Compensation. Usually entered in mOhms in the software settings. So thats what causes it to jump from 10A to 100A! Its helping you behind the scenes. Once friction is overcome, amps then drop back to your 10% before your chair spins out of control.

Now, increasing voltage, or lowering impedance helps. Or using some kind of counting in a brushless controller, to determine position helps. And thats what the Invacare motors/controller does. Hence the TT or True Trac name...

You are in for a very steep learning period! Its easy on the face of it... But it’s not!

I need to get a clamp meter to measure how may amps my Q300R with 4 pole motors draw on a 90amp unit. Low curbs of 3 cms and the motors stall which drives me crazy. I’m using VR2 90amp. And the chair moves slower and lazy on grass or thick carpet. Why is that? I mean, it does NOT stall on grass but the control unit reduces power I Guess because of the high amps that the motors draw. Can it be changed with programming to NOT reduce power when riding on grass or similar??

[Burgerman]

The controllers can only provide full current if impedance is low enough or the motor is not turning (stall current) and if load compensation and torque setting is high enough to do so.

The actual amps at the motor depends on all those things. As a chair moves from 0mph to say 3 mph on a 6 mph chair its motor which is a generator too, is now PRODUCING 12V... So now, even if there was no controller in between battery and motor it wouldnt draw that many Amps anyway as you are only applying half the 24V battery voltage. Thats 12V more than the motor is already making on its own So the faster you move the less current is pulled from the battery regardless.

The controller itself has some internal logic that does many things.
It reduces max current over a time limit. This can be 1 second, 3 seconds, 10 seconds...
It reduces max current due to the mosfet temperatre internally. This may begin happening at say 45C and it increases over time/temperature in seconds or minutes depending on history / current boost limits etc.
As a motor internal windings warm up as current increases those too increase in resistance and now draw less current too.

Since most of these settings are at a lower level than any programmer has access to, may vary with firmware versions etc we cant really know how its configured behind the sccenes.

There are a FEW settings that we can CAN change. This is for NEW VR2.

BOOST DRIVE CURRENT - can be set too low? Set to 90 which is max!
CURRENT LIMIT - can be set too low? This is the max current AFTER BOOST ENDS! Set to 80 Max.
BOOST CURRENT TIME - can be set too low? 1 to 10 secs I think on VR2, set to max! But this will heat it up...
BOOST CURRENT FOLDBACK - can be set too low... This is where it goes after the boost ends.
CURRENT FOLDBACK TIME - Set too low?? This is where the 80A normal leve you set above goes when its out of time.
CURRENT FOLDBACK LEVEL - same shit... This is where it drops to when its done its 80A bit.
CURRENT FOLDBACK TEMPERATURE? This is independent of the above, and reduces max current available due to mosfet internal temperature that happens fast under high currents.
CURRENT LIMIT MINIMUM? Dont know what that does???
COMPENSATION? This if set low will absolutely limit current available in ALL scenarios... Like most chairs.

Not sure a current clamp meter will tell you much.

[Burgerman]

Remember that the more you increase the settings that allow power/torque the faster it heats up and the faster the temp rollback happens.

The real answer is a 120A controller. Same happens but it has higher output before it gets rolled back.

[shirley_hkg]

A clamp metre may or may not give you the information. What's next if you had those values. Sue the manufacturer ?

Most of all, you can't change anything, can you ? You are on the wrong direction.

I bought a USB link (£25) recently on a Chinese site to re-program a VR2 pm. It does what I want. Software is from this site.

That brings back a lost puzzle which we missed since woodygb passed away.