An ebike for the hills?

[hillbilly]

Well... I was kinda hoping to build up the suspense but as long as you ask, here's the description from Holmes Hobbies for the Puma:

400 watt (ridiculous low factory rating)
36 volt
Sensored Brushless compatible
8.5 pounds
Internally geared for better torque
36 spoke hole
Compatible with 6 speed freewheels with stock spacing
Comes with dropout washers, nuts, and proper spacers
ISO standard disc brake mount integrated to hub body
138mm spacing fits most mountain bikes

 

[Ian]

start off your e-biking with a simple, basic complete kit and add a wattsup meter to monitor battery. keeping to a slow speed you should be fine with a brush motor.

this one has a lifepo battery - the chemistry to look for.
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=5026

 

[HighTekBikes]

That sounds like a nice setup. I heard the Puma is an excellent motor, a little pricey but good quality. I didn't mention it because I have no first hand experience with it. I'd be interested in hearing how it does on the hills and what current it needs. I think you will be happy with your decision. As you can see there is no shortage of opinions on here and you got some good advice. The technical expertise, experience and down right passion of the members on this forum is unmatched. Visiting here can get addicting actually.

I figured someone would pipe up about my blatant advertising I do operate a company but I'm more of an engineer than a salesman. When I make a recommendation it's not a pitch, it's the result of direct experience, testing, and analyzing data. Living in the San Francisco bay area, I do know a bit about hills. My main interest happens to be practical ebikes and power systems, meaning it does the job in an efficient and economic way. Sure the Crystalite 5300 will power you up a hill, no question. But you need $1000 worth of batteries to feed this monster. When the batteries go dead, you can barely pedal the bike. Can it go up a hill running on 36V and 15 amps? No way. A fine motor that has a loyal following, most of whom are ebike hobbyists with fat wallets. To each his own.

I wouldn't mind stringing this thread out a bit more. Hill climbing is a very important feature for ebikes. It allows people living on hills to use bikes. In addition people who have to commute over hills have an option now. The important issue is to get people out of cars. The more spirited conversation about the merits of each hill climbing setup the better.

 

[Miles]

I wouldn't mind stringing this thread out a bit more. Hill climbing is a very important feature for ebikes. It allows people living on hills to use bikes. In addition people who have to commute over hills have an option now. The important issue is to get people out of cars. The more spirited conversation about the merits of each hill climbing setup the better.

Agreed.

Leaving the motor aside for a moment, it's worth bearing in mind that it takes less energy to increase your average speed by going faster up the hills than by increasing your top speed on the flat...

 

[paultrafalgar]

Leaving the motor aside for a moment, it's worth bearing in mind that it takes less energy to increase your average speed by going faster up the hills than by increasing your top speed on the flat...

Now that surprises me. The implication is that work against wind resistance is greater than the work against gravity, n'est-ce pas? Surely, that depends on how aerodynamic you are (velomobile vs upright), how heavy you are and how fast you are going?

 

[Miles]

It will always be true, because the gravity element of the work is directly proportional and the wind resistance element is to the second power.

 

[paultrafalgar]

It will always be true, because the gravity element of the work is directly proportional and the wind resistance element is to the second power.

Doesn't that imply that we should all fit aerodynamic fairings before electric motors! and that the weight of those fairings is less important than their CD?

 

[Miles]

No, because at bicycle speeds the power requirement for hill climbing is usually the dominant factor.

 

[paultrafalgar]

I'm clearly suffering from dementia because I'm finding it really difficult to reconcile your two statements:
"it takes less energy to increase your average speed by going faster up the hills than by increasing your top speed on the flat..."
AND
"at bicycle speeds the power requirement for hill climbing is usually the dominant factor."

Help!!!!!!!!!!!!!!!

 

[Miles]

It doesn't matter which is the greater of the inputs, the differential requirement against speed will remain

What matters, in this case, is energy expended against journey time.

 

[dogman dan]

That does sound a bit confusing, but it makes sense if you add one more piece of data, How fast on the flat. Most of us don't have ebikes that go fast enough to appreciate the exponential effect of wind, while we nearly all have a hill we can climb. Once you go a bit faster, the wind effect becomes much more noticeable. My 150 cc scooter simply hits a wind effect wall at about 50 mph that you can really feel. Hills are barely noticed at all.

To hillbilly, That sounds like a good choice, that is supposed to be very similar to the BMC 400 watt. JRH will lace it for you in a rim that blows away the quality of what you get in a kit, which may be a help when pounding up a logging road. I do agree with Terry that a good gearmotor will climb better, that is indisputable, and when, not if, you have to pedal home unpowered it will do that much better. I will say agan, though, that a properly set up 5305 will climb a hill farther without overheating. Terry is right that one of those is for rich people. However lame it may be compared to it's full potential, my 5304 at 20 amps 36v, still climbs as steep a hill as I can get up and stay on the dang bike. At some point, the grade gets too steep and I just wheelie off the thing. But if I lived in a cooler climate, a gearmotor would have more appeal.

That is not meaning you are garanteed to fry your puma, just that the point when you need to stop will come sooner than with a 530x. It's up to you to monitor temps on the motor as you climb steep hills for miles. In my tests with a fusin gearmotor, 12% grade brought the motor temp up to the safe upper limit in 3 miles, so any ride shorter than that should be no problemo. Just remember that with gearmotors, the case temps can be very cool while the inside is broiling. The place to check temperatures is on the stub of the axle where the wires come out. Add at least 40F to that measurement, and you will be close to the temp inside in summer. A ten buck car indoor outdoor thermometer can have it's sensor taped to the axle stub to continuously keep track of temps. It will be more accurate if you put some foam tape over the sensor to eliminate wind cooling.

I think you have made a great choice, but after all this discussion, we do expect you to post a nice review thread later, and tell us all about the performance of your choice. We understand that a cycleanalyst is expensive, but if you simply monitor the power used to charge back up with a cheaper killawatt meter you will still get good data on energy used to climb steep hills. A killawatt shoud be in every home anyway to lower your electric bills without wasting time trying to shave nothing off the bill. The killawatt will tell you what is worth worrying about and what isn't.

As for the brushed motor suggestion, :lol: :lol: :lol: Go climb some extra steep hills with one, and then I'll teach you how to glue the melted off magnets back on.

 

[dscline]

I'm clearly suffering from dementia because I'm finding it really difficult to reconcile your two statements:
"it takes less energy to increase your average speed by going faster up the hills than by increasing your top speed on the flat..."
AND
"at bicycle speeds the power requirement for hill climbing is usually the dominant factor."

Help!!!!!!!!!!!!!!!

Just to continue this interesting tangent for a bit...
To get your mass up a hill, ultimately, the same amount of work has to be done regardless of how fast you do it. So the only variable factor in any case is wind resistance. Because of the exponential effect of speed, doubling your speed on hills from 10MPH to 20MPH is less of an energy increase per mile than doubling your speed from 20 to 40 on flats. Furthermore, increasing speed on hills saves more time than on flats... if a course has 10 miles of hill and 10 miles of flats, and you can do 10MPH on the hill and 20MPH on the flats, doubling your speed on the hill will save 30 mins, while doubling your speed on the flats will only save 15 mins.

 

[paultrafalgar]

Thanks, dscline, thought I was losing it there! That makes it clear what Miles was on about.

 

[tostino]

Also, keep in mind you are really just storing energy when going up a hill. You get to release that energy after you reach the peak, and are going down hill. While going faster on the flat, the extra energy you are using is just lost due to wind resistance.

 

[hillbilly]

dogman and others,

First of all, I will definitely be posting a review and photos of the Trek conversion. I'm very pleased that the Puma meets your approval, though I take no credit for having selected that option -- John Holmes suggested this as a upgrade over the Bafang (he is building the wheel) and my wife approved the special budget appropriation. (The member who will do the real work of putting the bike together had already planned to install temp sensors, as well as a V-3 data logger.)

I like the Kill-A-Watt idea and we use one in our cabin, so that will be easy.

It is going to take a while to receive the components but once the bike is built I'll be posting some detailed reports, as I think there are many others -- especially total ebike noobies like myself -- who can also benefit from the great info and support I'm getting here.

Finally... I've been using online forums and message boards for my work and personal projects all the way back to prehistoric internet time, such as UseNet and CompuServe. In my experience, this site rates among the very best. My hat is off to all of you.

Carl Franz

 

[pwbset]

I figured someone would pipe up about my blatant advertising

:wink: I'd be doing the same thing believe me. Most would. No harm done at all.

Living in the San Francisco bay area, I do know a bit about hills. Sure the Crystalite 5300 will power you up a hill, no question. But you need $1000 worth of batteries to feed this monster. When the batteries go dead, you can barely pedal the bike. Can it go up a hill running on 36V and 15 amps? No way. A fine motor that has a loyal following, most of whom are ebike hobbyists with fat wallets. To each his own.

I climb 1,600ft vertical every morning commuting to the ski resort in Montana I work at so I know a bit about hill climbing too. For long term reliability the 5 series, I would argue, will outlive anything else out there under the rigors of sustained hill climbing. It absorbs punishment/heat etc. incredibly well. And to clarify a point or two... a single $50 Bosch fatpack will easily pump 1,000+ watts sustained into a 5 series.. sure only for a couple miles on the flats, but everyone claiming these motors need $1,000 batteries are living on last year's tech. $300 in fatpacks would easily get me up the mountain I climb. An EVComponents 48v10ah Headway pack for $350 would also do it. You're right it won't climb well @ 36v15A, but at 36v60A it climbs like a monkey. Really it's all about the watts. 2kw is 2kw no matter how you slice it. And yes, there are arguably better solutions that wouldn't need 2kw to do the same job, but again it boils down to reliability and speed. If I went with a lower power geared setup at 8-10mph I might as well drive or use legs only. With a 5 series I can sustain 20mph or more all the way up so it's a much more realistic commute time-wise. As you said though... to each his own, which is probably why turn-key ebike shops have such a hard time because there are so many different applications for all this tech... which is also why it's so fun and badass.

 

[Fishmasterdan]

You will like the Puma alot better than the Bafang. You made a good choice upgrading. Proper temp monitoring is mandatory for hill climbing so a Data logger was in order. Not sure of any other electronic device that can do what the eagle tree can with temps.

Carl if you really like Data get the GPS module also. I have some temp graphs around here somewhere for you to look at.

There has got to be some way to incorporate a better cooling system. Shoot they can cool a computer down by magical thermal paste, there has to be something out there to transfer the heat better.

 

[dogman dan]

Descline explalined well something I've noticed, that it takes just about the same ammount of power to climb a hill at 5mph, or 10 mph. The hill remains the same, and allways takes x ammount of power to climb. The wind resistance does increase from 5 mph to 10 mph, but the wind resistance is so low at 5 mph that doubling it to go 10 mph is barely noticed. So climbing a hill very slow doesn't really save much battery power, unless you pedal hard. If you do pedal hard, then rididng slower can increase the percentage of the pedaling contribution to the total amount of energy it takes to lift your weight up the hill.

Heat, on the other hand is another issue. The more watts you put into the motor, the faster it heats up. So for continuous climbing, doing it at half throttle may be the best way. It just depends on the motor size. On a 350 watt bafang, half throttle is around 200 watts and isn't going to get you up a steep hill very fast. A BMC with 20 amps of 48v would put out about 500 watts at half throttle and get up the same hill faster. At 48v 40 amps, a 5305 would have even more watts to get up the hill, even at half throttle, and would likely be doing it fast enough to not need the advantage of gears as much.

So which one will get hottest? The 5305 right? The more watts the faster it heats up right? The rest of the heat equation is time. So the bafang may take so long to get up the hill it hits the heat limit before the top of the hill, partly because gearmotors have an internal motor and an outer case and shed heat a bit slower. The 5304 may get up the hill before it even warms up. The BMC might climb fast enough to be a close second to the 5305 and be a great choice in the middle.

But for sustained climbing, where the motor is going uphill for as much as an hour or more non stop, a 5305 will shed the heat best, and be likely to have the longest range for continuous climbing compared to other motors running at the same wattage.

One last comment. Everybody says a 530x motor needs a lot of watts to run it. Not exactly true. A 530x runs better with a lot of watts. But I find the perfomance of a 5304 at 1000 watts to be very similar to the performance of an aotema at 1000 watts. There may be some differences in efficiency, but not enough for me to notice in terms of total range. You don't HAVE to use all the power you have to get up a hill, you just have to use what you need. It's like my one ton pickup truck with a 457 engine. I sure as hell don't need to drive it around with the pedal mashed to the floor. 1/10 of what that motor can do is all I need most of the time. Anyway, my 5304 on 20 amps of 48v climbs fast enough for me, and mostly I climb hills at half throttle with it. That's a puny 10-15 amps of 48v but it gets up the hills just fine. I don't set speed records, but on the dirt bike, I want to make the 8 mile range take awhile so I can enjoy it, and not be back at the car in 20 minuites. I used to ski the same way, once I realized that more runs actually meant a higher percentage of the day spent on the charlift. Slowing down actually meant I spent more of the day skiing.

 

[dscline]

Heat, on the other hand is another issue. The more watts you put into the motor, the faster it heats up. So for continuous climbing, doing it at half throttle may be the best way.

Yes, the comparisons I made were based completely on the power it takes to do the work, and completely ignores changes in efficiency of the drive system under different conditions. That will vary depending on the set-up, so it's hard to include it in the comparison. But in a situation where hills are a factor, it does help support the notion that you want to focus on the hills more than the flats... a motor that focuses more on torque vs. speed (be it from gears, more turns, etc.) is probably going to be more efficient on hills than a motor that is better for speed but lugs on the hills. Since we've already established that from a work perspective, you can realize more improvements in the hills than via speed, choosing a motor that can better address that aspect will help the overall efficiency even more. It seems to me that when choosing a motor, looking for good torque is a bit "safer"... if you don't have enough speed you can always add more voltage. But a motor that is inefficient in low speed torque will always be that way. At least that's my take on it.

 

[dogman dan]

Actually all this focus on efficiency is not what I think should be the issue, but rather, a very practical question of " does the motor melt from climbing the hill" Maybe I get biased on this by having two brushed motors that spit out the stinking smoke, but even with brushelss motors, efficiency won't matter if the motor melts. If a certain motor is slightly less efficient, a slightly larger ah battery could be used, but if a motor smokes itself, it's useless.

Pwbset may have more vertical under his belt than anybody, with me not too far behind. Funny, but we both now own hill bikes that are close to identical.

 

[tostino]

dogman, on the contrary, I think efficiency does still play a big role! Because that is what determines how much of the energy is being used for forward motion, and how much is going to heat. So yes, you should use a motor that will not melt when going up hill, but after that you need to focus on efficiency to get the most out of your bike.

 

[mclovin]

Descline explalined well something I've noticed, that it takes just about the same ammount of power to climb a hill at 5mph, or 10 mph. The hill remains the same, and allways takes x ammount of power to climb.

Just to clarify, do you mean battery power?

 

[tostino]

Descline explalined well something I've noticed, that it takes just about the same ammount of power to climb a hill at 5mph, or 10 mph. The hill remains the same, and allways takes x ammount of power to climb.

Just to clarify, do you mean battery power?

He just means energy. Weather that is gotten from a battery or your legs.

If you have the same efficiency at 10mph than at 5mph, going up the hill twice as fast, with twice as much power will use the same amount of WH.

 

[jag]

Descline explalined well something I've noticed, that it takes just about the same ammount of power to climb a hill at 5mph, or 10 mph. The hill remains the same, and allways takes x ammount of power to climb.

Just to clarify, do you mean battery power?

He just means energy. Weather that is gotten from a battery or your legs.

If you have the same efficiency at 10mph than at 5mph, going up the hill twice as fast, with twice as much power will use the same amount of WH.

There may be cases where going slowly uphill actually uses more energy than going faster. Just holding the bike against the grade of the hill takes torque, and generating this torque takes battery energy (that is lost as motor heat). Going slowly this loss may dominate.

 

[dogman dan]

I guess I opened a can of worms with that comment. Goody, the debate is allways so educational!

I was refering to the battery energy, but yes, the total energy would be similar too, since the size of the hill doesn't change. The point I was trying to make was that at my bikes hill climbing speeds, that are generally under 15 mph, the effect of wind is less noticeable than when going say 25 mph on the flats.

At one point, I got the idea in my head than slowing down to climb a hill would extend my range. Normaly, on the flat, the slower you go, there is a noticable increase in range. But on a steep hill, the power used to lift the weight up it dwarfs any savings caused by riding slower, so the savings from riding slower is not very noticeable. On a steep hill, it will take x number of watthours to get up it, plus whatever watthours are needed to go a certain speed. In perhaps 300 trips up my hill on the way home now, I've tried all sorts of things, but only turning off the motor and pedaling up it seems to save any battery capacity that I can tell. It just costs you to lift weight up to a higher elevation no matter what.

As for going even slower, my lowest gear pedals at about 6 mph at a comfy cadence for me. Even slower most likely would get into the motors stalling range, which would create more heat. It's hard to balance that slow anyway, so I doubt I'll do any testing slower than 6 mph. My ususal strategy to get up my mile and a half of 5-6% grade is to drop a few gears, spin the pedals fast, and ride at about 15 mph. I could climb the hill faster in a higher gear, but I found I had to pedal too hard. Now I try to keep up 15 mph, and pedal fast, but with less power on each pedal stroke. On very long steep hills, then I go to the lowest gear, and use only as much trottle as I need to go 6 mph, trying to use the motor only as much as I need. The reason for this, is to lower the wattage, so the motor may get up the hill without overheating

On efficiency, I should have qualified my statement to incude only the commonly avaliable brushless bike motors. I understand that the guys using RC motors and such are exploring higher efficiency in interesting ways. And of course, anything brushed has horrible efficiency and will make more heat instead of motion than brushless hubmotors.

I just find the difference in efficiency between say a bmc 600 watt and a clyte 5305 to be not that much to be worried about. They may use widely different ammounts of watthours, but most likely that is due primarily to one motor being noticeably faster or faster to accelerate than the other. My killawatt tells me that my little bafang like gearmotor at 20 mph uses allmost exactly the same watthours to go a measured distance in the same weather as my dd aotema motor at 20 mph. Same thing with the 5304 at 20 mph. The fusin usually gets me home with less power used simply because I ride faster on the aotema. On a steep hill, the fusin heats up much faster, simply because it has less mass to be heated than the aotema. The clyte motor, at nearly twice the weight heats up the slowest, because it takes more heat to wam up 25 pounds of metal than 10 and it has more surface area to radiate. In my opinion, hubmotors need cooling fins.