Pikes Peak Race--Entering?

[Tiberius]

I could never do this race. The top is over 14,000ft? I'd surely get nasty altitude sickness.

Probably. The rules with aircraft are that the pilot has to go onto oxygen at 10,000 ft and the passengers at 12,000 ft. Unless the cabin is pressurised of course.

So the aviation authorities don't think people are alert above 10,000 and they don't think they should be there at all above 12,000.

Nick

 

[Tiberius]

IIUIC there are several issues with motors and controllers blowing up.

With motors its almost always a thermal issue. They are less efficient at lower rpms, so the worst thing to do is to run them at high input power and low speed. Most of the input power ends up as heat. In that case the heat dissipation will go down if you turn the throttle down.

With controllers there are two effects. The thermal one isn't purely about the current delivered. At less than 100% PWM, some of the current circulates through the body diodes of the FETS instead of the RdsOn resistance, so less than WOT can generate more heating. In most systems, I guess the worst case is about 2/3 WOT, but again it's going to vary with motor speed as that affects the current.

But there's another effect too. There are some pretty nasty transients generated with all the switching going on. As you vary the throttle position and motor speed you sweep the timings and frequencies around and there's a good chance that you will hit a resonance somewhere. That can generate large overvoltages in the circuitry and blow the FETs. That's the likely cause in the cases of controllers blowing up at low throttle settings.

Nick

 

[kfong]

Don't discount the altitude, especially if you are coming from a location that is much lower as I did. I usually need a day or two to get use to any high altitude ski resort. You get winded very easily. My foot climb up Pikes Peak was very tiring. If you are not in good shape or acclimated to the altitude. You won't be much help to the motor, if any. I took a nice long rest while at the top, it still did not help when I snowboarded down. I practically had to stop every couple of turns to rest and catch my breath. I was rather bummed that the ride down wasn't as epic as I had hoped it would be. The altitude just kicked my ass that time around.

 

[John in CR]

I don't disagree with Luke at all, but suspect that what he's observed was a not pedaling style of riding.

I still maintian that you can climb a big long hill cool enough by throttling back. But you MUST also pedal that thing enough to put the motor back into the "happy place". If you don't, you will melt er down. At full thottle blasing along on flat land, you use few watts, you see this on the CA. At 3/4 throttle, you see the same effect, IF you pedal up to a speed that allows the motor to work less. No doubt the controller is getting hotter than at full throttle. But what the controller "feels" is as though it was not climbing a hill, but just motoring down the road on the flat, in economy mode. Which doesn't make a controller well matched to its motor melt down. I've never had my controllers get abnormally hot climbing a large mountain at 3/4 throttle. Half throttle is never enough for a big hill, so I never tested that in real world. Always at least 3/4 throttle, and 10% sections would take full throttle anyway.

Dogman,
Don't forget that you've melted hubmotors with your method, so it doesn't work too well. I don't pedal, and I fly up mountains at 30+mph with a motor that has an almost identical surface area as the 10 turn 9C you melted at much lower speed.

 

[Bike_on]

Sounds like we (endless sphere folk) need a couple of entrants. Each would use a slightly different strategy, so as to try to discover what would work, or not. Each entrant would discuss with the other their strategy (and stick to it during the race no matter what). Maybe someone would try WOT, the other attempts to average 20mph with pedaling, another 15mph with pedaling, etc... We don't want everyone going full-tilt-boogie up the hill (like in the Death Race). We just want to beat Opti, and the record.

The more it is discussed on ES, the less positive effort I read. Are there any committed ES contestents yet using a hub design? Will OPtibike remain the Best Mountain climbing e-bike in the world, by default?
Who?
With what?

 

[John in CR]

Rpms is what keeps your motor cool by dissipating more heat, and the small gains in less heat generated as calculated by Alan are more than offset by diminished ability to dissipate heat. Anyone who doesn't think this is true, just get your motor hot, stop and turn off your motor, and watch how crazy long it takes to get cool. Then do the same, but instead of turning it off, lift the wheel and run it WOT. Despite the fact that you're running it at near 0 efficiency, it will get out of the thermal danger zone much more quickly, because the turbulent air movement both inside and outside of the motor greatly enhances the cooling, and just like wind resistance relative to speed, the change isn't linear.

Proper gearing to enable high rpms up the maximum grade of the ride is the route to success. On unknown roads and grades, all you have to know is your motor's limits and what minimum speed you need to be able to maintain at WOT. On grades that push you below that speed you can't maintain a continuous climb at any throttle position, and you will have to stop for a cooling off break, which I like to do while stopped running the motor with the wheel off the ground. Each of the arguments presented to the contrary omit critical parts of the puzzle.

My motors absolutely ran hotter up mountains when I ran them at lower power resulting in lower speed. The same mountain, identical bike, same voltage pack, with the only difference being current limitd, and now the motor runs cooler at higher power due to the higher speed that the higher current limit creates. Actually, I'm running about 20lbs more load at higher speed, because I've gained 10lbs and I added 10lbs of battery. The only detrimental difference is that the minimum speed threshold has increased, since running higher power the motor has to dissipate more heat since I doubt efficiency has increase much.

Next in line is blowing away the common misconception that high turn count motors are better for climbing mountains. They are slower, lower power motors, and are actually worse for climbing mountains. They're good for limiting top speed and give you more pulling torque at low currents, but it's only beneficial for short hills. In continuous operation up mountains that advantage evaporates due to the mismatch of the narrow power and efficiency curves.

BTW, this is all with my daily rider cargo bike with the motor sealed and stock. Nothing has changed since I installed in in Dec '08. My ventilated motors run cooler at higher power, but that's outside of this topic, other than to say for a ride up Pike's I would absolutely go actively ventilated with a few blowers mounted in the drum brake cover, forcing air in that way.

 

[Alan B]

I don't disagree with Luke at all, but suspect that what he's observed was a not pedaling style of riding.

I still maintian that you can climb a big long hill cool enough by throttling back. But you MUST also pedal that thing enough to put the motor back into the "happy place". If you don't, you will melt er down. At full thottle blasing along on flat land, you use few watts, you see this on the CA. At 3/4 throttle, you see the same effect, IF you pedal up to a speed that allows the motor to work less. No doubt the controller is getting hotter than at full throttle. But what the controller "feels" is as though it was not climbing a hill, but just motoring down the road on the flat, in economy mode. Which doesn't make a controller well matched to its motor melt down. I've never had my controllers get abnormally hot climbing a large mountain at 3/4 throttle. Half throttle is never enough for a big hill, so I never tested that in real world. Always at least 3/4 throttle, and 10% sections would take full throttle anyway.

Dogman,
Don't forget that you've melted hubmotors with your method, so it doesn't work too well. I don't pedal, and I fly up mountains at 30+mph with a motor that has an almost identical surface area as the 10 turn 9C you melted at much lower speed.

John, your hills do not compare with Dogman's low speed off road riding. And he is absolutely right - if you are dumping 2-3kw into a hubmotor that is essentially stalled, it will melt quickly. If you pedal that same setup to 15 mph it will be fine. But look at the difference - by pedaling we have extracted significant amounts of work from the motor (it is doing the climbing, the pedaling is almost effort-free) which means we have moved it into a speed efficient range instead of a stall inefficient range.

We already established that low speed inefficiency melts the motor, not a little less throttle. Don't confuse the two when they occur together. If the speed drops too low under heavy load, reducing throttle reduces heat but not enough to save the motor. If the speed is low and load is high, at any throttle setting, the motor is in danger. That's when you change gears, pedal, or push.

There are several effects going on here, and separating them is important to understanding the system correctly. Motor efficiency and PWM losses are separate effects. Resonances and transients are yet another set of effects. Add to all this the most common controllers we use are not very good at FET switching. Add to that the modifications to push them into territory they were never designed for, and you get some spectacular failures that lead to some of these misunderstandings. Look at the FET drive signal quality in one of these controllers and it is no wonder that their PWM losses are higher than they should be. But we don't need to accept that as "the way it has to be". It can be improved, and there are several efforts ongoing to make controllers that will be better, as well as better commercial products available being tried.

We have also established that a lowly pair of 9x7's could easily make this climb, according to Justin's motor model. But it is a significant effort and investment to try, so perhaps no one will bother. And if someone did, and beat Opti, they would just claim it wasn't fair to use two motors, or it wasn't fair because it used too much power, or whatever. This is all interesting, but it is not important to many. I hope someone tries it but I'm not holding my breath.

 

[MadScientist]

My motors just highlight the controller issue. It doesn't change the simple fact that the relationship of the power and efficiency curves changes ... for the worse as you increase the turn count in the windings of an otherwise identical hubmotor.

That does not make sense. A BLDC motor's Km constant is independent of winding. In other words resistive losses are a function of torque, not turns. Iron losses (eddy currents) depend only on n*I (turns times current) - they are determined by torque (and speed) and are likewise independent of winding. Put plainly, re-winding does not change motor efficiency at a given torque and speed.

Of course, you need to wind for a Kv that is compatible with your battery and controller. Generally the lowest Kv that provides the power needed at your desired top speed is best.

It quickly becomes obvious that the lowest turn count motors are far better motors, because not only are they capable of greater power, but their prime operating range is very broad. For a real eye opener take the 5302 and pair it with just a 20A controller and 66V and see how broad and how well matched the power and efficiency curves are.

I looked at this combination on the ebikes.ca simulator. It predicts a maximum speed of just under 32mph (flat road, no wind), using 920W at 72% efficiency (662W net). That's assuming it takes 680W to maintain 32mph. Now, look at the 5305 hub (keeping other factors constant) and you'll find it hits the same speed but at 82% efficiency (820W in, 672W net)! That's 100W less heat generation: 150W of losses for the 5305 compared to 257W for the 5302.

To succeed with that kind of set up, you just have to make sure you can maintain a certain speed up hills.

If you want to build a special purpose Assault on the Peak bike, choose the torquiest hub(s) you can find, and run at efficient power/speed combinations. A pair of 5305's laced to 20" wheels would do the trick. Much less than that, and you'll have some challenges coping with 10% grades and gale force winds near the summit. Of course a strong wind at your back might just be what it takes with a more conventional (and generally useful) configuration. Has anyone checked the weather report?


On another note, I am excited about a prototype ebike Josk K. at RunAbout Cycles is building using Ron Z.'s 750W chain puller. I've offered to sponsor Josh's entry in the ride. Let's hope the bike is ready!

 

[liveforphysics]

This is all interesting, but it is not important to many. I hope someone tries it but I'm not holding my breath.

I can absolutely 100% win this, even if I have to use a hubmotor.

The problem for me is lack of incentive.

Even if you bring it and win (which I would easily do), then they say, ohh, you brought an illegal hot-rod motorcycle with pedals and won (even though it would be a bicycle with a hubmotor).

The logistics cost to glory ratio seems very poor on entering.

Perhaps somebody wants to make a wager to create some incentive, something like the logistics costs of attending paid to the winner perhaps?

 

[MikeFairbanks]

Has anyone considered bringing in a ringer?

What I mean is that we could find a college student who rides competitively and get him on a good e-road bike.

Something to think about.

It would take tons of training to make it, ebike or not.

What kind of motor is on that Optibike anyway?

 

[Green Machine]

A ringer????

If you mean opti ringer you mean nimbuzz's 90lb asian girlfriend riding atop a hopped up 1500 watt opti with bunch of lipos strapped to her back strap on the back style...and from what i hear nimbuzzes girl is in very good riding shape...let's just call her a "jockey".

But in ES terms...i think physics would count as a "ringer" ....and physics 120lb girlfriend riding atop a physics machine....now that.....that is from a differnet stratosphere....its what they call in the industry a "physics jockey". And from what i hear physics has got a whole stable of ringers from all different weight classes ready to gallop for him on any one of his stable full of electric horses.

But seriously guys....do you really want to go there? Boondocks colorado? In the peek of summer?

This is no fun anymore...this is like a NBA allstar team showing up at a denver high school basketball team...yeah its high altitude...but these are nba allstars forget-about-it-they-will-cope...lets stop being bad ass bullies and just forget about this "sunday ride".....what do you guys say we put a lock on this thread and call it quits? I think ES already won the race theoretically... lets just run the race in dr bass's new e bike dyno just for play play and drink a beer and call it finished. Why pick on opti's only clame to fame besides for being a top class fitness machine for overweight seniors?

And all this techno mumbo jumbo really really reminds me of how the US analayzed the iraq 3rd largest military in the world in the press for months before flying in with its airforce bully session.

You guys realize if the ES gang shows up to this "ride" its just gonna be a big bully session? Come on show some respect and some sympathy. Opti need its Pikes Climb Title for its entire 12k bike marketing scheme.

i am sure i can get the opti top brass to concede this race and even donate to the ES fund....i will arrange an electric power breakfast between tyler and craig and come up with some agreement...lets just redirect the entire es army to SF instead of boulder.

How about the sf hill climb on may 14th??? Now thats a race not a ride. Lets plan for that one instead.

 

[John in CR]

Alan,

If the 100W or so that you can add via the pedals is enough to make a difference then you're way underpowered or going way too slow. If on a continuous climb your motor is at an equilibrium right at it's thermal limit, then slowing down will push it over the edge and overheat. It's irrelevant that less heat is generated, because the motor also dissipates less heat. I appreciate that it's counter-intuitive at first, but our statements are based on real world results, and once you consider the relationship of rpm and cooling capacity for a given motor, they correspond with the numbers coming out of the simulations, and they also correspond with real world failures too.

Also, your view can't reconcile the fact that my cargo bike zips up an 8% grade at 35mph with a total load of 375lbs, much less that it runs cooler doing so than it did at 25mph. Yet that's exactly what happens. My motor isn't significantly more efficient and has about the same surface area to dissipate heat and obviously can't handle higher temperature than 9C's, but that load and speed requires significantly more power, so what happens to all the extra heat? With a 20" wheel, my motor spins faster at 35mph than typical hubmotors, almost 600rpm.

Thanks for being persistent with the incorrect conclusions, because I just accepted the results before, and this discussion really forced me to fully understand why.

BTW, I agree about a dual hub rig as the easy route, and I'm still baffled why Dogman or someone else didn't show up with a 2wd at the Death Race and bring home the gold for hubbies. Paul's a fine rider, and built a solid bike, but it's not like he set the bar very high in terms of power.

 

[Alan B]

John, there is much about the physics of how this all works that you are apparently not grasping. Perhaps this is because you don't pedal your ebikes that you miss this experience.

Let's take a really simple case. When I had this experience the first time it took a moment to understand what was happening:

You are sitting on an ebike on a 10% grade. The ebike you are on has just more torque than required to roll up this hill, full throttle goes uphill but very slowly. You are putting 2.5 kw into the motor, and clearly most of it is going into heat.

So you start pedaling. Amazingly, it is like pedaling on a level surface with a tailwind. It takes very little effort to pedal at 15 miles per hour up this 10% grade. Less effort than pedaling a standard bike on a flat road at that speed. The power input to the motor is about the same, 2.5 kw. But now you are extracting a lot of useful work from the motor, so much less is going into heat. The motor is fairly efficient.

It is a balancing equation. It is not your 100 watts plus the motor's 2.5kw. It is the motor's torque ofsetting the gradient, and your 100 watts working against a very light remaining load. So 100 watts against almost zero. Huge difference.

It is surprising the first time you experience it. Clearly 100 watts should not make that much difference. But in fact it does. The physics is just not quite what one would expect initially. It is like pedaling a frictionless bike.

 

[MadRhino]

..lets just redirect the entire es army to SF instead of boulder.

How about the sf hill climb on may 14th??? Now thats a race not a ride. Lets plan for that one instead.

We're just discussing how a hubmotor should be set up do the long climb, cause it's an interesting challenge. This is theory, and it's unlikely that one of ES member will show up there this year to do it, since it's not a race.

Your SF quarter mile hill race has alot more chances to attract ES members. It does not need alot of discussion though, almost everyone has that kind of climb near enough to experiment, and find by himself what is needed to compete. If I was closer, I would be there for sure, for it's my 2nd favourite race, after racing it downhill of course. We have a race here, where everyone start altogether at the top, and ride any trails they want to a meeting point at the bottom. Considering that the nountain is full of trails and the bets are sometimes considerable, it is a very strategic, and very fast race.

 

[Alan B]

..lets just redirect the entire es army to SF instead of boulder.

How about the sf hill climb on may 14th??? Now thats a race not a ride. Lets plan for that one instead.

We're just discussing how a hubmotor should be set up do the long climb, cause it's an interesting challenge. This is theory, and it's unlikely that one of ES member will show up there this year to do it, since it's not a race.

Your SF quarter mile hill race has alot more chances to attract ES members. It does not need alot of discussion though, almost everyone has that kind of climb near enough to experiment, and find by himself what is needed to compete. If I was closer, I would be there for sure, for it's my 2nd favourite race, after racing it downhill of course. We have a race here, where everyone start altogether at the top, and ride any trails they want to a meeting point at the bottom. Considering that the nountain is full of trails and the bets are sometimes considerable, it is a very strategic, and very fast race.

The hill climb is only a few miles from here, but I will be a couple of hundred of miles away on that date. My commuter ebike will easily make that climb. Sounds like fun. Hopefully no injury and no unintentional plasma. Looks green enough they won't start a fire, at least.

 

[John in CR]

John, there is much about the physics of how this all works that you are apparently not grasping. Perhaps this is because you don't pedal your ebikes that you miss this experience.

Let's take a really simple case. When I had this experience the first time it took a moment to understand what was happening:

You are sitting on an ebike on a 10% grade. The ebike you are on has just more torque than required to roll up this hill, full throttle goes uphill but very slowly. You are putting 2.5 kw into the motor, and clearly most of it is going into heat.

So you start pedaling. Amazingly, it is like pedaling on a level surface with a tailwind. It takes very little effort to pedal at 15 miles per hour up this 10% grade. Less effort than pedaling a standard bike on a flat road at that speed. The power input to the motor is about the same, 2.5 kw. But now you are extracting a lot of useful work from the motor, so much less is going into heat. The motor is fairly efficient.

It is a balancing equation. It is not your 100 watts plus the motor's 2.5kw. It is the motor's torque ofsetting the gradient, and your 100 watts working against a very light remaining load. So 100 watts against almost zero. Huge difference.

It is surprising the first time you experience it. Clearly 100 watts should not make that much difference. But in fact it does. The physics is just not quite what one would expect initially. It is like pedaling a frictionless bike.

It takes a lot of gall to accuse me of not grasping the physics, when your attempt at balancing with pedal power misses the mark wildly. To climb a grade at a certain speed requires a fixed amount of power, period. If you input 100W of that with the pedals, then the motor has to make up the difference, period. If the motor is in it's very low efficiency point and the power required from it at the wheel is more than some nominal amount, then you will melt the motor. Dogman and everyone else who has burned up hubbies trying to climbing mountains has proved it all too well.

The correct way to go about it would be to know the minimum speed your motor must carry up grades. Then if the grade gets so steep that you start to fall below that speed, add your pedal assist to try to maintain it. If that doesn't happen, then you have to drop down to the other end of the spectrum (remember I mentioned 2 points to cross in a long ago post), where you pedal up the mountain and add what little assist the motor can provide without melting at that low rpm. You better have a heat sensor and really know the motor's limits, because that way is playing with fire since there's little room for error. That's definitely not something to encourage others to do. Even an experienced guy like Dogman has melted motors that way. Plus the phase current spikes of very low speed high load operation is likely to kill the controller while you're focused on trying not to blow the motor.

 

[dogman dan]

Exactly right John. Especially about the motor needing a minimum speed to make it up a long grade.

except for one minor point.

All but one of my melted motors were happening when trying to WOT up a hill or series of hills. I have never melted a motor or controller while walking the razor edge, inputing a minimum wattage, and pedaling like hell. But you are darn right, it's a narrow sweet spot, and not easy to stay in for long. Thankfully, the hill I ride the most is only 1.5 miles long. Riding with a thermometer inside the motor was a key thing for me to learn that method. I could be dead wrong, but my impression was that if you put less watts in, then the minimum speed can be less. You might be even less efficient, but the key thing is the heat is not more than the hub can radiate. Range will suck, but you get up the long hill unmelted.

The one melted motor on flat ground was at the death race, trying to run with a flat tire.

 

[Alan B]

OK John. Sorry if I used the same tone you have used with me.

So, to summarize, you suggested early on in this discussion that I run Justin's simulator, and I did so, showing that it in fact contradicted some of your theories but you did not accept that, and now I showed an experiment that is both simple and has been conducted by myself and others, and you indicate it is invalid.

I guess we just aren't going to be able to help you with this. I tried. Hopefully Luke will find a controller that works better for you since some of your problems come from flaws in the controller, not the physics. This stuff is not simple, so we all need to seek better information and more accurate data. Unfortunately some of the information and data we are presented with is bad, and we need to work through that. Make sure to check your assumptions and do the calculations. There are many ways to misinterpret the data. Physics is not easy or simple.

I do hope that others enjoyed the discussion, and that some useful learning has taken place.

Enjoy that wonderful CR weather! We're having a little of that here in the Bay Area this week.

As far as the non-race to Pike's prominence is concerned, maybe we should all chip in a few bucks for Luke to go. As long as he promises to plasma AFTER the win!

 

[MadRhino]

I do hope that others enjoyed the discussion, and that some useful learning has taken place.

Oh yes, very interesting points have been made, and I already tried today to ride some practical comparisons. Unfortunately, the weather here is not as good as yours, and I had to leave the mountain under heavy cold rain, in muddy slippery trails. But I will get back at it as soon as the trail dries, and carefully monitor the incidence of both ridind style in the same climb.

 

[John in CR]

Sorry Dogman, I got that from Alan, re you trudging up hills at slow speed and high power. I haven't read all of the motor meltings. It's bothered me for a while that your 10 turn 9C burned up on a climb, since we all thought those high turn count motors were better for hills. I knew they weren't capable of the same power as the faster wind motors, but It wasn't until I did some comparative sims during this thread that the answer became obvious. It's because their max power occurs at significantly lower efficiency, and power falls off drastically before the motor gets into its good efficiency range. They really are quite ugly performance curves.

We've been told plenty of times that the winding count isn't like gearing. It's just that the low current torque and slow speed made it feel like 1st gear in a car. It may even still feel like it as the hill starts, but with decreasing efficiency as the power demand of a climb kicks in, overheating is soon to follow. Then you throw in the low rpm to make heat dissipation terrible, and the motor doesn't have a chance. You'd probably have to take those kinds of motors to 2 or 3 hundred volts to wake those motors up and get the performance curves looking decent.

One thing I did research that bothered me after you've stated it a few times, is regarding humidity. It turns out that it has virtually a nil effect on cooling our motors, because water vapor is lighter than air, though not by much. We think of humidity as heavy and sweltering, but there's actually less mass in the air with more humidity (though there are more moles, making it pretty much a push) Getting down to brass tacks lower humidity means slightly better cooling...another of those counter-intuitive things due to the way humidity feels to us, or maybe it was how well swamp coolers work that threw you a curve.

Ambient temps is your big enemy in the desert, but I don't know what altitude you're at. My house is right at 1km of altitude, but the cool breeze off the mountains seems to offset the difference from the thinner air, so I haven't noticed any difference between rides here at up to a mile high with temps going from the 70's at the house down to the 60's up high in the mountains, and rides down at beach level where temps are in the upper 80's.

 

[John in CR]

I guess we just aren't going to be able to help you with this. I tried.

More of the crap. Please do make a list of who "we" is, because Tiberius backed off as soon as I introduced the relationship of heat dissipation and speed. I'm sorry that some initial explanations of my own real world results were incomplete, but the overall premise is and was spot on. WOT is the best way to climb a mountain, and if it's too steep for WOT, then going to partial throttle will only help kill it faster. That's because the faster you go for a given setup, the more efficient your motor will run AND the more heat the motor can dissipate. Conversely, going slower decreases efficiency and decreases heat dissipation, resulting in a net negative effect despite the decrease in waste heat from running lower power. Your efforts to try to change the subject by introducing pedal effort are irrelevant, and with proper gearing pedal effort can be added at WOT too for those who want to pedal, and it's plain silly to bring up an example of pedaling to 5mph and adding a bit of low power electric assist up a 14,000 foot mountain.

If the mountain is too steep to maintain a minimum safe speed for your motor (virtually guaranteed for most hubmotored rigs with normal weight riders up the Pikes Peak run), then the correct solution is to lower the gearing by decreasing the wheel size. This allows the motor to run at a higher rpm for a given load, which will lower that minimum safe speed, and allow the motor to run at a greater efficiency for a given speed.

 

[dogman dan]

Yup, smaller wheel is how to lower the gearing on a hubmotor.

My most spectacular motor melts have been like many others have been. The motor is rated for about 800 watts, and I'm putting 3000+ into it. Gee I wonder why it melted? In the DR, I had heavy loading due to riding on a flat. On the 2810, I was climibing REALLY steep hills. Ones 4x4's have trouble with, and dismounting to walk up them with a bike, it's hard not to slip and bust ass.

So however you are riding, once you overwatt a motor by 4x or so, you are asking to overheat. Pedaling when running such a overwatted motor is pointless, It has little effect. Pretty much all you can do is vent the covers, and then make sure your ride stops before the motor reaches 400F. The ride gets very short of course, if you include hills too steep to even stand up on.


Now, as for humidity affecting air cooling metal. Thousands of desert dwelling VW bug owners know you are wrong. Too many of us learned that in June, you had to stop in time or you'd suck the valve on cylinder 3, where the oil cooler blocked some of the air flow in a doghouse motor. This problem pretty much dissapeared in July, when the monsoon rains arrived, and you'd have water molecules in the air and ambient temps just as high. Ambient makes a difference too though, as you say. In the spring, humidity might be just as low, but ambient temp below 90F meant better cooling, and no problems with the 3# exhaust valve. This effect is noticed both in high desert like my town, and in low desert like Yuma AZ. The ambient in Yuma is so high though, that you have to be carefull with a bug in that town all summer, not just in june.

Riding my hubmotors with a thermometer, I observed the same thing. In june a hot hub tended to stay hot a long time, while in July a hot hubmotor could cool off again a lot quicker. A nitrogen molecule has very little abilty to absorb heat. A water molecule can absorb a huge amount. That's a fact. Put btu's into air and watch how fast it heats up. Put same btu's into water and you can barely measure a rise in temp.

For most people ouside of the sahara or middle east, it's hard to get it how low the humidity can be here. Below 5% humidity is really really low, and only a few places in the world get that low, We do. At the death race, btw, humidity was only about 5%. All the gassers were concerned about cooling too. Most weathermen will start talking about low humidity because it's 30%. At 30% humidity, we never worried about our bugs cooling good enough. It's not about evaporative cooling. But of course, if you want to cool off hot metal fast, wetting it and letting evaporative cooling happen works great.

Density altitude is a different subject, and really hard to understand, let alone explain. It's the most flunked subject of all on a pilot exam. That effect is very counterintuitve, and how temp and humidity affect propellors, engines, and wings is totally different thant the dry air doesn't cool effects I keep talking about.

 

[Green Machine]

Density altitude is a different subject, and really hard to understand, let alone explain. It's the most flunked subject of all on a pilot exam. That effect is very counterintuitve, and how temp and humidity affect propellors, engines, and wings is totally different thant the dry air doesn't cool effects I keep talking about.

Wait wait...i think i finally got one on the dogman.

Calculating Density altitude for a new pilot is indeed a tricky task...but I can explain it easy in one line:

Density altitude is how high the plane thinks its at, based on air pressure differences because of heat. For example you could be at 6000 feet on a hot denver airport, and the plane thinks its at 9000 feet. This is a real factor for internal combustion airplanes...i am not sure at all how altitude effects electric motor cooling...but air is thinner up high.

its probably top 5 killer of small pilots in reality...trying to take off from high mountain airports without calculating density altitude first. I had an faa investigator tell me that #3 these days with modern gps is running out of gas...imagine that. Pilots are pretty stupid actually compared the the ES folk ..or lazy. Here is one for you...run a plane out of gas one time lose your pilot certificate....thats the rule faa is using these days.

So lets say considering temperature in Colorado during that race...density altitude may be as high as 16,000 feet effectively at that race depending on temperature of that day.

By the way passing out and all that jazz isnt an issue as much for drivers as it is for pilots. Thats why people are allowed to drive cars that high without oxygen. Also in a plane you get to those altitudes ALOT faster than you do in a car so its really a non issue in a car being that high as a driver.

I have flown gliders and airplanes up to the 14,000 feet legally without oxygen...you are allowed to be up that high for intervals of 30 minutes but in reality many pilots push that limit depending on personal threshholds. All competitive glider pilots are encouraged and are allowed to use air force pressure chambers to simulate high flying conditions to explore their own threshholds. I have done this test and its trippy.

I like being at these altitudes for long lengths of time because I personally get a nice healthy buzz semi legally and cheaply...only time you can fly a plane with that intoxicated feeling without risking your pilot ticket...

Whew...its about time i was able to add to an ES technical discussion. I thought it would never happen...hope you guys learned something from me to help you squash that ant with a sledge hammer up in pikes come race day.

 

[Tiberius]

.... Tiberius backed off as soon as I introduced the relationship of heat dissipation and speed.

Hey, I'm just standing back watching; we don't get this sort of entertainment in my country. Oh hang on, we do, its polling day today in a national referendum and the quality of political argument has plumbed new depths.

Anyway, I was just posting about a technical issue that I think the simulators don't cover. They don't cover heat dissipation versus speed either.

I think the best way to settle it is a race.

Nick

 

[Tiberius]

its probably top 5 killer of small pilots in reality...trying to take off from high mountain airports without calculating density altitude first. I had an faa investigator tell me that #3 these days with modern gps is running out of gas...imagine that. Pilots are pretty stupid actually compared the the ES folk ..or lazy. Here is one for you...run a plane out of gas one time lose your pilot certificate....thats the rule faa is using these days.

I'de have to check but I think #1 over here is officially described as "controlled flight into terrain", which in English means crashing. Of course, no-one on ES has ever crashed on an e-bike.

Nick