DD Hub as a mid drive motor pros and cons?

Warren said:

I had the paperback decades ago. Looks like it is all available on his site for free.

http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

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You didn't get it from me... :wink:

https://drive.google.com/file/d/0B3fQ3rXOgeWWLTEtcV9vMHRnUFE/edit

macribs said:

Should we really worry to much about squat for an electric e-bike build? I mean lets be honest, those pedals are most for show and legal issues. For me anyway. And for power and torque, we got abundances of it. We can afford to be a little nonchalant about it. Those who pedals electric bike for the exercise might not care about squat either, as they can use throttle to adjust for squat.

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Absolutely we should worry about it on a powered bike. Yes reducing pedal bob is a primary design constraint for MTB suspension engineers but traction is essential to everyone on wheels. If you are in a turn anywhere near the limit of traction on any surface and you apply throttle the last thing you want is to have the weight distribution between the tires change drastically. This could easily unweight the front or back tire and cause it to slip. All the power and all the brakes in the world are useless without the suspension being able to properly apply them to the ground. If you land a jump and immediately hit the throttle then anti-squat could send you right up and over your handlebars. Brake dive can also send you flying. It doesn't mean all ebike frames are useless it just means when designing you should shoot for the best not ignore a century of development.

I've been trying to visualize the anti-squat forces that John in the CR is talking about. I think I get it now. If the bike were 2 lines with a hinge at the pivot point and a tire on each end then the rear wheel trying to accelerate towards the front would have to stand the pivot point up higher effectively lifting the frame its attached to. It clicked when he said higher pivot point provides more anti-squat.

I can also visualize a second reaction where a hub motor induces a force on the swingarm opposite the wheel as if the swing arm were trying to do a wheelie. If the Swing-arm is attached to a bike then this wheelie force would effectively be trying to lift the bike at the pivot point also having the effect of extending the suspension.

So all this leads me to think that maybe hub motors should be mounted in a block that can freely rotate and a linkage directly to the frame could be used to tune the anti-squat the way a chain is normally able to manipulate the swing-arm. Perhaps this is why some 4link suspension bikes have the dropouts on the chainstays and others on the seatstays.

craigsj said:

Regarding 4-bar suspensions, ones with pivots on the seat stays (dropout on the chain stay) are not true 4-bar and are nicknamed "faux-bar". They are, in fact, single pivot designs where the seat stay is really just a long linkage to the shock (typically). They are a bit odd in that the brake is therefore mounted on a linkage component rather than the swingarm itself.

True 4-bar designs include the horst links and the various mini-link designs, not the faux-bar ones.

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Interesting. I have a specialized big hit with what I believe is a true 4-bar horst link FSR setup. It feels totally different than my genesis which has the faux-bar design further exaggerated by the custom swing arm that extends the wheelbase. The genesis has way more bob when the brake is applied whereas the specialized the brake seems to have little influence on the suspension action.

That brake linkage you speak of is kinda what I was picturing with my hypothetical floating hub motor mount.

When I was trying to do a mid-drive setup on the specialized I could not find the effective pivot point of the suspension. I was hoping to mount a jackshaft at that location to minimize chain growth. I suspected the pivot point was virtual and it probably would have had a terrible effect on the suspension even if I had found it.

The genesis has an RC drive mounted to the swing-arm so I have a wide variety of designs to experiment with in my attempts to understand all of this suspension science.

Yes, that's it DanGT. No need to change the hubmotor mounts though (except to spread the tremendous axle forces trying to spin further from the center of the axle), since the anti-squat helps counter the squat forces from the inertia of the rider.

Nice discussion. Maybe it will lead to getting electric motors out of the frame and where they belong, which ideally is centered in the pivot point but anchored to the swingarm. Why tolerate the negative effects of having a motor act directly on the suspension, which is the inevitable result of anchoring it in the frame? As batteries get lighter this will become more and more important as reduced mass will allow our favorite EVs to have more compliant suspensions like modern MTBs. The power of a motorcycle with the agility of a downhill bike is what I look forward to.

John in CR said:

Nice discussion. Maybe it will lead to getting electric motors out of the frame and where they belong, which ideally is centered in the pivot point but anchored to the swingarm. Why tolerate the negative effects of having a motor act directly on the suspension, which is the inevitable result of anchoring it in the frame? As batteries get lighter this will become more and more important as reduced mass will allow our favorite EVs to have more compliant suspensions like modern MTBs. The power of a motorcycle with the agility of a downhill bike is what I look forward to.

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i'm still in design phase so i can still modify but i've been designing the motor to be mounted on the frame. it's just a relatively small/weak BHT motor to be fed ~63v at around 60A max.

you think i'll see a lot of benefit by mounting the BHT to the swingarm? it'll be for general trail riding. nothing extreme

Before this thread I really thought the optimal placement of any motor was just as you placed it on your drawing. In the swing arm pivot point. I look forward to hear what the more skilled ones say about your placement vs on the swing arm. Learning a lot of this thread, things I have never given any real thoughts. The road to a perfect e-bike is like never ending. Just when you feel you got a clear image of what makes a good bike something new pops up and forces you to rethink everything. And the wealth of skilled people and great information on the forum never stops to amaze me. For all this info I would even be a paying patreon.

craigsj I got to admit I started reading the book last night. Like you said it is well written and easy to follow even for people like me without a engineer degree. Hopefully it will stay that way through out the book.

This post was in response to Ryzen's post?

Ok thx craig. I will look closely at the numbers in the morning, about time to turn in here.
The gain is that ratio between front/rear sprocket?

I think the 3T motor is about the fastest winding possible without making motor hard on controllers. To up the RPM I guess volting up would be the only real choice. That does limit usable controllers a bit, and probably will require a more expensive controller.

I will look over the numbers in the morning and try to play with the max RPM to see what the effect will be.

I'm really surprised that racers like Ripperton haven't experimented with motor placement in this manner, because all I see are positives.

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Yes I have experimented with SwingArm mounted motors and I did drive this vehicle and it DID behave in exactly the way I described in my first post.
I cant find any photos of it but it was a large 2 seater reverse trike.
What you all need to realise firstly is that Im not talking about suspension geometry.
I am talking about basic Newtonian Physics ie action = reaction. Still none of you have agreed to the fact that there is a torque reaction in the hub motor axle and that torque acts on the swingarm in this case.
This bike looks like it is ridable so lets see if someone can come up with a video of it.

Ripperton-
Is the torque reaction you speak of caused by the motor torque (red arrow) wanting to use the chain tension to crank it self in a circular path around the wheel axle (blue arrow path)? Or are are you suggesting that it is a reaction due to inertia from the mass of the motor accelerating?

DanGT86 said:

Ripperton-
Is the torque reaction you speak of caused by the motor torque (red arrow) wanting to use the chain tension to crank it self in a circular path around the wheel axle (blue arrow path)? Or are are you suggesting that it is a reaction due to inertia from the mass of the motor accelerating?

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Neither. Its the torque reaction between the magnets in the rotor and the stator teeth.
Under accel, the magnets are propelled clockwise and the stator is forced to turn anti-clockwise, so is the swingarm.
The swingarm is effectively floating, ie it doesnt have 2 wheels holding it level to the ground so it is subject to rotating should any torque be applied to it.
Im reading from Isaac Newton and you are reading from Tony Foale.
Heres the trike I built the power tail for. It has an 8kW Kelly motor sitting under the shocks bracketed to the swingarm and T Belted to the rear wheel.

The Newtonian reference I made was to action = reaction which will transcend time and still be quoted when we are flying around in antigravity pods.
I also never meant to deride Foale but highlight the fact that there are 2 sets of physics working here.
So now you have finally acknowledged the torque in the hub motor axle and even that it has worked its way into whatever framework holding said axle BUT then you think it dissipates into nothingness and has no further effect.
The swingarm is floating because the swingarm / frame relationship is articulated at the swingarm pivot.
Floating means there is nothing holding the swingarm at a fixed angle and any torque applied to the swingarm will change its angle.
The motors rotor/sprocket has a dynamic floating anchor point in the tire contact patch animated by the resistive load represented by you sitting on the bike.
It is from this anchor point that all torque reactions are based (rise or squat).
I have to go now my carpet python just pissed on me.

edited to remove any harsh words.
keeping it scientific.

That yellow bike would have a terrible case of squat under throttle. Yuck.

I learned in an anger management class to to stop, count to ten and then check if I was still in a rage. If I still was on fire I would start the count all over again. As many times as needed. I still can be a hot head but my responses are hopefully better then it used to be. And hey my blood pressure dropped to that of a twenty year old.

The comment I was about to make when I hit this thread was about the book. I am really impressed. He takes it from the very basic and even give us a brief history of motorcycles. I thought this book would be like I was back in school, but in fact it is more like a pulp fiction book you picked up at the news stand to enjoy on a weekend. Hopefully I don't enjoy it so much I don't remember what I've read.

Ripperton, with the motor attached to the swingarm your red and blue net to zero effect on the suspension. There's no need for worries about chain routing effects on suspension. The lines of force on the bike become simplified for analysis purposes, ie contact patch to pivot point for the driving (and braking) force of the motor) along with weight shift during acceleration and deceleration.

John in CR said:

Ripperton, with the motor attached to the swingarm your red and blue net to zero effect on the suspension. There's no need for worries about chain routing effects on suspension. The lines of force on the bike become simplified for analysis purposes, ie contact patch to pivot point for the driving (and braking) force of the motor) along with weight shift during acceleration and deceleration.

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What do you mean "my" red and blue.We are not talking about the same thing.
https://www.youtube.com/watch?v=iRiWvpIawlw
Heres a video of the "Silverfish" trike I built the power tail for. I need a better video to demonstrate what Im taking about but at 12 seconds, Charles gives the throttle a bit of a blip and the rear seems to rise but its not clear enough, the trike is too far away and he doesnt jab the throttle hard enough.
I drove this thing myself and I vowed never to mount another motor on a swingarm ever. Major design fail.


edited

RIPPERTON said:

If you simpletons are too head up arse to listen, its your own fault.

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RIPPERTON said:

What do you mean "my" red and blue. Cant you get it through your thick skulls that we are not talking about the same thing.
You guys are blind. I categorically dont give a shit about the chain routing or the suspension geometry that you incessantly ramble on about.

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For what its worth, I have been trying for 3 pages of this thread to get clarification of the "torque reaction" you speak of. I get it now and agree with your invoking Newtons 3rd law to describe the forces acting on the swingarm. Through that narrow lens I would agree that we aren't all talking about the same thing. However, as soon as that swingarm is mounted on a bike then Newton becomes part of the bigger picture of suspension geometry and function. If you wanted to duck out of the conversation at that point by just stating Newton and dropping the mic that's your choice.

Newton tells us the magnitude and direction of the force. Its then engineering and chassis geometry that allows us to apply that information to achieve a desired result.

I do think that your warnings about the effects of swingarm motor mounting on ride quality are literally examples of you giving "a shit about the chain routing or the suspension geometry that we incessantly ramble on about". I absolutely would not call Craigsj's data and math heavy analysis on frame geometry incessant rambling. Especially not on a bike forum full of diy builders. If we aren't on this forum to share knowledge so we can build better bikes then what is the point?

Based on the work I have seen from you on the electric car forum and your racing a 200kw+ motorcycle I figured you would give a massive shit about suspension geometry and bike mechanics including chain routing. I don't think it makes me or anyone else a "simpleton" for thinking you wanted to talk about geometry when you entered the thread talking about the geometry of that frame. Sorry for the inconvenience.

It'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. My disappointment is not your problem. You have never stated a desire to be some kind of EV role model. I just thought it might be valuable on some level to let you know how this conversation is perceived on my end.

:lol: That's our Ripperton...


If you want to know if your bike exhibits squat or anti-squat, sit on the bike, then stand up, put the front brake on, and gently start to twist the throttle. If you feel the seat start to hike up a few mm - you have antisquat. If you feel it sink, you have squat. Generally speaking, a small amount of anti-squat is a good thing, and any squat is a bad thing.

1+ DGT.

This thread was posted as a chance for me and others to learn about motor placement, the good and the bad. What makes it work and how it works. As an everyjoe with no engineering background I don't have the physical foundation to understand how geometry affects or impact the choice of removing motor out of the rear wheel and into the very front of the swing arm. Most likely I am not the only one chances are that there will others looking into this thread later down the road too. Pls don't derail thread into all hate and vocal comebacks.

I'm no engineer so I would just like to see a video of the bike operating.
A decent video of the bike when throttle on and off will show the real time characteristics vs theoretical Mumbo jumbo.
I'm here to learn what works, build a bike and ride, not discredit anyone's qualifications or experiences.
Is there any footage

jonescg said:

:lol: That's our Ripperton...


If you want to know if your bike exhibits squat or anti-squat, sit on the bike, then stand up, put the front brake on, and gently start to twist the throttle. If you feel the seat start to hike up a few mm - you have antisquat. If you feel it sink, you have squat. Generally speaking, a small amount of anti-squat is a good thing, and any squat is a bad thing.

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thank you sooo much for that clarification

just to understand a single pivot supension now:
in summary, every hub motor driven and swing arm motor mounted bike (no matter if the motor sits in the pivot point or anywhere else on the swingarm) will produce anti-squat during acceleration, and absolutely no squat.
when braking in the rear, it is the opposite: the BB (or foot pegs) goes downwards so it has braking squat.

well, how bad is braking squat?
any other downsides of low single pivots (aside from pedalling influences or such..)?

It doesn't directly belong to this thread, but what about the horst link suspension like my loved Votec V.FR bike has, or the often converted Genesis V2100:



the dropouts which transfer the motor torque are attached to the upper linkage bar just as the brake caliper, so there should be very little squat when accelerating or (regen)braking.

craigsj, my i ask what's your thougts?
is it more a good or rather bad type of suspension for a hub driven bike?

Jonescg-
thanks for that practical tip for determining anti-squat.

madin88-
Here's how I think one would analyze that bike based on just a few days of researching this stuff. Hopefully Craigsj can tell me if I am completely wrong. Looks to me like the pedaling and braking would be pretty neutral for this bike. When I applied the same analysis to my DH bike which is a specialized Bit Hit 2, the anti-squat intersection line between the chainring and axle to IC line was all the way up in the front fork. That is far into the low anti-squat zone which means pedaling will provide very little anti-squat force. This is very much inline with what Craigsj said and also makes sense considering it is a DH bike so its not designed for climbing or pedaling much.


This is another useful graphic from a super informative youtube series about mountain bike suspension.
https://youtu.be/D0bAVTiFyy4

I'm likely going to download the Linkage3 software which is a cad program made specially for bikes. Unfortunately I don't think it will help analyze the effects of a hub motor's torque. That is unless the method for calculating hub motor torque is the same as calculating brake anti-rise just using the bottom side of the hub for the braking force since its kinda the same thing but in the other direction.

Good to know. I wouldn't be spending $300 for the pro version anyway.

So just for a sanity check, are my previous graphics correct? I know there are no numbers but is the method right?

I was just playing around with my dimensions from the Genesis V2100 and the 4 bar looking suspension with the wheel mounted to the chainstay looks like a terrible idea now. If my thinking is correct then the intersection of the instant center line and chainline is way behind the axle in what the youtube guy calls the Negative antisquat zone. If negative means less than zero then that's got to be the worst possible place rigth?

Seems like If I cared about pedaling it then it might be worth moving the pivot higher like this.

The 45deg line was something I kept seeing in youtube vids. I wasnt sure where it came from but it seemed logical enough to maybe be significant.

All this makes me wonder if its best to power a bike through the bottom bracket since that was the engineers intent. On the other hand they werent intending to have people cranking over big drops and hits and pedal bob is different than torque.