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  1. #1
    Senior Member Shahmatt's Avatar
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    A high power, low speed e-assist kit for climbing only

    I"m currently in the process of building a commuting city bike and I am trying to work out the best gear range.

    The setup I'm looking at has gear inches ranging from 40 to around 90.

    I'm looking at trying to reach a GI of around 100, but don't want to compromise the lower end too much in case I have to climb. A low end GI of 50 is too high I guess.

    An e-assist seems to introduce some possibilities. I wonder if there are motors available which don't have high speed but can help just with climbing.

    So low speed and high power is what I'm looking at. Something to cover a gear range of around 20 to 40, and something that's lightweight. I don't need a large battery since I won't be cruising with it and won't need range. Once I get up to speed I switch off the motor and go on pedal power alone.

    Are there e-assist kits out there that fit this profile?
    Last edited by Shahmatt; 12-12-13 at 11:21 PM.

  2. #2
    Transportation Cyclist turbo1889's Avatar
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    Not that I have found, at least anything decent in a commercially available kit. I've had to build my own "hill climber ONLY motor" builds from scratch.

    I agree with you that it is a highly desirable set-up and a niche that isn't currently being filled by any commercial kit I know of, it is possible to build your own from scratch though. Most common option is to sacrifice the rear disk brake and put a good set of V-brakes on the rear wheel and mount a big sprocket on the six bolt disk mount pattern and run a second chain up to a motor in the frame with a small tooth count freewheel on the motor. There are other options of course some even better then that most common set-up.

    There is another thread or two on this forum about them one very recent and should be just a few spaces down below this one on the first page. And then there are some builds over on the endless-sphere forum along these lines. I've built a couple myself but haven't bothered to put up a build thread. The purest form of electric assisted bicycle I know of since you only use the motor when climbing hills or for a short burst when pulling out from a dead stop and on the flat you can pedal faster then the motor so you still do a lot of pedaling and only use the motor when you most need it and aren't tempted to get lazy and use it any other time.

  3. #3
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    I also am planning a similar build. The thread turbo1889 is rererring to is here:http://www.bikeforums.net/showthread...duction-Thanks. I got some good info from turbo on that one. Also endlesssphere is helpful, though a bit more focused on the electrics. It seems that if torque is your primary goal, you need a way to gear the motor down. Mid-drive, non-hub setups seem to accomplish this best. I'm planning to use a motor/controller/wiring/throttle/etc from a scooter, they can be found here fairly cheap used. To do it, the motor/jackshaft brackets will have to be fabricated from scratch from aluminum plate/angle/billet. Jackshafts/bearings/gears can be found at staton and elsewhere. Online scooter part stores also have this type of stuff.

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    Quote Originally Posted by turbo1889 View Post
    Not that I have found, at least anything decent in a commercially available kit. I've had to build my own "hill climber ONLY motor" builds from scratch.
    I've built a couple myself but haven't bothered to put up a build thread.
    I would be interested to see your builds. The BF electric bike forum is lacking in homebrew build threads and I think it would be cool to see what some others have done. I think that the mechanics of the systems are not given much airtime.

  5. #5
    Senior Member Shahmatt's Avatar
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    Thanks for the info.

    I intend to make use of the non-drive wheel. What about some of the hub motors mentioned in this post?

    http://www.electricbike.com/hubmotors/

    What kind of wattage should I be looking at in order that the motor climb easily?

  6. #6
    put our Heads Together cerewa's Avatar
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    Quote Originally Posted by Shahmatt View Post
    What about some of the hub motors mentioned in this post?

    http://www.electricbike.com/hubmotors/

    What kind of wattage should I be looking at in order that the motor climb easily?
    That post contains great info. The writer puts his focus on hub motors-- hub motors are great because of their simplicity and reliability, in addition to being affordable and widely available. Geared hub motors are preferable if you need something that works on steep hills. None of the common setups are ideal for going less than 10 mph at high power but if you want to be adventurous you could take a common geared hub motor and run it at fairly high power & low voltage (something like 12 to 24 volts, with an amperage limit of 30A or more). This would give the motor a low top speed and good climbing ability. (for a given motor, increased amps give increased torque while increased volts give increased top speed-- higher voltages usually run less efficiently at low speed)

    The author of your post says there are hub motors with steel, nylon, or composite gears inside, and he recommends composite. I don't know if composite gears work for your situation (low speed high torque) but I am pretty sure steel gears would work. Steel gears are probably noisier than composite, and they may run hotter (this would be a problem at high speeds) but they'll tolerate a lot of torque. Nylon gears can lose their gear teeth and become useless when they are not used in the typical manner (moderate power and moderate speed).

    The picture in this link shows a steep grade of 25%. A very small percentage of roads are as steep as this one. To climb it at 8 to 10 miles per hour, you'd have to pedal (moderate or strong pedaling) and have a good 1000-watt motor setup.
    http://www.frontiernet.net/~rochball...wns/rialto.htm

    This is based on the kreutzotter bicycle speed / power calculator http://www.kreuzotter.de/english/espeed.htm
    Last edited by cerewa; 12-14-13 at 09:20 AM.
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    coprolite fietsbob's Avatar
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    I've seen what amounts to an indirect drive , motor drives left hand chainring,
    Tandem crossover parts, then the right side has the final drive
    there you have the ratios of a Mountain bike..

    Not sure if CleverCycles in Portland Patented it, the 'stoke monkey'.

    it requires the space of a long tail ala Extracycle.

  8. #8
    Senior Member 15rms's Avatar
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    Maybe you could consider a recumbent bike with a 20 inch front wheel. They are more comfortble and with the smaller front wheel a hub would have greater power.

  9. #9
    Senior Member Shahmatt's Avatar
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    Quote Originally Posted by 15rms View Post
    Maybe you could consider a recumbent bike with a 20 inch front wheel. They are more comfortble and with the smaller front wheel a hub would have greater power.
    Incidentally I am building a recumbent with 16 inch wheels on front and back. The intention is also for it to be a Cruzbike conversion - meaning forward wheel drive.

    I am considering installing the hub on the rear wheel. Weight is an issue since the bike on its own (after Cruzbike conversion) is likely to be around 17kgs. With this hub I'm guessing it will easily top 20kg. Trying to keep it below 20kg if I can. I am around 80kgs.

    Am I right in guessing that 16" wheels will be easier for powering up hills as torque is magnified? I also don't mind helping the motor along. The idea is that I need assistance for power but gradually change to pedal power on the flats.

    On this basis would the Bafang 250W motors at low voltages and low gearing be good enough for the purpose?
    Last edited by Shahmatt; 12-14-13 at 09:48 PM.

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    Here is a list on mid drives.
    http://www.electricbike.com/mid-drive-kits/

  11. #11
    Senior Member 15rms's Avatar
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    Shahmatt I have never used a geared hub. Especially a 250 watt. Hopefully others will chime in here and answer your questions.

  12. #12
    Transportation Cyclist turbo1889's Avatar
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    With that small of a wheel size and rear wheel mounting you might be able to get a hub-motor to do the job you want it too. For conventional full size wheels (24", 26", 27" and 700c) especially front fork mounting there are few if any hub-motors that do a truly good job of hill-climbing and few front forks that are strong enough to handle the ones that are.

    If you want to do it with a hub motor your best bet is probably going to be one of larger size internally gear reduction freewheeling hubs (usually advertised as being at least 500-watts).

    The main issue that makes most hub-motors not very good strong and efficient hill climbers is gear reduction, using a smaller diameter wheel has the effect of reducing the gearing so that will help you a lot especially since you don't loose any strength in the drive and actually gain some in-fact by going to a smaller wheel size. This is why so often the good hill climbers are not hub motors but rather chain drive where the chain drive offers a way of substantially reducing the gearing and being very strong to handle the high torque loads. Also hub-motors with their reaction torqued axles put incredible torque loads on the bikes drop-outs which a chain drive does not do.

    It's entirely within the technical limits of geared hub motor technology to build one specifically designed as a "hill climbing helper ONLY motor" for most bikes it would need to be rear mounted with at least one torque arm like a coaster brake hub minimum but a double stage planetary gear reduction (all current internal gear reduction hub motors have only one reduction stage and you can only get so much gear down in only one stage) with some good high end steel gears would be required to get the necessary reduction ratio and strength necessary to handle the resulting toque loads on a full size bike wheel and have good strong hill climbing ability. I know of no such hub motor currently being manufactured. With a small wheel though as I said you might be able to make one of the bigger more powerful hubs do the job because of the reduction in ratio you will get as a result of the smaller wheel.
    Last edited by turbo1889; 12-14-13 at 10:38 PM.

  13. #13
    Transportation Cyclist turbo1889's Avatar
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    Also, someone suggested running a hub-motor on lower volts and pumping up the amps. That poster is correct that with electric motors the voltage roughly translates to speed and the amps to torque. BUT, unless you rewind the motor coils inside with larger diameter wire there is a limit to how much amps you can push regardless of the voltage. Try to push too many amps through too small of a wire diameter and you will have red hot glowing wires which works great in a toaster to heat up your bagels but is not so good of a thing inside of an electric motor.

    Long story short you can push the amps up a little beyond what a hub motor is rated for, especially if you lower the voltage which helps a little on keeping the heat down but long story short you can't continuously push 40+ amps through a motor only designed to take 15 amps without burning it up in fairly short order regardless of whether or not you cut the voltage down by half at the same time or not. Cut the voltage down and push 20 amps maybe 25 amps through a motor rated for 15 amps at higher voltage and that can work but you can't do much more then that and get away with it without pushing your motor into melt-down mode.

  14. #14
    Senior Member Shahmatt's Avatar
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    Quote Originally Posted by aztarget View Post
    Here is a list on mid drives.
    http://www.electricbike.com/mid-drive-kits/
    Thanks. But since I intend to use the free wheel and save weight I'm hoping just a hub motor might do.

    Quote Originally Posted by turbo1889 View Post
    With that small of a wheel size and rear wheel mounting you might be able to get a hub-motor to do the job you want it too. For conventional full size wheels (24", 26", 27" and 700c) especially front fork mounting there are few if any hub-motors that do a truly good job of hill-climbing and few front forks that are strong enough to handle the ones that are.

    If you want to do it with a hub motor your best bet is probably going to be one of larger size internally gear reduction freewheeling hubs (usually advertised as being at least 500-watts).

    The main issue that makes most hub-motors not very good strong and efficient hill climbers is gear reduction, using a smaller diameter wheel has the effect of reducing the gearing so that will help you a lot especially since you don't loose any strength in the drive and actually gain some in-fact by going to a smaller wheel size. This is why so often the good hill climbers are not hub motors but rather chain drive where the chain drive offers a way of substantially reducing the gearing and being very strong to handle the high torque loads. Also hub-motors with their reaction torqued axles put incredible torque loads on the bikes drop-outs which a chain drive does not do.

    It's entirely within the technical limits of geared hub motor technology to build one specifically designed as a "hill climbing helper ONLY motor" for most bikes it would need to be rear mounted with at least one torque arm like a coaster brake hub minimum but a double stage planetary gear reduction (all current internal gear reduction hub motors have only one reduction stage and you can only get so much gear down in only one stage) with some good high end steel gears would be required to get the necessary reduction ratio and strength necessary to handle the resulting toque loads on a full size bike wheel and have good strong hill climbing ability. I know of no such hub motor currently being manufactured. With a small wheel though as I said you might be able to make one of the bigger more powerful hubs do the job because of the reduction in ratio you will get as a result of the smaller wheel.
    Thanks.

    So based on the wheel size you believe this to be feasible.

    The Cruzbike conversion I am doing brings the rear (drive wheel) to the front dropout position and vice versa.

    The rear dropout, which is designed for chain drive forces, just accommodates free wheel forces post conversion.

    On this basis I'm hoping that the bike will manage the torque from any motor I may install.

    This article elaborates somewhat on 250W motors:

    www.electricbike.com/250-watt-hub-motor/

    Based on what is said it seems like 250W may be enough for my purpose. Note I am going to use this bike on the road and still supply some assistance. What say you?

    Based on your suggestion of 500W, what brand/model and setup would you suggest I use?

  15. #15
    Senior Member Ypedal's Avatar
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    At the risk of breaking forum rules, shameless plug time :
    http://ypedal.com/kit/kit.htm

    This is a 250w sized motor driven at 36v 15amps for 500w output, has thicker gears to cope with the extra power than the bafang, so it retains the light weight, runs a bit warmer, but does not require the expensive high-powered batteries of Direct Drive 30+ amp controllers... it's a compromise that works well.

    If you do not want to pedal and intend to climb big hills with a cargo bike, fully loaded, then you really should get a higher powered setup, but the reality is that these smaller geared motors will get the job done for just about everyone who does pedal and keeps your bicycle riding like a bicycle and not a tank..

    My KMX trike with crystalyte X5 in a 20" rim , running 100v and 80 amps can burn rubber :
    https://www.youtube.com/watch?v=AJnPxF9hpSI

    But it's a bear to pedal up any hill without power, and you really don't need that much power for cycling.. at all.

  16. #16
    rugged individualist wphamilton's Avatar
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    I'm sympathetic to this plan and I've thought of a 250 watt hub motor myself just for hills assist. But what has stopped me is this: I think the idea that you won't need as large a battery is too optimistic. While there are a lot of "it depends" variables, I reason like this:

    With a lot of rolling hills, even if I simply coast on the downslope with no power applied I'll still spend less time unpowered going down than powered going up. Less than half, likely way less than half. Power is power, 250 watts going up down level at any speed is still just power, times time applied is the energy used (battery capacity). Timewise if you only use it uphill, unpowered is some fraction of one half. So if the given motor plus battery estimates a range of 20 miles for example, we can't say "I'm only using it for 10 miles of uphill so I'd get 30 miles, so I only need two thirds the battery." That's a natural feeling assumption but it's wrong.

    So even with this plan I think you still need the big battery, with the expense and weight, and more is better. I'm still cheering you on, but I don't want you to be disappointed by buying half the battery you need.

  17. #17
    Senior Member Ypedal's Avatar
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    Capacity and Power are separate things, i'm testing a 3ah RC lipo pack *(20C cells ) that can deliver 15 amps easily, puny light weight pack for short range.... however if you opted for a less powerfull battery pack like a ping, or those water bottle battery packs made with 18650 cells, you need at least 10ah worth, minimum to cope with the 15 amp demand....

    now that being said, if you wanted a long range pack, almost all of the 15ah or less capacity packs can deliver 15 amps ( 1C )...

    However, if you run a Direct Drive motor with a 40 amp controller, you need a very powerfull battery, or one very large and heavy big capacity pack, otherwise it will overheat and die in quick fashion.

    Edit to add : you need to decide what you prefer between a light power assited bicycle and an electric motorcycle with pedals ! ;-)

    The only thing that can power my trike is RC lipo, using Nano-Tech 50C cells.... anything less simply does not hold up. more power, more money, more weight, more danger... it's a slippery slope.
    Last edited by Ypedal; 12-15-13 at 09:32 AM. Reason: added info.

  18. #18
    rugged individualist wphamilton's Avatar
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    You're talking about the maximum current discharge rates, which also vary.

    It's not that complicated. Amp-hours times average voltage is the energy the battery can hold. Which is the amount of power the motor can apply times the time applied.

  19. #19
    Transportation Cyclist turbo1889's Avatar
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    @ OP

    The only 500+ watt internal gear reduction hub-motor I personally have used is an EM3. Not guaranteeing that it is the best one in that category or that you can't get one just as good for less money somewhere else. What I do know is that it climbs hills just as good as a direct drive hub I've got that has over twice the watts of power because the direct drive hub wastes so much more power while hill climbing (and gets a lot hotter from all that waste heat and drains batteries a lot faster). Granted its not near as powerful of a hill climber or even half as efficient as my dedicated hill helper only builds that use smaller motors in the frames running through a large reduction chain drive or my mid-drives that can also gear down really well.

    But then I'm using it in a 26" wheel so if you use it in a 16" wheel you should get 162.5% of the torque I'm getting just by the smaller wheel size and you might get even more if you go with one of their models with a higher winding count then mine has (can't remember which I ordered but it wasn't the one with the highest winding count). Winding count refers to how many turns are used in the electromagnet coils inside the motor. More turns on the coils means more torque and less speed, less turns means less torque and more speed. I didn't get the lowest torque one but I didn't get the highest one either.

    Realize I didn't use my one motor in this category on a "hill climbing helper motor ONLY" build but rather on just a regular build but I can tell you that of all my just regular old hub-motor builds it climbs the best. Just not the kind of climbing ability I would personally demand from a "hill climbing helper motor ONLY" build because I know that better performance with less power usage is possible by other methods. But with you using a smaller wheel size it might do the trick for you and a hub motor of "that type/category" is probably your best bet if you insist on a hub-motor set-up.



    On most of my "hill climbing helper motor ONLY" builds I have used RC type Li-Poly packs for a small and light weight package and usually try to shoot for having a half hour worth of climbing power in the pack capacity which works out just about right for my needs usually and doesn't over-stress the packs with the usual high discharge rate those packs have.
    Last edited by turbo1889; 12-15-13 at 01:19 PM.

  20. #20
    Senior Member Shahmatt's Avatar
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    @Turbo

    This the hub motor you mean?:
    http://em3ev.com/store/index.php?rou...product_id=107

    Does it freewheel easily when not powered?

  21. #21
    Transportation Cyclist turbo1889's Avatar
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    Yup, that's the one. There is a tiny bit of drag you feel when just pedaling and you do feel a little inertial lag from its weight when accelerating under pedal power alone but its nothing like trying to pedal only with a direct drive hub.

    They don't seem to have your small 16" wheel rim size so your probably going to have to buy just the bare motor and have your LBS lace it into a rim for you. (Unless you know how to lace your own wheels something I could never master myself. I can do everything else on a bike including weld my own frames but every time I've tried to lace and true my own wheels I've ended up screaming words I shouldn't and about pulling my hair out.)

    There are other places that sell those type of bigger size internal gear reduction hub motors that aren't just the little 250-watt internal gear reduction hubs and I would always encourage anyone to shop around before making a choice. That should give you an idea though of what kind of hub-motor is going to give you a good chance of doing what you want it too.

  22. #22
    Senior Member Shahmatt's Avatar
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    Quote Originally Posted by turbo1889 View Post
    Yup, that's the one. There is a tiny bit of drag you feel when just pedaling and you do feel a little inertial lag from its weight when accelerating under pedal power alone but its nothing like trying to pedal only with a direct drive hub.

    They don't seem to have your small 16" wheel rim size so your probably going to have to buy just the bare motor and have your LBS lace it into a rim for you. (Unless you know how to lace your own wheels something I could never master myself. I can do everything else on a bike including weld my own frames but every time I've tried to lace and true my own wheels I've ended up screaming words I shouldn't and about pulling my hair out.)

    There are other places that sell those type of bigger size internal gear reduction hub motors that aren't just the little 250-watt internal gear reduction hubs and I would always encourage anyone to shop around before making a choice. That should give you an idea though of what kind of hub-motor is going to give you a good chance of doing what you want it too.

    Thanks very much. I've only recently begun to look into the details of bike mechanics and so am still very green in these matters.

    Unfortunately wheel building and truing is quite expensive to do here in Singapore. One shop quoted me 56USD for workmanship plus 0.80 to 2.40USD per spoke (depending on quality). This excludes the cost of the rim.

    I will be trying my best to get the wheel built before shipping. It may be cheaper.

  23. #23
    Transportation Cyclist turbo1889's Avatar
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    It is way cheaper and there are also some shops on the internet that specialize in wheel builds especially with non-standard hubs that you can have them get the hub for you and build it into a wheel and ship it to you.

    Those prices aren't actually too bad. Up here I'm paying a local charge of $40-$80 labor (some wheels take more time for him to lace up then others) plus the cost of the spokes themselves with a guy I found at one bike shop that is "good at taking instructions" and will build the wheel exactly like I tell him I want it and does a good job without trying to tell me I should do it some other way. With some of the more custom configurations I have to prep everything for him but he does a great job for me. If I tell him I want a 48-spoke wheel with 12ga. stainless spokes and find him a rim and hub that works for that he just does it and doesn't give me a bunch of guff about that being overkill and ridiculous and try to talk me into something else. A problem I've had with other people I've paid to build wheels for me.

  24. #24
    Senior Member Shahmatt's Avatar
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    Quote Originally Posted by wphamilton View Post
    I'm sympathetic to this plan and I've thought of a 250 watt hub motor myself just for hills assist. But what has stopped me is this: I think the idea that you won't need as large a battery is too optimistic. While there are a lot of "it depends" variables, I reason like this:

    With a lot of rolling hills, even if I simply coast on the downslope with no power applied I'll still spend less time unpowered going down than powered going up. Less than half, likely way less than half. Power is power, 250 watts going up down level at any speed is still just power, times time applied is the energy used (battery capacity). Timewise if you only use it uphill, unpowered is some fraction of one half. So if the given motor plus battery estimates a range of 20 miles for example, we can't say "I'm only using it for 10 miles of uphill so I'd get 30 miles, so I only need two thirds the battery." That's a natural feeling assumption but it's wrong.

    So even with this plan I think you still need the big battery, with the expense and weight, and more is better. I'm still cheering you on, but I don't want you to be disappointed by buying half the battery you need.
    I don't really know anything about batteries and capacities. Say I go with the 500W motor. Also assuming that I'll mainly use this motor for very little hill climbing but mainly for the short boost to get started at traffic lights within the city.

    Assuming a commute range of around 16 miles. Maybe (conservatively) around 32 junctions within this range plus another 50% random other stops. Make it around 45 stops. Assuming 15 seconds of power to getting started at each stop. That's 675 seconds. Multiply that by two for a return journey. So 1350 seconds (or 23 minutes) of power is what I guess I would need. Does this calculation sound about right?

    Based on this how much of a battery capacity should I be looking at? Maybe add another 20% to account for natural deterioration of the battery with time.

  25. #25
    rugged individualist wphamilton's Avatar
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    Quote Originally Posted by Shahmatt View Post
    I don't really know anything about batteries and capacities. Say I go with the 500W motor. Also assuming that I'll mainly use this motor for very little hill climbing but mainly for the short boost to get started at traffic lights within the city.

    Assuming a commute range of around 16 miles. Maybe (conservatively) around 32 junctions within this range plus another 50% random other stops. Make it around 45 stops. Assuming 15 seconds of power to getting started at each stop. That's 675 seconds. Multiply that by two for a return journey. So 1350 seconds (or 23 minutes) of power is what I guess I would need. Does this calculation sound about right?

    Based on this how much of a battery capacity should I be looking at? Maybe add another 20% to account for natural deterioration of the battery with time.
    With that estimate, with low speed and flat, I'd say that your plan will work. Maybe something like 10amp-hr 24V tho other configurations might be better. My caution is that hills can eat more power than we might expect.

    I gather that generally ebike owners come to feel that more is better.

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