Off the line torque - DD motors

Electric motors are supposed to produce max torque as soon as they start spinning?
Is that also true for DD motors?

I ask as I have been some DD motor videos where the bike kicks dirt and takes off and some buzz and shake like a engraving machine for the first few yards.
Yet, there is a video of a 205 50H QS that just takes off, not sure if it does the whole buzzing with vibration.

My experience with DD motors (very first one) has been dismal, I bought a yescomusa (say NO to yes com, lol) 750w front hub and it is a massager/hub combo IMHO, a crotch massager for the first many hundred feet and finally I think around 8 to 10 mph, the massaging feature ceases.

Leafbike 1500w, does it buzz/vibrate from dead stop? what kind of torque does it produce at low rpms?

Thats odd, but I would say its just the amount of amps dumped into the motor.
Once a motor setup is dialed in then its sweet sailing, all to often its just cobbled together stuff and more often then not the rider puts weight on the handlebars to throw dirt, cheater indeed, they want to look cool so they unload the rear to spin dirt, uncool in my books. The riders got to load up the rear wheel with weight to be a cool cat, burning bicycle rubber.

gobi said:

My experience with DD motors (very first one) has been dismal, I bought a yescomusa (say NO to yes com, lol) 750w front hub and it is a massager/hub combo IMHO, a crotch massager for the first many hundred feet and finally I think around 8 to 10 mph, the massaging feature ceases.

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The buzzing is a function of the controller, not the motor. A square/trapazoidal wave controller will produce the buzz, while sine wave or FOC controllers will be silent.

E-HP said:

gobi said:

My experience with DD motors (very first one) has been dismal, I bought a yescomusa (say NO to yes com, lol) 750w front hub and it is a massager/hub combo IMHO, a crotch massager for the first many hundred feet and finally I think around 8 to 10 mph, the massaging feature ceases.

Click to expand...

The buzzing is a function of the controller, not the motor. A square/trapazoidal wave controller will produce the buzz, while sine wave or FOC controllers will be silent.

Click to expand...

calab said:

Thats odd, but I would say its just the amount of amps dumped into the motor.
Once a motor setup is dialed in then its sweet sailing, all to often its just cobbled together stuff and more often then not the rider puts weight on the handlebars to throw dirt, cheater indeed, they want to look cool so they unload the rear to spin dirt, uncool in my books. The riders got to load up the rear wheel with weight to be a cool cat, burning bicycle rubber.

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E-HP, I am using the stock controller from the kit, the stock controller has a funky connector, I need to see what I have in my stash that does Sine Wave.
The ones I bought from PSWPwr were 500w, but this motor is 750w, I measured the max current during take off and then hard run, 28 amp at 50v.
Not sure if Yescom uses the same 9 pin plug as bafang. If yes, then I use adapter I have now.

Calab, Yes, the riders were leaning forward to prevent front wheel from kicking up, nice amount of torque on those. Burntout are out of the question for me, mine barely moves from deadstop.

Thats what I figure, I am always pretty close in my figuring.
When they compromise nothing, I may smirk and give a thumbs up.

You just need power, its all in the amps because your voltage maxes out on ebikes as there aint much selection in 100+ volt controllers.

gobi said:

Calab, Yes, the riders were leaning forward to prevent front wheel from kicking up, nice amount of torque on those. Burntout are out of the question for me, mine barely moves from deadstop.

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When considering "starting from a stop torque" with a "kit" supplied 48v DD, consider the advantage that might be available if it had the 5:1 gears of a geared hub motor. Or for yet more, the gearing available to a mid drive!

The bottom line is you need a lot of voltage and amperage to really launch a DD motor. On 48v, you need gears for the advantage they are able to provide.

Agree on the buzzing/squealing square wave controllers (junk).

For an inexpensive option, check out the 35a KT sine wave controllers.

calab said:

You just need power, its all in the amps because your voltage maxes out on ebikes as there aint much selection in 100+ volt controllers.

gobi said:

Calab, Yes, the riders were leaning forward to prevent front wheel from kicking up, nice amount of torque on those. Burntout are out of the question for me, mine barely moves from deadstop.

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AHicks said:

When considering "starting from a stop torque" with a "kit" supplied 48v DD, consider the advantage that might be available if it had the 5:1 gears of a geared hub motor. Or for yet more, the gearing available to a mid drive!

Agree on the buzzing/squealing square wave controllers (junk).

For an inexpensive option, check out the 35a KT sine wave controllers.

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AHicks - I have a bafang uber hub bike, my very first build, I am blown away by it, I mean it rock, the bike pulled me up a 20% grade from dead stop with nearly dead hoverboard 10s2p pack.
DD - I want one, simple, but I am still learning the language of ebiking.


Calab - My battery pack is capable of 40A, It was enough amps I think, I amp'd it and it drew nearly 30A.

Sort of but you're all missing the key points.

Efficiency. At zero RPM the efficiency is zero. Its just a heater at that point.

As motion begins, efficiency increases from zero. Think in terms of the frequency of shifting poles as the motor rotates. Once a more efficient frequency is reached the motor converts more power to propulsion than heating. Geared motors can be designed with big advantages at low speeds.

Off the line even the best Field Oriented Controllers need a tuned set Hall Sensors to launch and at that power ramping is somewhat softened to avoid jerkiness.

E-HP said:

gobi said:

My experience with DD motors (very first one) has been dismal, I bought a yescomusa (say NO to yes com, lol) 750w front hub and it is a massager/hub combo IMHO, a crotch massager for the first many hundred feet and finally I think around 8 to 10 mph, the massaging feature ceases.

Click to expand...

The buzzing is a function of the controller, not the motor. A square/trapazoidal wave controller will produce the buzz, while sine wave or FOC controllers will be silent.

Click to expand...

This ^^^, and also, sometimes just due to the resonant frequencies of your frame (each bike is somewhat unique as it’s due to the stiffness of the frame/frame components/the lengths and geometries/how tight it’s bolted together etc.). If it’s not stiff enough which could be the case of your front fork or how it’s mounted/reinforced with a heavy hub motor, it’s resonant frequency could be in the range of the vibrational frequencies of the DD hub at that lower rpm range. A stiffer frame/motor mounting/torque arm setup will either have a resonant frequency higher than the range of the motor’s vibrations or be heavy enough to absorb/dampen it out. Racks and other loose shit can amplify this a lot too if not isolated with rubber or bolted tight enough. The square wave controller will make the noises much more obvious. Sine wave or FOC are much quieter.

Electric motors, the ones we use, produce some cogging effect at low rpm. At higher rpm it's there but not noticeable. Cogging is normal and noticeable at low rpm. It comes from magnets and poles passing each other.

Comparing direct drive with gear drive: if a DD hub motor has cogging you can feel from 0 to 5 mph, then a geared motor might have cogging you can feel from 0 to 1 mph, assuming the GD motor has 5:1 motor to hub speed. The GD hubs motor gets up above cogging rpm at lower wheel speed, because of the gear reduction.

But, the DD motor is also bigger and heavier, so its cogging is more likely to be felt.

Square wave noise happened at more like 8 to 14 mph and certain throttle settings on my DD hub motor. The MAC 12 turn, 5:1 geared hub motor I'm using now doesn't have very noticeable square wave noise. Sine wave controllers should produce less wave noise than square wave controllers.

Because motor poles may not be in favorable alignment at 0 speed, torque might not be maximum during start, but become maximum at some low motor rpm just after start. Using maximum torque at low speeds is likely to spin out drop outs and torque arm holes. DD hub motors are easier on dropouts and torque arms than GD hub motors.

Power is what accelerates the rider and bike. Power is rotational speed times torque. Power units can be horse power or foot pounds per second. 1 HP = 550 ftlb/s. Torque is in ftlb. Rotational speed is in radians per second. Radians is not included in units, as in ftxlbxradians/second, or ftlbradians/s, instead this ftlb/s is used. RPM is changed to radians per second for the calculations. This is for the mechanical power units. Oh, there's two Pi radians per revolution. 2 x 3.1416 radians per 1 revolution.

Electrical power is volts x amps. The units are watts = volts times amps. W = VxA. 746 watts = 1 horsepower = 550 ftlb/s.

Electric motors produce lots of torque at low rpm, well most do, but not maximum power at low rpm, maybe, depending on the type motor. The relationship between torque and rpm isn't linear, back emf comes into play and other stuff too.

My experience has been that on flat ground I like the starting characteristics of DD more than GD. Starting on and up-hill is different, there I like the GD better than the DD. Besides that, the gear drive has less weight than the direct drive and so the GD puts less road shock into the pedals, seat and handle bars.

Hope this helps

Almost forgot, thrust times road speed = power. The units are thrust in pounds, road speed in feet per second and power in foot pounds per second. V x F = P. ft/s x lb = ftlb/s.

All this is in American units, Imperial units, or whatever you want to call them.

Triketech said:

Sort of but you're all missing the key points.

Efficiency. At zero RPM the efficiency is zero. Its just a heater at that point.

MikeSSS said:

Electric motors, the ones we use, produce some cogging effect at low rpm. At higher rpm it's there but not noticeable. Cogging is normal and noticeable at low rpm. It comes from magnets and poles passing each other.

Comparing direct drive with gear drive: if a DD hub motor has cogging you can feel from 0 to 5 mph, then a geared motor might

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Triketech,
It was pretty cold outside and the motor did not heat up noticeably, but I will keep my eye on it.

MikeSSS,
The motor has the vibration/buzzing even when I am moving at 5 mph plus, my application of throttle results in the vibration.

I will make a video today and switch out the factory square wave to a sinewave one, I have a KT 500w one I will use. I don't have anything bigger. Both uses the higlo connector.

DC motors are "supposed" to produce max torque at 1rpm?
Do the DDs suck due to the PWM voltage pulse that the controller sends out?

gobi said:

Leafbike 1500w, does it buzz/vibrate from dead stop? what kind of torque does it produce at low rpms?

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My Leaf is dead silent, except under hard regen, where it will make a slight hum. 160NM according to the Grin simlator with my setup.
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_80_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&wheel=25i&mass=110

That torque is unusable anyway. I feel like anything more that 90NM from a dead stop is too dangerous for regular riding, at least for a bicycle.

gobi said:

DC motors are "supposed" to produce max torque at 1rpm?

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Max torque is at zero, but is limited by how much current your battery and controller can provide. If the current is limited, it won't be the max torque the motor is capable of, it's the max that it can produce with that current. If you look at system A below, it's limited by the 20A current limit. so the torque curve is just a flat horizontal line. When you provide all the current the motor can handle, the torque curve is smooth and reaches the maximum torque.