Ebike Design Idea - Please Critique!

General Discussion about electric bicycles.
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teacher81   1 µW

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Please Critique My First Design Idea!

Post by teacher81 » Aug 17 2014 4:56pm

Hello Everyone,

I've been on these threads for quite a while trying to soak it all in. I'm thinking about designing my first ebike. I'm currently riding an iZip e3 Dash. It's not a bad bike, but I have a few complaints (range, top speed, torque, etc.).

This is my idea for a first build. Please let me know what issues I'm likely to face. Or if anything looks way off.

Greyborg Warp Frame Set with Sclumpf Drive
BMC v4 Cruiser or Speed kit (with CA, controller, wires, etc.)
26" wheels, Schwalbe Marathon Plus tires
Single speed freewheel in the rear
Two em3ev 50v 22ah NCA batteries in parallel (total of 2210ah but with a low C rate allowing only 35a continuous discharge for each battery)
Low to middle grade front and rear suspension (open to ideas)
Hydraulic brakes in the front and rear

Design goals:
(1) 100mile + range with light to moderate pedaling at 20mph, (2) when desired, comfortable throttle only cruising in the low 30's mph, (3) ability to hit 40mph for short bursts, (5) reasonable weight (maybe 80lbs?), (6) decent torque, (7) ability to pedal assist without cogging for increased range or if battery dies/fails.

Specific questions
(1) The two NCA high energy batteries weigh only 25 lbs total and provide over 2kwh in energy. Too good to be true? Even if run them at 40amps for 2000w of power, I'd still be at less than 1c for the 44ah total battery. Am I doing the math right? Does this make sense if I don't need more than 2000w and want range in a lighter package?

(2) With 26" wheels, what kind of top speed can I expect with this build? The ebikes.ca simulator doesn't have the v4 BMC.

(3) If this bike is designed for mostly road and light off-road use, do I really need an expensive double crown suspension? Can I pick apart a $500-750 bikesdirect.com mountain bike for parts?

(4) How difficult will this be to wire? Will I likely have to cut my own hole in the Greyborg frame for a charger?

(5) Any other ideas from the group?

Thanks so much in advance!

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Drunkskunk   100 GW

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Re: Please Critique My First Design Idea!

Post by Drunkskunk » Aug 17 2014 11:19pm

Nice idea. But wrong motor for the job. The BMC can't handle the heat and power needed for those speeds. Also, a geared motor is less efficient for cruising long distances than a direct drive motor would be. And as a third issue, BMC is a fine motor, but it has been surpassed by the MAC, which is essentially a clone, but built to a higher spec now. 25-30% more power and a stronger clutch design.

What you need is a direct drive motor, and if 40mph is your goal with a heavy bike like the Borg carrying a huge battery, Also consider that hitting 40mph on just 50 volts needs a high speed wound motor, that will slurp down amps like a fat kid with a milk shake on a hot day when you try to accelerate or climb hills. You're going to need a heavy duty motor, and you might want to re-think your voltage, going for 100 volts instead.

Normally we say to plan a battery capacity size for 36 watts per mile. you'll often use less, but 36w/mi accounts for the extra power you'll need for fighting headwinds, low tires, hills, and the normal degradation of a battery over time, while not letting the battery drop below 20% in use(which is bad for batteries). Since you plan to pedal along, you can size your battery while factoring in the amount of power you can contribute per mile, but at 20mph, your battery can only reliably carry you 61 miles minimum. Single speed rear is probably not going work out since you'll need to supply 40% power to hit that 100 mile range goal.

Low grade suspension is worse than nothing. It basically turns your bike into a pogo stick, and kills your pedal efficacy. all your effort goes into making the bike bob, and you tire fast. Go for used, and get the best you can afford, or consider going with none.

Those tires are just too thin for the speeds you want. you need a larger contact patch for traction, handling, and braking. 2" minimum. 2.5" is better. keeping with your Schwalble theme, the Big Apple comes in 26 x 2.15 with the Racegaurd liner, similar to the puncture protection of the tires you picked. As an added advantage, Schwalbe has proven that wider esquires roll more efficiently.

As for brakes, Hydro is a matter of choice, but offers no actual performance advantage, despite all the hype. Braking is actually a function of the tire and it's grip. A tire at the point of skidding is at the maximum braking force you can achieve. Any brake that will skid the wheel is capable of maximum braking performance. And any brake that can't skid the wheel should be thrown away. Since you were going for budget suspension, perhaps this is a better place to save money. Avid BB7 are about the best mech brakes you can buy, and probably 4 times cheaper than the same quality hydro. Shop for discounted last year models, or shop takeoffs for the best deals.
Buy the ticket, take the ride.
Monster Bike:http://endless-sphere.com/forums/viewto ... =6&t=38667

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Samd   1.21 GW

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Re: Please Critique My First Design Idea!

Post by Samd » Aug 17 2014 11:48pm

A Borg with a big DD motor is a V8 hummer. Best served with 1.5 to 2 kWhr of batteries.

A BMC/Mac on a lighter frame with under a kilowatt hour of batteries is a nice agile Impreza WRX.

A small gear hub on a big borg frame is an odd partnership.
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dogman dan   100 GW

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Re: Ebike Design Idea - Please Critique!

Post by dogman dan » Aug 18 2014 7:24am

DD motor for sure. It would have to be a crazy fast winding to hit 40 mph on "48v". That would suck for everything else but cruising fast.

Settle for 30, perhaps 33 mph when it's fresh off the charger, and use a moderately fast winding. Crystalyte HS motor for example.

Or go for it, get a cromotor for that frame and run 72v or more. Be aware that on the street it will be an illegal homemade motorcycle in most places, and obviously so. Nothing under the radar about a bike that does 40+ mph.

30 mph goes remarkably un noticed, even if illegal where you are.

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arkmundi   1 GW

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Re: Ebike Design Idea - Please Critique!

Post by arkmundi » Aug 18 2014 8:37am

Yea OK, don't mean to hijack the thread, but I'm in the same position of considering my second build, different than my first and looking for a quicker, longer ride. I got my '85 Ross Mt Whitney frame and its a beautiful sleek well built road machine. I'm considering the upgraded MAC from EM3ev:
http://em3ev.com/store/index.php?route= ... uct_id=138
  • Upgrade EM3ev vers. Mac , 500/1000W Pick'n'Mix Kit
  • Controller Type Infineon 9 fet 30A (36-75V, IRFB4110)
  • Motor Speed 410rpm loaded @36V 6T Upgrade
  • Front/Rear Motor: Rear
  • Wheel Type 26" Alex DM24 CNC
  • Spoke Type Sapim Upgrade (Silver)
  • Throttle Type Thumb Throttle
  • Ebrakes HWBS Sensor
And as before, building my own battery pack with A123 cells. Probably back to the AMP20 prismatic cells, a 20S2P for 60V and 40AH. And put Maxxis Hookworm tires and heavy duty tubes on the wheel.

I'm gearing up for a 2-3 days/week commute Worcester to Clinton and back, to build my small house on the pond. Pretty flat, so am sacrificing torque for speed & distance. That's about 30 miles round trip. What do you think?

Note: revised on the basis of http://endless-sphere.com/forums/viewto ... er#p935255
:mrgreen:
Last edited by arkmundi on Aug 28 2014 5:34pm, edited 2 times in total.

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Ykick   100 GW

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Re: Ebike Design Idea - Please Critique!

Post by Ykick » Aug 18 2014 8:45am

arkmundi wrote:Yea OK, don't mean to hijack the thread, but I'm in the same position of considering my second build, different than my first and looking for a quicker, longer ride. I got my '85 Ross Mt Whitney frame and its a beautiful sleek well built road machine. I'm considering the upgraded MAC from EM3ev:
http://em3ev.com/store/index.php?route= ... uct_id=138
  • Upgrade EM3ev vers. Mac , 500/1000W Pick'n'Mix Kit
  • Controller Type 9 fet 30A (36-75V, IRFB4110)
  • Motor Speed 410rpm loaded @36V 6T Upgrade
  • Front/Rear Motor: Rear
  • Wheel Type 26" Alex DM24 CNC
  • Spoke Type Sapim Upgrade (Silver)
  • Throttle Type Thumb Throttle
  • Ebrakes HWBS Sensor
And as before, building my own battery pack with A123 cells. Probably back to the AMP20 prismatic cells, a 20S2P for 60V and 40AH. And put Maxxis Hookworm tires and heavy duty tubes on the wheel.

I'm gearing up for a 2-3 days/week commute Worcester to Clinton and back, to build my small house on the pond. Pretty flat, so am sacrificing torque for speed & distance. That's about 30 miles round trip. What do you think? :mrgreen:
Below 75V HOT off charger use 3077 FET controller.
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arkmundi   1 GW

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Re: Ebike Design Idea - Please Critique!

Post by arkmundi » Aug 18 2014 8:57am

Ykick wrote:Below 75V HOT off charger use 3077 FET controller.
Thanks, modified my order for that. Also added, per recommendation of the site: Thumb Throttle with 3sp Switch for EM3ev Infineon since its a match to that controller. Anything else? :roll:
Last edited by arkmundi on Aug 18 2014 9:12am, edited 1 time in total.

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Drunkskunk   100 GW

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Re: Ebike Design Idea - Please Critique!

Post by Drunkskunk » Aug 18 2014 9:02am

arkmundi wrote:Yea OK, don't mean to hijack the thread, but I'm in the same position of considering my second build, different than my first and looking for a quicker, longer ride. I got my '85 Ross Mt Whitney frame and its a beautiful sleek well built road machine. I'm considering the upgraded MAC from EM3ev:
http://em3ev.com/store/index.php?route= ... uct_id=138
  • Upgrade EM3ev vers. Mac , 500/1000W Pick'n'Mix Kit
  • Controller Type 9 fet 30A (36-75V, IRFB4110)
  • Motor Speed 410rpm loaded @36V 6T Upgrade
  • Front/Rear Motor: Rear
  • Wheel Type 26" Alex DM24 CNC
  • Spoke Type Sapim Upgrade (Silver)
  • Throttle Type Thumb Throttle
  • Ebrakes HWBS Sensor
And as before, building my own battery pack with A123 cells. Probably back to the AMP20 prismatic cells, a 20S2P for 60V and 40AH. And put Maxxis Hookworm tires and heavy duty tubes on the wheel.

I'm gearing up for a 2-3 days/week commute Worcester to Clinton and back, to build my small house on the pond. Pretty flat, so am sacrificing torque for speed & distance. That's about 30 miles round trip. What do you think? :mrgreen:

If you want speed and distance, why go with a geared motor, with it's lower efficiency and being run outside it's power range? If you want to cruise at high speeds, get a motor that can handle it. A direct drive.

A couple pounds difference between the MAC and a 9C would be insignificant when you're carrying the weight of a kindergartener in batteries.
Buy the ticket, take the ride.
Monster Bike:http://endless-sphere.com/forums/viewto ... =6&t=38667

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arkmundi   1 GW

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Re: Ebike Design Idea - Please Critique!

Post by arkmundi » Aug 18 2014 9:07am

Drunkskunk wrote:If you want speed and distance, why go with a geared motor, with it's lower efficiency and being run outside it's power range? If you want to cruise at high speeds, get a motor that can handle it. A direct drive.

A couple pounds difference between the MAC and a 9C would be insignificant when you're carrying the weight of a kindergartener in batteries.
Thanks for the comment - yea I'll do that motor comparison. FYI, yes I do have hills to contend with. I live at the top of one Worcester's seven hills. Then when I get to Clinton, I've got a bitch of a long uphill driveway to contend with. And I'm a heavy dude. So some torque is good.

teacher81   1 µW

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Re: Please Critique My First Design Idea!

Post by teacher81 » Aug 25 2014 7:30pm

Drunkskunk wrote:Nice idea. But wrong motor for the job. The BMC can't handle the heat and power needed for those speeds. Also, a geared motor is less efficient for cruising long distances than a direct drive motor would be. And as a third issue, BMC is a fine motor, but it has been surpassed by the MAC, which is essentially a clone, but built to a higher spec now. 25-30% more power and a stronger clutch design.

What you need is a direct drive motor, and if 40mph is your goal with a heavy bike like the Borg carrying a huge battery, Also consider that hitting 40mph on just 50 volts needs a high speed wound motor, that will slurp down amps like a fat kid with a milk shake on a hot day when you try to accelerate or climb hills. You're going to need a heavy duty motor, and you might want to re-think your voltage, going for 100 volts instead.

Normally we say to plan a battery capacity size for 36 watts per mile. you'll often use less, but 36w/mi accounts for the extra power you'll need for fighting headwinds, low tires, hills, and the normal degradation of a battery over time, while not letting the battery drop below 20% in use(which is bad for batteries). Since you plan to pedal along, you can size your battery while factoring in the amount of power you can contribute per mile, but at 20mph, your battery can only reliably carry you 61 miles minimum. Single speed rear is probably not going work out since you'll need to supply 40% power to hit that 100 mile range goal.

Low grade suspension is worse than nothing. It basically turns your bike into a pogo stick, and kills your pedal efficacy. all your effort goes into making the bike bob, and you tire fast. Go for used, and get the best you can afford, or consider going with none.

Those tires are just too thin for the speeds you want. you need a larger contact patch for traction, handling, and braking. 2" minimum. 2.5" is better. keeping with your Schwalble theme, the Big Apple comes in 26 x 2.15 with the Racegaurd liner, similar to the puncture protection of the tires you picked. As an added advantage, Schwalbe has proven that wider esquires roll more efficiently.

As for brakes, Hydro is a matter of choice, but offers no actual performance advantage, despite all the hype. Braking is actually a function of the tire and it's grip. A tire at the point of skidding is at the maximum braking force you can achieve. Any brake that will skid the wheel is capable of maximum braking performance. And any brake that can't skid the wheel should be thrown away. Since you were going for budget suspension, perhaps this is a better place to save money. Avid BB7 are about the best mech brakes you can buy, and probably 4 times cheaper than the same quality hydro. Shop for discounted last year models, or shop takeoffs for the best deals.
Thanks so much Drunkskunk and others for all of the comments. I really appreciate the time. In the end, I really want a bike that can has similar performance to a Stealth Fighter or Greyp. I just don't want to spend $8,000. What do you think would be be best solution?

Alternatively, does anyone live in the Boston area? If so, I'm willing to pay someone $500 to help me build it over a weekend.

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