Direct Drive: Do I have enough torque?

Technical discussion on converting internal combustion to electric
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leighf
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Direct Drive: Do I have enough torque?

Post by leighf »

Without wishing to hijack this thread totally -
EV2Go wrote: Still dont know how you can have peak torque at 0 rpm, if the motor isnt turning how can it possibly be producing torque. I must be superman because I can hold the shaft from turning at 0 rpm :) I digress...
Another way of looking at this is to take a 10kg bag of potatoes and hold it horizontally straight out from your body with one hand, keeping it still.

The pain you feel in your shoulder is torque at 0 rpm Image ! In this example it's about 98 Nm.

Leigh

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Direct Drive: Do I have enough torque?

Post by Electrocycle »

yes, torque is a force, like weight, or pushing on something.

Technically, no work is being done until there's movement - and that's when power starts being made (and used)
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Post by Goombi »

NO POWER--NO ENERGY --NO TORQUE -- NO POTATOS -- NO PAIN Image

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Post by Goombi »

Image

Diff from Rav dirrect coupling to 9" 8.5 KW DC Motor

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Post by Richo »

Richo wrote:Well he is asking about AC direct drive.
The motor he asked about is too small to work.
The next size up is the ones we have discussed.
As a down side he will go much faster.
As we have pointed out the motors don't come smaller than what we have suggested.


Actually this is not quite true Image
A 7.5kW 132-frame is the same physical size but:
weighs 10kg less (50kg)
approx $800 less
Peak torque approx 150Nm
But to keep it around 20kW nominal for highway driving it would have to be wound for 133Vac.
So as a result the peak torque of 150Nm would be from 0-4500RPM.
This would be around the 13sec mark for 0-100kph.
So the short answer is NO but the long answer is YES.
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Direct Drive: Do I have enough torque?

Post by acmotor »

At least the diff is waterproof !

Re the torque and power debate,
In order to produce the (say) 200Nm torque at 0 RPM the battery current may be 100A at 200V (motor current 1000A at 20V after controller).
(just typical example numbers of series DC, feel free to fill in your own numbers)

I make that 100 x 200 =20kW to produce 200Nm at 0 RPM !
Clearly the simple laws of physics must allow for the practicallity and efficiency of the drive.
In this case the drive is 0% efficient from a pure power point of view at 0 RPM.
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Post by Electrocycle »

yep, you make a lot of heat trying to accelerate from zero. At least it doesn't take too long, and the motor has a lot of thermal mass :)
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Post by acmotor »

We could always introduce the concept of thermal inertia. It usually sorts people out !   Image

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Post by Electrocycle »

hehe sounds like a good idea!
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Post by juk »

If you're going to mention thermal inertia, then you're just opening up a whole world of pain in the form of thermal momentum

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Post by Canberra32 »

Richo wrote:
Goombi wrote: Am I noticing that everyone is sidestepping the principle for conversion?

We are all now talking about 0-60km/h in 6 sec 400 m in 17 sec-- What the in the hell does it matter?
Well he is asking about AC direct drive.

The motor he asked about is too small to work.

The next size up is the ones we have discussed.

As a down side he will go much faster.

As we have pointed out the motors don't come smaller than what we have suggested.


Goombi wrote:
Safety- general performance on par with ICE and distance are the prerequisites for conversion..
Everyone has different opinions as to thier prerequisites for conversion.


Goombi wrote:
All this talk is a distraction from the real thing --Convert and Drive.
Nop - he is planning which is a valid step to getting what he wants.


Goombi wrote:
There is alo enough confusion about and the ones that are now driving their cars are best qualified to express their opinions and share their experiences..
Everyone has equal right here to express opinions.


Goombi wrote:Please separate the DC from AC in another website Folder


He is contemplating an AC conversion.

So your DC currents in your conversion are not relevant to this thread.


Goombi wrote:
Motors that run at 10,000 rpm will need special bearing cooling..


Maybe you should read the spec sheet fot the motor he has discussed.

It is designed for this RPM.

It does not need special anything.

It has a gearbox available for it as well.


Goombi wrote:
Motors running at 2959rpm are safe and proven performers.
2959RPM is very specific.

Are the ones going 2960RPM bad?


Goombi wrote:
All this talk is experimental-- that is not needed.


AC in not experimental.

Azure motors and controllers have been around for a while.

Industrial AC motors have been around for even longer.

Danfoss controllers have been around for longer than any cheap chinese controller in any DC eV.

This sort of thing is not helpful guys and yes everyone deserves their right to speak.
A normal gearbox is designed for its internals to sit mostly in the middle of the engines power band not in its peak or you will wear the guts out of the box.
So find the power band of the original motor then use a reduction gear (belt,pulley,cog,whatever) to put your engine in the right spot!!! Simple just remember most 4 cylinder cars cruise 100ks at around 3000 engine rpm make sure your motor sweet spot no matter how you gear it sits the same.
This is the most basic engineering I even think I learnt ratios in year 6 or something who new I would ever have to use it lol

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Post by Canberra32 »

And having said all that and read this thread...
Why DC or AC?
While everyone is wondering will this AC have the torque I'm busy replacing my big honky ford diff coz my DC stripped the diff centre from too much torque :) for the sake of how many cents a day in electricity did I sacrifice efficiency :)

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Direct Drive: Do I have enough torque?

Post by bladecar »

Hi,
Just a bit of info to do with the electron with TM4 gear.
The manufacturer is very keen for the car to be driven with 4 to 5000rmp showing on the tacho (though the motor itself may not actually be doing exactly what it says, I suspect).

They really recommend not using 1st gear at all.

Driving in 2nd give 3800, say, on the tacho at 60kph.

On the freeway, the tacho is up near the redline as you approach 100kph and going to 3rd gives 4-5000 as requested.

They want the car to be driven in the 4 to 5000 rev zone because they suggest the motor is most "efficient" in that range.

If I assume there is something to that, then using direct drive would mean that the car should be driven within some particular speed range to go the furthest on the least.

While I'd like to have a direct-drive car, and I see that the g'box is both excess weight, space, and vulnerable, it does provide a lot of options.

My car can handle significant hills (from a standing start) in second, possibly 3rd but I don't try. You can imagine what it can do in first (like stress mounts, etc).

It can match the average car out there in roll-on acceleration with ease, all in 2nd gear.

Someone is going to predict the demise of my g'box in response to this but I guess that's not a massive problem in the greater scheme of things, and it will depend on how I drive.

2nd gear does everything around town. Not designed for it? Not designed for an electric motor either. I'm happy.








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Post by Jeff Owen »

bladecar wrote:
Someone is going to predict the demise of my g'box in response to this but I guess that's not a massive problem in the greater scheme of things, and it will depend on how I drive.

2nd gear does everything around town. Not designed for it? Not designed for an electric motor either. I'm happy.

I am not going to predict the demise of your gearbox. My car was converted at over 150,000 km and has since travelled over 100,000 km with nearly all of it in 2nd gear. So far, the gearbox is doing just fine.

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Post by Richo »

Canberra32 wrote:Why DC or AC?
Because this thread was started with a conversion in mind using an AC motor that is commonly available.
Canberra32 wrote: I'm busy replacing my big honky ford diff coz my DC stripped the diff centre from too much torque
Image Image Yes a nice problem to have
Better than being stalled trying to get up a hill...
So the short answer is NO but the long answer is YES.
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Post by Canberra32 »

Yeah it's sort of a good problem and not :)
Can always drive around a hill but broken stuff is just plain broken :)

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Post by unheardofinstruments »

I can see a simple reduction drive using belts or planetary or both could do away with the diff as well and use 2 ac motors, one for each cv. Just pick the optimal ratio or have a two stage planetary gear.
Still no decision from the engineer if he will allow a car with no diff

even better;
www.rexresearch.com/constran/1constran.htm
or craig carmicheals planetary torque converter project at turqouise energy

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Post by Canberra32 »

My engineer said two brushless motors with two controllers into driveshafts is no different than hub motors so its fine.

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Post by coulomb »

unheardofinstruments wrote: I can see a simple reduction drive using belts or planetary or both could do away with the diff as well and use 2 ac motors, one for each cv. Just pick the optimal ratio ...
If I understand you correctly, you want to do away with the differential by using two motors and "smarts" to effectively provide a "software diff".

The problem with this idea is that you are relying too much on technology just to drive straight. If one motor fails or stops or even slows more than a whisker compared to what it should, then tyre wear will be the least of your problems, if you get my drift (sorry).
or have a two stage planetary gear.

This sounds like it has the same problem, or is effectively a differential anyway.
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Post by coulomb »

Canberra32 wrote: ... is no different than hub motors so its fine.

Duh. It's just penetrated my thick skull that this means that hub motors have much the same problem as the two-motor-two-controller "software diff" idea. Image

Perhaps I'm overlooking something. Maybe there is a really simple way of limiting the difference in speed, though that would imply a shaft of some sort, which would hugely reduce the attraction of hub motors.

Maybe there's a reason no-one has made it work to date... Well I'm sure someone has done it, but have they been able to make it safe in the event of a single motor or single controller (etc. etc.) failure?

Oops, I may have contributed to some thread drift. Sorry.
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Post by Canberra32 »

As was explained to me.
With hub motors as you corner the difference in rotational speed between the wheels will not affect each other because the torque required for the inside wheel to keep up with the outside is huge and it simply doesn't.

With a high speed motor running a reduction gear then it has the torque=problem.
I came across this company and found something interesting that I remember seeing in a formula sae car.

A belt driven 2speed differential

http://www.directindustry.com/prod/rede ... 30881.html

This also brought to mind the control we get over motors on our CNC...
Perhaps considering the tiny adjustments used in CNC people might consider using their controller box to drive the speed controllers like the servo motors in big CNC machines to balance the rate of roll during a corner.
Just a thought

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Post by Johny »

coulomb wrote: The problem with this idea is that you are relying too much on technology just to drive straight. If one motor fails or stops or even slows more than a whisker compared to what it should, then tyre wear will be the least of your problems, if you get my drift (sorry).
I disagree. I think you over-estimate the problem if one wheel stops driving. If you plant a rear wheel in the wet and it loses traction, the rear of the vehicle will stil run true - point straight. If one wheel stopped driving the car would still be stable as both wheels point forward.

I think it would an event where it would be difficult to even tell it happened - other than a loss of power.
Of course I'm ignoring hairing around on the limit of adhesion.

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Post by Tritium_James »

Driving two wheels separately with two motors and two controllers is no problem. Run them both at the same motor current setpoint and you get a perfect diff action, it really is trivial.

Coulomb, losing one motor in this case won't cause the car to go sideways on you during normal driving. eg: plenty of four-wheel solarcars only drive one wheel.

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Post by unheardofinstruments »

Running two motors and two controllers in torque control mode instead of speed control mode essentially is trivial in every way but the cost of an extra controller. I kind of liked the idea of two motors in parallel and one controller doing twice the amps in that respect hence why I bought a high power igbt based controller.

I guess this is the discussion I have to have with my auto engineer, he said one motor failing at an in opportune moment would be something he could see as being an issue perhaps. I wonder if the difference in handling/tyre wear would be significant unless you spent all day in parking lots doing very tight turns.
I can imagine slippery surfaces being a bit strange like a limited slip diff in extreme, mind you in times when I have been bogged I wish i didn't have a diff. I noticed driving the tractor with the rear diff lock on makes it go straight on slippery terrain better than the steering does.

Go karts have no differential and handle well but the track width is small. I have heard of people doing it several different ways but rego is the real hurdle.


If a simple automatic torque converter system like George Constantinescue invented before the turn of the century (see links above in my previous post to the rex archives page and see the film on you tube from the 20's too) the simple matching of the oscillating weight to the torque of the motor is all that it requires to solve the reduction ratio and the torque control problem in one mechanical relatively failsafe system with a whole chunk of weight saving thrown in. I am looking for one of his gearboxes from those human powered rocking arm driven rail carts, it's only commercial uptake.
Craig from turquoise energy (the other link) is the only person I know who is trying it out so far but the idea of using twin planetary gear to achieve the same effect has appeared and disappeared from you tube, the guy was from western australia and he had done it and patented it too I seem to recall, the beauty with this way is you can get reverse as well with smooth changes in ratio with no extra complexity. It worked by having a dial in amount of counter-rotation being allowed between the two planetary gears by rotating a shaft at the right speed, very simple.

I started out converting a porsche 924, which I still have, there is ample room under the back where the fuel tank and transaxle were and I was contemplating using two agni 95R motors with toothed belts but wasn't sure if the starting torque would be enough (steep terrain, wanting to tow a trailer sometimes) if I still wanted to do 110kph at 7500rpm or if their promised bigger motor will happen.
AC would be even better but the controller becomes the huge bugbear in the expense department if you decide you need two, plus they tend to have heavy cases (X2) hence my interest in the AC drive dilemma, gearboxes/diffs and starting torque.

slightly off topic contoller tech query james;
I wonder if one motor could be induced to skip a few phases every now and then to catch up to the other until it gets in phase again rather than needing an extra controller perhaps a smarter option exists for a two motor controller, maybe with independant high current sections and gate drivers but the same low voltage section feeding them. In a DSP based system (which many ac controllers are) it would be a stereo delay or chorus effect which could model a diff using the same pulse width info from the throttle and I suspect angle related telemetry is used in the audi/vw traction control platform to do the awd system, can we cannabalise or interface with it I wonder?
I envisioned a buck converter for the regen could help switch the extra amps not needed back into the batteries/supercapacitor bank and be the ac to dc battery charger at the same time, I understand they both are switchmode regulated, maybe some back emf scavenging would be possible then too with the right switching.

I don't like the idea of a hub motor on my roads, hence a cv joint seems worth keeping as it can also keep the motor out of the dust as well as mechanical shock.

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Post by unheardofinstruments »

canberra32; did redex get back regarding the cost of that 2 speed spindle drive?
I have seen a similar one from the phillipines once for US $550 but not as torquey

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