Why are geared motors worse than direct drive for climbing hills?

I was playing around with the motor simulator and it seems geared motors overheat while direct drive motors have a longer range and do not overheat. Here is a comparison of the G310 vs RH212

https://www.ebikes.ca/tools/simulat...ll&mass_b=120&throt_b=40&grade_b=8&bopen=true

I thought the whole point of geared motors was to thrive at low speeds? Why is it that they seem to underperform direct drive motors when climbing hills?

The point of geared hub motors is to pack the power and torque into a smaller, lighter package.

Unfortunately, for a variety of reasons (less mass to soak up heat, much poorer heat transfer path due to the internal gearing), geared motors tend to heat up more, and overheat faster than direct-drive motors when overloaded.

That said, your chosen comparison isn't exactly fair. You're comparing a tiny, 250w-class geared hub to a large 1000w-class direct-drive hub. So, of course the DD hub dominates.

A much fairer comparison would be the RH212 vs. the GMAC, as shown here: https://www.ebikes.ca/tools/simulator.html?motor=GMAC10T&wheel=26i&cont=C25&frame=full&mass=120&axis=mph&grade=8&throt=36&autothrot=false&cont_b=C25&motor_b=9C212_7.5T&frame_b=full&mass_b=120&throt_b=40&grade_b=8&bopen=true

You're comparing a 2.5kg 350w motor against a 6.2kg 1000w motor. Of course it's going to be worse up a hill.

You might as well wonder why a Tesla P100D is slower than the Volvo FH 16 Tri drive when towing 175 tonnes. Aren't Tesla's designed for speed?

Any way, to your question there are at least two reasons why small geared motors under perform large hubs.

1. Mass and specifically thermal mass. The more metal you have to spread heat, the longer you have before over heat.

2. This one is harder to explain, but basically, the more resistance you have on a motor as a percentage of you power, the more heat you generate. So all motors if clamped to stand still will eventually melt given enough power. So say your hill (well, you and your bike on the hill) is creating a 200w gravity load on your motor. It's a larger percentage of your forward motive force of a 350w motor than of your 1000w motor, so it is less efficient, generating more heat.

If you compare motors that are the same weight and the same rated power, I don't think you'd find that direct drive motors are better except for limited long duration pulls, where the motor can become heat saturated.

There are advantages to DD motors, like reliability, gross efficiency, and cost. Pound for pound and watt for watt, though, geared motors are usually more potent.

If you look at the internal parts, the geared hubs have a very poor heat-shedding pathway from the stator to the outside air.

The direct drive hubmotors have a slightly better heat-shedding path, but adding a heat-transfer fluid to bridge the airgap makes an enormous difference in how much peak power they can provide.

Small direct drive hubmotors exist, but they are rare and low-powered. Since the rotor spins at the RPMs of the wheel, they are very inefficient, and easily overheat. The geared hubmotors have gears (obviously) and the gears typically allow the hubmotor to spin about 5 times for every wheel RPM, so...they increase the wheel-torque, and also increase efficiency.

The current size of the most common large geared hubmotors are right at the limit of how much power the gears can survive. People who have swapped out the plastic gears for metal gears report that the hubmotor runs very loud.

Sunder said:

2. This one is harder to explain, but basically, the more resistance you have on a motor as a percentage of you power, the more heat you generate. So all motors if clamped to stand still will eventually melt given enough power. So say your hill (well, you and your bike on the hill) is creating a 200w gravity load on your motor. It's a larger percentage of your forward motive force of a 350w motor than of your 1000w motor, so it is less efficient, generating more heat.

Click to expand...

Imagine an electric motor with a locked rotor while applying say 500 watts of power. It generates no motion and becomes a 500 watt heater, the efficiency is zero. The efficiency curve is dependent on how quickly the motor switches poles up to a point where other factors like saturation, permeability and reluctance come into play at higher switching frequencies.

Geared motors typically have fewer poles than an equally rated DD, generally about 2/3's the number. Most Geared motors have a 5:1 gear ratio, some even higher like 11:1. 5 * .66 = 3.3 - so a geared motor like a MAC will switch poles 3.3 times faster than a typical 1500 watt DD. That makes it more efficient at speeds up to about 200 RPM hub rotation.

Again these are generalizations, and intended to explain how the efficiencies differ but the numbers are pretty close.

Its complicated, but my simple explanation is that the geared motor is a smaller motor, Less copper in it, less wide magnets, less total potential power.

So its a bit of an apples to oranges comparison. Run both types at say 1000w, and one is running at much more of its total potential than the other.

Then there is the load. The potential load for a dd is a bit more weight than the smaller copper geared. So the same weight, the geared is more overloaded than the DD. Once overloaded, the design of the DD motor sheds heat faster, so it can run longer before the melt down than the geared, which has trouble shedding heat very fast. So,,, don't overload and overheat.

DONT overload either, and either one can climb hills magnificently. Both can climb amazingly long hills of 10% grade, if the total weight of the entire bike and rider is under 300 pounds. Or steeper, if the weight is even less. Part of what I did when I worked for E-Bikekit.com, was overload the motors and ride up mountains. We needed to know what the max load really was, and then we could warranty the motors for less, at 300 pounds.

What I keep wishing to see, is a geared motor with just as much copper weight, and just as many magnets, as the typical DD. It might even have to be heavier than the 15 pound 500w dd motor. But it could handle 2000w easy, and climb walls. Its size would allow even lower gear ratio than 5 to one, and its use would be pedicabs.

Good answers already. Logic.

To make it practical. If you need to climb steep and fast, the DD hub is a must. Steep and slow, you are better with a mid drive.

Geared motors really don’t like being overloaded. No steep climbing for them. But, when you don’t need to climb steep and can help with some crank work, they are letting you build light weight, cheap and efficient.

From a value for money POV:

400-500lb up going up long steep hills likely slowly

Combining a powerful cheap reliable DD hub

with a BB based or left-drive mid drive geared for super torque at low speed.

As opposed to one bigger latter-style motor like LR Big Block XL?

I like the redundancy of two motors when out in the middle of the desert. . .

I ended up getting a Crystalyte H3525 with a 48V battery. It outperforms almost all other motors in the simulator in terms of range on uphills and Grin had a deal on a pre-laced wheel that made it almost as inexpensive as the G310. I can't get a mid drive kit on my handcycle so DD seemed like my best option. It is difficult to gauge how much I need given that I am depending on arm power to compete with my able bodied buddies, so I erred on the side of more power. Hopefully with this kit I'll be able to kick their ass...

Currently I am riding at about half the speed I used to on my road bike before my accident, so I am hoping this 1,000W setup helps me make up the different.

Thanks for all the answers guys. I really appreciate the help.

If you want to see what I am converting, please check out this video I just uploaded with my plans. Let me know if you see any issues I should be aware of. My order has not shipped yet, so I can get some more parts or make changes if need be.

[youtube]TNoAhmKTuk8[/youtube]

MadRhino said:

Good answers already. Logic.

To make it practical. If you need to climb steep and fast, the DD hub is a must. Steep and slow, you are better with a mid drive.

Geared motors really don’t like being overloaded. No steep climbing for them. But, when you don’t need to climb steep and can help with some crank work, they are letting you build light weight, cheap and efficient.

Click to expand...

It depends: I am light (60kg) and I ride fast ( climb steep) (bike 17kg without battery), with 1500W (wheel 20).

No question about keeping up, you'll probably have to stop and wait for them at the top. 100W is a common figure for human power. Your friends are likely putting more than that in, but not 400W. These rigs run at high enough power that the human component kind of fades into irrelevance - and that's how they like to run under an uphill load. If it's a big and steep enough hill to pose any kind of challenge for the motor, I think you will see in the simulator that you get the best outcome at more or less full power, not grinding along at 1/4 throttle to keep pace with the flesh motors.

Anyway ... you may already have "torque arms" on order, little clamps that reinforce drop-outs that weren't built for this kind of stress, but that's worth mentioning just in case - must have.

zeccato said:

MadRhino said:

Good answers already. Logic.

To make it practical. If you need to climb steep and fast, the DD hub is a must. Steep and slow, you are better with a mid drive.

Geared motors really don’t like being overloaded. No steep climbing for them. But, when you don’t need to climb steep and can help with some crank work, they are letting you build light weight, cheap and efficient.

Click to expand...

It depends: I am light (60kg) and I ride fast ( climb steep) (bike 17kg without battery), with 1500W (wheel 20).

Click to expand...

So... I presume that you are riding a geared motor.

Building with a small wheel was definitely your best choice, if you have steep hills. I guess it doesn’t pull 1500w very long because of that, and your low riding weight. Geared motors can’t stand 1500w very long, nor very often.

Yes, Mac8T, I certainly don't have miles of climbs, but with 2000W (peak) it goes over 35km/h, I have fun, I had to lower the amps, it was too powerful.

youre using a handcycle, ive blown a few controllers and its a btch to pedal the 3540 home. I switched to the phaserunner and its been pelted with water,slush and snow where I used a hairdryer to melt it off the phaserunner, they mount anywhere. virtual electronic freewheeling, you can download the app to a cell phone so you make changes to the phaserunner with your cell phone, lets say your throttle dies or pas you could go into the phaserunner and put 10 or 20 amps of virtual freewheeling to get home, you wont be stranded. sometimes Grin has cosmetic defect phaserunners hiding around the shop, both of mine are cosmetic defect but you have to look hard for the defect. id spend the extra $100 for the phaserunner just for peace of mind and reliability.

here check this post out
https://endless-sphere.com/forums/viewtopic.php?f=2&t=105652

I saw the video of your trike, so a front wheel motor. the torque arms. I have a another trike that's a 3540 front hub with those v3 torque arms on my sons trike. I limit that trike to 20 amps and no regen and haven't had any issues but my son isn't even 100lbs. the motors heavy but still spins the front wheel going up a slight gravel grade with only 20 amps@48v

the phaserunner would easily mount where you want it, its tiny, almost fits inside a cardboard toilet paper roll.

you can adjust throttle torque ramp up so you don't torque the crap out of the front fork, the regen is fully adjustable and the regen torque ramp up is adjustable so the regen braking rolls on smooth. the phaserunner is fully programmable and if set-up right you wont need to worry about spinning the axle out of the drop-outs. if you add statorade for cooling, the statorade hasn't been absorbed by the glues that were used in my 3540 that I run at 2500 watts. i don't have much else to add, good luck.

goatman said:

youre using a handcycle, ive blown a few controllers and its a btch to pedal the 3540 home. I switched to the phaserunner and its been pelted with water,slush and snow where I used a hairdryer to melt it off the phaserunner, they mount anywhere. virtual electronic freewheeling, you can download the app to a cell phone so you make changes to the phaserunner with your cell phone, lets say your throttle dies or pas you could go into the phaserunner and put 10 or 20 amps of virtual freewheeling to get home, you wont be stranded. sometimes Grin has cosmetic defect phaserunners hiding around the shop, both of mine are cosmetic defect but you have to look hard for the defect. id spend the extra $100 for the phaserunner just for peace of mind and reliability.

Click to expand...

Thanks for the tip. I actually had the 25A grinfineon in my order so will have to ask for them to switch it out. So are you saying I can connect to the phaserunner with my phone (over bluetooth I assume)? That seems like a useful feature. Reliability is definitely a top concern for me.. Somehow I assumed these controllers are fail-safe, but it sounds like if I don't know what I am doing they are not hard to burn out.. Does this mean if I go too fast on a downhill I could burn out the controller with regen?

eecsflyer said:

goatman said:

youre using a handcycle, ive blown a few controllers and its a btch to pedal the 3540 home. I switched to the phaserunner and its been pelted with water,slush and snow where I used a hairdryer to melt it off the phaserunner, they mount anywhere. virtual electronic freewheeling, you can download the app to a cell phone so you make changes to the phaserunner with your cell phone, lets say your throttle dies or pas you could go into the phaserunner and put 10 or 20 amps of virtual freewheeling to get home, you wont be stranded. sometimes Grin has cosmetic defect phaserunners hiding around the shop, both of mine are cosmetic defect but you have to look hard for the defect. id spend the extra $100 for the phaserunner just for peace of mind and reliability.

Click to expand...

Thanks for the tip. I actually had the 25A grinfineon in my order so will have to ask for them to switch it out. So are you saying I can connect to the phaserunner with my phone (over bluetooth I assume)? That seems like a useful feature. Reliability is definitely a top concern for me.. Somehow I assumed these controllers are fail-safe, but it sounds like if I don't know what I am doing they are not hard to burn out.. Does this mean if I go too fast on a downhill I could burn out the controller with regen?

Click to expand...

phone through a cable to phaserunner. I blew a 40 amp infinion was at grin grabbed a used 20amp grinfinion and blew it within a month 20 amp was gutless and ran hot. me and that bike was about 300lbs. you need the amps and reliability. Phaserunner does thermal roll back. my phaserunner/trike lives outside, its like my winter commuter. so the phaserunner might be -5 Celsius at 6am in the morning. I take my battery attach it to the bike and go full throttle 2500 watts 12km to work then the bike sits there at freezing temperatures for 8 hours, get on bike and go full throttle, snow slush,rain. its never let me down. if I need to haul something I can put it in my bob yak trailer and no problems. I even put 3500 watts through the phaserunner but my batteries cant take the amp draw so I set the watts to 2500.
I don't know if you can program a 25a grinfinion with a CA3 to change torque ramp up or regen torque ramp.

This is a really valuable thread.

One of huge info takeaway is that direct drive hub motors shed heat much faster than geared hubs. It's really important and should have been obvious to me, but I didn't figure it out on my own. I was planning to put a small hub motor on the back of my full suspension bike and ride Moab Practice Loop and Slick Rock Loop. Plan was to climb slow in a low gear and pedal at about 80 rpm and 155 beats per minute. Small hub motor choice was based on low un-sprung weight and need for thrust. Now it looks like heat shedding would be a problem with that choice, on the climbs at Moab.

My bike handling skills off road are pretty bad compared to what they once were and I switched to road riding because of getting hurt on every off road ride, so they were never much. That was 30 years ago. Today the off road skills are gone from lack of practice and old age and the body is far more fragile. That's the reason for slow speed and wanting a low seating position without tearing up the knees from high torque, low rpm pedaling.

This thread is pointing me in the direction of renting a factory mid drive FS bike at Moab and just continuing to ride my DD bike at home. At home, with no significant long climbs, the small, light geared hub on the back of the FS bike would give a better ride than the rigid bike I'm using.

Again, the heat shedding on long climbs is a really big consideration.

How does the BBSHD do on low power output but long and steep climbs?

BB drives and other mid drives are doing very good in slow climbing, as good as the gears available on the bike. You could do the same with the geared hub if mounting it as a mid drive with a set of gears to shift.

With hub motors, you have a certain speed from which they are efficient, but riding slower is building heat. Big hubs and big power is the trick, so you can quickly accelerate above the inefficient speed zone. They are for fast riders of course, and very good at it. The advantage of acceleration to high speed without the need of shifting is making them even quicker, and their weight is giving good heat shedding ability.

Mike,, mid drive it for moab. Not so much because Moab is hotter than Texas, but because you might be taking longer rides than you would at home. More time climbing steep grades per hour than typical when riding at home. And you aren't a hot dirt rider, so you need slower up and slower down.

What I find riding a geared rear motor similar to a mac, on 22 amps controller, is that it works fine on any trail I have any business riding. I don't have the strength to ride for hours and hours, I can't afford the crash on the upper loop of the trails that are rock staircases, and so on. If I get perky and try to ride that shit anyway, I just have to walk the worst bits.

The key thing here is simple, my weight is under 200 pounds. So my motor is not so overloaded, till I start riding up a rock staircase. That is "Bike" trail. Made by bike riders. Get on the forest service horse trails in New Mexico, and you will melt your motor in about 45 min.

There is a huge difference between modern trails made by bike riders and forest service trails made in 1925. Ride the right direction on the loop on a bike trail, and there is a tolerable grade up it, then some wild descent down the other end of the loop. But any trail system, there will be some trails that only the crazy fit younger riders are seen on. You know it when you start up one, and can turn back once you realize it.

But if you mid drive it, you will be able to gear it down, and then climb a trail a bit more over your skill level than you can with a hub motor. Getting down without a broken collar bone, that becomes the problem.

eecsflyer said:

Somehow I assumed these controllers are fail-safe, but it sounds like if I don't know what I am doing they are not hard to burn out.. Does this mean if I go too fast on a downhill I could burn out the controller with regen?

Click to expand...

Not really. I'm sure you're getting the picture here, there is a very wide range of electric motor users here, and the people who are really into it, that we hear a lot from, tend to have special issues that the rest of us don't have because we don't ride 40mph, run 3000W etc. I'm using a plain old KH6 Infineon that came with a kit, from a guy I trust to pick out and configure good hardware, and I sure do not expect to ever burn it out. ebikes.ca likewise. I'm not saying the Phaserunner isn't a top quality unit, just that for ordinary purposes the stuff you're getting is going to meet or beat what you'd get in a commercial ebike and you don't have to sweat that.

I assume this is one of their ready to run kits, so the thing will be configured for the combination. That includes things like current limits, that relate to the battery, which you can more easily mess up with unsustainable current draws etc. I guess it will also be configured to support regen controls using the brake you're getting, which I expect means that while the controller may support "proportional" regen, you won't be getting it because you're engaging it with an on/off switch. So regen will probably run up to like 250W, hardly more than a trickle. That's configurable, but you don't want it much higher because too hard a regen grab could break your front tire loose.

Probably the most interesting thing with controllers and configuration thereof is going to be the PAS support, but it may be kind of challenging to pick that information out of the manuals and other documentation.

No matter how fast you are riding downhill, your controller is not at risk other than in a crash. It is uphill, or in hard acceleration that a controller is most likely to fail. The other common cause is damaged wiring, or poor connections.

if you look at page 52 of this pdf file its the front fork, I wouldn't be getting too crazy without some clamping torque arms, that's why I recommended the phaserunner if hes using the 3525. then with the chain jam blowing the controller, that's not good either.

https://www.sportaid.com/upload/products/19717/19717_1469742628_8271_owners_manual.pdf

actually, why would a chain jam blow a controller?