mid drive hub motor advantages?

[cajunjay]

I have at my disposal 3 different ebike kits one is a 36v 250w hub motor a 36v 500w hub motor and a cyclone knock off kit rated 48v 450w.

The 36v 250w motor is okay as I run it at 48v but is really just for commuting as it hasnt got much power at all, need to pedal on start up to get the bike moving as to not bog down the motor to much, hill climbing is non existent without pedaling obviously.

Now the 36v 500w kit run at 48v isnt really that bad, along with pedaling it can get upto speed pretty quick and i like this setup the most, the cyclone knockoff is the best performance wise but is a bit noisy for my liking as I prefer something more stealthy.

I have seen a decent thread where a guy made a mid drive hub motor running through some freewheeling cranks just wondering if anybody knows the advantages of running a hub motor this way instead of in a wheel? seems very stealthy and might have alot more torque aswell as being able to run through the gears.

This is the thread I saw and it does look pretty easy (for some) to implement a build like this.


viewtopic.php?f=28&t=17070&start=15

[Whiplash]

Yes, it will give much better climbing ability and a bit more top end if geared correctly. You want to set it up with the highest rpm does you feel comfortable with at the cranks to keep the motor happy...

[iperov]

Better than cyclone - because no gears and overheat.
Better then motor-wheel because spinning weight removed from wheel - more effeciency and removed gyro effect.

[neptronix]

A geared mid drive is going to help you on hills. On flats, not really. A motor is most efficient at it's top cruising speed. If you ride in your fastest gear with a mid drive.. then you've just got a hub motor with a tiny bit of friction added from the extra chain / freewheel / linkage needed.

[cajunjay]

So running the bike through the gears will help with torque and acceleration to an extent, also using the gears will keep the motor running at a more efficient speed.

Kind of the opposite of how a car or motorbike would work, you want to get max rpm out of each gear before changing this will prove more efficient whereas doing this in a combustion engine would empty your gas tank real quick.

Seems like a really cool concept, getting to rev the hell out of each gear before needing to change

[amberwolf]

If you do lots of complete stops and starts, like in city traffic, it will probably be more efficient to run thru the gears, especially if you and the bike are pretty heavy, and the bike's normal top speed is fast (>20MPH). If you haul cargo and have the other two conditions, it would almost certainly be better to go thru the gears.

If all you do is ride WOT for long runs without stopping, there's not much point in the gears.

[cajunjay]

Hi

My bike isnt really heavy at all neither am I, im like 75kg and the bike is about 30kg. I wouldnt be doing many complete stops just slowing down (braking) then accelerating back upto top speed.

From the answers I have here so far some say the hub mid drive is better than in the wheel others say its roughly the same thing


They guy who I pointed out in the original post said the mid drive hub puts out a surprising amount of torque which in a wheel is definately not the case.

[deardancer3]

You asked for the advantages, but you might want to conside the downside of each configuration.

There is no debate that running lots of power thru the chain and derailur make for lots of drive line issues that have to be attended to, vs a hub drive which takes stress off the chain. you will lube, adjust and change chains a lot more often. And you must use the gears all the time or the motor advantage is lost.
emergency stop in your highest gear and the motor is useless until you can downshift.... not true on hub motors.
You learn to shift smoother or you go thru drive line parts faster.

I run a chain drive cyclone because i have to.. big loads, start /stop, lots of hills. This was all a great advantage back when big batteries cost mega bucks to support 600 watt hub motors for max power and long range.

Now, one need not run a chain drive unless the loads/terrain are very demanding and it is important to keep the motor close to peak efficiency for those widely varying loads and issues.

At 225 lbs in the mountains carrying lots of loads, I have no choice. But I spend 4 times as much time on drive line service as i do on everything else.. tires, brakes etc.

I met a guy on the bike path that used to have the niftiest recumbent chain drive... 30mph 70 mile range... he swapped for a lesser efficient hub motor just because of the constant chain line problems.

my two watts worth

[Whiplash]

I will admit my chainlike takes more effort, cleaning and such, but if you want climbing power AND less power consumption to doing it there is only one choice to make...

[amberwolf]

he swapped for a lesser efficient hub motor just because of the constant chain line problems.

That is why CrazyBike2 has a hubbie instead of the powerchair chain drive, basically. But I still want to do the chain drive on the newer version frame if I ever get it finished.

[flyinmonkie]

I have run nothing but chain drives through the rear hub and dérailleur. I don't spend any more time on maintenance on the drive train than I do on my standard non motorized bike. I also have not had any issues with chains or sprockets wearing out faster yet. If you get your alignment correct, then everything wears nicely and runs smoothly.

The biggest differences are starting with installation. The hub in the wheel is going to be the quickest and easiest to install. Lace it in the wheel, come up with some torque arms and wire it up. Anything that drives the rear wheel with a chain is going to need a mounting bracket and time will need to be taken to align chains. That is extra cost and fabricating.

For both systems you will need to figure a way to mount your batteries. A hub in the wheel may give you more room in the triangle, depending on where the motor goes for a non-hub drive.

As for performance, that has really been covered. If you are hauling lots, or have a lot of hills, or want lots of low speed torque and a high top speed, then a non-hub drive is more suitable. If you live where it is flat and you can just cruise at top speed for a long time then a hub drive may be more suitable.

You have to weigh up all these factors to decide what is best for you, or what you want.

Clay

[deardancer3]

Flyin NZ, what motor and wattage you running? do you have a standard type bike with short chain lnes or extended length?

My 360w cyclone was running fine for quite a while till i bumped the cyclone idler wheel shaft, then a few days later I had to make it home without any pedalling (my Health), motor only. Spent weeks trying to find out what all went wrong, found the bent idle shaft, some fried lube in the cyclone xmission, and that 5000 miles on bike components designed for a weekend rider.

Everything is now upgraded, chains, cables, idlers, lube, motor heat sync, derailuer.

I think that a nuVinci or Nexus internal hub would make life much simpler for chain drives.

d

[John in CR]

Cajunjay,

If you're living in cajun land, and you're not planning on swamp riding your bike, then a direct drive hubmotor in wheel is all you need, since the biggest hill around is just a 15ft high indian mound.

Eat a couple of sacks of crawfish for me. It's been way too long since I've been home.

John

[cajunjay]

Well the Indian mound is at least 25-30ft high, you cant have been back home for over 10 years my friend.

The craw fish as still as good as ever but my wife is away and I cant make em the way she does. I'll probably just stick with the hub motor in the wheel as theres not much use going up the mound anymore anyway as the view isnt that good.

[flyinmonkie]

Flyin NZ, what motor and wattage you running? do you have a standard type bike with short chain lnes or extended length?

My 360w cyclone was running fine for quite a while till i bumped the cyclone idler wheel shaft, then a few days later I had to make it home without any pedalling (my Health), motor only. Spent weeks trying to find out what all went wrong, found the bent idle shaft, some fried lube in the cyclone xmission, and that 5000 miles on bike components designed for a weekend rider.

Everything is now upgraded, chains, cables, idlers, lube, motor heat sync, derailuer.

I think that a nuVinci or Nexus internal hub would make life much simpler for chain drives.

d

I was running a brushed currie motor with and average of 2500w and a peak of 5000w. I burned the motor up by running 100amps through it. So now I am running a cyclone 1200w and I am seeing around 2500w peak or so. I am using a Kona dirt jump frame and I drive the rear wheel through the dérailleur after a gear reduction. I DO NOT drive through the cranks.

[bzhwindtalker]

Having a mid drive is also a great thing when you are doing some offroad stuff, jumps ext...
1. Variable gearing let you adapt your pace to the terrain while staying efficient
2. A mid drive gets the weight out of the rear wheel, and does not frock up the suspension as much as a wheel hub
3. Having the weight centered on the frame helps to prevent wheelies and gives you better balance in jumps
4. Using a mid drive means you can use standard wheel sets that can be brought locally for super cheap, Decatlon in France sells very nice 26' disc mtb wheels 40€, when a strong rear hub motor wheel build can cost $$$...

[deardancer3]

Great thread

I hope the OP is getting the data that he is looking for.... this is turning into a nice non defensive comparison of the two drive techniques.

there are people here letting all see the personal side of what it takes and what you get for your investment for chain drive. no free lunch... dont use a kmart bike/components for chain drive.. you need to know how to set one up correctly. there might be some fabrication.. some research might in order. the payback is there if you need it-- a versatile and high performing ebike.

but dont fool yourself... if you are a desk jockey that does not know how to run a perfect chain line.. if you dont know how to tell what quality reliable components are and are willing to buy them... if you are not willing to take the time to get it perfect, be honest, and really consider if a hub motor would be more your style, or pay someone to do this for you.

But if you need the performance, if you enjoy the versatility, if you can and will get it right and take care of it... i think it is the way to go.

all good ebikes will get used a lot and are heavier and faster than a non electric bike, so pay attention to wheels tires and brakes.. frequently

my two watts worth.

[John in CR]

Jay,

I forgot to ask, are those hubbies direct drive or geared hubmotors? If direct drive then the motors are fine up to quite fun power levels, literally thousands of watts. Flat roads and your light load means much can be done easily at low cost or effort. From the sound of it the 500W must be direct drive, since a geared hub would pull better off the line. You may be able to get away with a 5 minute nearly free mod that at least doubles your acceleration.

Be warned though. The chase for more performance is addictive, and just to give you an idea my bike and I weigh almost 400lbs with the backpack I typically carry. My motor is rated at 800W at 48V. With good batteries at 74V and a powerful controller that motor pushes me at 55-60mph on the highway, and leaving stoplights I kick the crap out of every gas scooter I run across. I could never go back to riding a 48V500W ebike. Even with your light load your motor can't get you to the performance mine has, but 40mph and much much better takeoffs are within easy reach.

Have fun and let me know if you want me to walk you through easy mods. You'll need just a phillips screwdriver, a soldering iron, some solder, and a small piece of thin copper wire.

John

[cajunjay]

This has become very informative with loads of decent views and information.

To be totally honest Im not sure if my motor is geared or a direct drive its a standard ebike kit I got from China. Its also pretty big so if I was to run this mid drive it would have to mounted inside the frames triangle which I dont actually mind as I would have my battery in a back pack anyway.

My 48v 250 hub motor is much smaller and that could fit just in front of the bb which would be better but cant see much more power coming from that motor.

What is the mod that you mentioned, sounds simple enough?

[Rollodo]

You may be able to get away with a 5 minute nearly free mod that at least doubles your acceleration.

Be warned though. The chase for more performance is addictive, and just to give you an idea my bike and I weigh almost 400lbs with the backpack I typically carry. My motor is rated at 800W at 48V. With good batteries at 74V and a powerful controller that motor pushes me at 55-60mph on the highway, and leaving stoplights I kick the crap out of every gas scooter I run across. I could never go back to riding a 48V500W ebike. Even with your light load your motor can't get you to the performance mine has, but 40mph and much much better takeoffs are within easy reach.

Have fun and let me know if you want me to walk you through easy mods. You'll need just a phillips screwdriver, a soldering iron, some solder, and a small piece of thin copper wire.

John

Is it possible to modify the geared 1000W rear hub similarly?

[John in CR]

It's just a simple controller modification that makes the controller allow the motor to draw more current. You can often access it through the end cover on the controller making it even simpler. The mod is typically done in a manner that has unpredictable results, but I came up with a method that is both simple and controllable. http://endless-sphere.com/forums/viewtopic.php?f=2&t=31643

Rollodo- This is a controller mod, not a change in the motor. With geared hubs you do have to be more careful pushing their limits, because the gears and "clutch" have hard to predict rpm and torque upper limits and there's no easy way of knowing if you are approaching the limit. With a direct drive motor the limits aren't a defined point where pushing past it breaks the motor immediately like a plastic gear in a geared hub.

[Rollodo]

If a hub motor (or any motor for that matter) is rated at some wattage, how do we know how far we can push it and not let it overheat?

[Miles]

If you want the long answer:

[MattsAwesomeStuff]

If a hub motor (or any motor for that matter) is rated at some wattage, how do we know how far we can push it and not let it overheat?

There are several limitations:

1 - Motor integrity. Spin it too fast, it will tear itself apart.
2 - Motor heat buildup. Get it too hot, the insulation in the wires will melt (probably first), continue adding heat and eventually the copper itself will melt and short. Continue adding heat somehow, eventually the iron will melt (almost impossible). Also, more heat will mean weaker epoxies and material strengths.
3 - Motor insulation arcing. This would be from overvoltage.

#3 is almost negligible. Most enameled wire insulation is good for hundreds of volts before it will electrically arc through this to short cut to the next wire or the frame. So, overvoltage is probably never an issue unless you're doing 10x or something crazy.

#1 is dependent on voltage. More voltage means higher speeds means more structural forces. As a bonus, more speed means the spinning part of the motor brushes past air faster, helping keep it cool. As a negative, that means more "windage" losses, (air resistance) but these are miniscule. On a given motor, you can probably get away with 3-5x voltage (and thereby RPM) without the motor pulling itself apart via centrifugal forces. But it will be delicate. And stress the bearings more. And if you got a lemon that was poorly built but still plenty strong enough in normal range, it may fail. At some point, your losses increase faster than your RPM increase (efficiency per watt drops). This may be as much as 20% at 3-5x.

#2 is really the only thing worth talking about and dominates the discussion, the other two I only mentioned for thoroughness. Heat buildup comes from how much current (amps) are flowing in the wires. Note that this is cumulative heat buildup. Just about any given motor could be run at 10x wattage (call it, 3x voltage, 3x amperage), for a minute or two. You'd put 10 minutes of heat into it in 1 or 2 minutes. After that, you best let it rest for 5-8 minutes (not just normal temp, like, shut it off, drag racing style). Heat is almost the only thing that kills anything electrical, and you can always make the "continuous vs. surge" tradeoff. The motor doesn't care. Think of it like a chunk of metal under a torch.

Almost everything is overengineered, to be *sure* that it could be run at the given current for the given duty cycle (for most of us, 100% duty cycle, continuous). For example, a bridge rated for 200 tons of traffic doesn't fall apart if you put 200 tons of cars on it and then drive an extra vehicle on. (Bridges are often rated at 1/10th their actual calculated breaking point). There is no such thing as a motor than can provide X amps. Only, a motor that someone has decided is okay for X amps in Y situation. It's a somewhat made up limitation. A blender motor is "rated" at 10 amps often, because in expected residential blender use, (few seconds of vroom vroom, 5 minutes to drink the margarita), that's fine. The same motor when used as a continuous fan motor on the other hand, might be rated for 1 amp. "Is it a 10 amp or a 1amp motor then?" is what you're thinking, and the answer is both, it's a made up limitation based on expected use. A fan motor is generally 10x as big as a blender motor for the same ratings.

Helping us is that we're putting these on moving vehicles, in airflow. Generally the more we want out of them, the faster we're going, and the more airflow/cooling we're giving them. This lets us cheat a bit. Drive the same motor at the same load but sitting on rollers in a room, the motor may melt. Note that this matters for hills. Driving a 500W motor at 1000W on the flats to get extra speed yields bonus cooling. Driving a 500W motor to 1000W on an uphill yields same or slower speeds and thus less bonus cooling. What will not kill a motor at high speed will kill a motor at low speed, with power draw equal. Not a problem when obeying rated current, maybe a problem when ignoring ratings.

Here's how to think about heat limitations:

Moving motor parts have X amount of metal mass (copper and iron) which have to stay under Y temperature. That's about it. For max temperature, there's 3 things to consider. One is max temp before insulation melts. That's fairly easy and you can look it up in a book. Two is max temp before the insulation starts weakening and accelerating its way towards failure, perhaps after dozens/hundreds of heating/cooling cycles. Three is max temp where the insulation is fine indefinitely, not really undergoing thermal stresses. If you mistake one of the former for the latter, you may find your motor fails quickly, or, the worst "It was working fine, I took it on a dozen rides and then all of a sudden it failed! What the hell?" That's that #2 in play.

Still... go weigh, lookup, or guess at the mass of metal in the motor. Then look up the efficiency of the motor or test it (if it's 80% efficient, that means 20% of your output is heat energy added to the motor). 1000watts at 80% efficiency is 200 watts of energy pouring into heat. Then look up, or guess, a max temp that won't quickly lead to failure. Then figure from a cold room temp start, how much energy (presume ZERO cooling for now) you have to dump into the motor to heat up that much metal that many degrees. Basic multiplication. Power (watts) is energy per second so you pick any amount of seconds you want to dump the energy you want and that'll tell you how hard you can drive the motor to get there. That'll tell you your drag racing potential. (Motors may take 30 minutes to cool back down to air temp). One thing to note, the tiny little compact RC motors can't be short-term abused as much as bigger motors because there is no way getting around the fact that by being small they are low mass and respond rapidly to heat buildup. There's simple less metal to heat up. A cup of water in a pot on the stove boils faster than a gallon in a pot.

Then, remove the assumption of zero cooling fudge those numbers based on air cooling and try to guess at what point the temperature will stabalize at for a given load/airflow. If the difference indicates it's slightly increasing, it may take 20 minutes to stop appreciably increasing in heat when being driven at that load. One thing that helps, the higher the temp difference between the motor and ambient, the more effective air cooling is because they will rush even faster to match temperatures. The same amount of cooler air in the same time period will heat up hotter and take away more heat from the motor. So, in this respect, the penalty for overloading your motor actually decreases the more you abuse it. There's a bit of a free lunch.

Calculating cooling power requires somewhat complicated math to calculate. Math I barely know or don't really know. Fluid dynamics and rates of exchange and airspeeds and surface areas and all that and in the end even an engineer would only have a ballpark guess. You can easily calculate drag racing energy/heat. You can not easily calculate temperature stabilizing levels. So, don't bother trying unless, well, if you knew how you wouldn't be asking the question you'd be explaining the answer.

So long answer summarized... how do we know? We don't know. It just seems reasonable that they could be overdriven, we tried it, and it worked. The more you want to abuse it, the more of a gamble you're taking. Just like overloading a bridge. The only guarantee is that it will work when used at or below continuous rating.

Note that all of this heat buildup stuff applies to amps only. If you want to jack up the voltage, you'll increase amps too, (and anything you do will lead to increased amps), but not as much as getting the same power out by overloading the motor directly. With voltage you only have to be worried about insulation and structural integrity.

Extra amps, you can probably cheat by 25-50% most of the time just to account for conservative ratings. Extra voltage, much as you want (3-5x, not that you'd ever give it that much), just observe how much extra current flows when you do it.

Bonus complication: the inside of the motor, where not exposed to air, will heat up much hotter than the surface windings and laminations. You will melt the internals while the outside may still feel cool enough to touch. The math and modelling for this is delightfully messy and mostly guesswork.

Easiest way of saving your motor... throw a temperature-controlled breaker onto it (several inside every microwave) so that the motor simply refuses to allow power to flow if it gets too hot. You'll figure out experimentally how much you can punish and abuse it on average.

Complicated way of saying "it depends". And that was without actually explaining any of the math.

Make sense, sort of?

[Whiplash]

Are these temp controlled breakers small enough and are they expensive? I like that idea for sure to keep people from damaging their motors in my kits. I think it would go a long way towards happy customers!