"peak power" - Trek 4300 20" Magic Pie build.

[neptronix]

But you will need speed to keep the motor from bogging down, but no matter how you look at it the watts will be a lot, I really think you should install a temp sensor, just in case and before you start drilling covers!

or, or hang a curry off the side

haha Just not a Vindaloo or the whole lot will go up in smoke!

LOL!!
Now that you mention it... A long wind geared hubbie on a bit lower voltage might be a good accomplice to keep the speed up when i hit 12-16% hills. That would of course just make things more complicated.

I'm sort of dithering whether i should continue this build, as the budget is adding up and the pocketbook does not agree:

18FET Lyen Controller - $250 shipped
20AH 10S lipo unit - $344 x 2 = $688 shipped, for a total of the 30S 20AH needed to get up pike's peak.
Cycle Analyst - $120 shipped
20" Magic pie - ~$240 shipped
Addl. Charging equipment = $~200

Total: $1498 + some unknown $..

So, $1500 to get a bike that will ruin optibike up pike's peak.. that probably won't use outside of this city as it's far from stealth

I must say that i'm relenting a little. Maybe someone here will get their wish about buying a very, very lightly used pie

[o00scorpion00o]

Yeah this stuff adds up, and then there is the stuff we forget about (or like to forget about)

Why don't you take it for a spin up the mountain to see how it works out before you make a final decision ? Do you need to get up fast ?

Maybe chain drive ?

[heathyoung]

Pity you can't fit a motorbike tyre onto the rim... Or could you? Sounds like a great hill climber for offroad.

[Alan B]

I would think 24S would be plenty. Don't need jackrabbit speed, need consistent efficient low heat climbing.

[iovaykind]

^Agreed. We honestly don't need much above 30mph.. but having the ability to get to that speed quicker than most of us do is sought after

[neptronix]

Well, the thing is that i'm going to be hitting 12% - 16% grade peaks, with an overall average of 7%, and i need to average 25mph to beat optibike. I can expect to lose a good amount of that speed on the steeper stuff.

30mph on the flat would be the minimum speed needed. That's assuming that i still have a good amount of torque in the low end. I believe that optibike hits up to 40mph. So that may be cutting it too close.

I think 23S would get me to that 30mph number, allowing me to keep the 12FET and not make the investment in an 18FET, But they'll gain on me really hard on the flatter sections.

The more i think about this build, the more i am convinced that a higher power mid drive would be a great way to beat the snot out of them. I am leaning towards scrapping this low speed wind hub motor idea.

[jmygann]

Josh did the pikes peak climb on 24 volts ... so it is not necessarily voltage

[neptronix]

It is if you want to make Optibike's $11k snob machine look like overpriced garbage, and your motor of choice is a slow wound magic pie that needs ludicrous power to get up the hill

What i have to do with volts on this motor, Josh did with amps. Wasn't he running some monster-sized thunder sky cells?
Watts are watts my friend..

[Lenk42602]

The more i think about this build, the more i am convinced that a higher power mid drive would be a great way to beat the snot out of them. I am leaning towards scrapping this low speed wind hub motor idea.

viewtopic.php?f=28&t=33416

I sold the MAC, but as you read through the posts and see the final configuration I came to, I still have the tandem cranks, LH freewheel, and fixed gear w/lockring for a complete drivetrain set up. Unlike Whip's design, my configuration places the hub motor behind the crankset and seat post, not in front of it.

I am pretty confident that set up will be a contender, but I had just finished my 1-year bike build at the time. Just absolutely crazy to start diving into another build when I have a great machine to enjoy already. I would however, feel much less guilty bolting on one of those MP's and seeing what happens at the race next year.

Len

[cwah]

you have both the mac and the magic pie.

At similar speed, what motor is the most efficient? I bet the mac is more efficient than the Magic pie at low speed. But at high speed, is the magic pie handling it better than the mac?

[neptronix]

I can almost guarantee that the MAC is going to be loads more efficient.
But it will not handle the power level for long at all. All 24-25 miles will overheat the crap out of it, as geared motors are very bad at shedding heat.

Anyways i thought about it, and i'm officially back in the game. I realized i could use those lipos to do what i've always wanted to do: build something that can go over a hundred miles.

I already have 25AH of 38v/10S power, so i am not far from running another 25AH of 46v/12S on top of that, for a total of 22S / 25AH. That's 92.4v fully charged. I would be riding the 12FET's 100v limit.

The question is.. will the 12FET handle the constant 20-50 amp load with a low wind motor? will have to find out..

If the calculations are correct, I should hit about 30mph on the flats nominally with pedaling, and be able to hit maybe 35mph with the 120% setting. This should help eliminate their gains on me. On the hill, i will be doing more like 20mph.. well within their average speed.

I think i will come within a few minutes of their win time. I may not win, but i will either have to settle for striking a little fear into them, or just not even bother competing ( as everyone else has done .... )

I will try out my 20S/10AH on the nearest monster hill within the next few days, then re-assess.

Thank you for your support, and pushing me on, guys.

[cwah]

I can almost guarantee that the MAC is going to be loads more efficient.
But it will not handle the power level for long at all. All 24-25 miles will overheat the crap out of it, as geared motors are very bad at shedding heat.

Is 24-25 miles a speed or a distance? Because if it's speed it would be quite low

[jmygann]

For efficiency It comes down to Whr/mi/lb .... assuming round trip

[neptronix]

I can almost guarantee that the MAC is going to be loads more efficient.
But it will not handle the power level for long at all. All 24-25 miles will overheat the crap out of it, as geared motors are very bad at shedding heat.

Is 24-25 miles a speed or a distance? Because if it's speed it would be quite low

It's approx 26 miles. Speed is actually 20mph average for optibike, that's why i was originally shooting for 25mph average.

http://www.ridepikespeak.com/Assault_2011.1/Home.html

[cwah]

How come the Mac overheat at 20 or 25 mph average? I thought it can handle a lot of watts? Is it the mac 350W?

Maybe you just put too many amps on it? You can still have high speed but with less torque and less amps.

[o00scorpion00o]

How come the Mac overheat at 20 or 25 mph average? I thought it can handle a lot of watts? Is it the mac 350W?

Maybe you just put too many amps on it? You can still have high speed but with less torque and less amps.

The Mac is a monster of a motor and will climb anything. The problem is it's inability to shed heat quickly.

I have the 320 rpm mac and I have ran 3500 watts through it, damaged my clutch, but it's such fun!

I've never had a problem with heat, Eve at 35-40 mph runs, but long steep hill climbs could kill it unless you back off the power, even at 600 watts you would be surprised how well the mac climbs!

I run 60 volts nominal (16s LiPo) through it, so helping to keep the current lower, that's about 58 amps on acceleration, and about 35 amps to cruise at 35-40 mph on level ground.

Now go to 48-50 volts and that 3500 watts on acceleration becomes 70 amps, and already that's a significant increase in current. Interestingly enough, cruise speed will be less because your top speed will now be 30-31 mph.

So by using 10 less volts your current increases by about 12 amps and that can be enough to get phase cables too hot, especially on hills, so the more voltage you got the, the less amps you pull and the faster you get up the hill taking less time to get things hot.

[Alan B]

Changing battery voltage won't change the motor phase current for the same motor operating conditions. Motor operating conditions (load, rpm, temperature) determine motor voltage and phase current. Battery voltage gets converted to this by controller. Changing battery voltage will change battery current to feed the same power. But if motor is operating at the same speed and load the motor voltages and currents will not be different.

The problem in climbing this big hill is power dissipation. Gearmotors can dissipate about half what direct drive motors can dissipate. Gearmotors are operating at a more efficient RPM but it becomes a trading game of efficiency versus dissipation. In the various modelling I did the only way to win was dual motors to double the dissipation. Boring holes and forcing air through the motor could be important also. Avoiding hard acceleration and other heat drivers can also help. Liquid cooling would really change the game. Then one small motor could do the job. Put coolant through the frame tubes for a distributed radiator.

[neptronix]

Nailed it..

And yep, liquid cooling would change the game, big time. Hot copper = high resistance = wasting more power and/or getting less and less torque out of the motor as she heats up.. the efficiency level is going to be terrible and copper that is gradually getting hotter sure isn't going to help things.

For everyone's reference, here is the thread where i decided i was going to take this task on. After a few pages, i settle on the magic pie motor per Luke's suggestion & also from watching oooscorpionooo dump 5-6kw into his, doing a fairly major hill climb, then the worst thing that happened to him was that the halls busted.. lol.

http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=31490&hilit=pikes+peak+magicpie&start=75

[o00scorpion00o]

Nailed it..

And yep, liquid cooling would change the game, big time. Hot copper = high resistance = wasting more power and/or getting less and less torque out of the motor as she heats up.. the efficiency level is going to be terrible and copper that is gradually getting hotter sure isn't going to help things.

For everyone's reference, here is the thread where i decided i was going to take this task on. After a few pages, i settle on the magic pie motor per Luke's suggestion & also from watching oooscorpionooo dump 5-6kw into his, doing a fairly major hill climb, then the worst thing that happened to him was that the halls busted.. lol.

http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=31490&hilit=pikes+peak+magicpie&start=75

HAHA funny!

Don't give up Dave, not at least until you try it, that motor will eat hills like the mac, though not nearly as fast, but I can only imagine the torque in a 20"

But I would go the high voltage less amps route and let speed take you up, giving less time for heat, just be careful with the regen, I would not use it again after a long climb! That pie takes a very, very long time to cool off!!!

I rember smelling it in the back of the car all the way home and my Girlfriend saying "how much is that gone up in smoke ?"
It's still getting me around in sensorless, but it's definitely lacking without halls!

Just watch the heat and you know yourself when it's too hot, then it's time to drill covers.

How much it bogs down is another matter that will depend on how much it heats and that I can't tell you in a 20" wheel, in a 26" wheel at 13 mph on 60 volts, 3500 watts 10-15 mins is the max run time on 16% grade, and frock me is that spooky when the front wheel keeps flipping and you risk falling over the edge, but hey it's all part of the E-Bike fun!!! yeah

[o00scorpion00o]

Changing battery voltage won't change the motor phase current for the same motor operating conditions. Motor operating conditions (load, rpm, temperature) determine motor voltage and phase current. Battery voltage gets converted to this by controller. Changing battery voltage will change battery current to feed the same power. But if motor is operating at the same speed and load the motor voltages and currents will not be different.

The problem in climbing this big hill is power dissipation. Gearmotors can dissipate about half what direct drive motors can dissipate. Gearmotors are operating at a more efficient RPM but it becomes a trading game of efficiency versus dissipation. In the various modelling I did the only way to win was dual motors to double the dissipation. Boring holes and forcing air through the motor could be important also. Avoiding hard acceleration and other heat drivers can also help. Liquid cooling would really change the game. Then one small motor could do the job. Put coolant through the frame tubes for a distributed radiator.

Hi Alan,

I see what you mean, but the thing I noticed is that for a lesser grade of hill a 48 volt battery will get you up fine, but give it another few % and the motor slows down enough to be pulling a lot of amps and the motor is not nearly efficient creating a lot of heat. Volt it up and it spins faster more in the efficiency zone pulling less amps, making less heat and getting you up faster not allowing more time for heat. Does that make sense ? And I'm not nearly an expert, just my own experience.

[Alan B]

Changing the operating point does change things. Clearly the motor can be overheated by going too slow, and totally destroyed by applying too much power. So in between there must be a speed which minimizes net heating. Finding that speed is the difficulty, and then you need enough voltage and current to achieve that speed. Even at this optimal speed the motor may or may not melt before reaching the top.

It would be interesting if we could equip the bike with enough instrumentation to immediately read out the power input to the motor (easy) and the power output (not easy). Then we could immediately tell if this is sustainable (providing we already had some data for dissipation). Measuring motor temperature is an easier way to tell, but the data rate is very low so it might take many runs to determine the optimal speed. Essentially if the motor temperature is rising above some level then it is probably not sustainable for a long climb.

[o00scorpion00o]

What we need is water cooled motors, but I think that will be a long time.....if ever!

Even water cooling looses efficiency because of the pumping of coolant, it would save the motor for sure but wouldn't that still mean inefficiency, because heat means inefficiency, so water cooling only transfers the heat to the coolant? meaning transferring the inefficiency from the motor to the coolant ?

I got sooooo much to learn about motors!

[Alan B]

Operating the motor at lower temperatures improves efficiency by reducing copper losses.

Let's say the motor is 75% efficient and is doing 1500W of work climbing the hill, so we are putting in 2000W and it is dissipating 500W. If this is a gearmotor that can only dissipate 400W it will heat up and melt.

If we put in liquid cooling and bring that 500W of heat out of the motor into a radiator we can avoid melting the motor.

So cooling helps efficiency and allows survival.

I guess we don't want to put holes in a gearmotor for cooling, but holes in a DD motor can help. Perhaps even misting in some cooling water would be worthwhile. They hand out water on the way up Pike's Peak during the race, wonder if they would mind if you wanted a couple extra bottles. Then you wouldn't have to carry all that water from the bottom.

[neptronix]

It would be interesting if we could equip the bike with enough instrumentation to immediately read out the power input to the motor (easy) and the power output (not easy). Then we could immediately tell if this sustainable (providing we already had some data for dissipation). Measuring motor temperature is an easier way to tell, but the data rate is very low so it might take many runs to determine the optimal speed. Essentially if the motor temperature is rising above some level then it is probably not sustainable for a long climb.

I was just thinking about that today on my walk. I need a temp sensor, for sure.
BBQ thermometer with an extended wire up to the handlebars

Or can someone suggest a more elegant solution?

Also, it is highly likely that the covers will be drilled.
A misting system is a good idea. I could hide the tank in the rear topeak rack. Only have to fit 25AH/12S into the rear.. i could fit a few computer duster sized cans of something in there.

[veloman]

What size are your phase wires Nep? Did you upgrade them? The ones on my older Mac look really thin, maybe 16ga. Do you know what battery current is the limit for those? (I think phase currents will vary depending on winding and hub speed too though).