My FS E-Fatbike (updated 8-29-11 now with video)

First let me thank those that created, maintain, and contribute to this amazing forum. What a great place to learn. I'm starting this topic to show my progress on my E-Fatbike. This is my first attempt at a motorized bicycle as you will soon realize. I've built most of it from scratch because there's not much out there that fits 4 inch wide rims and tires. The tubing is 4130 and most of it is .049 wall. Some unique features are; rear suspension pivoting on the bottom bracket and the modified girder fork. The motor I'm using is the 1500watt BMC from thesuperkids.com. This will drive the freewheel crank which drives the extra wide Sturmey Archer 3 speed hub. The batteries are Ping 48v-30ah LiFePO4. So there's the progress, now the problem. When I finally got the batteries mounted and everything wired up, I was so excited to try it out. I noticed it was very, very sluggish right off, but continued to try and pick up speed. I made it .05 miles when it finally gasped and died. I could smell hot plastic coming from the controller and sure enough, after taking it apart, had fried at least 2 of the capacitors and probably more. I immediately knew I had a gearing problem, but I didn't realize how bad it actually was. So here is my gearing set up. 10T on motor to 44T on crank, 30T on crank to 25T on hub (actually 20T, but the hub gives me 25% in 1st gear). I found a gear ratio calculator on motoredbikes and plugged everything into it. Given that these tires are 26 inch but have the diameter of a 29 inch and the 4800 rpm that the superkids list the motor as, the calculator says I can go 112 mph in 1st gear and something like 210mph in 3rd. Do you guys feel that this is correct? If it is, it's no wonder the bike didn't want to take off very fast. I'm surprised it moved at all. I'm pretty sure I need a jack shaft and another reduction, even though I don't see this on very many ebikes with brushless motors. Playing with the gear ratio calculator, it looks like I'll need another 3:1 or 2.5:1 reduction. Here are the speeds the calculator gives for each of the 3 speeds of the hub. First with 3:1 jack shaft 23.6, 29.5, and 44mph. With 2.5:1 it gives 28.3, 35.4, and 52.8mph. If it's possible to go 30-40mph with my setup. Which of the jack shaft ratios would work the best in reality? I should mention that I've ordered a 24T for the crank and a 23Tfor the hub and also a new controller. Any advice and answers will be greatly appreciated.
But enough about the problems. Here are some pictures.
Modified bottom bracket to accept bearings.

Modified Noleen forks.

Frame before motor and batteries.

Bike before batteries.

Motor and controller.

Bike loaded down with batteries minus fried controller.


I plan to eventually enclose the triangle and rear battery, but that's a long ways down the road. I did install a Cycle Analyst, but need to know what maximums to look for (watts, amps, etc.).

Another great looking cromoly frame!

Welcome to the forum

What a superb first post!!! Welcome to the forum mate
fantastic bike LOVinG the frame, girder style fork and pivoting BB !!! All the best getting it finished, great to see her
in action to any chance of some vids down the track?

KiM

If you can borrow a controller from someone, perhaps put the rear wheel in the air and put it in the lowest gear, gently bring on the throttle and see what a cheap bike speedometer says the rear wheel speed is.

Just looking at it, i also think it needs additional reduction. Thats a good spot for the motor. Perhaps flip it over and put a jackshaft just in front of it? Maybe make the left-side primary drive from the motor to jackshaft a belt, and the right-side second stage a #219 Kart chain (smaller teeth, bigger reduction). Just a thought.

You could also buy a de-spoked geared hubmotor and attach a very small non-freewheeling cog. Since your pedals freewheel, it wouldn't be hard.

I really like the way you did the rear arm pivot bearings, Just looking at the pics, I am certain I could successfully copy that arrangement. I also like the front forks, did you weld those, or buy them? (if bought, could you post the link and price?)

pehaps the coolest thing I have seen!!

makes the surly bike look weeny next to yours!!!

4130 is where it is at!!!

will keep an eye on this one!!

Very nice build...
..but yes , you are way over geared as you have now figured out.
I would shoot for the 3:1 reduction ( even with the revised crank & hub sprockets ) as 50+ mph is going to really suck power from your batts and controller if you can actually get there at all. Better to have useable performance in the 20 -40 mph range.

spinningmagnets said:

.
I also like the front forks, did you weld those, or buy them? (if bought, could you post the link and price?)

Click to expand...

Pretty sure they are original Girvin forks that have been modified. They come up on ebay
from time to time, also available with carbon fiber legs, been trying to snare a pair for 2 years now grrr...

KiM

Thanks to everyone for the advice and compliments. To answer a question about the forks. The linkage and shock are from the original fork. I made new tubes from the .049 tubing I used on the bike. I was able to incorporate spacers into the tubes for the need of increased width. The new tubes are at least 5 inches longer than the originals. My first attempt was to extend the original carbon fiber tubes. This was a bad idea. The first time I used the front brake, the carbon broke just above the extention. I haven't been able to ride it much, but the forks feel like they should work well. I will post more pictures when I get the jack shaft on and everything working. I will also make a video if the bike works well and is something worth watching.

did you buy the crystalyte controller too?
I recently switched over to the bmc 1500 with a lyens 4100 controller. I am running it off 14 tooth / 110 tooth on the left side, single reduction belt drive. I used a fixed pulley on the disc brake side, so I only have the front avid disc.
I will get some pictures of it it you want to see it running on a single reduction setup with out the jackshaft.

Mike
Yes, I also have the 24/4 rears and 3/26 fronts fatbike arrangement

mdan said:

did you buy the crystalyte controller too?
I recently switched over to the bmc 1500 with a lyens 4100 controller. I am running it off 14 tooth / 110 tooth on the left side, single reduction belt drive. I used a fixed pulley on the disc brake side, so I only have the front avid disc.
I will get some pictures of it it you want to see it running on a single reduction setup with out the jackshaft.

Mike
Yes, I also have the 24/4 rears and 3/26 fronts fatbike arrangement

Click to expand...

I did buy the crystalyte controller as a package with the motor. Have you had good luck with your motor? Feel free to put a picture of yours in this thread. I'd like to see it.

I have been busy getting the jack shaft installed and operating. I'm pretty happy with how it turned out. I went with the 3:1 reduction. I installed the new controller and the bike moves now. That's the good news. The bad news is that motor seems very weak. It draws a lot of amps and watts, according to the cycle analyst, for no more power than I'm seeing. I've watched videos on youtube of people with 500w cyclone motors that would leave me in the dust. More bad news is that after a mile the controller and motor get warm and the maximum amps I can get is 7 or 8 until it sits for awhile. Top speed in first gear is about 12mph, so I'm pretty sure the gearing is adequately low. The maximum speed I could achieve was 16mph in 2nd gear going slightly downhill. I tried to keep the amps below 40, but for some reason I saw the watts spike to around 1800 even though I wasn't pushing it very hard at all. Needless to say I'm very disappointed with the performance. Everytime I email questions to thesuperkids.com, they send me back a number to a tech guy that never answers his phone or returns messages. I'm not happy about that either. Here's a link to the motor/controller that I'm using. http://www.thesuperkids.com/15wabmcbr24m.html If you guys have any advice on what the problem might be, let me know.

Here's some pictures of the jack shaft. I was pretty happy with how the tensioners turned out. I used torsion springs hooked into shaft collars so I could adjust the spring force.

I love the sculptural quality of your frame, especially the swingarm. What diameter and wall thickness is the tube you used for the rear suspension pushrods?

As for gearing, I'd expect better performance than you're getting from your second iteration with the jack shaft.

If the no-load speed of the motor is 4800 rpm and you have roughly a 12:1 reduction from motor to cranks, that means a top speed at the cranks of just under 400 rpm, with maximum power at around 200 rpm.

It looks as if you're geared up slightly from cranks to wheel, around 1.5 to 1? If that's right, your maximum (no load) rpm at the wheel will be just under 600 rpm, with maximum power at around 300 rpm. For a 29" dia wheel, 300 rpm would give a speed of 26 mph, which sounds reasonable for the motor you're using. Unless I'm missing something it seems there must be some other problem. Are you sure the motor and controller are wired correctly? Could you put a speedo on the rear wheel and measure the no load speed or rpm at full throttle with the wheel off the ground?

Regarding the high power consumption and excessive heat, have you checked the no-load amperage draw? It should be only a few amps. You'd hope the wiring would be sorted correctly from the dealer but its a possible culprit. Also, I've seen ES members have problems with magnet flux interacting with motor mounts in a way that creates heat and inefficiency. Maybe a more qualified person than I can comment more intelligently on those two possibilities.

I hope you get things sorted out so we can get a riding report for your great build.

Malcolm said:

I love the sculptural quality of your frame, especially the swingarm. What diameter and wall thickness is the tube you used for the rear suspension pushrods?

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Everything on the rear end is 1/2 inch .049wall. I think it's fine for the suspension pushrods, but I'm wondering if 3/4 inch would be better for the rest. It seems a little flexy, but I haven't got to ride it enough to know.

gogo said:

Regarding the high power consumption and excessive heat, have you checked the no-load amperage draw? It should be only a few amps. You'd hope the wiring would be sorted correctly from the dealer but its a possible culprit. Also, I've seen ES members have problems with magnet flux interacting with motor mounts in a way that creates heat and inefficiency. Maybe a more qualified person than I can comment more intelligently on those two possibilities.

I hope you get things sorted out so we can get a riding report for your great build.

Click to expand...

I tried the "no load" test and was getting 33amps and 1600-1700 watts just before the second controller fried. I have a feeling I know what might be wrong. I assumed this motor/controller was wired to spin CW. When i hooked them up they spun CCW. I turned the reversing key on the side of the controller, thinking that it was in the wrong position. This was probably not a good idea. I just sent an email to Superkids explaining the situation and the fact that they don't send any instructions with their products or provide technical assistance. I requested another controller at their expense this time. I'll let everyone know how it turns out. I really appreciate the advice and support. A split second before the controller fried, I realized that something was definetly wrong. Someday I'll get this thing going.

An incorrect hall/phase wiring combo is the cause of your problems. The incorrect firing sequence resulted in high input power and low output power, because the motor was essentially fighting against itself. Hopefully it didn't damage the motor along with the controller. In the future, always test the no load current before going for that first ride. With no load, the current should be very low, since little power is required just to spin the wheel.

Also, I understand that at least some of the BMC's require a controller especially for their motors. I believe it's because they don't run a neutral timing.

John

I believe your half link chains are upside down



The 'curved' side faces outward, the 'flat side' faces down...

KiM

Great build! Excited to see it get sorted out.

*subscribe*

Well, thesuperkids.com let me down. I'm going to describe the events again and let you guys decide wether I'm in the right or wrong. Don't worry about hurting my feelings, I'm a big boy and don't want to be closed minded on this topic. So I order the second controller. No where in the motor/controller description does it say that this thing is wired to spin counter clock wise. They offer it as a plug and play package. I plug it in, it plays backwards. Everytime I contact them with a technical question, they send back a phone number to their tech guy Tim. That's fine, but Tim doesn't answer his phone or reply to the three messages I left him. It's now been a week and he still hasn't called me back. Thinking that the reversing switch on the controller was in the wrong place, I turned the key and the motor spun clock wise. I was nervous about this so I immediately called the tech guy. You know what came of that and you know what eventually happened to the second controller. They said that by modifying or tweaking the controller, I could not get a refund. I told them that I could not have known I was doing these things without some sort of support from them. I know that these issues are pretty basic for a lot of people on this forum, but for a noob like me it wasn't. Do you guys think I was out of line in thinking they were somewhat responsible for this malfunction. When they ship their products, they don't include one scrap of paper explaining what and what not to do. I've always felt I was fairly easy to get along with, but I can always make mistakes and admit when I'm wrong. Let me know what you think.

Sounds like you're being pretty reasonable to me. It's a little crazy for a product like that to ship with zero documentation. It's a relatively complex product. To do what you did, did you have to disassemble the unit, or anything else that would not be considered part of normal use/installation?

TroySmith80 said:

Sounds like you're being pretty reasonable to me. It's a little crazy for a product like that to ship with zero documentation. It's a relatively complex product. To do what you did, did you have to disassemble the unit, or anything else that would not be considered part of normal use/installation?

Click to expand...

All I did was turn the little keyed switch on the side. There are no markings on it, so I thought it must be in the wrong position. I knew the reversing key didn't apply to this motor, I just didn't know this motor was supposed to spin backwards to what I wanted.

After some gearing issues and wiring issues, it's finally done. I need to thank Lyen for all his help with rewiring the motor for me. It's pure fun to ride and I can't wait to finish it.

[youtube]http://www.youtube.com/watch?v=MYWdU67668Y[/youtube]

Here's a link to the video incase it doesn't show up in the post.
http://www.youtube.com/watch?v=MYWdU67668Y

[youtube]MYWdU67668Y[/youtube]

Nice!

y do people say li-yen? Isn't it pronounced the same as lion? that's what i've always imagined at least.

awesome bike looks like its built to handle exactly what you want. In terms of pushing it, get a small temperature sensor for your motor so you know when it's heating, they are really cheap on ebay. if that is a 1500w motor then you should be fine with 3000w peaks; many motors (or electronics) are rated for continuous and peak power levels of about twice as much peak as continuous. But really the motor temperature will be the determining factor here; your controller should keep up no matter what. What is your top speed in lowest gear? Motors heat more when run continuously in an inefficient range , so you want to the motor to be spinning as fast as possible when your going as slow as you want. Looks like you have plenty of reduction there though, although that ends up being like a 30 inch wheel with endomoprhs right?

Very cool build! I like the setup, but if it was me, I would go with Lipo, just for the size/weight difference. Other than that, VERY cool indeed!!

Andje said:

y do people say li-yen? Isn't it pronounced the same as lion? that's what i've always imagined at least.

awesome bike looks like its built to handle exactly what you want. In terms of pushing it, get a small temperature sensor for your motor so you know when it's heating, they are really cheap on ebay. if that is a 1500w motor then you should be fine with 3000w peaks; many motors (or electronics) are rated for continuous and peak power levels of about twice as much peak as continuous. But really the motor temperature will be the determining factor here; your controller should keep up no matter what. What is your top speed in lowest gear? Motors heat more when run continuously in an inefficient range , so you want to the motor to be spinning as fast as possible when your going as slow as you want. Looks like you have plenty of reduction there though, although that ends up being like a 30 inch wheel with endomoprhs right?

Click to expand...

Thanks for the advice. The temperature sensor seems like a good idea. At what temperature should I start to get nervous and back off? My top speed in first gear is around 16mph I think. I could still stand some more reduction, but I don't think I can fit larger gears anywhere. The first builds are always a big learning experience. Usually the second one goes a lot smoother.