Electric Vehicles

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Progress

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.







Past Progress

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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