mathjax

2013-04-07

Electric Vehicle Part II: Frame Built

So the frame of the vehicle when last discussed was a highly non-structural frame with a seat some wheels and a motor. This is it now:


A much more structural thingy with a base board and supports and hot damn it even has a chain to transfer power. This thing is almost usable. All of the making the fork and headset and such happened of the course of a few months of off and on work. The making it structural bit happened in about two weeks of more dedicated work. This thing has existed too long in a semi constructed shape, hopefully it will be done soon; or at least rideable its hard to say when a project is done because then the mods and shiny bits start getting added.

 How ever on that note time to talk about structure a lot of the 80/20 carts made at MITERS have been planar creations supported by the sheer shear strength of the aluminum beams they sat on.  Since this bike/EV/thing is like 1.5m long and made out of 20mm 80/20 bars that wasn't going to fly. What the vehicle really needed was a larger moment of inertia to prevent flexing in the middle. This was achieved through the angular braces that form a bridge like structure under the seat. The ends of this bridge structure sit on horizontal bars that are fixed in between 1/4" plates this provides a solid base near the ends of the scooter. Unfortunately this meant the 80/20 had to connect at strange angles, this required bent brackets to accommodate the angles needed by the supports.

Rear brackets
Here is a picture of a bent and yet to be bent pair ofrear brackets. The aluminum is 1/8" thick and for size reference the holes are 20mm apart and fit M5 screws. That also gives a reference for the wrench in the next picture as a poor-man's brake. It is fucking huge. It is around 2' long and provides an excellent lever arm.
Each bracket was bent in small increments deforming one section at a time along the bend line. Despite the inaccurate method the brackets fit in place pretty well. Some brackets which needed larger angles were heated with a torch before bending this made it significantly easier to bend some of the brackets without ruining the intergrity of the metal(...well maybe its temper was ruined but w/e).

Whats was actually more obnoxious than the bending was cutting some of the 80/20 sections. Distinctly the braces on the rear of the vehicle. In order to provide natural support for the braces (both in the front and in the back) they were cut with a niche in the bottom so they could rest on top of the the brackets and supports on the frame base. Due to the odd 3-D angles getting the interface was a pain without using a mill but since I wanted to get this done quickly and precision was not a requirement the joints were band sawed then filed a bit.

Etched cut to make

Left: Cut Just made by bandsaw, chunk barely held in Right: mirror support without chunk of aluminum in place.

Yes that cut looks weird but that is actually how its supposed to be. When viewed from the proper angle it is just a 90 degree cut out like this:
Support bar from a less confusing angle
The angle in the end of each support fits over the edge bar or bracket it connects to, this way when some one is sitting on the scooter and these bars are loaded in compression and they transfer the forces more directly to the structural objects they sit on rather than the brackets that keep them in place. It also means I don't have to worry about them becoming displaced as easily   Either way not very exciting yadd yadda, after attaching the additional supports and what not the electric vehicle was quite solid. After the supports a large sheet of 1/2" plastic(it might be HDPE) that I found was fixed to the base. These steps are kind of boring and I'll skip posting more about the structure of this thing. It's a frame in the shape of a bike/scooter. The next discussion will be about the drive train/energy storage of the scooter.

Also holy crap I'm tired of referring the 'the electric vehicle' as a scooter , EV, minibike. From now on it shall be known as busscooter because it is long like bus and according to some people will have the turning radius of a bus....which is not entirely inaccurate given its length.


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