3 speed front wheel drive e-bike

Hi all – I built a front wheel drive e-bike and have completed some testing on it. You can read about the build and see some pix at http://endless-sphere.com/forums/viewtopic.php?f=6&t=12318 I’ve posted one view below. Here’s the basic description from that post: “I acquired a matched pair of old Huffy 3-speed bikes - the kind with the internal gears in the rear axle - what we called an English bike when I was growing up. I put the rear wheel from one on the front of the other with the sprocket on the right so it will engage to drive forward and freewheel when the motor is shut off. I wanted a bike that I could pedal but with an assist for the hills around here (New England). I used a 350W geared down motor from a Razor Dirt Quad over that wheel [Unite MY1016Z3]. Because I decided I would be using the motor at full power and pedaling to start, I ended up using a 40 amp Bosch type relay and a momentary toggle switch. I mounted the batteries (2-12v 12ah sla's) between my legs above the crank.”

The e-drive sprocket (front wheel) is attached to an internal gear 3-speed Sturmy-Archer hub. I have fixed it up so I can shift this hub but did most of the early test rides in 1st gear on the e-drive. The pedal crank is attached to the rear 3-speed hub that I can shift as well. The pedaling cadence when the motor is barely engaged (I can tell by the sound) is about 66 rpm in 1st gear and slower in the other gears. I’ll get back to this in a minute.

I took a 9.5 mile test ride earlier this week. It took me about 45 minutes. It is level then slightly downhill for the first mile, then gradual uphill (about 150 feet vertical) for 4.8 miles, then, on the return, has 2 steeper up and down hills. On this ride I found on level ground and the gradual uphills, I could shift the e-drive hub into 2nd gear and maintain better speed as long as I pedaled. With the rear hub also in 2nd gear, the pedaling cadence at “barely engaged” was (surprise!) 66 rpm. With front hub 2nd, rear hub 3rd , the pedaling cadence was about 45.

The next ride was a 7.5 mile ride out with an 8 mile return. Gradual down for a mile, moderate up for ½ mile then down about 400 vertical feet in 2 miles, with one steep section. The rest (~4 miles) is generally level. I made it down in 32 minutes. I did a good bit of this ride with the e-drive hub in 3rd gear. I don’t have a throttle/controller, just a momentary toggle switch and relay, so I pedaled to get to speed, pulsed the e-drive in 2nd, then shifted up to 3rd. I pulsed it probably 50% of the time through the level sections and nearly 100% on the gradual up inclines. Again, the cadence with both the e-hub and rear hub in 3rd gear is 66 rpm at full motor rpm.

I’m still testing the battery depth, so although there seemed to be plenty of charge, I didn’t want to go back the same way because of the steep section in the middle. I took a route that is about 8 miles back, mostly level for 6 miles then moderately uphill for 2. It took 41 minutes. I pedaled mostly in 3rd, and pulsed the e-drive in 3rd until the final hill. I used full e-assist in 1st and 2nd for that hill and arrived home with what seemed like plenty of battery. I’m using a 12 volt 5 amp auto charger with a built-in ammeter. I reconnect the 2 12v SLAs from series to parallel to charge them. After this ride they charged at 5 amps to start, had dropped back to 4 amps when I checked them at 90 minutes and were at 1 ½ amps at 2 hours.

I guesstimate the e-assist speed at full motor rpm to be 11-12 mph in 1st , 15-16 in 2nd and 19-20 in 3rd. I will try to confirm these with a GPS or maybe with my wife following in the car, although I realize the 2nd choice is risky, given the time I have spent on this project. I thought you all might be interested in the possibility of using gears to increase speed. I wonder if it would work with a derailleur. Hmm… - jd

I like it. Pretty ingenious set up. Needs a speed control and throttle though. I think I have a 24V speed controller from my first project. It came off of a small scooter and I fried the motor on a 15% grade. They are also available pretty cheap from the scooter parts places such as TNC. PM me if you are in the U.S. and I'll send it to you.

I love it, and here I am with a pair of 3 speed hubs in my possession right now along with plenty of motors. One word or caution, the geared hubs put twisting torque on the axle, unlike a regular bike wheel, so you'll want to include extra reinforcement of the dropouts. Torque arms are one way, but in your case I think the motor mount is the place to do it.

Hmmm, how do I either make use of the coaster brake on a front wheel/front drive, or attach a disk brake? Rim brakes just don't cut it at my weight and speeds.

John

John said:

how do I either make use of the coaster brake on a front wheel/front drive

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How about a toothed idle wheel on the chain. Then fab a little U-shaped hook attached to a brake cable so that when you apply the brake it grabs one of the idler teeth and rotates the idler backwards to engage the coaster brake. It would need a small spring that pulls the hook away when you release the brake. If you used one of those "two" cable brake levers you could also be applying the rim brake at the same time.

Expect to be copied soon. :wink:

Rassy said:

Needs a speed control and throttle though.

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Unless the hub is getting slammed hard, a relay contactor might be fine. I have an electric bike kit from the middle 70's that used a 12V battery and a relay contactor.

John in CR said:

Hmmm, how do I either make use of the coaster brake on a front wheel/front drive, or attach a disk brake? Rim brakes just don't cut it at my weight and speeds.

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I've seen 3 speed hubs with disc mounts.

John in CR said:

One word or caution, the geared hubs put twisting torque on the axle, unlike a regular bike wheel, so you'll want to include extra reinforcement of the dropouts. Torque arms are one way, but in your case I think the motor mount is the place to do it.

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This is where a coaster brake hub would be handy for the built-in torque arm.

gogo said:

Expect to be copied soon. :wink:

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Let me back up a bit. How can we make certain that when the chain comes off or breaks, as it most certainly will at some point with regular use, that it can't get tangled in that front wheel? Sorry but I have to bow out of this one guys. I have to design out all possibility of going over the handle bars, to the extent possible. I go too fast and don't heal as well as I used to.

John

Hey you guys are great! Lots of excellent ideas and some things I hadn't thought of. John's safety concern first:

John in CR said:

How can we make certain that when the chain comes off or breaks, as it most certainly will at some point with regular use, that it can't get tangled in that front wheel?

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We can't, of course. I think it's inherent in the design of any fwd. Hub motors can twist or break forks. I didn't have the motor/chain aligned when I first tried it in the shop and the chain promptly jumped the motor sprocket. (Yes my wife was watching. I could hear the snickers.) The wheel was able to freewheel, however, so a simple chain jump might not lead to disaster. I think the chain is most likely to break under load. The toughest load is when I engage the motor suddenly when I'm not up to speed for the gear I'm in. That's generally going uphill when I should be in a lower gear, at lower speed. Uphill at low speed would seem to be least likely to cause a header. So although it may be a long pedal back home, hopefully it won't involve red lights and sirens. However, this makes it clear that Rassy's speed control/throttle idea might save me some grief. Soft starts obviously put less stress on the chain. I'm intimidated by the number of wires coming out of a controller, so if I go that route, I might be back asking for some help hooking it up. I may be in touch, if I can figure out how to PM you, Rassy. :wink:

John in CR said:

One word or caution, the geared hubs put twisting torque on the axle, unlike a regular bike wheel, so you'll want to include extra reinforcement of the dropouts.

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These hub axles have flat spots on either side (double d?). The front dropouts have keyed washers (~3/32" steel) that have a short "L" that fits into a hole drilled in the fork. Not a very long lever arm, but they should help. Another place where soft starts might make a difference.

John in CR said:

Torque arms are one way, but in your case I think the motor mount is the place to do it

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How would you do that, John?

Thanks again for all the helpful suggestions - jd

John in CR said:

How can we make certain that when the chain comes off or breaks, as it most certainly will at some point with regular use, that it can't get tangled in that front wheel?

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Chain-tubes like 'bents and wheel disk...

Here's 2 torque arm threads with several popular choices and pics. Pic below is the classic "poor mans" TA

http://endless-sphere.com/forums/viewtopic.php?f=1&t=11570

http://endless-sphere.com/forums/viewtopic.php?f=2&t=134&p=1183

TylerDurden said:

John in CR said:

How can we make certain that when the chain comes off or breaks, as it most certainly will at some point with regular use, that it can't get tangled in that front wheel?

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Chain-tubes like 'bents and wheel disk...

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Yeah, a wheel disk sounds just like the ticket.

Regarding the torque arm, without a coaster brake in use on the geared hub, I think the axle torque is limited to the gearing differential from direct drive, so essentially 1/3 of that compared to a hub motor putting the same torque at the wheel. All I would do is incorporate a dropout shape that fits the flats of the axle into the motor mount's connection to the axle using 1/4" steel on each side. I double up the 1/4" flat plate I have to make 1/2" thick dropouts for all my hub motored bikes. Once the issue was known to me first hand in a lucky mishap, a motor coming off is an unacceptable event on my bikes. I haven't had so much as a loose nut since, and I abuse mine pretty good.

The freewheeling aspect for safety on a front drive plus 3 speeds are what caught my attention, and I think a wheel disk will sufficiently reduce the chances of an end-over due to a mechanical failure in my build.

John

Might I suggest a 3-speed hub that uses a drum brake? Should provide the torque arm like a coaster brake hub but with easier actuation if you're worried about this. Anyway, a three speed hub will only put a fraction of the drive torque on the axle. Add to this the low power of the motor and I'd expect a broken chain or spun axle to be rare. The axle on the dual-drive in my Linear has never shifted under power, even in my lowest gear pushing up a hill that was at least 100ft of >15% grade. (unglaciated area of Wisconsin on an old road)

I like the simple functionality of this machine. Get some matching paint on that motor mount and clean up the wires a bit and I bet you'll have people asking where you bought it 8)

Just crossed my mind, have you thought of linking the front and rear shift cables? I bet this could be shifted with just one lever then.

Lawson

Isn't axle torque strictly dependant on the power? If you pull the same load at the same rate as a DD hub motor, doesn't the axle experience the same force?

Yankee engineering at it's finest!

Here's another front wheel drive build: http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=7874

It's good to see people trying front wheel drives.

Miles said:

Here's another front wheel drive build: viewtopic.php?f=28&t=7874

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Whoa - "Surly" - that's certainly an appropriate name for that bike. Very nice work.

Here are 2 images of the mini torque arms that came on the bike. It's interesting that they were used on the front wheel but not the back wheel, but fit the rear axle. The support bracket that is visible is an old (very old) vinyl covered shelf bracket that happened to be exactly the right size to be a motor rack support. Sometimes there are advantages to being a packrat :wink: - jd

gogo said:

Isn't axle torque strictly dependant on the power? If you pull the same load at the same rate as a DD hub motor, doesn't the axle experience the same force?

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Not with the motor out of the wheel. eg Without a geared hub, normal bike wheel, there's no twisting torque on the axle. The chain spins the sprocket that turns the wheel directly with the wheel spinning freely due to bearings between it and the axle. With a geared hub it's a bit different, and the sprocket spins at a different speed than the wheel, so that gearing difference has to leverage against the dropouts via the flats on the axle of the geared hub. In 3rd gear on the 3 speed, the wheel spins something like 1.3 times per revolution of the sprocket, so the dropouts would only see about 1/3rd of the torque applied to the wheel.

John

John in CR said:

gogo said:

Isn't axle torque strictly dependant on the power? If you pull the same load at the same rate as a DD hub motor, doesn't the axle experience the same force?

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Not with the motor out of the wheel. eg Without a geared hub, normal bike wheel, there's no twisting torque on the axle. The chain spins the sprocket that turns the wheel directly with the wheel spinning freely due to bearings between it and the axle. With a geared hub it's a bit different, and the sprocket spins at a different speed than the wheel, so that gearing difference has to leverage against the dropouts via the flats on the axle of the geared hub. In 3rd gear on the 3 speed, the wheel spins something like 1.3 times per revolution of the sprocket, so the dropouts would only see about 1/3rd of the torque applied to the wheel.

John

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Thanks, It took awhile to conjure up the visualization of gears pushing against each other.

jdc, the part that looks like a small torque arm is actually a safety device to prevent the axle from dropping out of the forks if the nuts get loose.

Using it as a torque arm, its probably OK with only pedal power in steel forks, but its likely made from soft steel to make manufacture easier.

EDIT: after some thought, that part may also serve double duty as an anti-rotation washer. Found on geared hubs. Very much like a tiny torque arm, but clearly not as strong as a proper TA designed for a 1,000W motor.

Spinningmagnets, your little friend has good advice. My local bikeshop friend showed me a Sturmy Archer axle in passing one day and there were gear teeth. They were very small and thin, making me think there's not a lot of torque on them, but gears by definition mean torque. I am going to try to remember to preflight before every ride and treat the hub with TLC. I think elsewhere someone stated the average mortal pedals the equivalent of 150 watts and I've put a 350 watt motor to this hub (which is probably 30 years old), so anything I can do to keep the stresses down will help. - jd

Ya, the more I think about it, the more I'm worried about the shock from the motor engaging at full power. Does it feel like the hub is getting abused?

I've never engaged the motor when I wasn't moving. When the hub is in 1st gear, I'm usually pedaling faster than the motor drives, although if I'm on a hill I slow down until the motor is doing a good part of the work. I don't think that stresses anything. I never shift under load either. But I have to remember to be at or near no-load speed (cranking 66 rpm with the rear in the same gear as the front) when I hit the switch. I'm sure I'll order a controller and throttle soon, but until then, don't be surprised if you hear me saying "one thousand one, one thousand two..." when I'm riding by :wink: - jd

Well, I ordered a controller, a CT-201C6 from TNC, and I think I fried it when I was hooking it up the first time. I plugged in the motor to the motor plug and the 3 throttle wires to what I thought were the correct slots in the the plug labeled "timing," which I figured was Chinese for throttle. I had instructions that came with the controller and some with the throttle. The instructions showed a plug labeled "derailleur" but no plug had that label, and the "timing" plug had the right color wires coming out of it. There were also brake and charger plugs, which I left open. I hooked up the battery last and it sparked. I read somewhere that the wires might spark when you first plug the controller in, but then the controller let out a hiss and it started smoking right away. The throttle was closed. The front wheel was off the ground and the motor didn't seem to be trying to turn, so I think it was the controller shorting out. The motor needs reverse polarity to run correctly so that's how I hooked up the controller - the red wire to the negative terminal on the battery and the black to the positive. I'm guessing that's what fried it. Maybe I burned up some diodes or something? The controller, battery and motor are electrically isolated from the frame. I'll go back to the relay and momentary switch until I figure out what happened. Suggestions are welcome - jd

The motor needs reverse polarity to run correctly so that's how I hooked up the controller - the red wire to the negative terminal on the battery and the black to the positive

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I believe you are right, this is what fried your controller. On a brushed motor you can reverse the direction the motor turns by reversing the polarity, but it is the positive and negative between the controller and motor that needs to be reversed, not the positive and negative between the battery and controller.

I bought that same controller and a 36V throttle from TNC. The throttle wires do hook into the "timing" plug but the colors don't match up. I can find out which colors worked for me if you'd like.

I've looked inside that controller and mine was potted with some black stuff. They're cheap enough that it'd probably cost less to get another than fix it.

col

very cool

I love the never been done ones that could be done from just a little more than you might have in your garage basement shed if one only thought of it. the mother of invention itself