The real argument against Direct Drive Front hubs

[caleb7777]

Thanks, this makes me rethink my pedal first controller for my new 9C I am getting.. hmmm

I was going to do a star delta switch mod with relays... this would make this even more likely I am guessing.
You probably shouldn't do that mod on front wheel eh?

 

[caleb7777]

Could you make a picture of the the 3 phases and what causes the lock up?
So that I would know if it would be worse with star delta switch

Thanks

 

[OneWayTraffic]

Isn't regen simply a reversal of current back into the controller and battery?

Why not a simple diode connected in series to the motor?

That would kill both regen and this problem.

 

[Toorbough ULL-Zeveigh]

Notice how silent vendors of non-freewheeling front hubs and resident electronics whizzes have been silent wrt to this thread.

ur reading the wrong thing into the lack of response.

how many times do u need whizzes & gurus pound into ur head that u shouldn't do any kind of high speed/high power DD hub motor in the front b4 sounding like gramps continually berating you to keep turning off the lights, damnit.
the silence stems from this not coming as any kind of surprise, although the particulars are interesting as yet another failure mode & one more reason for pushing from the back.
what more can be said cept 'told ya so' which don't add a whole lot to the conversation.

put it this way.
how many bikes has Ypedal built with a front DD hub?
i may have missed it, but none that i can remember.
his actions speak louder leading by example.

 

[John in CR]

Notice how silent vendors of non-freewheeling front hubs and resident electronics whizzes have been silent wrt to this thread.

ur reading the wrong thing into the lack of response.

how many times do u need whizzes & gurus pound into ur head that u shouldn't do any kind of high speed/high power DD hub motor in the front b4 sounding like gramps continually berating you to keep turning off the lights, damnit.
the silence stems from this not coming as any kind of surprise, although the particulars are interesting as yet another failure mode & one more reason for pushing from the back.
what more can be said cept 'told ya so' which don't add a whole lot to the conversation.

put it this way.
how many bikes has Ypedal built with a front DD hub?
i may have missed it, but none that i can remember.
his actions speak louder leading by example.

TUZ,

We're on the same page, but disagree on approach. I think a lot more head pounding is needed, since the apparent consensus around here seems to be that front drive is ok as long as you take measures to prevent axle spin. One vendor is even going in what I see as exactly the wrong direction by no longer offering rear drive motors after recently liquidating their rear hub stock.

John

 

[dogman dan]

Maybe a few things that happened here in the US doesn't offset data from china where front hubs have been used for years, in the millions. Of course you don't worry about liability so much there.

I definitely think there is a point where hub motors are too powerfull to be safe on a front fork, or a rear dropout. But I don't think 800 watts is dangerous on the front hub, IF , its installed properly. BTW, that doesn't mean torque arms. Maybe at some point, its safer to spin the axle? Rather than go over the handlebars? I sorta think hub motors don't belong on aluminum, front or back.

 

[SamSpeed]

This thread had caught my interest, or more accurately my concern. I've never gone over the handlebars, but have seen it happen and it ain't pretty.

So I did an experiment. I have an Aotema front hub. If it's open, or disconnected, there is very little rolling resistance. I can peddle pretty well and coast pretty far. I tried shorting out two of the leads from the motor and observed spinning by hand there was a significant increase in rolling resistance that seemed to increase with speed. As fast as I could spin it, it would stop right away.

Next step, I rigged up a switch on the handlebars and shorted it at various speeds. This is peddling all the way mind you -- left the battery at home. I started at very slow speeds, shorted the motor to feel the results. Then repeated at gradually increasing speeds.

At any speed that there was a slight increase in rolling resistance, like lightly touching the brakes. But there was a huge and audible vibration that increased with speed. At just over 15mph the vibration was intense so I went no further, thinking I was somehow being unkind to the bike.

The jumper wires and switch got quickly warm indicating high currents. I put on an automotive ammeter (the only instrument I got) and saw that it would swing wildly to AC extremes and so was useless. Gotta dig and see if I can find a suitable rectifier to measure the current.

In any case, with my setup (and my understanding of the problem), I do not see this kindof shorting as a significant risk to safety. The braking effect by itself would not compromise controllability. The axle/dropout connection is strong enough to not fail even under these worst of circumstances.



BTW -- I was like 12 and the girl from down the street came riding by showing off the bike her big brother had just fixed up for her. She might have been trying to do a wheelie when her front wheel just came off. The forks hit the alleyway pavement and she flew like I'd never seen before. I scooped her up unconscious and carried her home...

 

[caleb7777]

I am no electronic guru but could this not be fixed if you had a relay in between the controller and the motor that would disconnect all 3 phases immediately if a warning circuit kicked in?
if you could have a little circuit that monitored regen current and kicked the relay in at some preset current until you reset it.

the relay would normally be closed but if the regen current hit say 10A power goes to the relay and disconnects everything. At most you would feel a quick brake and then BAM! safety.

I just don't know how hard it would be to have a relay controlled by regen current alone.

This would alleviate alot of safety issues though right?

Or would this cause damage to the controller if the phase wires are disconnected?

 

[graevus]

Im not sure a relay would be fast enough for this type of application, depending on the relay...Thing is, it needs to stop the three phase full on signal before it hits the motor; even a 1/10th of a sec might be enough to fly at 20mph. Maybe a frequency filter on each of the 3 phases might work. When the frequency of the phase dropped below a certain hz, such as straight DC, it keeps it from hitting the motor, filters are fast. Your problem occures, on brushless, when all three phases to the motor go and stay high at the same time, right? If none of them could go straight DC the issue would be solved. Probably be tricky to make a filter for the business end of the FETS though, thats a lotta juice. It might work better on the controler side just before the switching FET input.

Makes sense to me, your results may vary.

 

[kazbluesky]

Good Lord !! I'm so happy that I decided on a little extra hassle and bought a rear motor. The thought of all my 120 kgs being thrown down hard face first in front of a bike traveling at up to 30mph is very scary.

 

[Instant Karma]

I would never use a front hub motor again, hall wires got cut because of the motor spinning the axle, before that the forks were spreading out gradually and had to fix that and that was with a 400 hub motor at 48 volts. If anyone sells a 5000 Xlyte motor for the front they ought to be charged with endangerment. I was fooling around spinning the front wheel with the electronics exposed just testing once, with the bike upside down and two of the hall sensors accidentally touched and the wheel stopped on a dime and I was thinking back then how dangerous that would be if a short happened. And if the torque eventually breaks a fork at 20+ mph, good luck. Who knows how many people are injured with front hubs and they end up just putting the bike in a garage to gather dust and never drive it again.

 

[huskydave]

Well the reason we have front hubs is it is very easy to add a rear rack slap on some batteries a controller and your off to the races. The fronthub has many disadvantages 1. extra stress on the fork which it is not designed for. 2. extra stress on the headset bearings 3. added weight to the front makes lifting the wheel over curbs etc.. harder. 3. You will go over the bars if something goes wrong example controller failure or a short in any wire. 4. the axles are usually smaller in dia on a front hub.

I would not install a front hub on anyones bike. I think a rearhub with the batteries mounted near the front of the bike is the best way to go. I also would never install a hubmotor on an aluminum dropout and chromoly is not the best either it tends to crack rather than stretch as mildsteel will. With a smaller motor the fronthub will have less risks but a rear is much better overall.

 

[John in CR]

Thanks for that example Instant Karma...a hall wire short causing instant stop. As spindly as hall sensor wires are and the fact that they are solid core wires, just imagine how easily a short could develop over time with the vibrations of a bike.

SamSpeed,
The issue probably isn't as great with your Aotema hub, because the risk increases with motors of higher torque, but keep in mind that your test was only half of the potential of maximum plug braking, since you only shorted 2 of the phases. Instant Karma's example of a hall wire problem could prove even greater with the controller sending current.

John

 

[diver]

I have two trikes that are front hub powered. They both weigh in at 450 with driver with speeds of 30-40 mph plus. I bet i have over 5000 miles on each and Never, I repeat never had a front fork fail or a hub fall out..90% of my braking is with the front. My riding is all street and paved not off road in dirt. I think you all have fork nitius. ..lol.. If one installs hub right with the tq arm on both sides of hub , fork failure is uncommon and hub will not fall out with the tq arms on each end... I bet more guys go over the handle bars on motorcycles then you all with your front hubs..lol

 

[John in CR]

I have two trikes that are front hub powered. They both weigh in at 450 with driver with speeds of 30-40 mph plus. I bet i have over 5000 miles on each and Never, I repeat never had a front fork fail or a hub fall out..90% of my braking is with the front. My riding is all street and paved not off road in dirt. I think you all have fork nitius. ..lol.. If one installs hub right with the tq arm on both sides of hub , fork failure is uncommon and hub will not fall out with the tq arms on each end... I bet more guys go over the handle bars on motorcycles then you all with your front hubs..lol

Diver,

This thread has nothing to do with the common misconception that the only risk with a front hub is a fork or dropout failure, but in addition there are wiring and controller failures that can cause full force plug braking or stronger, as Instant Karma's example pointed out, controller powered hub lockup. It sound like your trike is built strong and heavy, thus minimizing your risk, but if you think about a curving downhill stretch at high speed and how catastrophic a sudden surprise strong braking of your front hub could be, then you'll realize that even your trike isn't immune to this risk.

John

 

[StudEbiker]

Well, I'd say the BEST way to make sure you don't go over your handle bars is not to get on a bike. However, for most of us here this is not an option. My point is that riding a bike is more dangerous than not riding a bike, riding a bike with a motor in one of the wheels (i.e. doing something the bike wasn't designed for) is more dangerous than riding a bike without a motor in one of the wheels, while riding a bike with a motor in the front wheel is probably more dangerous than riding a bike with a motor in the rear wheel. How much more dangerous is the question. This is a pretty extensive forum with thousands of miles logged collectively by its members on front and rear wheel motors. How many examples of motor shorting, plug braking occurring, and this actually throwing someone off the bike causing bodily harm been reported? And in those cases, what were the circumstances?? Was the equipment being pushed beyond it's normal operating ranges?

 

[StevenR]

I have run regen on the X5 front hub and, unless it can make ALOT more braking under this plug failure, it is not going to put you over the bars. I have seen about 20 amps regen at high speed and low battery voltage. I also blew up a C'lyte 4840 controller that had the cap shake loose when I kicked in regen. Toasted the FETS and blew something off the board when I did it but it just died - no lockup, not even any regen any more. You put enough current through it to put you over the bars and you do not need a fuze in the phase wires - all the parts blowing up and letting out their smoke will open up that circuit in a BIG hurry.

Running an X5 on either end, you MUST have torque arms (plural) for regen and at least one good one in any case. I do not consider the stock C'lyte arm to be a good one. You need to have NO SLACK in the arm - it must not move AT ALL. The arm should be wound up to take out any slop. I use an arm on either side and have them set up so that one is against the front of the fork and one is against the back. Let me repeat, clarify and amplify:

The dropouts should not be required to restrain the rotation in any way. The rotation is entirely restrained by the torque arms.

If the axle spins the bolts go loose and there goes the wheel - front or back. Neither one is a pretty picture at speed with the front only marginally worse.

 

[fifthmass]

Wonderful, I must say I've gotten a little spooked reading this thread.

Back when I first got my 408 I rode to work in a light rain without fenders. I did not think about it at the time but road spray was hitting my controller. After about 6 miles I experienced a sudden strong vibrational decelleration to a stop. The bike was virtually impossible to pedal after that until I disconnected the motor power connector. I sent the controller back to Electric Rider who told me I shorted a FET. They fixed it and sent it back to me. No issues since and now have fenders.

Was that plug braking that I experienced? I was going about 18 mph when it happened and it was more startling than anything. At no time did the wheel lock up or did I lose control.

What are the best torque arms I could get retail online? I'm getting two of them now.

Next motor will be a rear geared motor.

Regards,
Bill

 

[spinningmagnets]

I have a list of plusses and minusses between the various electric kits. The most enthusiastic front-hub people seem to be E-bike riders in snow country. Pedalling provides 2WD, and the front hub tends to pull the bike around curves instead of sliding straight when trying to turn.

If an internally geared motor with a freewheel (Bafang?) froze up from shorting, would the freewheel prevent the dreaded You Tube "Superman flying through the air ending with a face plant" ?

 

[The Stig]

...riding a bike is more dangerous than not riding a bike...

actually if you were to walk to your destination that would be more dangerous than riding a bike.

 

[Dan K]

I just want to chime in here that you don't have to be "Joe 6 pack with no mechanical skills" to go over the bars. I've been building my bikes, component by component, since I was a wee lad. I do 90% of the wrenching on my truck, and 100% of the wrenching on my dirt bike. Top ends, carbs, etc. I race RC trucks, which I build piece by piece. I fly RC planes and do aerial photography, and I build my planes from glider-only kits, building the kit and choosing each component. I also don't drink. So, in short, I'm not drunk when I work on my shit, I do know bikes inside and out, and I am far more mechanical than your average Joe. That said, I lost a front wheel today, and went over the bars as a result. I had been tightening my axle nuts daily, and carrying the wrench with me (as well as the charger). I had steel forks. I think what happened is the force of the motor actually spread the dropouts, although I have not verified that yet. What I have verified are my injuries, and the very expensive damage to my e-bike. Just throwing it out there.

 

[StudEbiker]

...riding a bike is more dangerous than not riding a bike...

actually if you were to walk to your destination that would be more dangerous than riding a bike.

That may be, but not going to your destination at all would be the safest. My point is that how "safe" do you want to be? Dogman went over his handlebars because of a mishap with a water bottle. How many of us are going to stop carrying water bottles now because they aren't safe?

 

[Rassy]

Spinningmagnets wrote:

If an internally geared motor with a freewheel (Bafang?) froze up from shorting, would the freewheel prevent the dreaded You Tube "Superman flying through the air ending with a face plant" ?

Yes, the Bafang will not lock up because of a short, but there are many reasons a front wheel can lock up, such as a squirrel in the spokes or a broken fork or axle, etc.

My main objections to rear hubs include adding power to the wheel that is already fully stressed weight wise (broken spokes) and messing with the original gearing of the bike.

As far as multi-geared e-bikes, those mostly appeal to folks that want motorcycle speeds without registration, insurance, etc. Lots of great examples on the forum, but not of much use for anyone that just wants a normal e-bike for riding on bike paths and at legal and safe bike speeds.

I currently have a Bafang on the front of my recumbent, and it is working out great (of course, if it ever breaks the front fork I'll have to eat crow and post it). However, I am really pro power trailers, which put virtually no additional stresses on the original bicycle components, plus they increase your ability to carry things.

 

[fifthmass]

I just want to chime in here that you don't have to be "Joe 6 pack with no mechanical skills" to go over the bars. I've been building my bikes, component by component, since I was a wee lad. I do 90% of the wrenching on my truck, and 100% of the wrenching on my dirt bike. Top ends, carbs, etc. I race RC trucks, which I build piece by piece. I fly RC planes and do aerial photography, and I build my planes from glider-only kits, building the kit and choosing each component. I also don't drink. So, in short, I'm not drunk when I work on my shit, I do know bikes inside and out, and I am far more mechanical than your average Joe. That said, I lost a front wheel today, and went over the bars as a result. I had been tightening my axle nuts daily, and carrying the wrench with me (as well as the charger). I had steel forks. I think what happened is the force of the motor actually spread the dropouts, although I have not verified that yet. What I have verified are my injuries, and the very expensive damage to my e-bike. Just throwing it out there.

Dan I hope you were not seriously hurt.

What kind of setup did you end up getting? If you got a 408 and that happened to you I'm REAL nervous now.

Bill

 

[Rassy]

Dan K. wrote:

I had been tightening my axle nuts daily, and carrying the wrench with me (as well as the charger). I had steel forks.

Dan, did you have any torque arms on your axle? Sorry to hear about your accident, but as a knowledgeable mechanic you should have known something was wrong if you always had to tighten the axle nuts. I had a similar problem on my very first e-trailer, and was lucky to only ruin some spokes when the wheel folded under the trailer. Since then I have been putting torque arms on everything and have had no further problems.