DD Hub as a mid drive motor pros and cons?

ripperton, you seem to be very passionate about this subject. Help me learn...please post your "best compromise" frame configuration and motor placement.

What will be the difference with these three motor placements? Swing arm, frame and directly in the pivot point?
For arguments sake, lets assume the fork angle are the same, so focus on what effect the different motor placement will have, how it will affect the riding and how bumps, acceleration and braking will feel different.

madin88 said:

more battery room, where?? or do you mean INSTEAD of a main frame mounted motor?

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yeah. look at the battery cavity on the yellow bike, MASSIVE. Even though it has faults, it also has good design features.
Just the fact the battery is on a 45 degree angle causes the motor to remain low and ground clearance is only 300mm.
If the battery was more or less straight up and down from the 365mm line up then the motor could also be raised up to that line
making ground clearance 365mm and using the frame to protect the motor when bottoming. The motor will swing out of the way a bit
when bottoming.

spinningmagnets said:

ripperton, you seem to be very passionate about this subject. Help me learn...please post your "best compromise" frame configuration and motor placement.

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Sure, I would start with the Yellow bike and make a few changes. See what I can do.
This thread seems to have risen from the ashes.

Battery box is 500x300x150, could fit 3.5 - 4 kWh in there.

Ripperton you are hard core man. Just came across this on the tube. 210 kw electric R1. And no chicken strips, you pushed hard man.

[youtube]vdKDOfXBRMM[/youtube]

macribs said:

Ripperton you are hard core man. Just came across this on the tube. 210 kw electric R1. And no chicken strips, you pushed hard man.

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Thanks macribs, very kind but I have to confess.
The lack of chicken strips are courtesy of my rider (Brad Swallow) as these tires were on the bike at the last round of the eFXC at Eastern Creek in November (middle of summer).
He would definitely be pulling bigger angles than me on that day.
That day at wakefield was almost middle of winter and track was cold plus I hadnt been on the bike for 8 months so I was taking it pretty easy. Plus that track has a very smooth looking surface and always looks slippery to me even when its dry so it weirds me out.

Only once in the past where I have had "no chicken strips" on the front tire, there were very rare track conditions. ie at Phillip Island turn 2 massive left hand sweeper, middle of summer 2005 the R1 was still in ICE config and was only on the left side of the tire.
So now you know I get other people to make my tires look good but Im still hard core yO. :wink:
The 210kW bit is Bruno doing his own maths. 175v x 1200A. The 2 Kelly 600A ctlrs arnt set to 100%. Maybe has 90kW

I don't wear out the tires on the sides anymore. In fact the speed triple gets fewer and fewer miles each summer. But I can't seem to be able to get rid of it either. There is something about a 3 cyl liter bike and twisty country roads that never stops to amuse me. But the lean angle and corner speed is not like when I was in the early 20's and immortal.

That track day seemed like a lot of fun, and I think you did well in the bends. You overtook plenty of gassers.

RIPPERTON said:

Battery box is 500x300x150, could fit 3.5 - 4 kWh in there.

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Nice! Actually could fit substantially more than that with 18650's, easily package 800 cells - 8.6kWh and 50KW of power potential. More than you would need/want on this type of ride for various reasons. Cell weight alone would be 37kg.

On my Giant DH comp running a hub motor the reaction forces that Ripperton is describing under quick acceleration on the stand results in the swing arm SLAMMING into full droop. On the street with a rear heavy weight bias it results in a mild anti-squat motion under serious acceleration - from what jonescg was referring to that's somewhat desirable?

On a purpose built machine capable of higher wheel torque (without flipping over) this may be a much bigger deal than on something that's geometry limited.

Ohbse said:

RIPPERTON said:

Battery box is 500x300x150, could fit 3.5 - 4 kWh in there.

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Nice! Actually could fit substantially more than that with 18650's, easily package 800 cells - 8.6kWh and 50KW of power potential. More than you would need/want on this type of ride for various reasons. Cell weight alone would be 37kg.

On my Giant DH comp running a hub motor the reaction forces that Ripperton is describing under quick acceleration on the stand results in the swing arm SLAMMING into full droop. On the street with a rear heavy weight bias it results in a mild anti-squat motion under serious acceleration - from what jonescg was referring to that's somewhat desirable?

On a purpose built machine capable of higher wheel torque (without flipping over) this may be a much bigger deal than on something that's geometry limited.

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it'd be great to see a vid of that happening, if possible? even if its just in a sandpit or something.

Ohbse said:

On my Giant DH comp running a hub motor the reaction forces that Ripperton is describing under quick acceleration on the stand results in the swing arm SLAMMING into full droop.

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Where does the stand support the bike. By the axles or the BB.
When you say droop you mean the swingarm drops down ?

No load reaction of motor effects is close to meaningless. Any motorized bike will jump around when you spin up motor and wheel while suspended. Ripperton whines about the reactionary forces with the wheel in contact with the ground, but his experience with it is with a short swingarm and without the rider(s) and frame CG sufficiently leveraged against the lifting force at the pivot. With proper design the forces under acceleration and during regen a beneficial, so he's totally missing the boat with blanket statements that it's the wrong way to go. In the long run the compact power of electrics will allow what simply isn't possible with smoke belching machines, and motors affixed to the swingarm will become the norm.

John in CR said:

motors affixed to the swingarm will become the norm.

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If your a good salesman, go ahead, convince the world that pogoing up and down is the way to go.
Dont forget the torque reaction is proportionate to the torque of the motor.
The more power you have the more obvious the problem.
Personally I dont think the public is that dumb and in the end they will settle for what works best.
The biggest problem isnt the jacking because its hindered by both gravity and weight shift.
When you chop the throttle, the squat is twice as abrupt as the jacking because its gravity assisted.

No, the torque of the motor acts on the rigid swingarm, and has no effects on the suspension. It's the torque at the wheel lifting the pivot, and regen pulling it down. If what you've been pushing was true, then on your big emoto the frame mounted motor torque would be making your front suspension pogo, but that doesn't happen does it? Reactionary forces of changing the rpm of a spinning mass are pretty insignificant, and to the extent they're wheel related, they're unavoidable.

The simple fact is that motor anywhere on the swingarm completely eliminates chain pull effects on the suspension, which is a good thing, especially when you're talking about a very compliant bicycle suspension.

Oh, and BTW your blue bar in the earlier drawing, will cause the motor torque to act on the suspension.

John in CR said:

Oh, and BTW your blue bar in the earlier drawing, will cause the motor torque to act on the suspension.

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No it wont because its no longer torque. Its been converted into thrust and aimed directly at the swingarm pivot therby neutralising it.
The blue arm is in tension under accel so the reaction is for the motor axle to force linearly toward the swingarm pivot.
This force has no triangulation so no effect on suspension movement.

RIPPERTON said:

This force has no triangulation so no effect on suspension movement.

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It's two pivot points and the swingarm pivot form the triangle, and it will unquestionably cause forces on the suspension due to the motor torque it is helping prevent from spinning.

OTOH the motor affixed to the swingarm, whether in the dropouts or anywhere along it, is the only way for the motor to not directly affect the suspension during acceleration and/or regen. Of course the resulting thrust or braking forces at the tire affect the suspension, but it helps counter the squat and jacking forces inherent when accelerating or decelerating the center of gravity.

It's baffling why you can't see such simple concepts. I guess it's just your limited experience with hubmotors, and the real reason it was problematic on that trike. The CG of the trike was so low relative to the pivot point that squat forces from accelerating the mass were almost non-existent. In that case, of course there would be "jacking" from the thrust at the wheel acting through the pivot point. Poor design due to inadequate consideration of the rudimentary physics involved is to blame, not that there's an inherent flaw in hubmotor drives other than the effect on unsprung mass.

I must say I do not really comprehend this dual pivot point vs single pivot point. Nor am I fully able to picture how the various forces are working depending on the placement of the hubmotor. Like what happens with motor in frame. What changes if motor is moved to the pivot point? And again if motor is mounted in the swing arm as close as possible to the pivot point. I don't have any simulation software so I guess there is only one way to really grasp this and get a full understanding for this important subject, would be to make a small scale model and try various placements and possible be able to capture the forces on camera. But hey family vacation in the caravan, maybe I send the "wild bunch" down to the beach and start carving into the fire logs :wink:

John in CR said:

The CG of the trike was so low relative to the pivot point that squat forces from accelerating the mass were almost non-existent. In that case, of course there would be "jacking" from the thrust at the wheel acting through the pivot point.

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Hang on, let me get this right, You actually think that the accelerative jacking in the trike is from wheel thrust acting on the swingarm pivot. ?
ok Im going to have to right you off now, may I suggest you go get the same counsellor as craigsj.
After all this you still cannot understand torque reaction jacking ?

macribs said:

What changes if motor is moved to the pivot point? And again if motor is mounted in the swing arm as close as possible to the pivot point.

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The reaction with the motor in the pivot point will depend on where the torque is anchored. ie a hubbie in the pivot point with the torque arm affixed to the swingarm would be the ideal (no unsprung mass of the motor, AND that torque will have no direct effect on the suspension (the same as mounted anywhere on the swingarm).

If you attach the torque arm to the frame (even by convoluted means like the Ripper tried passing off) then it will apply forces to the suspension.

RIPPERTON said:

ok Im going to have to right you off now..

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Good!

John in CR said:

I've tried to bring this topic up a few times related to mid-drives, but it never gained traction. The only time I've seen it brought up by someone in the know was Toolman2, who mentioned a "jacking effect" during acceleration that was noticeably different, but it was easy to become accustomed to it. He mentioned the same positive "digging in" effect as Nutspecial mentioned with his hubmotor(s) earlier in this thread.

I'm really surprised that racers like Ripperton haven't experimented with motor placement in this manner, because all I see are positives. It's probably just a bit too much carryover from gassers, where the motors are too big and heavy to anchor their torque in the swingarm.

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Ive spotted this thread late, and only caught a bit of craigsj quality input (i have page 2 of his posts still sitting on a computer that i might quote from so they are not all lost, and so be it if thats against the rules and is taken down) -it seems odd that if we are searching for the truth here, that a technical matter like this could get that emotional. :?

Also i hope i didn't lead you astray John -that a swingarm mounted motor is ultimately the best solution when we spoke of this stuff a while back the bike (pics below) i was optimistic about it and trying hard to make it work and then had a ca120 bike with a simple and light 2 speed gearbox on the swingarm and it eventually maxed out at 11.3kw output (on a dyno) and about 300NM to the wheel. i was in the midst then of learning about and to tune my way around the effects of the jacking from the swingarm etc and trying to get the bike good enough to compete in dirtbike races, these jacking effects were both good and bad..

The good side (once tuned for zero squat by lowering the pivot eventually to the floor under the pegs -video that demonstrates it here with the camera mounted under the bike looking back at the minimal swingarm movement when on or off the power, shredded rear tyre but nonetheless: https://youtu.be/BFmL5p4uFC0[youtube]BFmL5p4uFC0[/youtube] ) it was good for rear bite under power, setting the tyre into the ground hard and being really rigid to launch the rider and the ability to then run quite soft plush settings on the rear shock for bumps.

The bad side was that you got this leapfrog type effect (in general when getting on the throttle) but worse when you hit the throttle to lift the front over a jump or log (and you get way more air than you may have been after) but also the snappyness of losing the rear or high-siding, where it would bite lots and then potentially snap out on the exit of a corner. -more grip until breakaway and then quite suddenly none. -more on all that stuff if folks want it.



By trying to tune this machine for optimum speed on often rough dirt tracks i found myself having to lower the swingarm pivot below the height of the rear axle and an extra long swingarm etc etc to try and compensate and reached the limit of these types of compromises and other aspects of the bike, i then changed things around for the next frame design with all this in mind and went for a frame mounted motor, the result was more predictable handling under greater torque levels up to 400NM and the one with the joby was then capable enough to enter races with gassers.

In general though john, i still think a motor on the swingarm could be a good design choice and well suited to what you and many others are doing, i believe you have a bit of weight onbourd , a long swingarm and smaller diameter wheels, lots of squat is no good either, and i doubt you are keen to battle a bunch of madmen on dirtbikes across a rough paddock. :wink: So yep id have no hesitation in mounting a motor on the swingarm on yours and many other bikes.

And Ripperton, that drawing is a very clever way of reducing the jacking on this type of bike that i could even put to use. But do you not think the length of the red arm would change the degree of influence? :wink:

Thanks for sharing those details Toolman2. You're right I'm bigger, though 30kg less than before, but it's probably the pure street riding that limits the negatives even more. Plus there's vehicle weight too, since my next bike will need to be strong enough for at least 4kwh of batteries, mx wheels, and take a pounding. It sounds like I really should go concentric in the pivot for this trail bike I plan, so I can easily try it both ways by including an option to anchor the motor to the swingarm or the frame with an easy switch in where the torque arms bolt. With our mountainous terrain and relatively low rpm motor, I'd bet that I'll prefer locked on the swingarm, since no way I'd like extra dive when regen braking down hill.

Is there an off the shelf sprocket that can mounted to the 6 bolt disc rotor holes? Or are the guys building these mid drives customizing motorcycle sprockets to fit on the hub side cover?

No off the shelf such sprockets.
There are phase wires in that cover side coming out of the axle too. There is bearly enough space to install regular bicycle brake rotor.

I see two options:
On freewheel hub cover side bolt on sprocket 31teeeth by drilling holes in hub cover or
CNC new cover-adapter for MC sprocket.

Share pics of what can be done to attach MC sprocket to 150mm hub version.

The problem with moto front sprockets is that the largest bore is 20mm and its splined.
Drilling out the hardened steel is a challenge.
Rear sprockets usually have a too large bore for the 44mm disc rotor hole diameter.

So custom is probably the only option.

veloman said:

Is there an off the shelf sprocket that can mounted to the 6 bolt disc rotor holes? Or are the guys building these mid drives customizing motorcycle sprockets to fit on the hub side cover?

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If it were me, I'd make a plate with the 44mm 6 bolt pattern to fit the disc rotor interface, and a 74mm or 110mm 5 bolt pattern to fit any one of a number of chainrings. 74mm for rings under 34t, or 110mm for rings from 34t up. It would be easy enough to get it laser cut, or else drill it using an indexing head.

Modifying a sprocket means having to throw that work away when the sprocket wears out.