Hill climb

[greasypants]

Well I went and measured the big hill on my commute home before I decide on my bike build . It measued 9 degrees on the steepest section ( measured with plumb bob and angle tool thing). If I am correct this translates to about 16-17 % grade . I will be using 5304 in the rear on 26" wheel with 35 amp controller and and trying to decide between 72v or 84v battey set up . The hill is probably only a few hundred meters long and only a portion of it is 16-17% grade. Is it worth the extra cost and weight to go 84v or will 72v setup be able to get me up the hill , or will I have to peddle with both setups ? I plane on using 18ah nimh packs from ebikes .
Thanks
Greg

 

[xyster]

If I am correct this translates to about 16-17 % grade . I will be using 5304 in the rear on 26" wheel with 35 amp controller and and trying to decide between 72v or 84v battey set up .

Very steep. If it's a relatively short section as it sounds, if you hit the hill at 20mph or so, you should zoom right up without pedaling, slowing a bit with 72v and 35 amps.

The 40 amp controller is only 15$ more:
http://www.poweridestore.com/Hub-Motor-Acces/Series-500-Controllers
(this is where I bought my 35 amp controller -- a very positive experience)

If I was you I'd go 40 amps at 72 or 84 volts. Also for more torque I'd consider a 24" wheel instead of a 26" -- unless the rear brake can't be made to work with a smaller wheel.

At 35 amps and 80 volts, my 5304/24" without pedaling accelerates from zero to ~20mph up a hill that I've estimated from topo maps to be 12% with 15% sections of 100m or so.

 

[greasypants]

Thanks again xyster. I thought abought the 40 amp controller but I prefer to buy locally . The brokerage fees can be very expensive when using UPS to ship to Canada.Plus running the numbers on the ebikes simulator looks like you only get an increase in torque of 5% over the 35 amp controller . I would also prefer to keep a 26" wheel because of the brake issues and the fact that the rest of my commute is relatively flat so it would be better for high speed. The trail I take pops out right at the bottom off the hill at 90% to the road so a running start isn't possible. I suppose if I can't make it up the hill it wouldn't kill me actually peddle my by bicycle a bit , or I coould take a longer route home and avoid the hill all together.

 

[Ypedal]

If you don't make it up that hill with an X5 at 72/80v 35 amps.... cars ain't doing it either ! lol...

 

[xyster]

Thanks again xyster. I thought abought the 40 amp controller but I prefer to buy locally . The brokerage fees can be very expensive when using UPS to ship to Canada.

Gotcha. I got my hubmotor from ebikes.ca. The fee was $54 USD. Another canadian dealer told me, and I have no idea if it's true or not, that using US Priority Mail one direction and Canadian Post the other avoids brokerage fees associated with the private carrier.

The bicycle power calculator says 1750 watts to the road (35a X 72v X 70% efficiency) on a 17% incline give 17mph.
http://www.kreuzotter.de/english/espeed.htm
I found this calculator quite accurate on lesser slopes.

I bet your bike makes it up the hill just fine. Another 12v would definitely help.

 

[safe]

Anything above 12% and my bike (even in the lowest gears) can no longer run in the most powerful part of the powerband. I'm not even sure if my bike could make it up a 16% - 17% slope. That's very steep. For short distances you can handle it... plus with that 25 lbs worth of hub motor "big iron" you have a lot of "heat capacity" to absorb before the heat becomes noticeable. My little 8 lb 750 Watt motor is so light weight that it heats up easier.

An advantage to having a 25 lb hub motor!

 

[knightmb]

If you don't make it up that hill with an X5 at 72/80v 35 amps.... cars ain't doing it either ! lol...

I have to agree, I use my 406 motor in a 700C wheel at only 48 volts and I can make it up short hills that steep if I'm already moving and have momentum. The bike will slow down to 10 mph, but the motor keeps going all the way to the top. Some hills are the steep ones that you have to get off the bike and walk up normally or have a mountain bike that has the really, really small front sprocket.

I don't think my motor would make it far from a dead stop in the middle of the steep hill, but if I'm already moving forward it's much easier.

 

[safe]

Throttle Control - As An Artform?

Okay, probably a little "over the top" with that statement (our goal I guess), but here's the question. Let's say you approach a hill at full speed, as you begin the transition up the hill (in my case) you go through the gears one by one until you are now down to first gear. Hub motors are always in first gear, so we are now "together" at this point philosophically.

At what point to you "make the switch" to go to the low rpms?

In my case it's a rather dangerous thing to do to let the rpm's drop without at least trying to "carry" the gear. I've memorized the mph that each gear is in it's "peak power" (first gear is 13.3 mph) so when I see that at full throttle the speed drops below that level then I "know" the rpm that I'm in. (it's sort of a reverse logic) I know that from the moment that the speed drops below 13.3 mph I'm now entering dangerous territory. For the tall gear it's 20 mph.

So the question becomes whether it's best to "hold onto as long as possible" the high rpms and then when that fails drop down (by then your motor is already overheating) or do you risk dropping ALL the way down right off the bat and risk being stuck at the bottom of the hill rather than part of the way up?

If your load situation is "unworkable" (in other words there's no way PWM "effect" or otherwise to get up the hill without a "death spiral") it's hard to figure what is better to do.

 

[xyster]

Safe, it's like you're trying to win the Indy with a stock car.
Tweaks here and gears there will get you slightly closer to your goals, but without more power, you're just spinning your wheels, frying your motor, whipping your horse with a noodle, and beating your head against a wall too -- all at the same time.

It's frustrating for some of us to watch...

Dude, you need more go, not more graphs.

 

[Mathurin]

Steep hill: Ease off the throttle by a hair to cut amps used by nearly half, the effective power stays very close to what full throttle would yield. Continue pedaling normally & go up the hill 4X faster then if the bicycle had no motor. That one's a no brainer.

Edit: Obviously, motorcycles lacking basic instrumentation need not apply...

 

[Ypedal]

Dude, you need more go, not more graphs.

LMAO .. that's a good one.. we should get a " Best Quotes on E.S. " thread... this one could go with my " Why own a minivan when you can have 6 E-Bikes "

 

[Reid Welch]

It is funny to observe

cranks calling each other bent









__________
Just as with any underpowered ICE engined vehicle,
safe and I would need lower gearing and settle for slower climbing.

I have pedals, so there's my granny gear for moderate hills.

For 16%? I think I'd get off and walk with the present setup.

Safe needs pedals
like some of the very first horseless carriages "needed"
(still had) a whip socket. Safe needs much lower gearing.

------------

"Unsafe at Any Speed" (ralph nader book denoucing the Corvair)

"Unsafe Without Pedals" (the next nader book)


----

safe gets lots of friendly ribbing.

Q for safe from The Great Beyond:

"Sir, can you phone a graph?


Thank you,

T. Edison"





---end humor---


what humor????

 

[xyster]

It is funny to observe

cranks calling each other bent

Clarify, please.

 

[Reid Welch]

It is funny to observe

cranks calling each other bent

Clarify, please.

Figure it out. Take your bike to the LBS or to the 4H fair and extoll the virtues of it all.

No matter that you're right at heart, they'll look at the bike and think you a crank.

Same as with me. We are cranks of our hobby, period, all of us.

And that's not bad, really.
It is the misunderstood and often fumbling errant crank who turns the bigger wheels in time

Don Quixote notwithstanding

 

[safe]

My next two projects will take different directions to resolve the hill climbing issue.

Project One:

Big Power (2hp) and wider gears.
Top speed 50 mph. (on flat land)
Range about 60 miles.
1440 Watt/Hours for a battery. (likely)
This should be able to climb anything.

Project Two:

Legal Power (1hp) wider gears and pedals.
Top speed 40 mph. (on flat land)
Range projected to be over 100 miles.
1440 Watt/Hours for a battery. (maybe)
This will need pedal effort for the steeper climbs.

 

[Mathurin]

Well thing is, with no instrumentation there's no way to know when you're in the motor's sweet spot, and without pedals - you can't use pedals.



Take my MTB, in first gear the pedals spin a little faster then the wheels, given the average steep hill around here I'll top out at my prefered hill climbing cadence of 75-80rpm in either first or second gear, if I'm in a really good mood I'll sometimes get to use third gear. Speed wise that yields almost twice faster then if I was walking the bike up the hill.

Pushing fairly hard going down such a hill, at best I'll be using 2-3 gears up from last in order to get a decent cadence. I've only really used top gear as cruising range going down hill. It makes accelerating eventual, and it's too steep to keep going fast with on the flats because it keeps you bogged down. But get this: One day, for the heck of it I climbed this same hill I described earlier while in top gear. In this case, I went up slightly faster then if walking my bike up the hill.

I've also climbed these hills on a fixed gear MTB setup with a gear range chose to be optimal on the flats, the extra speed there more then made up for what I lost going up/down hills.


Climbing hills is something anyone can do, but it has to be learned. If you don't bother to, then a bike with a crawling gear won't help you: you'll go part way up and then die, not unlike with a single speed or fixed gear bike.

Don't blame a lack of hill climbing ability on the bike...

 

[eP]

The bicycle power calculator says 1750 watts to the road (35a X 72v X 70% efficiency) on a 17% incline give 17mph.
http://www.kreuzotter.de/english/espeed.htm
I found this calculator quite accurate on lesser slopes.

I bet your bike makes it up the hill just fine. Another 12v would definitely help.

Hi xyster
Tell me what yours calculations could let you assume 70% efficiency.
I strongly suspect you are badly wrong at that point.

At my assumptions: mass of bike+driver = 100kg at 16% slope you need 160N to move from the stall point and around 180N to move at 8 m/s speed.
So at 24'' rims you need 54 Nm of tork. (180N * 0.3m ).
X5304 motor at 72V 40A at max. Pout have around 40 Nm at 24'' rims (and 60% eff. at this point) so this indicate motor will work at falling edge of Pout curve. So I estimate 50% efficiency for 54 Nm tork.

For greater total mass the efficiency are badly hurt by raising tork as Pout falling at this curve edge.

Pedaling can't improve the situation as cyclist cant add much force at 8 m/s speed.
For example at 200 W it is 25N only at that speed.

For X5304 tork i've extrapolated the graph you can find here

Correct me if i'm wrong.
Thanks in advanse.

 

[Lowell]

Looks like 70% eff. at 17mph to me...

 

[safe]

It makes a big difference on how much your bike weighs. I've used numbers like:

185 lb rider
100 lb bike

And with numbers like that you get something like this. (see charts and numbers)

In the "real world" with that much weight you would not get up to your "peak power" and so you are stuck down at lower speeds. So weight is critical at that steepness. I'm only seeing 1276 Watts at 43% and only a 12 mph top speed. So depending on the ACTUAL weight things could be very different. I doubt that on a 17% slope you will attain anything close to your "peak power"... you will "bog down" at low rpms.... (I'm very suspicious of a real world 17% slope... most roads are not allowed to be built that steep because cars cannot make it up them... Streets of San Francisco maybe?)

You have to keep in mind that your "peak power" at 74 Volts (assuming Lithium pack) happens at 48.7 mph!

 

[Lowell]

12mph looks like 55% eff.

Peak power at 48.7mph in a 24" wheel is very optimistic, and would require something like A123 power and very low loss connections. Now if you really had lithium power, I would hope the bike wouldn't weigh 100lbs, and it would put out a lot more torque.

My bike looks to be over 110Nm at 17mph so it should cruise up that hill quite nicely. After looking at the numbers from my 35.4mph, 12.8% grade test, I should be pretty close to 30mph up a 17% hill. The 17lbs of extra weight I was carrying is worth 1.3mph on the weight alone, not accounting for aero losses.

 

[scottclarke]

Just as with any underpowered ICE engined vehicle,
safe and I would need lower gearing and settle for slower climbing.

STOP IT!!!!

Now I know you didn't mean it in this way - but I'm constantly battling people opinions ebike vs car!

My bike, yours and Safe's are NOT underpowered!

Despite what we are doing I still firmly believe bikes should be doing less than 30mph and preferably less than 25mph 99% of the time. Only pure downhill bikes really have the stuff to a) handle the power and b) deal with road irregularities in a safe manner. In the UK they have set an overly sensible limit of 15mph - I lobby for a raise to 25 - knowing at best it will go to 20. I travel around the 25mph mark on a fully suspended bike and the back end skips all over the place on corners where if you were pedalling you would be doing 15mph. The roads are bad!

My point - most bikes (even solids) are ok most of the time at 15mph.

Sure, our bikes go faster - but if the slowest it goes up the steepest hill local to me is >15mph then thats fine and dandy - the fact it can go faster on the flat does not make it underpowered - by that logic every vehicle is underpowered!

So, you might say my bikes cruise speed is 17mph - though it can go much faster on the flat - what is your cruise speed? (maniac hills aside!)

Scott

 

[Geebee]

For f...sake it's power ASSIST if your bike won't do it without struggling PEDAL

 

[Reid Welch]

harumph, ha ha. I did not say our ebikes are underpowered.
I said they are best managed in the same way as underpowered cars and overloaded lorries must: in a lower gear and at a lower speed.

This is also true of peda-lonely bikes because.... the human is so sadly underpowered.


baddaboom and all that. :wink:

_________

Scott, have you any pictures here of your bikes?
I like capable ebikes and the coming of eVelos.

words in play: e Velo Solution evelosolution....never evoslolution ever slo: u shun

 

[safe]

In the UK they have set an overly sensible limit of 15mph - I lobby for a raise to 25 - knowing at best it will go to 20.

Europe seems to have "fixed" their view of an electric bike to be limited to 250 Watts... one third of a horsepower. Here in America it's already legal now and will likely be legal for the distant future to use 750 Watts... a FULL one horsepower.

Now a FULL horsepower can "at best" (assuming some relatively good aerodynamics) push a bike to about 30 mph. The law here limits it to 20 mph nationally, but most states individually allow 30 mph. There are people here who have "gone bonkers" (myself included) and have tricked out our bikes so that they can go a lot faster than this, but I think eventually the "bottom line" for America will be about 30 mph in most places.

So I think the major "divide" is between Europes laws and Americas laws... a three to one advantage in power changes everything for us here...

 

[Malcolm]

a three to one advantage in power changes everything for us

Maybe, but if I really wanted to I could cycle (unassisted) from the east coast to the west coast in a day