Tuesday, July 9, 2013

Component Modeling

Although we had a general idea of what our vehicle would like, and roughly what components were needed in its construction, we needed to start designing those components for production.
CELERIS’ core structure was simple – 2 80/20 beams mounted side by side on a 15 degree incline, with a bicycle steering shaft holding the front wheel and the upper end up.
Thus, we broke down CELERIS into the key components that needed to be attached to these two bars, and thought about how they would be connected to these bars in a manner that would be safe and could bear the load sufficiently. In the end, we decided in the interest of ease, we would use a series of plates to attach our key components.

The key components mentioned in this post are:

Battery Plate:

CELERIS is powered by 3 A123 batteries in series. Each of these batteries are rather large (about 6 inches by 3 inches) and quite heavy. We decided to mount the batteries on a single aluminum plate, which would be bolted to the frame. In terms of modeling, the battery plate was probably the most straightforward component – a rectangular plate. Even so, the precision required in considering where to cut the holes and mount the batteries was significant – as you can see from the picture below.
Lots of smart dimension-ing. And this is the ‘easy’ model

We also had to think deeply about how to attach the batteries securely to the plate. The batteries are pretty much smooth rectangular blocks, so there were no direct ways to bolt or screw something to the battery. The batteries also had to be fastened tightly – if they bumped around during the vehicle’s operation, they could be damaged or worse.

In the end, we settled for Velcro strips. The batteries would be held down by a series of Velcro straps that were tightened in loops.

Rectangular holes are for the Velcro strips to pass through and loop onto themselves
The batteries would be secured with a total of 5 of these loops

Motor/Controller Plate

The Motor/Controller Plate is mounted behind the driver’s seat, as it needed to be near to the rear wheel. Power would be transmitted by a gear belt connecting the motor and the rear wheel directly.

The controller is bolted on the front of the plate (left side in this picture), while the motor is supported by the two raised plates.

The Motor/Controller Plate represented multiple challenges. While the controller came with two points of attachment that allowed it to be bolted directly to the plate, the motor was a single cylindrical block, with its points of attachments perpendicular to the plate.

To attach the motor, we employed the Magic Finger Joints as shown in Charles’ instructables guide. This allowed us to attach two plates at right angles securely (you can see the space for the screw and nut on the vertical plates). Now, we could attach the motor to these vertical plates and have it transmit the force down on the horizontal plate.

Another key issue we noted was the positioning of the motor. The sprocket on the motor had to be in a straight line with that of the rear wheel in order to transmit power. Thus, we had to employ Vernier Calipers to measure the distances involved and decide where to place the motor on the plate. Thus, as you have probably noted on the picture, the motor is actually mounted slightly to one side in order to compensate for this.

Seat Plate

The Seat plate was perhaps the most challenging component to model. CELERIS was designed with a 15 degree incline in mind, so if the driver were to sit upright (for comfort and field-of-vision purposes), his seat could not be mounted directly to the frame.

Instead, the seat would have to be vertically offset by 15 degrees. In addition, the method of joining the plate to the beam would have to be extremely sturdy, as most of the load on the vehicle (in the form of the driver and the seat) would be exerted on these joints.

The challenges of the Motor/Controller plate arise once more, in the form of joining plates at right angles in order to obtain a 15 degree offset. The method we chose in the end is shown below:
To compensate for the higher load, supporting plates would be mounted on both sides of each bar.

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