Electric Vehicles

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Another Battery Update

Fresh batteries arrived Priority Mail today, and things are not well...

Find Out Why

I suspect this means that I'll be moving to a full Mk. 2 model in the near future, probably having cog-belt drive (for noise) and less crap... (and hopefully a better frame, with less error... In my 10mph tests, there's lots of slop in this frame... I can see why someone trashed it)

Battery Update

With desulfator now in hand, I'm working to recover enough batteries to get this vehicle on the road.

Progress

Tonight, the electric bike lives. The batteries are in place, though not fantastic. I need to get a desulfator built. For now, I'm just using (essentially) a giant transistor to control power, all or nothin. Eventually, PWM will be the order of the day, but at the moment, this will get the bike on the road. The derailleur was exactly what I needed to fix the chain problems, as I really havent had an issue since. I may still need to narrow the teeth on the rear sprocket a bit, as there is still some slight binding, even after lubing the chain tonight (thanks to Jason for his unwanted chain oil), but it doesnt seem to hurt anything major. Tomorrow, I need to get brakes installed, though I've done quite a bit of the legwork already, measuring brake cables, test-fitting the double-fork that the caliper bolts to, etc. It should be a matter of cutting and welding.

In tests inside the warmth of my garage, acceleration is reasonable, though stall torque seems limited; It wont push the kickstand very far, but once it's moving, it picks up speed well. Based on this, I think the design speed of 20mph should be easily achievable.

In other news, I am still considering switching back to the Suspended donor's aluminum frame, leaving me with a more conventional bike design. This yields three main benefits: 1. people look at you less oddly; 2. It lightens the vehicle as my current frame is solid steel; 3. It provides a facility to attach the pedals and crank, required to be an electric bicycle; (here to for, I've not been too worried about this, as, like most electric bikes, I'm planning to include them only as an afterthought and technicality.

Anyhow, enjoy a picture; I intend on uploading a full slew of build pictures and some video, as I transition the bike to it's own "completed" page.

Past Progress

Basically everything before battery box and final assembly

Ron's brilliant insight was "use the derailleur off the bikes you've scrapped here". According to him, a motorcycle uses no tensioner, as the back wheel just slides front to aft (presumably in some kind of blocks) and that's what sets chain tension. He claims that a bicycle wheel would be impossible to square, using such an arrangement. Additionally, a bicycle wheel "Drops" into angled slants, which (likely) are intended to keep from losing the rear wheel.

Anyhow, tonight, I completed the tensioner. Basically, I locked the derailleur in the extended position, added a few links to the chain, and welded the derailleur to the frame in a way that kept it sprung against the chain. Initially, I'd thought I wanted to just press the chain together with it, but determined that it wasn't feasible, due to a lack of space, as well as the angle at which the spring start to apply pressure. Anyhow, this ended up pretty well, and allows for a degree of adjustment, in case the chain tries to jump or starts to wear funny.

On another chain related note, I've got some issues with the rear gear being tight in some positions on the chain, causing the tensioner to "jump", rapidly increasing the tension and then slackening the chain, as the obstruction clears. I think this wont be an issue under heavier load, but if it is, I may have to take an angle grinder to the rear gear teeth to narrow them up a bit. I think that this is directly related to the fact that the rear gear was removed from the crank of a BMX bike, which, in addition to being single-speed, seems to have a "heavier" chain, possibly of a different pitch.

A final chain issue is thus: I discovered that some pins on the chain weren't flexing properly. Specifically, the points that I'd "serviced" with a chain breaker. Something about the splicing process lead to joints that didn't want to flex right, in some cases. I found that, by (Carefully) tweaking the 2 adjacent links with a pliers, I was able to alleviate the problem.

Now, all that remains are the electronics and the brakes. I have parts to set up the 20"s front brakes for a 20" tire on the suspended fork, it's just a matter of welding up an appropriately rigid support and running the control cable. I'm planning on using a canned 500w controller from TNCScooters, which I think is pretty reasonably priced (about $45 for controller, connectors, twist throttle and S&H). I expect, given my calculations below, that it will be the performance limiting factor for the bike, as it supports current limiting. If need be, I could probably use it as a pulse generator to drive an even larger output stage (this would eliminate the current-limiting functionality, because the trigger for such a stage would draw almost nothing).

I also need to find 24v worth of decent batteries in my stash. I have 4 additional ones from Ron, but the one that's on the charger tonight seems to be trash. I do have two more (identical) batteries yet in a box, that I've never tested since receiving them. At the very worst, when I finish my computer overhaul project, I can steal the 4 off the UPS, when I scrap that out.

Slightly Shorter Period

I got a wild hair today and decided that this would be the day to complete the gearbox mounting and try to make a go at complete drivetrain testing. Mission Accomplished.

I started by reinforcing the gearbox assembly by welding some 3/16 x 1" steel between the forks, and cutting the headset-end off. I'd previously assembled a chain for the first sub-drive, spinning the jackshaft. I also affixed the small sprocket to the motor shaft. I'd initially intended on using a screw to hold it in place, but when I broke off the (brand new) 4-40 tap in the hole, I decided to just tack the sprocket to the shaft itself. I mounted the gearbox to the swingarm, but had underestimated the amount of torque produced by that motor, simply spinning the jackshaft. The torque of that alone is enough to make the whole gearbox bounce up and down on the first, temporary weld. I added two more pieces of strap, to hold it securely to the frame. I also tacked the motor mount itself to the cross-bar, making the entire gearbox rigid to the frame. While the alignment looks a bit... precarious, it's necessary to align the chain properly, while avoiding both the swingarm itself and the tire.

Following that, I raised the back tire, and attempted to connect the main drive chain between the jackshaft and rear wheel gear. This is the part that didn't go so well. Basically, there's too much flex in the whole assembly (assembly being the rear swingarm itself) to work with a fixed-length chain. It works just fine, mostly (it'd work better if I could get a single link somehow)... I think my solution is going to be a spring tensioner, like those used on a bike derailleur, unless Ron has some brilliant plan.

In any case, I've seen the back wheel turn under it's own power. That feels good.


Here's a video I shot of the drivetrain in action.







First Long Period

Finished the motor mount and jackshaft tonight.

I still need to figure out the chains thing, and get the motor sprocket sorted. I did get the stock brake mounts ground off. I still need to build and mount the new ones. Given the way the bike is designed, the rear unit is almost entirely self contained... Gearing, motors, brakes, etc. Basically, the rest of the bike is just dumb frame, which could easily be scrapped, redesigned, etc, at some future point.









"Day" 5

Well, the "Manhattan Project" phase of this project is over. I'm no longer posting daily updates, but have still accomplished quite a bit. Since last update:

  • Reassemble and re-lube rear freewheel.
  • Design and weld the rear "seat frame"
  • Grind all the doo-dads off the rear swingarm, to make space for the powertrain
  • Mount larger rear gear
  • Build jackshaft and mount both larger and smaller gears

Major mechanical pieces remaining:

  • Mount motor and jackshaft
  • Build motor->Sprocket adapter
  • Acquire appropriate chains
  • Brakes ;)
  • Install front fork bearings... Hopefully help some steering pull I'm seeing.

Aside from that, there's the electrical side, which I'm pretty comfortable with. I think I'll be ordering a controller from TNC Scooters, on Frank's advice. Given the 1hp rating at 24v of my motor, I think I'll stay there, carrying either 1 or 2 banks of SLAs...

Day 4

Here's what I did tonight:

  • Assemble front-tube to bottom tube connection
  • Cut, drill, cut some more and assemble rear shock support
  • Reinforce welds overall

Hooray! Today is Rolling Chassis day! I'm not sure everything is entirely square, but it's pretty good. It rolls straight anyhow. I sort of wonder if the rear swing-arm (salvaged off the suspended Mongoose) isn't tweaked a bit. I suspect that I can resolve some of this when I mount the rear wheel. Now, all that's left for the frame is to build the seat mount. This will also support the batteries... We'll see how this ends up :)

The suspension seems to work well, but it might need stiffened a bit. I've never actually used a fully suspended bike, so I don't know quite how it should feel. It has plenty of travel, and doesn't bottom out, but I might need to stiffen things up a bit, once I work out the battery situation.

Day 3

Here's what I did tonight:

  • Assembled the lower linkage of the rear suspension
  • Disassembled rear freewheel in preparation for mounting a larger sprocket
  • Cleared paint to mount the bottom tube

I also tested the motor, which Ron donated a while back. It seems to be in the 250w range, though I can't tell as I don't have 24v worth of good batteries charged. At 12v, locked rotor, it drags my bench supply down to 8.5 volts, sucking down 11.7 amps. That's 100w right there. Given this calculator, if the motor holds that rate linearly (which it doesn't, as a brushed motor), it'd slurp down 33 amps, making a whopping 793 watts or 1.06 horsepower.

Further, I borrowed an ancient but really awesome mechanical tachometer from Blake and measured the motor at 2700 to 2800 rpm, at 24 volts. It's about linear from 5v to 24v. This allows me to finish designing my gear train. For a 20" tire to do 20 mph (my design top speed, to stay a "power assist bike"), you need 336 rpm. 1/(336/2800) = 8.33:1 final drive ratio.

Day 2

Here's what I did tonight:

    • Cut the headset off the 20" frame
    • Welded the front post
    • Swapped in the suspended fork
    • Made up a temporary handlebar
    • Disassembled all available cassettes

Blake is bringing me a mechanical tachometer tomorrow so I can finish designing my gearing system. From there, I'll need to get creative with the rest of the frame, get the rear swingarm installed and design a seat. Sounds like fun.

Day 1

A friend of mine hooked me up with a local bike shop, where I was able to procure some "junk" bikes. In the end, I'd say they're a bit better than junk. This first night, we managed to do most of the unit disassembly, and lay out a mockup. Have a look!







Overview

Ok, you caught me... I don't actually have ONE electric vehicle, let alone MANY electric vehicles thus necessitating an entire page for them... But, I do have an interest in starting to experiment with Light-EVs. I'm thinking that for a first project, some sort of electric scooter... Sorta like a Razor, but a bit beefier, to give me space for batteries and stuff. The larger wheel-size is an added bonus.


Update: I've recently given a lot of thought to this, after having serviced my UPS, and having read some of Frank's exploits. Given the issues with licensing and insuring a "real vehicle", I'm starting to think that a "power-assist" bicycle is the way to be. The rules say that it has to be capable of being human powered. I think it'd be a fairly trivial task to build something that looks (sort of) like a bike, could be pedaled but was never really intended to be man-powered as it's primary mode of locomotion...

Parts

Speed Controllers

Ron found this PWM speed control schematic.

My take: They've got kinda a little mosfet, but something like this could even be used to drive a bigger output stage... It's just a pulse. The circuit itself is based on the NE556 timer (Which is just a pair of 555s in one case); It's similar to the Frequency Width Modulation that I'm doing, but with the added benefit of being mostly silicon (where the more basic single 555 based circuit is controlled by the loading of a capacitor)... The schematic isnt all that complicated, but for $25, their Printed Circuit board might be worth it (not to mention the pot, and random other stuff)...

Batteries

After reading some sites, there are TONS of options for power sources. Good ones are expensive, cheap ones are not so good. For my scooter, I'm sort of planning on salvaging as many laptop LI-ION batteries as I can. The Fujitsu Lifebook 531T that I (was) turning into a Picture Frame had 3 batteries (capacities forthcoming).

Links

Chevy Volt

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