E-bike mid-drive motors hardly outperforms hub motors

[ebike4healthandfitness]

Geared hubs are much less efficient at shedding heat, and also melt down at much lower temps.

So heavy weights & big steep hills likely better off with DD.

I'll bet a DD that weighs the same as a GMAC would melt down a lot faster than a GMAC....even with statorade.

So why not make a bigger, beefier and heavier locked clutch geared hub motor? If battery tech charging rate for Regen is catching up maybe they should do that?

 

[john61ct]

Best to deal with reality as it is

if wishes were fishes…

 

[Chalo]

I'll bet a DD that weighs the same as a GMAC would melt down a lot faster than a GMAC....even with statorade.

If you think that, it only demonstrates that you don't understand the technical principles in play. A geared hub motor is like a direct drive hub motor enclosed in a box. It hits its thermal limits much more quickly and without recourse.

 

[ebike4healthandfitness]

I'll bet a DD that weighs the same as a GMAC would melt down a lot faster than a GMAC....even with statorade.

If you think that, it only demonstrates that you don't understand the technical principles in play. A geared hub motor is like a direct drive hub motor enclosed in a box. It hits its thermal limits much more quickly and without recourse.

But the geared motor will make less heat.

So while dissipation is reduced the lower amount of heat generated more than offsets that.

 

[Chalo]

I'll bet a DD that weighs the same as a GMAC would melt down a lot faster than a GMAC....even with statorade.

If you think that, it only demonstrates that you don't understand the technical principles in play. A geared hub motor is like a direct drive hub motor enclosed in a box. It hits its thermal limits much more quickly and without recourse.

But the geared motor will make less heat.

So while dissipation is reduced the lower amount of heat generated more than offsets that.

You can wish it, but that does not make it so.

These motors can all be run within their specifications, in which case overheating is mostly hypothetical. But when you overdrive them enough that heat becomes a factor, it's remediable with a direct drive motor but not a geared motor.

 

[ebike4healthandfitness]

I'll bet a DD that weighs the same as a GMAC would melt down a lot faster than a GMAC....even with statorade.

If you think that, it only demonstrates that you don't understand the technical principles in play. A geared hub motor is like a direct drive hub motor enclosed in a box. It hits its thermal limits much more quickly and without recourse.

But the geared motor will make less heat.

So while dissipation is reduced the lower amount of heat generated more than offsets that.

You can wish it, but that does not make it so.

These motors can all be run within their specifications, in which case overheating is mostly hypothetical. But when you overdrive them enough that heat becomes a factor, it's remediable with a direct drive motor but not a geared motor.

John and I were talking about the overheating that comes from going up steep hills with lots of weight. In this respect pound for pound a geared hub motor should always win despite a lower amount of heat dissipation pound for pound.

What you are talking about is high speed on flat ground (wheel speed is high (not low))....yeah I agree DD is better in that area because it has both better efficiency and better heat dissipation.

 

[john61ct]

Never say "always".

I'm shooting for 400# if possible and crossing steep mountains, long ling climbs.

I don't think GMAC could handle it, magic smoke would escape.

Here's a reasonable thread to parse
https://endless-sphere.com/forums/viewtopic.php?t=50703

 

[ebike4healthandfitness]

I'm shooting for 400# if possible and crossing steep mountains, long ling climbs.

I don't think GMAC could handle it, magic smoke would escape.

I don't think it would handle it either. GMAC is just a 3.8 kg hub and even the basic nine continent DD hub (e.g. 2806 to 2812) is 6.4 kg to 7 kg.

6.4 kg to 7 kg of mass with proportionally better heat dissipation would likely win even if it makes more waste heat at low speed.

Buy then.what if MAC one day decided to supersize it's existing 500 watt 3.8 kg hub and started calling it a 1000 watt hub accompanied by a 6.4 kg to 7 kg weight. I think this would be the one to get...not the 6.4 kg to 7 kg DD hub.

 

[BalorNG]

Just like it was said already in this tread, the ultimate bike motor is left side fixed gear belt/chain middrive using RC-grade high KV motors, replacing the rear brake. It can be either extremely cheap, extremely powerful or something inbetween.

This one (on the rear) costs 40$, weight less than 2 pounds for the motor and about 10$ and an other pound for mounting hardware (yea, would be pricier if you don't have access to a large delta printer).
It has about 30nm of torque peak, 1kw continous, 50kmh-ish top speed with some application of human power... from 24v battery!

By marginally increasing the price and increasing weight only by about a 1 pound you can also nearly double the power and torque, but I'm limited by 24v system (maybe I'll change that).

The point about 'hard to fit into a bicycle formfactor' still stands though
Of course, 30nm peak is pretty pedestrian and I'm having problems starting from stop on a gentle uphill even with human power added (entire things plus me weighting a ton does not help things as well).

That's where adding a 'crankdrive' ON TOP of that is going to help things... also freewheels so pedalling is affected only by 'fixed gear middrive' and implementing virtual freewheeling using smart controllers is very easy.

Currently I'm having problems with sensorless motor (VESC HFI didn't turn out as reliable as I hoped), will be replacing it with sensored shortly however.

This way you can have both meaningful regenerative braking, efficient cruising, light weight and low unsuspended mass, and huge amount of torque at low speed on demand (efficient, too!), and since it will be used intermittently - additional wear on 'human drivetrain' will be minimal.

 

[donn]

So ... the small grey box clamped to the seatstay, is the motor? Did you print the ring gear?

 

[ebike4healthandfitness]

Just like it was said already in this tread, the ultimate bike motor is left side fixed gear belt/chain middrive using RC-grade high KV motors, replacing the rear brake. It can be either extremely cheap, extremely powerful or something inbetween.

This one (on the rear) costs 40$, weight less than 2 pounds for the motor and about 10$ and an other pound for mounting hardware (yea, would be pricier if you don't have access to a large delta printer).
It has about 30nm of torque peak, 1kw continous, 50kmh-ish top speed with some application of human power... from 24v battery!

By marginally increasing the price and increasing weight only by about a 1 pound you can also nearly double the power and torque, but I'm limited by 24v system (maybe I'll change that).

The point about 'hard to fit into a bicycle formfactor' still stands though
Of course, 30nm peak is pretty pedestrian and I'm having problems starting from stop on a gentle uphill even with human power added (entire things plus me weighting a ton does not help things as well).

That's where adding a 'crankdrive' ON TOP of that is going to help things... also freewheels so pedalling is affected only by 'fixed gear middrive' and implementing virtual freewheeling using smart controllers is very easy.

Currently I'm having problems with sensorless motor (VESC HFI didn't turn out as reliable as I hoped), will be replacing it with sensored shortly however.

This way you can have both meaningful regenerative braking, efficient cruising, light weight and low unsuspended mass, and huge amount of torque at low speed on demand (efficient, too!), and since it will be used intermittently - additional wear on 'human drivetrain' will be minimal.

Have you thought about adding a planetary gearbox?

Something like the one shown in the attached images?

 

[BalorNG]

So ... the small grey box clamped to the seatstay, is the motor? Did you print the ring gear?

That's a clamp, the motor is small black cylinder A 40$ 6374 motor from aliexpress.
Not a ring gear though, it's a belt pulley. Both the motor and and the belt are virtually silent - at least barely heard above typical tire/wind noise.

 

[BalorNG]

Have you thought about adding a planetary gearbox?

Something like the one shown in the attached images?

Currently do not need one, but that's an option, yes. A typical stepper motor gearbox will make a pretty good pair for a high-KV motor and a 'crank drive', willl make the system pretty compact, I'm not exactly sure about life expectancy but if used intermittently it should last for a long time.

 

[ebike4healthandfitness]

Have you thought about adding a planetary gearbox?

Something like the one shown in the attached images?

Currently do not need one, but that's an option, yes. A typical stepper motor gearbox will make a pretty good pair for a high-KV motor and a 'crank drive', willl make the system pretty compact, I'm not exactly sure about life expectancy but if used intermittently it should last for a long time.

The one in the picture is the Neugart PLE60:

https://www.neugart.com/en-us/products/planetary-gearboxes-with-output-shaft/ple#PLE60

Max output torque is 51.4 foot pounds (re: pound force inches listed in the Neugart spec = .083 foot pounds)
Nominal output torque is 32.2 foot pounds.

Gearbox reduction range anywhere from 3:1 to 512:1. The greater the reduction the lower the efficiency and the lower the input torque needs to be in order to not exceed maximum output torque. (remember max output torque is 51.4 foot pounds so that, for example, would be 5.71 foot pounds max input torque for a 9:1 reduction or .1 foot pounds max input torque for the 512:1 reduction)

51.4 foot pound maximum output torque and 32.2 foot pound nominal torque seems OK to me when we consider an additional reduction from the gearbox to the wheel either by chain or belt will multiple torque further.

 

[JackFlorey]

Or a bif geared mid drive best of all.

Agreed. Hard to beat a mid drive for steep hills/heavy loads.

 

[john61ct]

Biffer the beggar

 

[ebike4healthandfitness]

Or a bif geared mid drive best of all.

Agreed. Hard to beat a mid drive for steep hills/heavy loads.

One problem with the big mid drives (like Lightning rods big block) is that bicycle chains were never meant to deal with that kind of power. Also they will no doubt be hard on the cassette teeth and the freehub mechanism.

 

[JackFlorey]

One problem with the big mid drives (like Lightning rods big block) is that bicycle chains were never meant to deal with that kind of power. Also they will no doubt be hard on the cassette teeth and the freehub mechanism.

Yep. I think it's a mistake to go with anything other than a standard 8 speed cassette with a standard (7.3mm width) chain for a mid drive, and also a mistake to try to put more than about 1000 watts through it (which is what an Olympic class biker can put out for about 15 seconds.) Narrower chains and/or more power is just asking for trouble.

And even if you keep the power down and the chain wide, regular replacements of both the cassette and the chain should be planned for.

 

[markz]

Thats the price you have to pay if you require a mid drive for lots of hills, cargo, heavy weights.
Most people do not require a mid drive, some do.

 

[john61ct]

high-torque IGH and a belt drive

separate the Big Block drivetrain from pedaling
https://endless-sphere.com/forums/viewtopic.php?t=106182

 

[ebike4healthandfitness]

high-torque IGH and a belt drive

That can work up to a point:

https://www.electricbike.com/mid-drive-kit-igh/

P.S. Check out the Kindernay Igh.

 

[Chalo]

high-torque IGH and a belt drive

Gearhubs and belt drives are at odds with each other. Belts don't work right unless they have plenty of static tension; internally geared hubs don't work right if they do.

 

[BalorNG]

One problem with the big mid drives (like Lightning rods big block) is that bicycle chains were never meant to deal with that kind of power. Also they will no doubt be hard on the cassette teeth and the freehub mechanism.

Yep. I think it's a mistake to go with anything other than a standard 8 speed cassette with a standard (7.3mm width) chain for a mid drive, and also a mistake to try to put more than about 1000 watts through it (which is what an Olympic class biker can put out for about 15 seconds.) Narrower chains and/or more power is just asking for trouble.

And even if you keep the power down and the chain wide, regular replacements of both the cassette and the chain should be planned for.

I'm definitely not an olympic level cyclist, but I can output 1000w for 10 sec They can do 2000+.
But that's kinda misleading. It is chain *tension* that kills the chain, and first and foremost poor lubrication.
Human power is highly pulsatile - when you pedal 1000w, you actually doing a 'sine wave' with like 2000w in peaks.

Also, when you pedal steep uphill in a small chainring, combined with low RPM standing pedalling, peak chain tensions are MUCH greater than when you ride at high speed with a huge chairing upfront pumping out like 3kw. What you must take care about is not bending chainrings with extreme gear combos (that's where recumbents shine again), and typical wet lubes turn into abrasive paste as soon as they see a tiny bit of dust.

When advent of wax chain lubrication that lasts for a thousand miles per application and gets chain wear to almost zero, I'd say a middrive will be much more viable regarding drivetrain wear (cog wear will always be nearly nonexistent provided you keep your chain in 'almost new' condition at all times).

Also, my HDT5 belt has very little tension, but after I've made sure everything aligned well never skips - due to rather pedestrian torques and, most importantly, not much belt tension but huge pulley.

Belts are not great when, again, paired with human power that is low RPM and high torque and needs considerable *multiplication* to get to useful speeds... If you don't care about overall efficiency much, than electric transmission with automatic gear shifting and dual motors is perhaps the most attractive option.

I've experimented with that sans gears and kinda liked the result:

But with motors that were severely underpowered to fair. With a bit more powerful motors and gears it would be a blast - 'always being in a right gear' is pretty cool.

 

[ebike4healthandfitness]

separate the Big Block drivetrain from pedaling
https://endless-sphere.com/forums/viewtopic.php? t=106182

Inrunner motor (the design of motor used by lightning rods in their mid drive kits) is very good at shedding heat.

Would be interesting to see an inrunner, planetary gearbox and motorcycle chain or belt driving a sprocket attached to the left side of a bicycle hub. Then compare this to Lightning Rods big block mid drive kit with each using a large enough battery that regen isn't held back too much for the left side drive arrangement.

Hypothetically the Lightnings Rods big block should win in any contest involving the heaviest weight on the steepest hill. This because it has lowest gears available to it.....but then again at such heavy weights and incline how much can a bicycle chain, cassette and freehub really hold up? If the bicycle components are the weak link then it doesn't have advantage. Who knows maybe single speed with motorcycle chain or belt (driving sprocket on left side of rear hub) turns out to better at steepest hill and heaviest load? (Not because it has the most torque - it doesn't - but rather because it's thicker chain running a perfectly straight chainline doesn't break, etc.)

Edit: I found some evidence Lightning Rods big block kit is also available as a right side drive single speed with what looks like thicker chainring, chain.and cog. I am assuming this freewheels and thus doesn't have Regen.

 

[ebike4healthandfitness]

Here is an article about Lightning rods Big block mid drive:

https://www.electricbike.com/lightning-rods-big-block/

Interesting that the motor used on the big block kit comes from china with a fan (See text under the second picture of the article)...but lightning rods removes the fan.

A fan should allow an inrunner motor to dissipate even more heat. I wonder if a left hand side drive single speed using that same motor would allow keeping the fan?