Electric Motocross Bicycle build (Tons of big pictures)

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Electric Motocross Bicycle build (Tons of big pictures)

Post by dpearce » Jan 10 2011 7:38am

Hello all, I am new to this forum, I just recently came across it and have been checking out everyone's bikes and have been learning a lot. I wish I had found it sooner, I could have saved a lot of money and time researching, and undoubtedly produced a better bike . Although I am a newbie noobie noob whatever, I have something to contribute, I present to ES my electric bike, it was built as a mechanical engineering senior design project with the help of two other M.E. students. It is not 100% finished yet, but it is functional, maybe 5-10% more work until I am satisfied. This bike was designed and built in less than 4 months. Consequently, without sufficient time to reinvent the wheel, the focus of this build was on something that the ebike world seems to be lacking, a purpose built structure, designed from the ground up to be uniquely integrated with off the shelf components. So here it is, hopefully this build can provide some useful information to the members here undertaking similar projects.

The structure's (chassis, frame) function is to act as a housing for the electronic components, support for the suspension and rider, and tie everything together in a sleek appearing package. The project was started with classification and rating schemes to systematically find good solutions for the requirements set forth, and the project was to be completed within the budget of $4000.

Specifications:

Total weight 90lbs
Carbon fiber monocoque frame, <9lbs.
Custom built swingarm ~2.5 lbs.
CR80 motorcycle front forks and rear shock, rear ratio is 3" wheel travel per inch shock travel with progressive rate geometry.
Setup to provide 9.5" suspension travel front and rear.
72V 10ah Lipo batteries, ~8lbs (as of now), but it was designed to accommodate at least 72v 20 ah, as well as another controller for a front hub motor.
26" x 2.7" tires on 26 x 2.5" rims
Hayes 203mm / 8" hydraulic discs
5 speed
BMC rear hub motor, V2T, 10ga phase wires up to axle exit
BMC 50A controller
consumption 20-40 watt*hr
Headlight, tailight, brakelight, Cycle analyst, moped plate.
Top speed around just under 30mph w/o pedaling
Cost $4000, could have been much cheaper had I found this forum sooner.
Future plans-Double battery capacity (to 20Ah) and add front hub motor.

One of the first steps in the design was to make a dynamic sketch in Solidworks (SW), a 2D geometry model defining the wheelbase, suspension vectors, wheel size, head tube angle, seat height, battery placement etc. From this basic geometry model, with no dimensions set in stone yet, a conceptual model was made, modeled around standard mountain bike parts.

conceptual geometry model (1st iteration, not actual dimensions or geometry used):

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Since this was a clean sheet design, not based off any existing bike or motorcycle, geometry was designed specifically to keep the batteries as low and centralized as practical, while still retaining adequate ground clearance at full compression of the suspension. The extra speed and weight of the electric components were considered in the selection of the wheelbase, seat height and other dimensions, providing a good compromise between mountain bike and motocross dirtbike proportions and rider position, which truly makes this an Electric Motocross Bicycle.

Solidworks Conceptual Model

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Next was the embodiment of the design around actual parts that were to be used. Parts were selected to fulfill wished and demands withing the budget, after purchase parts were modeled as they became available in the order of their arrival. As more and more concrete dimensions became available from the presence of these parts, dimensions of some important parts were finalized with priority so they could be built first, since other parts might be dependent on their completion (for example frame inserts and sub components must be made before the frame)


The whole project would not have been possible without adhering to a strict production schedule in order to finish on time.
After checking clearances, refining suspension geometry, considering ergonomics, component access + servicability, etc., a detailed, fully functioning 3D model was made around the parts to be used. For a separate course, Analysis and Design of Machine Components, analysis was performed with the aid of Solidworks finite element analysis software, with a focus on critical areas of structural components, to ensure safety and durability during the intended use and abuse.

Once satisfied with analysis results the conceptual model could start to be realized in more detail.This model was then used to design and build the parts needed to make everything compatible, such as those shown below. In the detail design phase things such as hardware selection, chain path, bearing selection, etc. were determined so we don't find any surprises when we start to assemble things.


Transparency showing possible battery configuration (72V, 20Ah)

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Rendering of detailed model:

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Solidworks Animation:

[youtube]http://www.youtube.com/watch?v=UHsjXhiDpTY[/youtube]

Some parts made on the lathe:
Machined head tube to accept CR80 forks, bottom bracket shell to accommodate raceface external bearing downhill cranks, and other frame inserts.
Knurled finish to help with adhesion of the composite, alodine coated to prevent corrosion

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Positive frame mold:

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Swingarm pivot / bottom bracket frame sub component

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Staggered layers of carbon fiber bottom layer are oriented 0-90, 2nd layer is 45-45, but with this stuff each layer also already has built in 0-90 and 45-45 degree fiber orientations.

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Here is a picture cutting the patterns out that demonstrates the different orientations. 1:1 patterns were printed on paper and traced onto the carbon fiber to be cut out. Using wet layup methods there is a little bit of leeway with these dimensions, but too much would be better than too little here, since it is easy to cut off excess after it cures.

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Self Jigging frame mold, with reinforcements prebuilt in to subcomponents. Eliminates need for external jig to hold inserts in during curing, which would complicate the vacuum bagging.

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There are 2 layers around the edges of the frame, and 1 layer in the large areas subject to dominant shear loads. 1 layer cured with vacuum bag = ~1/16", 2 layers ~.125". In some places the layers are stacked up to as much as 3/8" thick. Samples were cured and tested for integrity and dimensional consistency, since many parts are designed around these carbon layer thicknesses.
This picture is a laser scan of the actual frame superimposed over the computer model, showing the dimensional variances.

Laser Scan color map: Different colors represent different dimension variations

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Courtesy of Polyworks

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Factor of safety color map. The numbers here are not what we were interested, just the qualitative data that can be interpreted from these tools, that can give an idea of where the stress concentrations and critical areas are, where reinforcement may be necessary and where material may be removed. With carbon fiber being so light weight penalties were acceptable, broken frames are not, so reinforcements were made accordingly.

Finished Frame:
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Custom seat made from modified MX bike seat.

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Finished Swingarm, built with 6061 rectangular aluminum extrude and plate, machined lower shock mount, brake caliper mount, pivot bushing mounts, and dropouts (3/8" thick). Welded in a jig, then ground smooth, then taken to be heat treated back to T6 condition and straightened. (Thanks to Newton heat treating, City of Industry, CA.)

computer Model:
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Finished Swingarm:
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Simplified swingarm model factor of safety map. With known materials (6061 T6), and uncertain dynamic loading, the swingarm was designed to have a safety factor of about 4. However the model is very simplified, and the results are trivial without some sort of real world validation. Again here the results are useful quantitatively, showing that the highest stress areas are in the middle of the swingarm around the shock mount and at the corners. The Model also does not take into account material discontinuities due to welding. From there large fillets were added in the areas of highest stress, and the swingarm was reinforced further, again with safety being more of a concern than weight.

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Finished Bike:

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I have about 100miles on it so far, mostly street with light off roading, up + down some stairs here and there. I have been monitoring temperatures and all seems ok, but so far I have trying to use the power sensibly. We will see how long the motor holds up, I plan on getting the front hub motor and extra battery capacity to ease the load, and for steep hill climbing, and I still have set up the suspension better for me, along with the never ending list of other things that have to be done. Right now I am just enjoying riding it so it is hard to get back to working on it!
Last edited by dpearce on Sep 16 2011 12:57pm, edited 2 times in total.

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beast775   100 kW

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by beast775 » Jan 10 2011 9:28am

hello,very nice work. :D
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by turbodan78 » Jan 10 2011 9:31am

Not bad at all!! so exciting to see people interested in wanting and designing these kinda bikes and seing you're skill and dedication to a mx style e-bike is what alot of people who are'nt worry'd about standing out are keen on

looks pretty light and now you have started getting into this site i'm sure you can only make even better bikes again! alot of helpfull and keen people on this site

ya'll have to get some vids up for everyone!

how strong do you think the frame would be? good enough for some light downhill riding or more?

getting my new bomber soon which is very good and feeling prettty amped but i'm jelous of you're bike as well

ya have to keep this updated and get some more figures down and stuff + improvements hey :D 8)

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by bigmoose » Jan 10 2011 9:47am

Outstanding design and execution! You definitely have a design worthy of production!! ... and welcome to the forum.
Last edited by bigmoose on Aug 07 2011 6:08pm, edited 2 times in total.
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by etard » Jan 10 2011 10:03am

Very nicely done! I love everything on the design except the front fender. I'm guessing you guys are from Cal Poly Fullerton? What are your impressions of it so far compared to other MX bikes?

Nice execution! :twisted:
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by docnjoj » Jan 10 2011 11:16am

Beautiful machine work and super composite execution. Simply great! Definitely a fine example of engineering school work in action.
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by dontsendbubbamail » Jan 10 2011 11:30am

I was impressed with how close the actual frame dimensions were to the drawing. How about a shot of the battery compartment door? Was the internal foam removed by some process of left in place?

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by dbaker » Jan 10 2011 11:39am

Very nice project :mrgreen: What was the actual weight? What batteries did you use? Please show a photo of the battery access.

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by liveforphysics » Jan 10 2011 11:42am

Outstanding! Nice work!
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by Thud » Jan 10 2011 11:52am

Simply beautiful.
Did you do any measured load stressing of completed components before ridng trials? (the again would Evil Knevil? :lol: )
Also would love to see the FEA graphs if you have them.
I salute your design & exicution! Well done.
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by John in CR » Jan 10 2011 4:59pm

Excellent! I wish you had come sooner too, so I could have copied stuff along the way instead of just talking about building something quite similar. With such a light frame and swingarm, along with a fairly light geared hubbie, you must have lead batteries in there. Just wait till you upgrade to some proper lithium. :mrgreen:

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by vanilla ice » Jan 10 2011 5:04pm

I'll take two.

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by Drunkskunk » Jan 10 2011 5:45pm

Simply Amazing. That bike begs for Lipo.
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by katou » Jan 10 2011 6:29pm

I've seen a lot of engineering projects, and very few operate as advertised out of the box. You must have a hell of a machinist working for you? And was this your first foray into vacuum bagging?

Very impressive. I'd love to know which parts you did, vs farmed out.

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by torker » Jan 10 2011 7:16pm

Drunkskunk wrote:Simply Amazing. That bike begs for Lipo.
At the very top he says " 72v 10 ah 8 lbs. lipo Supposed to have room to double that to 20 ah.

Very cool !!
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by x88x » Jan 10 2011 7:48pm

Very nicely done! Could you post more info on the sub-components? Specifically, their design and connection to the frame proper? After the analysis do you have any concerns with any of the metal/composite joints? That seems to be the most common cause for concern with hybrid material frames like these.
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by dpearce » Jan 11 2011 4:41am

Thank you all for your compliments, they are greatly appreciated.

turbodan78:
How strong do you think the frame would be? good enough for some light downhill riding or more?

Only time testing will tell, but it feels very strong, and was designed with downhill / MX / urban offroad type use in mind, it should be called the hooligan. The analysis gives confidence, but not certainty.

etard:
What are your impressions of it so far compared to other MX bikes?

The suspension is not set up for me yet so it has not gone through any hard off-road testing , but it handles very nice, and it is very fun to ride on the street, just finding things to jump wherever possible. Of course the biggest comparison is the power, which compared to (an ICE powered) dirtbike..it does not compare..but not being a dirtbike, that is ok. Compared to pedaling around a downhill mountain bike…it feels like a really lightweight motorcycle, very nimble. I definitely want more power, but I think that to keep the pedals practical I have to draw the line somewhere. I do want to do double burnouts like methods though…and that is where the HD front fork and headset come in handy for future plans of ft. hub motor. The suspension is heavy duty, and makes it feel more like a motorcycle. Downhill MTB forks could shave 15+lbs off the front, but they were not in line with the budget.

dontsendbubbamail:
How about a shot of the battery compartment door? Was the internal foam removed by some process of left in place?

Right now the batteries enter from under the seat, one of the things on my list is to make them quickly removable. The motor controller is mounted on top of a bracket that holds them and their insulation in place. I will probably also mount the charger in there. The foam was removed with a speedbore, then a putty knife. Once the core was turned to shreds with the speedbore the rest chunked off the sides pretty easily. There is no foam left in place, it was high density foam, which was pretty heavy. The male mold method was quick and dirty, a female mold would produce the nice outer finish but for this project would have complicated the integration of the subcomponents.

Thud:
Did you do any measured load stressing of completed components before ridng trials? (the again would Evil Knevil? )
Also would love to see the FEA graphs if you have them.

I edited a screenshot of a frame Factor of safety map in the first post. At this point it will just be test it and see if there are any weak links.

katou:
I've seen a lot of engineering projects, and very few operate as advertised out of the box. You must have a hell of a machinist working for you? And was this your first foray into vacuum bagging?
Very impressive. I'd love to know which parts you did, vs farmed out.

Thank you, I take that as a compliment! All work was done in house at the schools machine shop by me and my 2 group members. Nothing was farmed out, except taking the swingarm to get heat treated I guess. I built the headtube, the bottom bracket shell, and the swingarm. This was my first experience working with carbon fiber and vacuum bagging. One of the group members had some experience with simple carbon stuff in the schools rocket lab, and we were able to get some good advice from people around campus. It was a good learning experience, we had to come up with our own methods for many of the procedures. You have to know exactly what you are going to do as soon as you get the carbon fiber wet with resin, it would be a bad time to find out - surprise! that’s not gonna work. It is a one shot deal.

x88x:
Could you post more info on the sub-components? Specifically, their design and connection to the frame proper? After the analysis do you have any concerns with any of the metal/composite joints? That seems to be the most common cause for concern with hybrid material frames like these
That was a concern, but the methods we came up with makes the metal parts one with the carbon fiber, I am pretty sure it would break around it before the inserts came loose. The parts are physically locked into the carbon fiber by their geometry, and do not rely on the incidental chemical bond.

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by thewmatusmoloki » Jan 11 2011 5:11am

When I look at the finished product, I keep thinking of words like, superlative,fabulous,outstanding and cool !

Welcome and very well done.

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by j3tch1u » Jan 11 2011 5:43am

excellent build--you should definitely think about producing that bike! solidworks student edition box for the template--priceless 8)

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by nicobie » Jan 11 2011 1:13pm

Simply stunning!

If it ends up working as good as it looks, you've got a winner.
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by pdf » Jan 11 2011 1:55pm

Great job. I work with students all the time and I am impressed. Would have liked working with them.

I have a question or two that has/have been bugging me for some time. It looks like the people reading this thread would have insight. So anyone can respond who thinks they can address it. First of all, I've never ridden a dirt bike and am probably too old now to start (47, with kids, etc). Had a 500cc street bike when I was a youngster. I ride my ebike for commuting and really like it. However, I would like to know what it feels like to ride a bike of the type these students built (large hub motor, designed for off-road). My observations are the following:
1) in my LIMITED personal experience, hub motors bog down in situations that require high torque. Dirt bikes will climb a virtually vertical wall from a standing start. On my test rides, the hub motors (BMC V1, 9C, eZee, all at 48v) did not even climb a moderate paved hill with confidence unless I was on the pedals. Can't imagine trying to compare any of these to a dirt bike. I know the motors I've tried and the voltage are not the most torquey but they were so far off, I did not see any reason to continue with hub motors. Now I am wondering.
2) I've seen web videos of ebikes based on large RC motors that will wheelie on a dime so must be high torque. Have not seen the same with hub motors.
3) Saw a posting by user "chroot" that indicates he has a hub motor (I think it is a 9C running at 72 V?) that will easily wheelie so apparently there are some impressive hub motor bikes.
4) most people with hub motors seem more interested in speed than torque. I am the opposite but this is driven mainly by the fact that my ride is not long but is very hilly. Also, wheelies would be fun!

So I've been thinking the future of ebikes will be in bottom bracket drives due to the lack of torque at low speed from hub motors. Even dirt bikes have gears. But I've not tested a good example of a hub motor, apparently.

My questions are:
1) Is there even a legitimate comparison to be made between a electric bike and a dirt bike, in terms of low speed torque? I am only thinking of hub motors here, not true electric motorcycles.
2) My perception is that systems based on RC motors are still in the experimental phase. I've seen some amazing bikes on here but seems like there are still significant issues around how to get them to run best. Is an RC motor, geared way down, the best way to go if torque is your thing? Some of these seem amazing.

Not having ridden either an RC-based bike or a powerful hub motor-based bike, it is hard for me to know. 5 minutes on one would answer all my questions, which basically boil down to "What is it like to ride the best hub motor bikes?"

One thing I've learned about ebikes is that people's personal use tempers their advice a good deal. That is, the view of a commuter biker is quite different from that of a high-end experimenter. Also, the views of the flat-land commuter and those in hilly areas vary a lot. What would be passible performance on a flat would be poor in a hilly area carrying a load. Right now, there aren't many shops where you can take test drives. It is nearly an act of faith to lay out the cash, which can be considerable. There are likley to be a lot of disappointed folks out there who thought they would get a certain level of performance and did not. I've been reading this forum pretty regularly for over a year and I still don't have a good idea of what each type system can do. Maybe without testing each one, it can't be known to my satisfaction.
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by deVries » Jan 11 2011 2:54pm

pdf wrote:Is an RC motor, geared way down, the best way to go if torque is your thing? Some of these seem amazing.
Gwhy! has "the answer" for you, imo. :wink:

You have hills, want to commute, like high torque, and you've said nothing about high speed requirements, sooo...

An RC build, such as Gwhy!'s, can get you high-torque & 28mph with one reduction from motor to rear sprocket. That design is relatively easy to do, and I believe Gwhy! has worked-out most of "the bugs" other RC builds have encountered but he has avoided. :twisted:

Also, he has a motorcycle motocross (racing?) background, so I think he knows what's "upscale" from eBike vs motorcycle.

Of course, you could always add a second RC motor to the drive, & I personally think this is the ideal solution for maximum performance AND less wear-n-tear on the motors & controllers... super high torque, shared loads, less concern for burn-out from heat & high loads, climb anything, pop wheelies, and go waayyy faster than 28mph. :twisted: Or, not. :lol:

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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by x88x » Jan 11 2011 4:06pm

dpearce wrote:x88x:
Could you post more info on the sub-components? Specifically, their design and connection to the frame proper? After the analysis do you have any concerns with any of the metal/composite joints? That seems to be the most common cause for concern with hybrid material frames like these
That was a concern, but the methods we came up with makes the metal parts one with the carbon fiber, I am pretty sure it would break around it before the inserts came loose. The parts are physically locked into the carbon fiber by their geometry, and do not rely on the incidental chemical bond.
Is that from the knurling and the large lip? Good to know. I don't really have any experience with CF atm but it's one route I'm considering for a custom frame build if I can convince myself that there won't be any issues with stuff like that.
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by Drunkskunk » Jan 11 2011 4:10pm

pdf wrote: My questions are:
1) Is there even a legitimate comparison to be made between a electric bike and a dirt bike, in terms of low speed torque? ...
2) ... Is an RC motor, geared way down, the best way to go if torque is your thing?

...5 minutes on one would answer all my questions, which basically boil down to "What is it like to ride the best hub motor bikes?"

1) no. yes. it depends. The torque curves are backwards of each other from Ice to electric. A gas motor gains torque as it revs, an electric loses it, with peak torque being at just over Zero RPM.
2) Yes.

Whats your definition of the best hubs? Mine runs 3k peak. It will climb a flight of steps, But the torque doesn't "feel" that strong. there is no "kick in the tail" when I twist the throttle. Instead, the torque and power come on in a way that feels more like I'm coasting down a hill. Even with 10 times the power I would have peddling, the riding style that works best is more like a peddle bike than a motorbike.
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Re: Electric Motocross Bicycle build (Tons of big pictures)

Post by pdf » Jan 11 2011 5:24pm

I guess all I really need to say is, will a good hub system do this?
http://endless-sphere.com/forums/viewto ... 86#p337377

That is basically what I am asking. That is a a pretty nice bike, but is an electric trial bike, not an ebike.

Anyway, sorry to hijack the thread. Back to your regular channel.
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Jamis Commuter 1.0/Xtracycle Stokemonkey 36V LiFePO4, 15 ahr
Giant Boulder 9C 8x8, 48v, 10 Ahr LiMn from ebikes.ca

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