Electric Assist Recumbent
Electric Assist Recumbent Bicycle

By Warren Beauchamp

I have been giving thought to an energy efficient way to get commute to work, without showing up  all sweaty and stinky. After much consideration, I have decided to build an electric assist SWB recumbent, with about a 20 inch seat height. This will allow me to feel comfortable in traffic, while retaining a relatively aerodynamic and comfy seating position.

A while ago, Dana Barlow pointed out this cheap Mongoose ($300) pedal/electric motocross bike. It has 20 inch wheels and a front disk brake, along with a 450 watt electric motor. It only weighs 85 lbs... The motor drives a lefty BMX freewheel cog, and the human powered pedals drive the BMX freewheel on the right side, so each system is independent.

I rode it once, it was fun. Unfortunately it doesn't fit my body or riding style, so I took it all apart and it's now in 100 pieces strewn across the basement.

I'm planning on building a new bike frame and using the rear subframe and E/V stuff from the bike above. Here's a Frankenstein photoshop mockup combining the E/V rear subframe and my Street Cuda quazi-lowracer.
That would work, but I have decided that it would be better to design and build a new purpose built frame.

The 450 watt motor in this EV system runs on 24 volts. It drives the rear wheel directly, and tops out at about 15MPH. Because I'm going to use this for commuting, I'd like to go about 30MPH.  To do this I'm going to try two things. First I will try just gearing up the drivetrain, by running the motor through a jackshaft. That will allow my to keep the existing batteries and controller electronics. If that doesn't do it, the alternative plan is to add another 12 v battery (existing system used 2 - 12 volt batteries) for 36 volts total. Running electric motors at higher than rated voltage is a common way for E/V builders to get higher speeds from their systems. This would require a new controller.

I'm thinking the new EV/HPV hybrid bike will look something like this. Dual 406mm wheels, full suspension, wide tires, heavy duty 2" x 0.049" frame.
After agonizing over how to set up the drivetrain for entirely too long, I have decided to dump the jackshaft idea as "too difficult", add a larger cog at the motor side to gear it up, and stay with driving the left side of the rear wheel directly. Still easier said than done as finding a 7/16 ID 20 tooth cog to replace the 9 tooth cog that came with it was not happening. After poring over the McMaster Carr catalog, I decided to purchase a 18T and a 21T cog with 5/8" ID, and then use a bushing to get it down to 7/16". The cog will be brazed to the bushing, an I'll cut a keyway into the inside of the bushing to mate with the existing keyway on the motor's driveshaft. The 18T should be good for 30MPH, and the 21T should be good for 35MPH.

With 450watts, my HPV simulator says I'll be to top out at 30MPH on flat ground with a bare "high racer" (0.244 CdA). Perfect! With another 200 watts help from the human engine, I should be able to go the 35MPH needed to ride with the traffic.

21T Flat Sprocket, 5/8" ID - McMasterCarr# 2299K28 - $14.05
18T Flat Sprocket, 5/8" ID - McMasterCarr# 2299K25 - $13.18
7/16"ID, 5/8"OD bushing - McMasterCarr# 8491A616 - $4.53

It turns out that the McMaster Carr sprockets are too thick for use with bicycle chain.  I brazed in the bushings and made an axle to enable the sprocket to be mounted in a lathe. Rick Wianecki will cut them down to the proper width.


I built an intermediary drive that screws into the old bottom bracket shell. The biggest gear will drive the rear wheel. The other 7 gears will be shifted via a derailleur that I will mount to the bolt sticking out of the center of the cluster.

Rather than purchase a new head tube, I cut the one out of my old Cuda-W subframe, and ground off all the braze. This head tube actually started life in the original Barracuda frame. The third frame is the charm...

Here are the parts for the rear suspension pivot. All the parts except the center tube came from the donor EV-bike. The center tube will be brazed into the main recumbent frame tube.
Here's the pivot parts assembled without the center tube. As seen in the photo above, the dark bearing sleeves will be pressed into the center tube. The chromed pieces then slide into the bearing sleeves and can rotate. An Allen bolt holds the chromed pieces together.
Here's the rear subframe showing how the center tube fits into the main recumbent frame tube, and how the tube aligns with the rear subframe.

The center tube with the bearing sleeves pressed in fits into the rear subframe suspension  bracket, and the chromed pieces are inserted through the suspension bracket into the bearings

Here are the major parts of the bike, laid out on the floor. It's time to do some brazing soon.
After cutting the hole in the frame tube, I trimmed end of the frame tube to allow clearance for pivoting. I then made a paper template for the end cap, and then used it to mark the sheet metal. I cut out the end cap with some aviation snips.
Bend Bend Hammer Hammer File File...

Here's the end cap in place on the frame tube.

Where's that torch?

I brazed up the pivot one night, cleaned it up and mounted it to the rear subframe. Tonight I brazed on the shock/seat stay, and it's reinforcement tube.

Both the shock and the seat back will be mounted with the usual frame clamps. 

This past weekend I brazed up the shock unit bracket, cut the head tube hole in the frame and brazed the head tube in, then brazed on the boom tube clamps. Good progress!
Don't think that I can do this without my share of problems. I noticed that the rear subframe didn't line up with the front subframe. Because I didn't want the bike to "dog leg" down the road, I cut the frame just in front of the suspension pivot almost all the way across, closed the hacksaw width gap on the open side, and tacked it with some braze. All better. Then I had to add some big ugly patches to make sure it was still strong. Arg. Amazing that a hacksaw width misalignment at one end of the frame can make it off by a couple inches at the other.
This past weekend I brazed on the seat brackets and rear rack mount, and mounted the seat. The fore-aft position is set in one position, but the seat will tilt forward and backward quite a bit. I also swapped out the gnarly knobbies for some Comp Pool slicks. The battery pack will mount on the frame tube behind the seat. This will be a nice stable and out of the way location.
Rick Wianecki machined the gears to the correct width for the BMX chain. The two gears will allow me to figure out what gearing works best for motor + pedaling.
I installed the smaller gear on the bike last night, hooked up the battery and played with it for a while on the trainer. It has lots or torque even with the bigger gear. Very cool. Looks like I need another speedometer...

I still need to braze up the handlebars and add a brake before I can test it in EV only mode.

Here's the new gear mounted on the motor.

Here's something not to try. I took the back cover off the motor to see if I could add a longer power cord to it. After pulling the cover off, all the stator brushes, which were mounted to the cover, jumped out and bounced around. Arg. It was not easy to put back together. I had to make some small sheet metal hooks to hold the 4 brushes in their spring loaded mounts while I slid it back together, then jigger the hooks out. It still works. Whew!

Ever wonder how to attach a cluster carrier to a bottom bracket cup, without having a machine shop at your disposal?  I'm happy you asked...

First you need a steel bottom bracket cup from a cheesy bike with a non-sealed-bearing-BB (item 1). Then you need to rip apart a perfectly good rear cluster, remove the pals so it turns both directions, and put it back together (item 2). Hack the threads off the hollow star nut that held the carrier to the hub so you can use it as a sleeve (item4). Use an old solid bike axle (item 3), plus a bunch of axle spacers and washer to complement...

Slide the axle with the "item 4" sleeve into the carrier. An axle nut and a spacer and another nut are to the right of the sleeve. The additional spacer and sleeve will be used to mount the derailleur later.
Add another spacer to the back of the carrier, to keep the axle centered in the hole back there, and to space it out a bit from the BB cup.
Add the big washer, and another spacer. This fills in that huge hole in the BB cup, and centers the axle in there.

Note that there is a certain amount of slop between axle and the sleeve, and between the spacers and the BB cup hole. That's ok, when it all tightened down it will be plenty strong.

Add the BB cup, a couple more washers, and a nut. Tighten to a torque of one grunt.

Uh. That last nut sitting there forlornly is left over.

Move along now...

Here's the cluster carrier screwed into the BB.

It's been too rainy and yucky outside after work the last couple days to do any brazing.

You can calculate your battery power needs by using motor wattage / battery voltage = battery current needed. In this case 450 watts/ 24 volts = 18.75 amps. This means that this system is already a bit under powered. I'm guessing the controller probably limits the amperage even further.

The lead acid batteries will not last very long, so I'll need to plan on replacing them with something eventually. If I recharge them every day, they should last a couple months. Benefits of  using NiMH (or Li-Ion if you can afford them) over the lead acid batteries are increased range, a better power curve, increased battery life, and decreased recharge time. Oh, and they weigh about 10 pounds less...

Last night I brazed up the handlebars, temporarily strapped the battery to the bike, soldered in an extension to the electro-drive controls, and hooked up a brake. Ladies and gentlemen, we have liftoff. I motored the bike across the basement floor. Takeoff was not brisk. I'll need to recharge the battery and try again. 

I machined the derailleur hanger, and the torque bar for it. In hindsight, if I would have threaded the part of the hanger that fits over the cluster axle, I would not have needed the torque bar. I added the front chain, and brazed in the bolt for the return chain idler. It's a real bike now. I still need to mess around with the gearing to tweak it. I also added some braze-ons to route the brake and derailleur cables to the back. They are on the other side of the frame... I also shortened the kickstand, so it will actually work. This is my first bike with a kickstand since I was 12.
This shows how the battery will mount. I still need to add the brackets to hold it in place. The handlebars need more work, as they are too narrow. On my test ride going straight they felt fine, but turning was a bit scary. I just need to make them wider. The bike handles nicely otherwise. The electric motor cranks up nicely with a slow acceleration to somewhere over 20MPH on the flat. I can't tell how fast 'till I get a speedo but I am very curious to see if the speed matches my calculations.
I hooked up a speedo and spun up the e/v drive to it's max speed on the trainer. It topped out at 26.8 MPH. That's over 3 MPH slower than the 30 MPH I was predicting. This weekend I'm going to braze up the rear rack that will stabilize the battery unit, remake the handlebars, and take it for another test ride. Next test will be to see if actual street speed maxes out at 26 MPH too. If so, maybe there's enough power to switch to the bigger gear for a couple more MPH.
I spent most of Sunday morning brazing away on this rack and rebuilding the handlebars. The rack pictured here is designed to hold the battery for now. When these batteries die,  I'll mount the new ones under the seat, and mount the controller somewhere less conspicuous as well. Then the rack will be for transporting stuff like a bag of groceries or my lunch.
Here's the ev-bike ready to go for a test ride. The handlebars are now 12" wide, which feels much better. I took the bike on my 5 mile test loop, and it ran at about 26MPH, or 28MPH with half hearted pedaling. I cranked the throttle to max practically the whole way, and by  the time I got back, the battery was pretty well toasted. The bike rode nicely, felt very stable, and turned well. I'm happy.
Since the bike is about done, I weighed it just for giggles. It weighs 50lbs without the battery pack, and 70 lbs with it. That's a lot, but it's 10 lbs less than the donor ev-bike. Going to NiMH batteries should cut at least 10 lbs off the bike's weight.

10/31/06 - More digression:
So lets say I'm going to be riding this thing to work every day. More than likely a one way 10 mile commute up and down hills is going to kill a 24 volt 12Ah battery. So then there are options. 

  • More Battery: Using an additional battery pack would add another 10 lbs minimum to the bike. Possible but not desirable.
  • Upgrade to NiMH battery pack, half the weight of Lead-Acid at twice the cost.
  • Upgrade to Li-Ion battery pack, 1/4 the weight at 4 times the cost.
  • Solar recharging: To recharge the 24V battery within 8 hours would require about $1000 worth of solar cells. Possible, but expensive. I would not feel safe leaving that bike outside.
  • Removable battery pack. This is perhaps the best option. The battery pack could be located in a removable unit that would include the charger. You could bring the unit in and plug it in.
  • The 1.2Amp charger would use about as much power as two 60 watt light bulbs.
  • Check out the power assist group for more info
  • After considerable research, I'm planning on obtaining a battery pack from ForsenUSA.
Finished up the front derailleur post. The post needed to be further forward than I could make it with the post mounted directly to the clamp, so I made an extension out of some thick steel. I had more trials and tribulations when I drilled out the wrong end of the tubing clamps, so I attached it with a hose clamp instead. It worked out to be very sturdy, and is lighter to boot.
After a long string of cold blustery days, a string of nice days materialized, and I was able to utilize one of them to paint the frame. Not a great paint job, but it's now silver all over. I spent the rest of the weekend putting it back together. It's about done now, except for the new battery pack that I'll be acquiring soon, and the tweaking that I'm sure it will need.
Here's the "finished bike" shot. I have convinced myself to purchase a 24V, 20Ah Li-Ion battery, which should mount behind the seat or under the suspension spring. This should give me about a 15 mile range at top speed.

Final Specs:

Designation - Cuda-e
Wheelbase - 58"
Suspension - front and rear
Weight - 50lbs - no battery
Lead Acid battery pack - 20 lbs
Wheels - Mongoose 406mm
Tires - Comp Pool wide slicks
Seat - Rans mesh back
Brakes - Mongoose
Mid drive - Shimano 105 - 5 speeds + gear to drive rear wheel
Cranks - Shimano triple

This was a great first time EV project, and over the course of this project I have learned a lot. It was cheap too since all the parts except for the donor bike were already cluttering up my basement.

I have of course given some thought to a "phase 2" EV recumbent.  This one would be faster and would cost more. I'd use a 600 watt+ hub motor designed for use on the drive wheel, on a 26" rim. This would greatly simplify the drive train. The bike would still be dual suspension, but would have disk brakes front and rear. Motor and batteries alone would be about $2000. Yikes. Other Source

I ordered a 24V lithium phosphate battery pack from ForsenUSA. I'm also thinking about how to increase the top end speed of the bike. The easiest way is to improve the aerodynamics a bit and I just happen to have the MOAT tail fairing hanging around in the barn unused. Here's a mockup of what the bike would look like with the MOAT mounted.
I would make the top half of the fairing removable so that I could easily access the trunk area. The MOAT would cover the motor and battery so the power assist bits were less obvious.

It will be interesting to see what the top and average speeds are with and without the fairing.

Two months after I ordered it, the $650, 24V, 20Ah, Li-Ion battery pack and charger arrived. It's a stack of 7 cells which weighs 10 lbs, and puts out over 26V when it's fully charged. The original lead acid batteries were only 12Ah, so this should last considerably longer.

The first order of business was figuring out how to mount it to the bike. Fortunately serendipity struck, and I located a heavy duty nylon bag in the attic that had been waiting for use in this project since I picked it up at a computer show 10 years ago. I was so excited to start working on it that I didn't even take any pictures until it was already in the bag.  

In the picture above, you can see the wires sticking out of the battery management circuitry. The cells are wrapped tightly in bright green heat shrink plastic. I added some cardboard and foam padding around the battery unit to make it fit tightly in the bag. There was room in the bag for the connectors and the original motor controller unit as well.

It's now all in a nice 10 pound bag that I can bungee securely and discreetly to the rear rack. This also makes it easy to carry inside with the handle to recharge.

Dana Barlow has built a LWB Electric Hybrid

I went for a test ride today. It was a nippy afternoon, with strong winds whipping across the barren fields. I was cruising into the wind at wide open throttle and pedaling lightly in the upper 20MPH range, which was nice. Or it was nice for 3.78 miles anyway, at which point I lost power and had to rely on myself to motivate the 60 lb vehicle. It looked like it shut off completely, no LED charge indicator lights on the throttle at all.. When I got home I checked the fuse, which was fine, the put it on the charger for a couple minutes. I then checked the voltage of the battery. 28V. Hmm, that's plenty of voltage. When I hooked it up it worked fine. What gives? I guess I'll have to charge it up, go for another test ride, and this time, no charging before I check the voltages!
I got another test ride in and discovered  that it's not the batteries. It appears that the controller is overheating and shuts down. If I wait a while it starts working again. I guess putting it in the bag was not a great idea. I added a heat sink to the controller, but I also need to rewire the system with the controller mounted under the seat where it will get good ventilation.
I found a good spot behind the seat to mount the controller. It's very inconspicuous, and should get good airflow. I still need to re-solder all of the cables and connectors considering the new component locations before taking the next test ride.
While testing the bike and it's annoying system cut-outs out in the country, I stuck my hand behind the seat to feel if the motor was hot and in a moment of stupidity put my hand on the side with the gears. It ate the end off my left ring finger. Arg. I now have 4 2/3 fingers on my left hand.
My finger has healed enough to ride just in time for "ride your bike to work" week. Rode the bike to work a couple times this week for the first time. It makes it almost the entire 7 miles before starting to cut out. The bike cruises at about 30 on a full charge, and runs at about 26 on the way home. It rides nicely. I can ride to work and back without recharging. I have to turn the battery off and back on to reset the controller each time it cuts out, so it's too annoying. I ordered a new controller that looks compatible with the old one. It's rated for 40A, while the old one is rated for 30A.
I ordered the CO-24-40 controller from www.electricvehiclesusa.com yesterday, and it's supposed to be delivered tomorrow. It looks like it may be a plug-in replacement for my current controller. Cool.

My wife asked me how much it costs to recharge the battery every night. Good question. The charger draws 2.5A at 24V, and it takes about 8 hours to charge the battery. ComEd charges about 10 cents per kilowatt hour (kwh). 2.5 * 24 = 60 watts (0.06 kilowatts). 0.06 kw * 8 hours = 0.48 kwh. 0.48 khw * .10 = 5 cents per day. Using the 2007 federal reimbursement rate of 48.5 cents per mile multiplied by the 15 mile round trip of my commute = $7.20 per day savings. If I can commute just half the days this year, my hybrid bike is paid for!
After riding the bike to work every day this week except one, I can safely say that 450 watts is plenty for my purposes. 80% of my commute is on 30MPH roads, and though I'm a bit slower than that, passing is minimized. On the one stretch of road with a 45MPH posted limit, it provides enough power to reduce passing frequency/speed to a safe feeling level. In addition it provides enough boost on the steep hills that I can cruise up them at 15MPH plus when pedaling. I could probably go faster up the hills, but the controller would overheat and cut out. While acceleration is not brisk, the big return is lower power use, and greater battery life. Yesterday I rode over 20 miles, plus I accidentally left the system on all day while I was at work, and still had had plenty of power at the end of the day. Eventually I will need to determine what my actual range is. On the other hand, the brakes are not so good. I need to figure out how to mount a disk brake to the front wheel.
I rode the bike to work twice this week. So far no problems except somehow the human powered side of the drive chain loosened up enough to allow it to derail. It tightened it back up n all is right in the world. I seem to have figured out how to get to work and back without causing the controller to fritz out, so I have not installed the new controller yet. I still don't know how far I can get on one charge. I did a web search to find out what the laws are for electric bikes in Illinois. According to Wikipedia the max legal speed for an electric bike in Illinois is 20 MPH.
I rode 23 miles yesterday using pedal and electric power, through city streets and up and down hills. The long flat sections I whizzed along at close to 30 MPH. The battery was not noticeably depleted when I got home.

Here's the bike in commuter mode. A Bacchetta Aerotrunk that I won at a race fits nicely on the Rans seat. Under it is the battery, and my ancient lock and cable.

I have been riding to work a few days a week as the weather permits. Also I finally installed the new controller last night. The power cables were pretty much plug in, the connectors matched. The throttle cable I had to splice in, but since the wire colors matched (yes I did take the controllers apart to determine that they were used for the same things), that was easy too.

A quick motor-only test ride showed that this did not fix the problem. At low RPM/high load, the controller still shuts off, and I have to switch the system off and back on to reset it. Since my knee has been bugging me I rode it to work today without pedaling at all, and had to reset the system about 5 times. Very annoying, but after the reset it seems to be able to work fine for extended time under moderate load conditions. I'll have to try it while pedaling to determine if more work needs to be done on the system. Beside that issue, the bike has been very fast and reliable.

I will probably replace the handlebars. They use an aluminum tube which is a little flexy, causing a "loose" feeling in corners and when going over big bumps.

I have ridden the bike to work and back a few days a week all summer. It's performed admirably. As long as I help the electric motor by pedaling while accelerating and up hills, it works fine with no power cut-offs. Cruising on the flats is great with no human assist needed to go 27MPH for long distances. Uphill is a bit slower, downhill a bit faster.

What's next?
I need a real front brake! I am replacing the 20" suspension fork with the MEKS CF disk brake fork.
New handlebars.
New motor? the Cyclone 500 Watt Brushless Motor w/ Gearbox (Taiwan source) looks enticing and will work with my 24V battery system. This will allow me to replace the heavy rear subframe, and I will be happy to be rid of the finicky Currie controller.

I have received the new fork, it's very pretty. The head tube is very long though and only threaded for a short distance, so I needed to get the threads cut further down the steerer tube. I don't have a tool to do this, and no local LBS would touch it, but fortunately I found a local road bike frame builder, Troy Courtney, who cut the threads for me.
Matt also researched the following, which says 30 MPH is legal on an e-bike in Illinois. Hey, I'm legal. Cool.

(625 ILCS 5/1-148.2) (FROM CH. 95 1/2, PAR. 1-148.2) SEC. 1-148.2 MOTORIZED PEDAL CYCLE. A motorized pedal cycle is a motor-driven cycle whose speed attainable in one mile is 30 mph or less, which is equipped with a motor that produces 2 brake horsepower or less. If an internal combustion engine is used, the displacement shall not exceed 50 cubic centimeter displacement and the power drive system shall not require the operator to shift gears. (Source: P.A. 83-820.)

The new suspension fork with disk brake is installed and I can stop much better now. I think at least a front disk brake is a must for a heavy e-bike. I also built some new steel handlebars. This also helps a lot. The old aluminum ones left me with a disconnected feeling.

I had a very typical ride into work on my commuter e-assist bike, then on the way back the chain fell off on the human powered side. It appeared that the mid-drive was a bit loose. I put the chain back on and it fell off again. The mid-drive was very loose. I decided to just use electric. This worked fine down into the Fox river valley, but coming up out of the valley where I normally pedal to help the motor, I had to walk a block up the steepest section. The electric motor held it's own, slowly up the rest of the big hill out of the valley. I had almost reached the top when the electric system went intermittent than died. Uh-Oh. Now stopped, I smelled the acrid odor of cooked electronics. Uh-Oh. Stepping off the bike I see the smoke emanating from my battery bag. Oh...

I pushed and coasted the rest of the way home, and then took the battery out of the bag, but there wasn't much I could tell without a voltage tester. Nothing looked obviously fried except for the fuse holder (!).

I rebuilt the mid-drive drive, and replaced the fuse and all was right again. The bike works fine. I replaced the fuse holder too as this one seemed to be "high resistance", which is why it had a meltdown.

Here you can see the new fork installed on the bike. Also I built a new set of handlebars for the bike. The new ones are steel and very stiff, plus they are more normal looking.

I have been commuting to work on this bike a couple times per week all year (It's been rainy). It's now got over 500 miles on it and is going strong.

This bike handles nicely, runs at a nice speed, is comfy, and looks nice, but I still don't like the anemic motor and it's tendency to cut out due to over-amperage just when I need it the most. On to e-bike #2!

To allow me to continue to commute in cold weather, I'm adding a fairing. See the build process at:
The e-cuda fairing page!

This bike lives on with a new more powerful RC drive system, and I commute to work on it regularly.



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