September 28, 2016

For this week, most of my time was spent preparing for the first presentation, which included calculating out a few numbers as well as coming up with some concept designs. One of the first calculations that I made this week was finding the stall torque of the motor that we already have at our disposal: A Crystalyte SAW_408 motor paired with a 48 volt, 25 amp motor driver. Through looking into the superway archives, I found a data sheet on this motor, giving the potential torque and rotations per second at various amperage, given it had a constant voltage of 48 volts. Which has a stall torque of about 105 Nm. Now given that last years design used this one motor as a direct drive system, I used the outer diameter of the hub (about .406 m) to find the force that the direct drive motor could produce; approximately 519 N of force without accounting for friction. Yet, the bogie, which we are weighing at 600 lbs or 272 kg, would have a force of 780N going down a 17 degree slope, so using one motor as a direct drive would not be a viable option.

From there, I went into determining a more realistic weight distribution between the two bogies as it rests in the middle of a 17 degree incline. Surprising, it appears that the wheel that is higher on the track supports more of the systems weight compared to the lower wheel, due to carriage being underneath the bogies and causing the rear to swing up. For the calculations, I based it on the idea that the carriage was 400 lbs hanging from the cross member in the middle, much like the summer team developed. Each of the bogies therefore weight about 100lbs and were support (vertically) by one wheel on the track. With the wheel base of the bogies being 26 inches and the pivot point of the  carriage hanging about 10 inches below the cross member. Upon running through the calculations for weight distribution, I discovered that both wheels would experience the same force sliding down the track 390N, but in terms of normal force, the front wheel would support 1583 N compared to the back wheel's 1015 N. What makes this information so important is that it give me a rough estimate of what size motor I would need for each bogie. And more importantly an idea of about the contact friction between the wheels and the metal rail.