DD Hub as a mid drive motor pros and cons?

[RIPPERTON]

DanGTIt's disappointing to see this thread devolve to the point of personal insults especially from a guy I have been looking up to in the EV community

NutSPecialRipperton you've lost me in the dust. Also, I think you might be full of it :lol:

As far as insults are concerned Dan, heres where the gloves came off. Page 1
And you expect me to keep my cool with this sort of babbling ????

Craigsj LOL, I'm quite confident Isaac Newton wrote nothing on the subject of electric motors in motorcycles

Page 1: This bike will squat under power, and not because of any torque reaction involving the hub motor.
Page 3: Regarding the torque of the motor acting on the swing arm, this produces an anti-squat force.

Very acrobatic Craig nice back flip there.
Glad you finally got your head around this one Craig, it only took you 3 pages and now your stating it like you invented it. deplorable.

Your antics have reaffirmed my choice of Forums and Im glad I dont call Endless Sphere my home.
You kids just carry on with your pissant bicycles and leave the real bikes to the pros over on DIY.

 

[RIPPERTON]

The content of my first post in this thread referred to the design fault in that trike.
The hard part is, you cant foresee the error in this case untill you get in and drive it.
I was warning everyone so they wouldnt make the same mistake I did.
But no one could understand a word I was saying.


edited

 

[jonescg]

Chill out Danny.

 

[madin88]

You just get dumber and dumber. The content of my first post in this thread referred to the design fault in that trike.
The fact is I DO know whats wrong with it.

come on, read your first post and than think about it.
It was made clear that, aside from the problem of the unsprung mass, a Hub drive or swing arm mounted motor with chain drive has no other bad influences on the suspension.
And as mentinoed, a little antisquat (rise of the seat during acc) isn't a bad thing.

Maybe you NOW do know what's not perfect with that frame suspension design, but it isn't the swing arm monted motor as you referred to be a big mistake (again: aside from the unsprung mass)!

btw: here is a riding vid of that frame:
https://www.youtube.com/watch?v=aeaebhgPU9s

 

[DanGT86]

Awesome, video of it running. I love that guy's helmet! Anyway, at 1:36 right after the burnout it hooks up and launches. To my eye it looks like it unloads the front wheel and extends the rear suspension lifting the bike. If I'm seeing it right then there is our answer. It also looks like the shock dampening is hopelessly loose in this video. That thing keeps bouncing like a pogo stick.

Looks like fun though.

 

[jonescg]

...It also looks like the shock dampening is hopelessly loose in this video. That thing keeps bouncing like a pogo stick..

That's the first thing I noticed too.

 

[jonescg]

[youtube]C81B6Z-9J5w[/youtube]

In case you aren't keen to do burnouts yourself

 

[skeetab5780]

Is it me or does that thing look horribly underpowered as i mentioned in another thread recently comparing the motoped mid hub mount kits also.

Need a trail ride vid to really see it in action but the motoped vids didnt look all that amazing either.

 

[DanGT86]

Hard to really say. Power doesnt show up in videos unless its a crazy amount. Ive shot gopro vids of whiteknuckle rides then showed people and felt dumb when It looks like a casual hike through the woods.

Getting back to McRibs original question that launched the thread, does anybody know the specifics of how motor diameter relates to rotatonal inertia? Does the increased torque from a large hub motor make up for the higher mass at a longer radius.

My mid drive at way less power feels really snappy and crisp compared to my hub. I figured it was the motor mass being easier to spin up.

Also, it sounds like most people agree that higher rpm makes motors happier but is there a point where a heavy hub might not be balanced well enough for mid drive rpm?

 

[DanGT86]

If your motor is connected to your bike then it "spins up" as the bike accelerates. The differences in rotational inertia of the motors is dwarfed by the overall kinetic energy of the bike and rider.

I guess we would need to graph it to see at what point this becomes an issue worth worrying about. Intuitively a 7lb inrunner with a rotor radius of 2" seems like a way better choice then a 20lb outrunner with a 4.5" rotor radius. Especially considering there are options on the market at similar prices to a big hub at the 8kw or less power point. If we're talking about 15kw then something like a $300-500 hub starts to look like an attractive option.

 

[macribs]

Btw I've seen a youtube vid of this bike where they went trail riding. Couldn't find back to it right a way but I will put link up as soon as I find it. Iirc I it was a russian vid.

 

[madin88]

I guess we would need to graph it to see at what point this becomes an issue worth worrying about. Intuitively a 7lb inrunner with a rotor radius of 2" seems like a way better choice then a 20lb outrunner with a 4.5" rotor radius. Especially considering there are options on the market at similar prices to a big hub at the 8kw or less power point. If we're talking about 15kw then something like a $300-500 hub starts to look like an attractive option.

running a hub motor as middrive is a less than ideal solution.
It is heavy for it's power density, and the heat path to the outside is quite poor without any cooling modifications.
why than use it?
Well i believe it is because these motors are not that expensive, widely available and the attachment to a frame is simply with it's axle and the existence of screw-on sprockets.

 

[macribs]

[youtube]NodHwO7WTkE[/youtube]

[youtube]NB_tBlfL_G8[/youtube]

 

[macribs]

[youtube]5I5UK7rtvPE[/youtube]

At least it does seems the frame and suspensions behave rather nice, both on and off the throttle.

 

[DanGT86]

@1:48 in that last vid it looks like the suspension works pretty well climbing that bumpy hill. The riders feet were dangling the whole time so he is essentially just dead weight and that bike does a great job keeping the rear tire biting. That also looks really fun and now I want to go ride instead of do yardwork.

So what about the effect on braking using a gear reduced heavy hub as a mid? If the gear reduction is 2:1 and the hub has all that spinning mass at a large radius then wouldn't the rear brake be feeling a lot of extra force during braking? Its on the less desirable end of the reduction at that point because the motor is acting like a flywheel and gets a mechanical advantage over the brake because of the sprocket ratios.

On that same line of thinking, If someone wanted to rig up a clutch to the hub motor they could spin all that mass up and dump the clutch for explosive power like a trials rider dumping the clutch. I bet a hub motor at speed has more stored rotational energy than a gas motor. Running with a clutch you could even have regen enabled at all times other than throttle and use the clutch to coast. This would feel a lot more natural to moto guys.

Whats becoming apparent is that this vector mid drive frame with a hubmotor seems like a great way to get big power and tons of batteries on moto wheels and moto forks without needing exotic expensive parts or a machine shop. Somebody who has built a basic hub and infineon controller ebike could get one of these and just scale everything up like more FETS more batteries and more motor without having to learn anything new. I see this simplicity of that as a very valuable thing for the market even if it does leave a few things to be desired in the design and efficiency departments.

If I needed an e-moto and only had a few days to build it, this vector frame seems like the best way to get there with off the shelf parts. This is all assuming it doesn't cost as much as an LMX or a Zero.

This vector is just asking for one of John in the CR's hub monsters with a pair of cheap 15kw controllers. I don't know of a cheaper way to get a 30kw ebike than that. You could even run a sprocket on each motor side cover and just flip the motor around depending on the type of riding you wanted to do that day.

 

[macribs]

1+ DanGT. I guess this frame is just begging for a more powerful hub then the 205. Imagine what a 273 would yield. Paired with say Mobipus 72600 from SamD. Now that would be 40 kw peak

QS motor also got the 8000 w rated 171 100H mid motor. Guessing that power output is going to be like 4 times the rated power at least for peak power. Spins at around 3000 RPM at 72v. Probably a good match for the Mobipus 72600 as well. That motor is a 500$ motor. If motor tops out at 30kw + peak that would be serious fun.

I like your idea of a clutch setup. Sure it will eat some efficiencies of the motor but imagine what you can do climbing in loose sand. Never need to run motor into meltdown, blip the clutch like on any mx bike and get that rear will spinning up again. Or as you say climb stuff not really ment to be climbed.

QS 8kw continuous mid motor:

 

[RIPPERTON]

So it did exactly what I predicted it would do, hate to gloat but HAha.
Whats really sad is theres not a single mention that I was right or a thankyou. In fact most of you are either in denial
that there is any jacking at all or are simply saying that the bike looks fun to ride.
Compare the yellow bike under throttle to this bike under throttle 1m44s. No jacking or rise at all.
https://www.youtube.com/watch?v=2PaKeCyw-jY
Same bike against gas bike 2m6s
https://www.youtube.com/watch?v=tZ9vkILtq14

 

[Aebrennan]

Thanks for posting those videos. If shown at the beginning of the thread it would have saved pages of ramblings!
It is reassuring to now know who this bike is perfectly suited to.
For those with no value for personal safety or ride quality this is a great machine.
Im sure it gives more of adrenaline rush when you ride a dangerously designed bike on an Eastern European road with no helmet or gloves surrounded by motorists with even less value for your life!

 

[Aebrennan]

What a great solution!
Tune the rear shock to not allow travel?
Why hasn't anyone else thought of that?
The world is in big trouble if our future engineers think this is the answer!

 

[RIPPERTON]

It's not clear that there is jacking

Its dead obvious to anyone that the rear of the bike is being jacked up through a substantial percentage of its sag.
This is due solely to motor torque reaction plus the front of the bike also lifts due to weight shift, basically trying to do a wheelie.
This concurs with my statement, "there are 2 sets of physics working here"
Then the whole bike squats back down on throttle chop, front and rear suspension simultaneously,
which concurs with my statements, "Playing havoc with suspension action" and "pogoing up and down"

I would still say the handling of the yellow bike IS fatally flawed.
Personally I would not like to ride this bike but thats just me. Ive been riding dirt bikes for 45 years and I know what good handling is.
The guy riding it looks like hes have fun so for him its a successful build,
good on him. Im certainly not going to let you quantify what is fatal or not.

edited

 

[DanGT86]

1+ DanGT. I guess this frame is just begging for a more powerful hub then the 205. Imagine what a 273 would yield. Paired with say Mobipus 72600 from SamD. Now that would be 40 kw peak

QS motor also got the 8000 w rated 171 100H mid motor. Guessing that power output is going to be like 4 times the rated power at least for peak power. Spins at around 3000 RPM at 72v. Probably a good match for the Mobipus 72600 as well. That motor is a 500$ motor. If motor tops out at 30kw + peak that would be serious fun.

I like your idea of a clutch setup. Sure it will eat some efficiencies of the motor but imagine what you can do climbing in loose sand. Never need to run motor into meltdown, blip the clutch like on any mx bike and get that rear will spinning up again. Or as you say climb stuff not really ment to be climbed.

I didn't mean to suggest that the QS205 would be inadequate. I was simply bench racing a combo that i thought would yield the maximum power per dollar. I think the 205 would be fine on this frame especially if it were allowed to spin some higher than normal RPM for a hub motor. Water cooling or a large side cover fan setup would be easier without the normal space constraints of a brake rotor and chain in a dropout.

I personally think the 273 is just too big and heavy to be of much use. If I needed that monster to move my bike I'd be looking towards high rpm mid drive motors or salvaged zero parts. Totally my opinion though. Some people might like a 40lb hub motor

I'm not sure what to think of that 8kw inrunner from QS. Seems kinda big and heavy for the specs they list. I'll let somebody else torture test one to find out what it will do.

 

[amberwolf]

This was a great discussion to read until y'all started getting personally insulting with each other.

Maybe tone down the ego and insults and keep it professional?



If you just *have* to do it, maybe keep it to PMs or emails outside the forum?

 

[madin88]

please calm down guys

i am definitely no expert in supension designs, but i would trust jonescg that:

squat is a bad thing, and for myself i would explain it like this:
the rear suspension gets compressed (you loose travel), and the geometry of the bike changes.
than i would assume, at the same time the front jackes up higher than it would usually do as a normal result of the counterforce force engaging at CoG due to the mass of the vehicle + rider when accelerating hard (hope this is understandable)
-> this cannot be good for the handling

and

a little anti squat isn't that bad, because:
even if the rear suspension becomes unloaded, the rear wheel is still pushed hard to the ground, and the influence to the front suspension should not be much different than usually.

and generally: a bike ANYWAY is going to wheelie at hard acceleration, so the front ALWAYS become unloaded!

In my opinion, the anti-squat of that discussed bike is probabaly too high (in considereation with the already high CoG), so RIPPERTON isn't that wrong about it.
However, i would not call a swingarm mounted motor, or hub motor powerd bike generally as "big design flaw" as he did. this is overexaggerated.

The suspension of the Motoped looks imo very well balanced from the vids, and if it really has a tiny little bit squat, could it not be improved by changing the geometry a little bit, or lowering the CoG by mounting the batteries lower (which would result in more anti-squat when acceleratin hard)?

 

[DanGT86]

When a bike is said to have 100% anti-squat, does that mean its neutral and the pedals have no influence on the suspension regardless of torque?

 

[jonescg]

I reckon we start a thread where we just upload videos of our bikes doing the static anti-squat test. And them maybe a burnout, because, well, you know, while you're there and all that

Besides, this thread has been too vitriolic. Lets start again.