Jay's Technical Talk » ebike

New electric bicycle motor mount

Jay — Sun, 03 Jan 2010 21:15:22 +0000

The simplistic motor mount I made for my electric bicycle (which consisted mostly of me bolting a motor to my wire basket and holding the basket away from the axle with a piece of PVC pipe) had been working well for five months. Until, that is, I ran over a particularly large pothole and the chain fell off. I took the hint that the PVC pipe and wire basket were not exactly up to my exacting quality standards and decided it was time to make something better.

I decided that the main problem was that my wire basket was not rigid enough, so my construction material of choice remained 3/4″ schedule 40 PVC pipe. This time I used TWO upright supports, one on either side of the axle and some C shaped metal shelf brackets bolted to my motor mount. (I also used PVC elbows and pipe to join the top of the supports.) This picture gives a good view of how the whole thing fits together. I am still using a hose clamp connecting it to my wire basket for left-to-right stability, but this produces much less stress on the basket, and a little left-to-right wiggle is unlikely to allow the chain to come off the gears.

I basically cut wedges in the bottom of each upright so that I could bolt them to the outside of the axle, and then notches so that the C shaped pieces of metal would fit into the pipes (for greater support that the simple wood-screws that hold the metal into the notches).

The main stresses on the system is vertical tension on the two PVC support pipes when the motor is powered as it tries to pull itself towards the axle along the chain. The motor also pulls the whole mounting system back towards the basket of the bike due to the direction of rotation. I added a torque brace that connects the chain side upright to the front fork of the bike using more PVC pipe and a hose clamp. Although probably not strictly required, it does stiffen up the whole assembly.

The picture at the top of the page shows the whole assembly spray painted (black) with the vacuform motor cover installed. The mounting system is relatively light, only adding 1.4 lbs to my bike, but the motor itself clocks in at 4.6 lbs. At least it’s not adding rolling weight (with the exception of the extra sprocket and chain), so this is equivalent to around a 3lb hub motor. This new motor mount added $7.33 to the cost of my electric bike, but I still have 6 feet of 3/4″ schedule 40 PVC pipe for the next project. You can read more about my inexpensive solar charged ebike by clicking here.

Ebike Solar Charging

Jay — Sun, 29 Nov 2009 02:42:51 +0000

My electric bicycle has a motor that draws up to 450 watts (if I drive it over its nominal 250 watt rating), and the batteries have only 5AH (approx 120 watt hours) total capacity. Keeping in mind that I should only discharge the lead acid batteries to 50% (approx 60 watt hours) this indicates that I can only use the motor at full blast for eight minutes.

But, since I only use the motor to help go up hills and provide extra acceleration, and most of the time it is not drawing the full 450 watts, I actually have a much longer run-time. I deliberately chose to put small batteries on the bike both to keep the weight down, and to allow them to be recharged using solar cells (8 watts) in a reasonable amount of time. Under full sun, hypothetically the solar cells will generate 60 watts of power to recharge the batteries from 50% to 100% charge in 7.5 hours. In actual practice, it takes more like 10 hours of sunlight, usually around two days.

How does this work in actual practice? Here are some examples.
Early Saturday morning I biked a 2.8 mile round trip to the post office, using the motor lightly. I left the bike outside all day and it was recharged by 4pm. On Sunday afternoon I rode the bike to a friends house ( a 2.5 mile round trip). Because it was overcast and raining, no charging occurred before I then rode the bike another 0.9 miles to the Marta station (up hill) and left it all day. (At this point the batteries had been used for 3.4 miles of travel without charging.) When I returned at the end of the day and rode the bike home (another 0.9 miles) it was not fully charged (due to the ride home) but the voltage had gone up significantly. After leaving it out in the sun for another day the batteries were fully charged.

In general usage, I typically only use the bike two or three days a week (rain, schedules matching up, etc) so the two day charging time fulfills my needs. If the bike was my only means of transportation, I’d probably have to supplement the solar charging with a grid tied charger, or install much larger solar panels at a fixed location to charge the bike.

Vacuuform motor cover

Jay — Mon, 09 Nov 2009 00:17:30 +0000

Ever since I mounted an electric motor to the front wheel of my
bicycle I have been keeping a plastic bag over the motor with a clothespin whenever the bike is parked. This does a decent job of keeping rain out of the motor, but the process of uncovering and covering the motor takes extra time. In an effort to make a permanent rain cover for the motor, I built a tool (mold form) out of wood and used a vacuuform machine to shape a piece of plastic over it.

My tool was built out of craft plywood in a box shape with a rounded top. The tool was assembled using wood glue, and is (just) strong enough to resist being “imploded” by the powerful atmospheric forces that squeeze the hot plastic around it in the vacuuforming process. (A tool made out of cardboard would deform under the vacuum.)

The process of using a vacuuform machine is simple.

Read the manual.
Turn on the heater and wait for 15 minutes for it to reach operating temperature.
Place your tool on the lowered tray.
Clamp a piece of plastic over the tool.
Pull the heater over the plastic.
Wait just the right amount of time. The “correct” amount of time will depend upon the type and thickness of the plastic, temperature of the heater, phase of the moon, etc…
While watching the plastic, you will see it go slack under the heat, then quickly raise up. After a while, the plastic will start to droop back down. At this point the plastic is almost ready. You still have to wait a bit longer until the plastic is melted enough to be pushed around the tool when you turn on the vacuum. You can push back the heater and poke the plastic (watch out, it’s hot!) to get a feel for just how pliable it is.
Once the plastic is ready, push the heater back all the way, and raise the platform that your tool is sitting on. Once the platform is all the way up, turn on the vacuum.
Wait until the plastic is pulled all around your tool. When you are happy with it (or if you hear the tool starting to break under the pressure) reverse the vacuum switch to blow a bit of air between the tool and plastic. This will make it easier to remove the tool from the plastic.
Unclamp your plastic and pull it out. Expect the tool to be embedded inside the plastic, but with some pulling and bending you should be able to get it out. (You did make your tool without any overhangs, right?)

Here is a video of the procedure:

After you have your piece of plastic, you will have to trim the edges off to get it down to what you want. A pair of scissors will work, but may cause cracks to appear going around sharp corners. A rotary cutting tool (Dremal) also does a good job cutting through the plastic.

Here you can see the piece of plastic mounted over the motor, protecting it from rain.

Update: Noise Dampening

Because this motor cover is made up of rigid but thin plastic, it acts as a sounding board for my motor, greatly amplifying its small hum to a loud noise. I certainly didn’t have to worry about sneaking up on anybody with my electric bike! To mostly eliminate this noise, I cut two pieces of neoprene rubber (from an old laptop case) that are used to sandwich the plastic motor cover and isolate it from the mounting bolts. This does a great job dampening the vibrations.

E-bike solar charging rack

Jay — Sun, 02 Aug 2009 02:42:06 +0000

An electric powered bike makes it easier to go up hills, and can turn a ride to the train station from a workout into a commute. Typically however, the batteries need to be plugged in to charge after your trip. Although electricity is cheap, this does require that you have removable batteries (or wheel your bike into the house or bring a charger outside). I decided to use the sun to recharge my bike, seeing as how I would be parking my bike outside at a train station all day. This way, it can be fully charged and ready for the ride home when I return.

To add solar recharging to my electric bike, I bought two 12 volt solar panels (providing 4 watts each) a rear bike rack, and some miscellaneous hardware. The bike rack attaches to the seat post of the bike. It has two metal rails on either side, and I used 3/4 inch two hole electrical conduit straps (bent into a circle) around the side rails of the rack to mount the solar panels. The panels had their own extruded aluminium frame. I drilled two holes in each solar cell’s frame and bolted the frames to the electrical conduit straps. This allows the solar panels to rotate nearly 180 degrees.

To prevent the panels from swinging into the spokes of the rear wheel while in motion (which could be fun!) and to provide a way to easily prop up the panels when in use, I added two zinc shelf brackets as supports between the rear axle of the bike and the rack. They are bolted onto the bike frame (M6 machine screw) and hose clamped to the rack. I cut some pieces of rubber from a mouse pad and used epoxy to glue them to the solar panel frames where they would hit the zinc shelf bracket to eliminate metal on metal rattles.
I cut two more 8 inch pieces of the same shelf bracket material to use as struts to hold up the solar panels. By cutting the ends at an angle, they fit into the notches in the supports. By placing them in different notches I can vary the angle of the solar panels (although so far I have simply placed both panels parallel to the ground). When not in use, the struts are attached to the bottom of the vertical brackets using 3 small high-strength magnets on each side. The magnets are small disks that fit inside of the slots in the shelf bracket, and hold themselves on so no adhesive is needed. So far, as long as I line up the magnets so they fit into the slots of both the attached vertical bracket and the 8″ support strut, they have not fallen off going over bumps.

The rear rack cost $17, and the miscellaneous hardware added another $10. The largest cost of course is the $70 for the two surplus solar panels, driving the cost of this solar charging addition to my electric bike to $97. (But, I also get the use of the rear rack.) The total weight of the bike with all accessories is 62 lbs

Bike Lighting: $15

Jay — Fri, 31 Jul 2009 02:07:25 +0000

In case I need to commute home after dark on my electric bike, I added a front headlight (5 watt MR11 halogen) and a rear tail light (Red LED tail light for “off-road” use). The front headlight enclosure was designed to be used on a bike, and included a nice mounting bracket and enough cord that I could harvest some to run to the rear tail light. Black zip-ties hold the wires to the frame. The rear tail light had no enclosure, so I soldered the wire directly to it and epoxied it into the back of my rear rack. Both lights run off of only one of the 12v batteries through a 5A blade fuse and an automotive switch mounted under the battery pack.
If you look at the picture of the tail light you can see that it is sitting between the two solar panels hinged on the rear rack, but those are another story.
Total cost, under $15.

Front Headlight: $5.65
Rear LED: $2.75
Switch: $1.52
Blade Fuse Holder: $1.27
5A blade fuse: $0.60
Zip Ties: $2.79

The $175 Electric Bike

Jay — Mon, 27 Jul 2009 01:50:30 +0000

Electric bikes are expensive. Even if you buy the cheapest electric bike you can find on deep discount at walmart, it costs $300. (Formerly $400 before they deeply discounted it.) I decided to build my own out of surplus parts and things I could buy at the local Ace Hardware for less than $300. (Mostly, for the fun of the build.)

So, I bought a surplus motor controller, handlebar mounted throttle, and a 250 watt electric motor. I bolted the motor to the front of my used $20 bike, built a battery holder out of PVC pipes, and made a vacuum formed cover.

Not counting the (high) cost of labor, here is my bill of materials:

Item – Cost

24vdc 40A motor control – 32.95
Two 12v 5AH sealed Lead Acid Battery – 32
250 watt PM motor – 25
Used Bike – 20
#25 Roller chain – 10
Twist Grip Throttle – 12.75
Consumables (solder/wire) – 10
PVC Pipe Joints (4 elbows, 2 t’s) – 4.74
90 tooth sprocket – 4
Four 10” bungee cords – 3.79
Bicycle wheel hub – 3.5
Four M6 hex-cap bolts – 3
5 pack 25amp fuse – 2.99
Auto Hitch power supply connector – 2.34
Five feet PVC Pipe – 1.5
Blade Fuse Holder – 1.5
Four Fender Washer – 1.2
motor controller case – 1
#25 Roller Chain master link – 1
Four 3/16 quick connects – 0.2
Two M10 1mm pitch nuts – 1.4

Ebike Total: 174.86

Next projects: Adding lights for night biking, and solar charging.

Vacuuform Battery Cover

Jay — Mon, 27 Jul 2009 00:35:04 +0000

After building a PVC pipe battery holder for my electric bike, I used a vacuum form machine to make a polystyrene battery cover. I built up a cheap tool form using cardboard (which turned out to be too week, but it was quick).

Vacuum form complete

As the vacuum was forming the polystyrene around the cardboard the box started to deform so I had to release the vacuum before the styrene had fully formed itself to the PVC pipes, but it got close enough to be screw mounted.
This cover will protect the batteries and a lot of the wire connections from rain, the weather, and prying fingers. In addition to the batteries, the cover protects two of the three fuses on the bike and a switch to control the lights.

Electric Bicycle power circuit

Jay — Sun, 12 Jul 2009 02:15:34 +0000

Bolting a DC motor to the front basket of a bike and running a chain to the front wheel takes care of the mechanical linkage needed to make an electric powered bicycle, but you also need to provide power to the motor, and control that power in some way.
Luckily, the same place that sold me the 250 watt motor also sold a 40 amp speed controler. (It cost $33, or more than any single other part of my e-bike project.)

The speed controler is controlled by most standard e-bike throttles, such as this one from Currie Technologies. I also attached two 12v 5AH batteries in series to provide 24 volts. Because I calculated that my 250 watt motor running at 24 volts would draw approximately 10 amps, (250/24 = 10.4), I added a 15 amp fuse to the circuit. (The first 15A fuse was replaced by a second 15 amp fuse after it saved my speed controler from damage when I accidentally reversed the polarity on the power…)

Everything was working great until the first time I turned the throttle on all the way during my first test ride. The motor ran for a few seconds, and then came to a complete stop. (This was my 2nd 15A fuse blowing…) It surprised me that the motor would draw more than 15A, so I replaced the fuse with a 40A one, and measured the current draw using a 0.5 ohm shunt and amp meter. (For testing purposes I had the batteries mounted in the front basket, however, this unbalances the bike, and for everyday use I am building a battery bracket that will mount them inside the frame.)

I found that my 250 watt motor (rated to 15A, or 360 watts) was actually drawing close to 21 amps, or 500 watts) at full throttle. I guess using a 40 amp motor controler on a 15A rated motor allows excess current to the motor. It would appear that the motor does not limit it’s current draw to it’s rating.

Adding an electric motor to a bicycle

Jay — Sun, 12 Jul 2009 01:08:44 +0000

I purchased a surplus 250 watt motor with a matching wheel hub and 90 tooth sprocket. The motor has an 11 tooth sprocket, and both the motor’s sprocket and the hub’s 90 tooth sprocket are designed for #25 motor chain, which is slightly smaller than standard bicycle chain.

To get the hub and 90 tooth sprocket on the wheel, I had to remove the existing hub and rebuild the wheel on the new hub. Luckily the two hubs were close enough in size that I could re-use the existing spokes. Following the instructions on Sheldon Brown’s website, and also refering to this website I was able to re-spoke the wheel.

The motor came with a bracket that had four holes threaded for M6 bolts. As my bicycle already had a wire basket mounted on the front handlebars, I used fender washers and a piece of angle iron to mount the motor to the basket directly over the front wheel.

Of course, the front basket was not sturdy enough to support the motor without bending once the motor turned on. (The motors pulls itself towards the hub along the chain.) Once the motor pulled down enough for slack to develop, the chain would pull off the sprockets.

To buttress the basket, I machined a honeycombed support strut out of T6061 aircraft aluminium using my 3 axis CNC machine. Well, not really. Instead, I used a cheaper material widely available at the local hardware store that can be machined using simple hand tools….that’s right, schedule 40 PVC pipe! Although not quite as strong as aluminium, it cost me less than $1 and has one other nice property. When somebody sees an electric bike locked up at the MARTA bike rack with a piece of PVC zip-tied to the front forks it screams out “Don’t even bother trying to steal me!”

If you look closely at the bottom of the pipe (visible more clearly on the right hand side of the top picture), you can see that I cut a wedge out of it, leaving about half the pipe. I then drilled a hole of suitable size for the axle (using a 1/4″ drill bit, and a dremel, as somebody had snapped off the 3/8″ drill bit into a tree stump). My original intention was to attach the pipe to the axle using another nut, but my local hardware store did not have M10 nuts with a 1.0mm thread spacing in stock. I found that a few zip-ties worked well enough. I also cut a small notch in the top of the pipe that supports a horizontal wire from the basket. In addition to the notch which does a good job of aligning the pipe to the wire, I used a few zip ties around the pipe, and through a few holes drilled in the top of the pipe to provide extra horizontal and vertical support where it connects to the basket. So at least the top and bottom of the pipe have matching zip-ties.

Update:
The local hardware store has re-stocked their M10 (1.0mm thread pitch) nuts, so I was able to use one to keep the PVC pipe support strut attached to the front axle (in addition to the zip ties).

Update 2: This simplistic motor mount worked fine for five months, until the chain fell off when I hit an excessive pothole. Check out my new better motor mount (Well, $7 better) by clicking here.

Currie Technologies 6 pin Diaganostic throttle pin-out

Jay — Sun, 28 Jun 2009 22:16:09 +0000

I purchased a surplus Currie Technologies “Diagnostic” throttle. (Which includes 3 LED’s labeled as 1/3, 2/3 and full charge indicators) It has a six pin (7 cable) connector with no pin-out diagram.

Currie Technologies diagnostic throttle

After opening it up, it appears that the blue, black, and red wires are connected to the throttle sensor itself, while the other four wires (White, Gray, Yellow, Green) connect to the LED circuit board.

The pin-out ordering is as follows, from the bottom of my picture up:

Red/White (Throttle/LED, sharing a pin, + voltage)
Black (to throttle, I assume Ground)
Blue (from throttle, I assume signal)
Green (Full LED)
Yellow (2/3 full LED)
Gray (1/3 full LED)

I connected the Red/Black/Blue wires to a motor speed controller that had a 3 wire throttle connection (matching them up to the Red/Black/Green wires from the controller) and it worked great!

The LED pin-out is as follows:
White (positive / Vcc)
Gray – 1/3 empty LED
Yellow – 2/3 full LED
Green – Full LED

Note that I was able to get the LED’s to light up with a 3V source, but I believe their forward voltage is less than 3V and you should use a current limited supply so that you do not burn the LED’s out.