3 speed front wheel drive e-bike

[jdcburg]

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 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

[Rassy]

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.

[John in CR]

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

[Rassy]

John said:

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

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.

[gogo]

Expect to be copied soon.

Needs a speed control and throttle though.

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.

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.

I've seen 3 speed hubs with disc mounts.

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.

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

[John in CR]

Expect to be copied soon.

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

[jdcburg]

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

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?

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.

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.

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.

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

How would you do that, John?

Thanks again for all the helpful suggestions - jd

[TylerDurden]

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?

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

[spinningmagnets]

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

[John in CR]

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?

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

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

[lawsonuw]

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

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

[gogo]

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?

[Drunkskunk]

Yankee engineering at it's finest!

[Miles]

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

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

[jdcburg]

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

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 - jd