Booger Welds: Scooter Build, Pt. 5

Marco Cross
Jul 21, 2017 · 8 min read

There’s a really unsexy part of making a complex-something-new that consumes a lot of time: planning and ordering parts. This week was filled with a decent amount of construction and a much larger portion of the ordering parts bit. Here’s the fun stuff:

Welding is harder than it looks, especially when it’s round

The MIG welding process was originally sold to me as the equivalent of a glue gun for metal. It boasted (originally) the option to basically fill gaps equal to the Hormuz Strait in width while retaining the strength of a small nuclear-capable nation state. While all this is patently true, that gap filling comes with the previously-unknown burden of producing welds that look like… well… boogers.

That’s not even the worst of it. I’m too embarrassed to show you the other end of those shiny downtubes.

Fortunately, all this can be cleaned up with a liberal application of angle grinder and rat-tail file. It’s just a shitload of extra work that I was not expecting. The moral of this story is that cutting tubing more precisely results in a whole lot less of a need to fill gaps in the first place. Lesson learned.

A terribly non-descriptive image of the frame as it currently sits.

Two things are visible (and new!) in the above photo. The first is that dual bent downtubes have been added to the top side of the frame. This represents the maximum designed extent of the frame. The only things that could potentially stick out beyond the end of those downtubes are a part of the rear wheel swing arm and/or part of the rear wheel itself. You can also see two wheels in the photo. Speaking of the wheels:

Center scooter hub replaced with adapter plate for the ATV 4-lug hub.

What you’re looking at here is an adapter place that I fabricated from some 3/16" plate steel. It’s currently only tacked in place as ensuring alignment on the DEAD NUTS CENTER of the wheel is of utmost importance at this point. Furthermore, the periphery of the adapter plate is still very rough. As I knew that significant grinding was going to be necessary to ensure an OEM-like finish on this hub, I specifically left it somewhat coarse. In any case, the 4 lug holes are correctly aligned, precisely measured, and tested for fit on the original hub. Ensuring DEAD NUTS concentricity was a faff and a half which I will spare you from. Suffice it to say that I spent far more brainpower considering my options than what was ultimately required for accuracy.

As an aside, this set of steel wheels is the second complete set that I purchased from Cycle Pros Salvage in Bridgewater, MA because I made a regrettable mistake the first time in buying non-weldable cast aluminum wheels. I’m selling those on eBay at the moment for- admittedly- far more than I paid for them. Similar wheels with similar tires sell for more so I’m hoping that this accident will result in a net monetary gain. If you’re in the market for a really nice set of cast aluminum wheels, I highly recommend that you purchase mine. They are listed on eBay for the low-low-low Marco’s Magic Deals Buy It Now price of $70 however as a reader of this post, you get a bit of inside information: the reserve price is set at $60. Cross that magic threshold and you too could be living the American dream of owning parts of a low horsepower scooter or moped. You’ll definitely be able to pass these down to your children*.

*Any statements on the generational longevity of these wheels are purely conjecture and do not represent any binding agreement or promise especially but not limited to any agreement or promise with proposed or actual human or non-human offspring. Good luck with you non-human offspring by the way. I hear that the future job market for giraffes is really looking up. You must be so proud.

A photo of the entrance to the Steel Yard at night.

Parts of parts, parts that look like parts but are not yet parts, and complete parts

The rest of this week’s working time was spent finding componentry for the scooter and actually purchasing the bits and bobs that go on the unit. In one of the earlier posts written in this series, I laid out my purchasing plan for drive train and braking components. I originally thought that those would come around later after the frame was fully constructed. In actually getting into the construction of the frame, I quickly realized something stupendously obvious- I need those parts for fitment and bracket design.

So, I ordered a motor and controller (both of which will require custom mounts) and a set of front and rear brakes. Although the brake levers bolt onto the handlebars, the lines do not and those must be run either through the frame or along it. Space must be allocated for either consideration and that’s difficult to do without the brakes on hand. While the battery is a large component that will factor into the frame design, I am simply leaving enough room for even the beefiest of batteries and will be delaying that purchase as long as possible. I’ve been able to keep costs relatively low to this point; the cost of the battery will basically represent the same amount of money that I’ve spent on the project to date.

In order to keep costs even lower, I made the decision to move away from using a brushless DC motor and controller and to instead use a brushed DC motor and controller. Brushed motors are cheaper and equally powerful although more “electrically noisy” as they operate by completing a circuit across a spinning contact wheel (commutator) many thousands of times a second whereas brushless motors have no such contact because they rely solely on magnetic interaction between a stator and rotor therefore producing no “electrical noise”.

Electrical noise: it’s akin to the difference between listening to music live versus listening to music over AM radio. It’s still the same music but it certainly isn’t as clear.

Functionally, this means that brushed motors are about 75–85% efficient whereas brushless motors are about 85%-95% efficient. For what it’s worth, almost every low-to-mid range electric scooter uses a brushed motor. If in the future should I wish to upgrade to a brushless motor with a little more power I can do so easily. Furthermore, I realized that I was setting my power expectations a little too high. While the legal limit of 1.5 horsepower (equal to 1119 watts) doesn’t seem like a whole lot, it’s actually quite a bit for around town commuting and the like. I ended up buying a motor with a rating of 800 watts (basically 1 horsepower) and I’m confident- without actually installing it- that this will be enough. Most of the electric scooters on the market live in the 500–750 watt range; my scooter will be both lighter and more powerful than those. For reference, look at the reviews for this 650 watt electric mini-ish motorcycle built by Razor. Again, should the need arise I can always upgrade and I will be building my support structures assuming that an upgrade is inevitable. I love speed and I love power; 800 watts is enough for now, but not forever.

Brushed motors are also a little bit more robust than their brushless brethren and the speed controllers used for regulating them are both not required and also simpler than brushless variants. Brushed motor controllers operate on a couple different principals from what I gather but the most successful of the bunch use a method called pulse width modulation (PWM) to regulate speed. Put simply, PWM controllers send short bursts of full power electricity to a motor to control rotation; the longer the pulse, the faster the motor spins until the controller just lets current through with no modulation. This wide open/no modulation state is the same as flooring the accelerator in a car. Succinctly, PWM is like flicking a switch on and off really rapidly. The controller makes this switching happen many times a second so it’s impossible to feel the pulsing occur. Coincidentally, dimmable LED lights largely use the same PWM method to vary light output.

If you simply connected a brushed motor directly to any power source outputting the motor’s rated voltage, it would turn just fine at the motor’s rated max speed- no controller required. In the event that the motor controller fails for whatever reason, this is a nice fail-safe as I can always limp the scooter home simply by applying power directly from the batteries to the motor while acting as a manual PWM controller.

Brushed motors also tend to have published duty cycle ratings whereas that information is not widely available (if at all) for brushless motors. A duty cycle is essentially a measure of how long a motor can operate without rest. For example, a motor with a duty cycle of 50% must rest one minute for every minute of use. The brushed motor I purchased is rated for continuous duty meaning that it requires no rest during operation. Duty cycles are usually a function of heat build up so they can be extended by providing better cooling. Conversely, a motor that’s been laying out in the sun already has a lot of heat built up within so it will have a lessened duty cycle. Also, a 30% (for example) duty cycle motor can’t be run continuously for an hour and then allowed to cool down for an hour and a half. At some point, the heat build up reaches a critical max and the motor begins to either eat itself, fall apart, or it ceases working.

The brakes I bought are basically replacements for the brakes that would have been installed on the ATV originally although the lines for the rear brake will almost certainly have to be extended because the distance between the rear caliper and the front handlebars has changed a great deal.

I’ve started regularly posting Stories on Instagram whenever I’m working on the scooter. Follow me there to see what’s happening as it’s happening. I’m [at]marceuxcroix.

Until next week.

Marco Cross is a competitive barn owl racer and industrial designer/design strategist for hire. His website is www.marcocross.com.

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Marco Cross

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Like a shark, I die if I stop moving (and also my eyes swivel 270 degrees).

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