Need help choosing a BLDC hub motor controller-Torque mode

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Rimwithbrim   1 µW

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Need help choosing a BLDC hub motor controller-Torque mode

Post by Rimwithbrim » Feb 13 2019 8:28pm

Hi All,

Complete newb here. I am working on a project that involves driving a 5-10kw hub motor. I am having some difficulty figuring out what motor controller to use though. I have been doing some research and have some ideas but I thought this might be a great place to see if some season veterans in this arena could give me some guidance. I'm worried I am having some nomenclature misunderstandings... I have two main requirements:

-Torque control scheme-where I am able to hold a throttle position and the torque will remain more or less constant at that setting while the rpm of the hub motor varies to accommodate the load encountered by the hub motor. Speed control is at the bottom of the list in terms of control needs or should be secondary. This application is similar to a constant tension device for a paper mill etc. where the diameter of the roll changes but the paper needs to be put on evenly tension wise.

-Proportional regenerative braking to near zero speed rpm- I need the controller to be able to provide braking proportionally by an input signal (preferable with something simple like a potentiometer). In this application the motor will be used as a brake which provides constant tension at 70% max torque load for about 5-7 mins of time while turning roughly 100-200rpm give or take. Pretty demanding I know...

The motor will be a hub motor designed for scooter with hall sensors by QS.
72-84v and about 5-10kw depending on motor. Expected amperage will be in the neighborhood of about 100-150.

I have spoken with the kelly controller people a little bit and it seems like they may have a controller that will do this but I am having a hard time understanding if this torque mode is possible. Kelly has stated it is a speed control loop only while the motor company I'm speaking with has suggested that the kelly controller can operate in the torque scenario. I had to explain it a little differently using a scooter going along a flat surface at a constant throttle and then encountering a hill...will it slow down to match the throttle setting or remain going the same speed? The motor people suggested the motor will slow down if the scooter encounters a hill. I'm having a hard time thinking these controllers would operate any other way but when I hear speed control loop it makes me think it will hold a constant speed at a certain throttle setting?

Before I drop the $1500 on motor and controller, I want to be sure I know that I haven't miss communicated or misunderstood something (highly likely knowing me :))

Can anyone confirm or direct me to a controller company that makes something that will work in the torque modes? The one being suggested to me currently is (KLS96601-8080H) I am fine with buying something slightly overkill to deal with power requirements for regen etc. as reliability is at the top of my list.

Thanks much in advance!

J

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by billvon » Feb 14 2019 12:54am

Rimwithbrim wrote:
Feb 13 2019 8:28pm
72-84v and about 5-10kw depending on motor. Expected amperage will be in the neighborhood of about 100-150.
Phaserunner would get you about halfway there. Good to about 90 volts and peak phase current of 96A (~45A continuous.) You might consider a _very_ well heatsinked version.
--bill von

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by amberwolf » Feb 14 2019 2:09am

At least *some* of the Kelly line can do torque (current) throttle control. I dont' remember which ones, but if you poke around for Kelly and Torque and Throttle some of the posts about them are bound to pop up.
https://endless-sphere.com/forums/searc ... mit=Search

But I don't know any from any brand that will brake the way you want down to zero that will hold a specific RPM. (could be some...I don't know about all that many controllers)

However, you can build a circuit that would monitor RPM and hold the brake to a specific point that keeps that RPM, and if it changes RPM it changes the brake to put it back.

The Cycle Analyst from http://ebikes.ca might be able to be used for this, using it's throttle output to control the brake, in speed-throttle mode, using the throttle input as the RPM setpoint input, with the wheel speed sensor as the RPM input.

(the CA can also be used to turn any regular open-loop PWM-throttle controller into a form of torque (current) throttle controller, by intercepting the throttle signal and monitoring battery current, and using feedback from that to allow the throttle to control the current.

Good torque (current) throttle mode controllers actually monitor phase current to do this rather than battery current, but either one works better than just the open-loop PWM throttle type. ;) )

There are also controllers under development here on ES:

You'd have to ask him about the braking part, but Incememed's SFOC5 does torque (current) control well and smoothly, and can have a mode where reducing the throttle input causes it to apply power reduction to the wheel such that it actively slows it down to "brake" it, though I have not tested this part myself yet, so don't know if it can go to zero.

Lebowski's controller chip can also do active braking, but I think that at some point he had disabled it's abiltiy to literally go down to zero for reasons I can't recall, but it should still go pretty close to zero. It's a completely DIY controller, but there are numerous threads about building them, including Arlo1's high power powerstage development thread (and at least one ohter member I can't recall the name of).


Also, note that those that will brake down to zero aren't doing *just* regen, they are actually actively braking the wheel by pushing more power into it, reversed from the usual pulses to move it forward. This heats the wheel and the wires and the controller, more than using it as a motor normally does.

To do this continuously for minutes at a time, especially at low RPM, is probably going to require extra cooling measures for the entire system. Possibly significant ones.

My SB Cruiser trike uses this mode for braking, with generic controllers. If I do my commute and use only mechanical brakes, the motors are not all that hot when done, though fairly warm. But if I use the EABS braking isntead, they can be quite hot, especially in summer. Not too hot to touch, but hot enough to be uncomfortable to keep my hand on.


Is the project for a winch, like wakeboarding, or glider launching, balloon reeling, or something similar?

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by John in CR » Feb 14 2019 4:49am

No controller for vehicles is going to do what you're asking. ie a fixed amount of torque with rpm varying with load. Then on top of that you want it to be able to handle a duty of 5-7min at a time at 70% of max torque while turning low rpm, while somehow acting as a brake. Our vehicles aren't ridden like that, so controllers aren't designed to deliver torque in that manner.

Also, take AW's cooling warning seriously. High torque means high current and our hubmotors main loss is copper losses, which go up with the square of current. Power = torque x rpm, and since you'll be running at the low rpm end of the scale, that means it's relatively low power output. Power input will be high since voltage hasn't changed and current is high to achieve the torque. This equates to low efficiency, which means turning much of the power drawn from the battery into heat (primarily in the motor) instead of work. To make matters worse, the motor doesn't dissipate heat as well at low rpm.

My advice for a durable system would be to use a gear reduction, so your typical torque demand is a relatively low% of peak torque potential. Then your motor will be running on easy street and in an efficient range of operation, which is how electric motors are used in industrial applications.

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by Merlin » Feb 14 2019 7:08am

my 2 cents to this wishlist:

Kelly has not a single controller what have a torqmode. no matter if they put this in their specslist.
they havent. Its all time only a speedthrottle and i dont get it why a company like kelly doing this.

about the braking to zero with ebrake: kellys variable braking on KLS controller works. but not that powerfull on speeds where you need it.
if you could buy an adaptto controller these days, it would fit better in terms of throttle (torque) and ebrake.

from ASI you will not find many "reviews". Nucular you have to wait months but for now it seems to be the "adaptto killer".

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by markz » Feb 18 2019 3:25pm

Merlin wrote:
Feb 14 2019 7:08am
Nucular you have to wait months but for now it seems to be the "adaptto killer".
I just had to search

http://nucularelectronics.wikidot.com/e ... ller-setup


https://evmc2.wordpress.com/2014/12/05/ ... e-control/
I never paid much attention to Torque Control myself
but I decided it would be a better thing to try to learn exactly what the difference was, and why you’d want to use one over another.
Pure torque control dials in the current to feed the motor until it gets to the requested speed. Torque control still has to monitor the speed, and yes, it controls the voltage, but that’s done as a secondary step (to put it in a way that will drive most EEs nuts). It’s a way of dialing in the rotational force until you reach a desired RPM.
It is all very interesting.

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by amberwolf » Feb 18 2019 10:01pm

markz wrote:
Feb 18 2019 3:25pm
I just had to search

http://nucularelectronics.wikidot.com/e ... ller-setup
its also in the for sale section of es

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by Rimwithbrim » Feb 18 2019 10:39pm

Thanks to everyone for chiming in. much appreciated!
amberwolf wrote:
Feb 14 2019 2:09am

But I don't know any from any brand that will brake the way you want down to zero that will hold a specific RPM. (could be some...I don't know about all that many controllers)

However, you can build a circuit that would monitor RPM and hold the brake to a specific point that keeps that RPM, and if it changes RPM it changes the brake to put it back.
I may have mispoken above. I'm not really trying to hold a specific rpm in either driving or regen modes. Rather just trying to control the torque output of the motor (when driving the motor) and let rpms dictate themselves by load encountered. The braking force needs to essentially do the same but has the nuance of needing to brake down to close to zero speed for momentary periods.
amberwolf wrote:
Feb 14 2019 2:09am
Also, note that those that will brake down to zero aren't doing *just* regen, they are actually actively braking the wheel by pushing more power into it, reversed from the usual pulses to move it forward. This heats the wheel and the wires and the controller, more than using it as a motor normally does.

To do this continuously for minutes at a time, especially at low RPM, is probably going to require extra cooling measures for the entire system. Possibly significant ones.
Gottcha. I suspected this is how they were operating since I've read about "novel ABS" methods of braking. The braking side of things will be generally operating in the 100-300 rpm range so shouldn't be stopped completely for a long time but it needs to be able to stop completely under load for the system to operate correctly for short periods of time. I'm not sure at what point the voltage/rpm generated is enough to provide actual charging...

Sounds like this is challenging heat wise for the duration I want. If the motor has a thermistor, it should just shut down if it gets too hot I think?

I have seen some really cool water cooled hub motors before but I'm hoping to not go there...The braking side is likley going to be a trial and error scenario to see how long it takes to get to hot.
amberwolf wrote:
Feb 14 2019 2:09am

Is the project for a winch, like wakeboarding, or glider launching, balloon reeling, or something similar?
you could probably say all of the above :-)

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by Rimwithbrim » Feb 18 2019 10:54pm

Merlin wrote:
Feb 14 2019 7:08am
my 2 cents to this wishlist:

Kelly has not a single controller what have a torqmode. no matter if they put this in their specslist.
they havent. Its all time only a speedthrottle and i dont get it why a company like kelly doing this.

about the braking to zero with ebrake: kellys variable braking on KLS controller works. but not that powerfull on speeds where you need it.
if you could buy an adaptto controller these days, it would fit better in terms of throttle (torque) and ebrake.

from ASI you will not find many "reviews". Nucular you have to wait months but for now it seems to be the "adaptto killer".
I tried to reach Adaptto but couldn't reach them. Are they out of business?

I will check on the others. Thanks!

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by amberwolf » Feb 18 2019 11:45pm

Rimwithbrim wrote:
Feb 18 2019 10:39pm
The braking side of things will be generally operating in the 100-300 rpm range so shouldn't be stopped completely for a long time but it needs to be able to stop completely under load for the system to operate correctly for short periods of time.
Essentially what the controller has to do for what you want is to actually reverse the motor direction, but only with enough torque to balance the load.

So you might want to look into torque-control type controllers that have an on-the-fly reverse function, that don't have to drop to zero RPM (and hold that for however long) before they can reverse, rather than controllers that can do specific braking types.

A stopped motor is going to have full current flowing, because there is no BEMF to counter it, and it is going to get very hot very fast if there is a load on it trying to turn it against that. It can be done...but you're almost certainly going to have to come up with a cooling system for both the controller and hte motor, and you're going to need a pretty big battery or power supply to handle that kind of current flow.

How much cooling, and how much battery/etc, depends on how much current you need, and for how long.

You may have to experiment to find out (and be prepared for catching escaped smoke ;) ).


I'm not sure at what point the voltage/rpm generated is enough to provide actual charging...
Depends on the motor winding vs the system voltage, and the design of the controller.

If you want that to happen, you need to pick the motor winding so it is going to be at that voltage at the RPM you would be braking at.

However, the winding also determines the speed at which it will spin at a particular voltage. So...it's a compromise.

I recommend going to http://ebikes.ca/simulator and experimenting with it to learn some about how these all interact, since there are a number of motors listed there that are identical other than their windings.



Some controllers are just rectifying the 3phase from the motor, once it spins fast enough to generate avoltage higher than the battery voltage...many or most of the more modern controllers do synchronous rectification where they use the motor coils as flyback devices, shorting the phase leads for a moment to generate braking, then releasing the short to get a voltage spike that then regens to the battery which also generates braking.

But the lower the RPM, the more challenging it is to brake, because it takes more current to stop it (and it's much harder to get anything back out of it). (it's pretty much just like using it as a motor, except for the sign of rotation).

Sounds like this is challenging heat wise for the duration I want. If the motor has a thermistor, it should just shut down if it gets too hot I think?
You're gonna want that in both controller and motor, and possibly in the battery or power supply, too. :)


FWIW, there are some threads here on various winches built from hubmotors/etc. IIRC Bazaki has several. Dunno if they ahve anything useful to you, but would be worth a poke around. :)

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by Rimwithbrim » Feb 19 2019 11:51am

amberwolf wrote:
Feb 18 2019 11:45pm

So you might want to look into torque-control type controllers that have an on-the-fly reverse function, that don't have to drop to zero RPM (and hold that for however long) before they can reverse, rather than controllers that can do specific braking types.
This would be very sweet. Not sure it will actually need to reverse but in an ideal world...
amberwolf wrote:
Feb 18 2019 11:45pm

A stopped motor is going to have full current flowing, because there is no BEMF to counter it, and it is going to get very hot very fast if there is a load on it trying to turn it against that. It can be done...but you're almost certainly going to have to come up with a cooling system for both the controller and hte motor, and you're going to need a pretty big battery or power supply to handle that kind of current flow.

How much cooling, and how much battery/etc, depends on how much current you need, and for how long.

You may have to experiment to find out (and be prepared for catching escaped smoke ;) ).
oh man...lol. that sounds terrifying...
amberwolf wrote:
Feb 18 2019 11:45pm

I recommend going to http://ebikes.ca/simulator and experimenting with it to learn some about how these all interact, since there are a number of motors listed there that are identical other than their windings.
Will do..

Thanks much for the help!

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by amberwolf » Feb 19 2019 10:48pm

Rimwithbrim wrote:
Feb 19 2019 11:51am
amberwolf wrote:
Feb 18 2019 11:45pm

So you might want to look into torque-control type controllers that have an on-the-fly reverse function, that don't have to drop to zero RPM (and hold that for however long) before they can reverse, rather than controllers that can do specific braking types.
This would be very sweet. Not sure it will actually need to reverse but in an ideal world...
For what you are after, for fully stopping the motor (cable, etc) I think it does actually need to run in reverse, because you won't likely get one that can do the braking like you want. I know of none that can brake to zero...just almost to zero. (Lebowski's DIY type used to, but it doesn't anymore, because of the heat / etc problems AFAICR.)

So using one that can reverse, instead of braking, *will* do what you want, simply by reversing (pulling, instead of pushing or reeling out) to the specific torque needed to counteract the pull of the line (or whatever) so that motion is stopped.

If you don't need the motor to actually reel out under power, but only reel in, then it doesn't have to reverse *or* brake. You'd simply reduce motor power to less than the torque level applied on the cable (or whatever) to allow it to reel out if you want a controlled reel-out, and apply more torque to brake it.


If you want to avoid the *really* high currents of completely stopping the motor, I think you will probably want to instead make a solenoid brake to latch the reel in a stopped position.

You coudl simply add ramps on the motor's circumference, and solenoid controlled pawls, so that during reel-in they won't get in the way (just liek a freewheel). Then during reel-out, the solenoids activate to pull the pawls away from the ramps to allow motion, but when you need to actively hold the cable at that spot, you can deactivate them to let the pawls grab the ramps and stop the motor. (at the same time you can then cease powering the motor).

THen power up the motor just an instant before you reactivate the solenoids so the motor takes the load off the pawls first, allowing them to release without stress.

THe solenoids would be deactivated by default so that the pawls would allow the reel to lock when no power is applied, so that a power or system failure wouldn't just let cable reel out unstoppably. :)



You could also use a motorcycle or car disc brake (or drum or other type, something that can dissipate a lot of heat without distortion) and also arrange it so the brake is engaged by default, and only released by powering it's mechanism up.

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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by flippy » Mar 14 2019 10:09am

might want to get back to the orginial demands and why.

real tourque control is NOT something you want on a moving vehicle. i set my sevcon to torque mode once to see what all the fuss is about and its bascially undrivable in that mode once you are putting down double digit kW's. and sevcon has REAL torque mode. its only used on serious industrial machines where the sevcon is designed for.
probably on the regular sub 2kW builds here it might drive differently but a pure torque setup (bascially how a CNC motor would be programmed) its completly useless. sevcon tells you this in captial letters everywere in the manual.

i built scooters and motorcycles generally with kellys for this very reason as my go to controller. they are cheap, can be customized as much as you want, i do miss some things but those are functions you only see in the sevcon pricerange.

if you have not chosen the motor and controller i want to recommmend getting the highest voltage you can get in both controller and motor config. so that is about 144v.
this will reduce the amps between the controller and battery wich makes for a much more controlled setup. no need to 300A+ setup with heavy duty busbars or whatever. less amps is better. it makes construction and dealing with amps a lot less complicated.
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Re: Need help choosing a BLDC hub motor controller-Torque mode

Post by amberwolf » Mar 14 2019 5:44pm

flippy wrote:
Mar 14 2019 10:09am
real tourque control is NOT something you want on a moving vehicle.
That's quite a condemnation, and I think you may be mistaken about which mode you're referring to.

If it *were* true, I'd feel sorry for all those poor sods driving EVs, since they're probably all controlled that way.

They're just about certainly not done by "speed" control, which is the other common option on ebikes and various cheap controller types, at least. "Power" control is essentially the same feel as torque (current) control, just adding the varying voltage drop in along with the current, and not a mode I recall seeing in the various commercial high-power large-vehicle controllers I've read about over the years.
I set my sevcon to torque mode once to see what all the fuss is about and its bascially undrivable in that mode once you are putting down double digit kW's.
Sounds like your throttle itself (or the throttle response curve programmed into the controller) is simply too sensitive, either along the whole range or just at the lower end.




My SB Cruiser trike, using Incememed's SFOC5, which uses torque (current) control, 1:1 throttle to current ratio, is easily "drivable", at about 4kW peak power )14s pack, 150A phase current limit, 80A battery) with just that controller and an MXUS 4503 motor. (once I finish the phase wire upgrades, I can probably safely up that significantly, as long as it doesn't break the axle again).

I'd bet there are plenty of others here on ES (and elsewhere) riding very "drivable" bikes and assorted other EVs using torque control throttle mode controllers, with much more than 2kw of power on tap, and probably a lot higher power-to-weight ratios than my trike.

flippy wrote:
Mar 14 2019 10:09am
probably on the regular sub 2kW builds here it might drive differently but a pure torque setup (bascially how a CNC motor would be programmed) its completly useless. sevcon tells you this in captial letters everywere in the manual.
Strange. I couldn't find this in the few online manuals I found, like this one:
http://www.thunderstruck-ev.com/Manuals ... l_V3.0.pdf
I *did* find that *SPEED* mode is not recommended for on-highway vehicles. This warning is repeated later in the manual, as well. Neither one is in capital letters, but they *are* bolded print.
Torque mode
In this mode Gen4 maintains the motor torque output at a constant value for a given throttle position.
This is similar to DC motors (in particular, series wound DC motors) and provides a driving experience
like a car. To prevent excessive speed when the load torque is low, for example when driving down hill, a
maximum vehicle speed can be set.

Speed mode
Speed mode (or speed control) is not recommended for on-highway vehicles as it can cause the
traction motor/wheel to remain locked or brake severely if the wheel is momentarily locked due
to loss of traction on a slippery surface and/or mechanical braking.

In this mode Gen4 maintains the motor at a constant speed for a given throttle position as long as
sufficient torque is available. Speed mode differs from torque mode in that the torque value applied to the
motor is calculated by the controller based on the operator‟s requested speed (determined by throttle
position) and the vehicle‟s actual speed. This mode is useful where accurate speed control is required
irrespective of the motor torque.

And this warning:
The Gen4 is a generic motor controller intended for use in both highway AND non-highway industrial
applications. Not all of the controller features are suitable for an on-highway vehicle. Some features, if
activated, could lead to the controller forcing a motor condition that is not directly requested by the
throttle, such as undesired drive or harsher than expected braking.

Sevcon recommends that the following features are DISABLED for any on-highway applications:
• Proportional Speed Limit.
• Hill Hold.
• Controlled Roll-Off.
• Speed mode (or speed control).
• Electromechanical Brake output.
• Inching.
• Belly switch.
• Unused Driveability Profiles.

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