There is less urethane and so more vibrations and shock is transferred to the motor. In addition to that, the motor needs to work harder to do the same amount of work. It is direct drive and so a 100kv motor will have more heat and more amps going through it.
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Hub motors are for special uses where certain trade offs are desired. I like my belt system because it is set and semi-permanent with little maintenance after you get rid of the teething problems. Hub motors will cost more due to design costs and less diy required. you basically get a pre made kit. Hub motors are almost pre built esk8 material unless you were re configuring a 149kv sk3 into a diy hub motor.
Yeah that’s what everyone says but no one ever explains why. Is the relation ship between kV and torque/speed not the same as gear ratio and torque/speed?
Since Carvons don’t need to deal with vibration are they not subject to those inefficiencies?
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Isn’t distance traveled over time just speed? Efficiency is energy put into the motor vs the mechanical energy obtain.
Hi @NickTheDude, this is the reason:
From http://vedder.se/2014/10/chosing-the-right-bldc-motor-and-battery-setup-for-an-electric-skateboard/
Let’s look at an example: Suppose an 8 turn motor has one ohm winding resistance. The winding resistance is proportional to the wire area times wire length. Making the same motor with 4 turns would allow twice as thick wire. Since that wire also is half as long, the resistance is four times lower: 0.25ohm. Further, since current times turns is proportional to torque, we need twice as high current with 4 turns to produce the same torque as with 8 turns. The copper losses are the voltage across the windings times the current: UI. The voltage across them is RI, so the losses are RII. This square relation means that doubling the current will produce four times as much losses, however, since we got four times lower resistance the losses are the same for the 4t motor with double the current as for the 8t motor with half the current. Also note that the 4t motor will spin twice as fast as the 8t motor at the same voltage, so it will have double the kv. Putting this together, the 4t motor is equivalent to the 8t motor, but at half the voltage and double the current.
So, regarding KV: different KV versions of the same motor are fully equivalent. KV only affects the battery and ESC choice. Therefore, while comparing motors, lets talk about torque instead of current because torque is proportional to current / KV and, as explained above, the KV value can be changed freely with the amount of turns and copper thickness.
RPM/Losses/gear reduction
Now we know that copper losses are proportional to the square of the torque produced by the motor, and at low RPM and high load they are dominant. As RPM increases, other losses start to add up exponentially. In my experience, these losses start to get significant around 60k electrical RPM, which for a 14-pole motor is about 8570 mechanical rpm (most 50mm+ outrunners have 14 poles, some unusual ones have 18). Because of the square relation, it is desirable to run at as high speed and low torque as possible as long as we stay below 8.6k RPM. To express the square relation in some numbers, having double the RPM and half the torque at a certain power output will cause four times less losses. The lesson from this is that: make sure the top speed you design the skateboard for is at around 8.6k rpm on the motor if you are using an 50mm-60mm outrunner.
Conclusion: To do a fair comparison you have to do the following:
A: Take the same motor and wind it to a lower KV, higher torque output, suitable for a hub drive. Use it inside a wheel with no gearing B: Take the same motor and wind it to a coordinated higher KV, lower torque, use it in a geared system (e.g. 1:2.5 reduction belt drive)
Now both systems result in a board/vehicle with roughly the same acceleration and top speed, but system A has high losses, while system B has low losses. The relation is non linear but a square one!
If you want both systems to have the same efficiency, same losses, your hub motor would need to be a lot heavier than the geared one. This big and heavy motor doesn’t fit inside the wheel any more. We are not talking about a slight increase in size. We are talking about roughly 3-5x the mass of the satellite motor! This motor will also be bigger in diameter and in consequence you will get wheel size gearing, working against you. The motor simply doesn’t fit!
In consequence system A will end up splitting the torque in half, using two motors instead of one. So you will end up needing two motors instead of one and you will still be a lot less efficient than the 1:2.5 geared system with one motor. And there is nothing you can do against it, since you can’t cheat physics!
The only thing you can do is compare to different systems and state that A is better than B or vice versa. But that is BS and tells nothing about the matter itself.
What you can do: You can optimize the motor and make it bigger and use two of them. This is what we currently see. 2.4 Kg of motor(s) vs. single 700gr satellite motor. But you have to be fair and apply the same optimizations and twin setup to the satellite system you compare it with. A race you can’t win if you are aiming at making a system that compares to a geared one. It only works if you compare two oranges to one apple. Apples to Apples doesn’t work.
If you say that the belts are the weak link in a geared system, so in consequence the hub is better because it has no belt, you need to look deeper into the matter.
Limits of Belts: How much a belt can transfer torquewise depends on the small pulley size, belt width and how many teeth interlock on the small pulley, + size of teeth. If a belt system is rates 3Nm and you gear down 1:2.5, that is 7.5Nm at the wheel. Usually you can transfer 1.5x as much, since there is a safety value in the calculations. Some geared systems don’t like belts to hop over (e.g. camshaft drives). But our systems won’t die because a belt hops once a while, so you can assume a 3Nm rated system can transfer up to 1.5x more in real life without having to much of an issue. If you improve the system a bit (longer belt, idler pulley), you can put 12-16Nm down to the tarmac without slipping the belt. The system is about 98% efficient and the 2% losses you have are nothing in comparison to the losses your 1:1 hub will have.
The belt is not to much of a weak link and the acceleration you can achieve is massive. And if you feel like needing 20+Nm on a board, you can always go for a twin drive. But this is crazy anyway and only a very few users can handle that amount of acceleration. 95% of the users can’t bring a good belt drive to the limits. Service is minimal and also hubs will need some service and bearing change (tricky).
The production/build cost The belt is probably the winner, since a single belt drive has the same or better performance as a twin hub. Two ESCs and two motors simply cost more than one ESC, one motor and one belt drive. So you have to compare price to performance wise.
Top Speed Hub setups claim to have the best top speed performance. This is partly true. Since you gear to 1:1 reduction, you have the best efficiency at a ridiculous top speed where wind drag gets so dominant, that you can’t make use of the efficiency at that speed. The motor has a hard time to work against that drag. The best possible setup has gearing which provides the best efficiency at the speeds you usually ride at. Some users face hills and in consequence they should pick a gearing suitable to climb these efficiently. The top speed claim is a statement reading like this: usage of incorrect gearing. Who wants to ride at 40 MPH? It’s ridiculous to gear to this speed in 99% of the cases. If you feel like this kind of gearing is appropriate, you can apply it to your geared system as well. Try to paddle your bike in a high gear at low to medium speeds + climbing hills. This is how your hub motor feels like most of the time. Exhausting, but the top speed is great! You could go to the gym and train your legs to compensate for that inefficiency, buy a tandem bike - or simply use an appropriate gearing. Tour de France cyclists don’t look like Arnold Schwarzenegger in his best ages, they paddle at high RPM and low torque output and use the correct gear for the situation.
Coasting This argument is often used to state that hubs are superior. It is not true at all. If your hub board outputs the same torque as a geared one, the drag produced by the motor will be pretty much the same. Compare Apples to apples again! Hub often simply lack torque and the drag resistance is lower in consequence. You could achieve the same behaviour with a belt system, simply choosing a motor with an equivalent low torque, high KV or use low gearing or smaller motors. If your hub motor has high torque and in consequence good brakes, it is not the best performer when it comes down to coasting. Apples to Apples again.
Hubs VS. Belt:
If you look at the physics its obvious what you want and who is the winner. Still you could argue in both directions. Some boards want to look stealthy, some riders don’t put lots of strain on the system (light, no steep hills, cool environment) etc, some boards compensate with a twin setup and heavy hub motors. Some want the board to be light and don’t want to carry 2.5Kg of motors all the time, some want to use different wheels + wheels from different vendors/manufacturers and experiment, others don’t want that option or don’t care for weight so much etc. Horses for courses! It comes down to personal preference and the average usage.
But if you want to debate the matter objective: Understand the matter and Apples to Apples please!
The entire thread is full from one apple to twin/quad oranges comparison. This is not leading anywhere. Keep it simple: single to single drive for best comparison. Personal preference matters should be separated from technical objective matters. Then you can say: I know the disadvantages but I’m happy to accept them for other reasons - or not. And you know why your hub is getting hot: Having double the RPM and half the torque at a certain power output will cause four times less losses. Losses = Heat. If your hub is getting hot it is simply operating with to much losses because the torque produced is to high.
Frank
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What you are not considering are physical size limitations and the role it plays in finding the best kv for a given size. Going too low effects efficiency. This why we don’t see small motors with really low KV. It is better to have more poles and stator slots if you want torque at low RPM but this is hardly a good solution in motors this small.
Agreed!
Frank
All of this is correct.
All of this is why i’m still running belts on all my builds and try to get people not to jump on the hub wagon just yet. Some people just have to have them though.
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This is the simplest explanation I have seen.
If you rise the number of turns you get a lower Kv (rpm/V) and a higher Kt (torque per amp) But you are obliged to decrease the amps … (under a new limit) so you don’t get more torque
To keep the same power you are obliged to increase the voltage … and returning to the same speed (and same torque but no more). If you keep the same voltage (lower rpm) you are limited to less power
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Barney from the German forum was so kind to ad in a calculator into the VESC-Website. We will try to ad more setups, batteries, motors etc.
http://www.vesc-project.com/calculators
Frank
lord … its like you can hear me muttering under my breath all the way over there…
hubs are almost like putting the pulleys in the wrong places. ITs not only not reduction, its almost accretion. Then they trap the heat on top of generating more of it.
Long stators, fat stators, more copper, less copper… if sinking the heat into the truck hangers isn’t a priority none of it matters as much as we’d like it to. Hubs deal with a fuckton more startup load than belts and then they just cage all that heat. Until they can reliably sink it and sink it quickly they’re going to keep degrading and won’t be something i even consider using on a regular basis.
Most aren’t there yet and the people who are aren’t sharing. I don’t consider Carvons to be hubs. Those are direct drives and solve a lot of problems hubs have. So many in fact that its not the same class of drive system and shouldn’t be called a hub drive. Enertion has hub drives but they’ve calling them direct drives and that’s just confusing people. They’re hubs.The stator is INSIDE the wheel. Everything about the rspec hubs is a vast improvement over everything else i’ve sen but i still don’t want them. Yet.
i can get north of 35mph on 190kv at 16/32 on 80mm kegels. I can get north of forty on 97mm flywheels. I can do that regularly and my fat ass motors are still cool enough to keep your hand on. And that’s on motors that we all know aren’t actually 190KV because of how Jollin was holding her pencil that day and how the wire was coming off the spool. Yes I like to imagine Jollin sitting there in a rocking chair winding all of the motors herself, with the winding wire feeding off of spools nestled neatly in a knitting basket next to her chair, while catching up on Game of Thrones and smiling sweetly.
the only thing attractive about hubs to me right now is how easy they would be to build with. Everything else about them is a non-starter for me.
One good application for them besides niche speed boards is inexpensive and reliable beginner boards. They make the build cheap and make <$700 boards possible, which is accessible to people interested in the sport but have zero experience. That is literally the only reason i’m even looking at koowheels right now. I gave one of my customers one at dealer pricing a couple months ago and he’s already trashed it.
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Because too small is too small. The stator we are using right now is around 4 times the size of the old r-spec 2 motors stator. So according to these formulas, I now have the same efficiency as that belt system with a hub motor.
We’re there, and sharing it.
Besides getting more thane for a better ride quality, what else do they solve? Both the raptor 2 and hummies hubs have an interface that allows us to make different wheels that are easily swappable also.
They introduce new problems too, such as what happens when you hit a stone larger than the space between the motor can and the street?
You can fit a motor 4 times the size into a wheel. We have done it and Enertion did also. This is why heat is not an issue for either of us anymore.
Look, @trampa, you should be the least scared of any of the belt drive vendors out there. I think it will be hard to replace off road boards completely with hubs. But for street boards, with these new round of direct drive/hub motors, we do get the same efficiency as a belt drive now due to the large motor size, so the option is simple for new builders.
Complexity (belt drive), or simplicity (hub motors)? Your getting the same efficiency either way now. It’s just one weights a bit more than the other. And that’s the only thing hubs can’t make up on belt drives, weight. We can match the performance otherwise by simply going larger.
Now you can say well, let me put a motor that large on my belt and pulley system, but again, the belt becomes the bottle neck for transferring power. There’s no bottle neck with hubs. It’s direct power to the pavement.
I honestly think you guys have no idea what the real size of these hub motors are… I didn’t realize how large the raptor 2 motors are until I saw them in person, pictures don’t do justice.
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Rode them already. First board shipped by Jason. A customer from Berlin met up with me… So I know what we are talking about. Even dropped VESC-Tool on, which worked just fine. Reinstalled the Jason FW later again. The motors are huge and there are two of them. I had a Carver with me, single drive 6364, 136 KV, 14/33 transmission. The performance was pretty much the same. And doing the maths from the settings in VESC-Tool, both boards should output the same amount of power (Watt wise). I could not feel to much difference. I gave both boards a full acceleration on the flat and up the hill. So the belt was no bottle neck, since I only had one Belt drive without idler vs two hubs.
Now you can say well, let me put a motor that large on my belt and pulley system, but again, the belt becomes the bottle neck for transferring power. There’s no bottle neck with hubs. It’s direct power to the pavement.
Well, you would wind the motor to have less torque and the issue is sorted. Same torque at wheel but a lot more efficient, single drive instead of twin possible!
Don’t get me wrong, I’m not totally against hubs! I just want people to understand the physics and that comparison is done Apples to Apples only. There is no one horse for all tracks and personal preference varies a lot. It’s the customers choice in the end. The more informed the customer is, the better he can decide what is good for him. And a lot of customers want hubs. Others want belts, so watt. Maybe we will make a hub drive one day, who knows…
Frank
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Lets just compare hub motor prices vs belt drive prices for a dual drive setup:
If we go to torqueboards store, we can buy everything except for esc’s, power switch, battery, and the deck for $480 for a dual drive belt system.
Now, everything in the hub version of those motors (hummies) right now is priced at $450 ($400 per pair if your doing 4wd or we’re desperate for cash, lol).
So for $30 less, you get a simpler motor, that runs just as efficiently, but with only downside being extra weight with the hub motors.
Why would the masses want to deal with belt drives anymore?
You also forgot that for most people, and I mean the vast majority of people, don’t need this kind of power to begin with. They are already more powerful then they need to be…
So even a single drive hub motor might be sufficient for lighter riders in flat areas who are going to go under 20 mph anyways. I watch these people riding all over sf on these cheap boards, and they ride very slow most of the time (under 15 mph), not just because it’s more efficient or the board can’t do faster, but because they don’t feel safe riding any faster. Unless your a skilled rider, 20 mph feels really fast, lets not forget that. To the riders who have been at this for 10+ years, 35-40 mph doesn’t feel unreachable at all, while the majority of riders out there will not want to go this fast.
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I agree, but the problem right now is, there’s a lot of mis information out there about hubs. Since you confirmed from vedder himself that you need a motor 4 times the size in a 1:1 to have the same efficiency for a given torque, and since we’ve shown it’s possible to do so, I think any belt drive vendor should give their customers the understanding that hubs can do the same as a belt drive, just in a much larger package.
The small hubs today are at best, double the size of the motors most are using today in belt drives. So as a result, you get terrible efficiency. These new larger hubs are are closer, if not 4 times the size of the motors used on most belt drive systems. So you can do the same from a hub motor.
Now vyou can use a lrger single drive motor and compare it to a dual hub motor board. But you can’t fit four of those large motors on a board, and I can fit 4 hub motors on any board. So neither is better in this case…
My whole goal on this forum has been t educate people. This is why I’ve written so many guides, and share a lot of what most would call trade secrets. I want to see this sport evolve faster, rather then slower.
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The BIGGEST problem. Cooling. Half of this conversation has been about caged heat. there’s no cage here. The second biggest problem: Wheels wear out and should be replaceable. Replaceable with the wheels you want not the wheels you’re stuck with.
About rocks. Ok so lets take a couple of 6355s and throw them out backboard to get them to a similar distance from the ground as the carvon drives are. Now they’re low as shit and banging on the street. https://www.instagram.com/p/BWokznFgq44/?taken-by=theonlykindajake
yeah motor cans can probably handle some rocks.
Of course different things have different problems. I ordered extra bacon on my steak club today and now i’m feeling a little greasy. IT was different, and now i have a different problem. The question is, are those better problems than you had before?
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Also, when they wear out, I don’t want to be vendorlocked to any certain polyurethane supplier/manufacturer. And I want to choose my wheels too. And I want wheels that are designed to be the best wheels for a longboard, not wheels that have been shoehorned in with other engineering goals. If your wheels suck, then your entire board sucks. The wheels are what makes it work.
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lol, people like Chris come here, and talk about wheels, but the reality is, they are not doing rocket science. There’s no reason why others can’t make wheels just as good. It’s a process, but that’s how they made them in the first place. They didn’t wake up one day, and say, oh, I’m going to start making wheels with this magic formula and they will be great. Give hub motor manufactures time. There will be a wide array of options, and wheels will just get better.
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That is correct. It is simply iterative formulaic science. Making good wheels is an iterative process that has had much, much longer to mature. Hubs have a ways to go thane wise. Materials science just isn’t there yet. You can’t absorb the same kinds of impacts with less thane as you can with more thane. Ride quality is directly affected. Chris didn’t spend several years trying and failing urethane formulas because any fool can make wheels. IF any fool can make wheels now, its because companies benefitting from thane formula trial and error such as Chris’s are popping them out.
Can i call up Labeda and throw $10k at them and get wheels? yes! Can i call Chris up and throw $10k at him and get SuperFly’s in pink and with a bizarre durometer? Yes!
Can i ever possibly get as much thane on a hub as I can on a direct drive or belt drive or gear drive? No!
Heat is still a problem, even though its a lot less of a problem than it was in two of the hub designer’s motors out of a swath of garbage out there. Thane is still a problem, though the degree varies subtly between hubs.
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