Wednesday, October 26, 2016

10/26/16

This week was spent more on cad than anything else, with the motor already selected, it was relatively easy to model the motor as well as a mounting bracket to attach it to attach it to the bogie as seen in the images below. In addition, a bevel gear, which was taken from a part supplier site, was mounted to the drive shaft of the motor and bogie, rotating the motion by 90 degrees. As fair as the brakes are concerned, we would have to go with something more compact than a disk brake to fit it onto the main axel. Even the smallest disk brake, which can be seen in the images below cannot fit into the tight space where the gears and motor are located. For this reason, we are looking at using a belt brake, which are typically used on pocket bikes due to their small form factor

Tuesday, October 18, 2016

10/19/2016

After weeks of calculations and determining various frictions, we have finally decided on a motor to use in the bogies as seen in the link below. Due to the lower power and high torque requirements needed for the bogie to move under solar power, the bogie itself will move quite slowly with the use of these motors. Although as we process further into the semester, the gearing can be altered to make the machine go faster than previously calculated due to having a lighter load than originally estimated (600lbs).

Motor
It should be noted that this motor will be geared to run at 45Nm at about 8rpm, running at 4 amps and 24 volts per motor. These motors already have gear boxes attached, in this case planetary which allows for the greatest gear reduction given the size. Due to the length of the motor, a few beveled gears will be needed to change the direction of the rotation, allowing for a chain to drive the wheels of the bogie. The brake will also be mounted to the shaft driving the chain and the caliper in a similar way. I am still working on the cad models for everything and those should be done over the weekend.

Further research is needed for finding a master cylinder for the brake caliper as well as a reservoir for the brake fluid.

Tuesday, October 11, 2016

10/12/16

This week, I spent time looking at gearing as well as the motor in general. The original idea for the motor was to use one that was 24volts and  200watts. Under the assumptions that the amount of power that could be delivered to the motor was 75 watts, divided up as 24 volts and 3.3amps. The motor could produce a torque of .275Nm. Considering the assumption that the bogies and pod weights 600lbs, the amount of torque needed to turn the 6 inch wheels would have been 35Nm. Meaning that the motor would have to be gear 1:125 just to turn the wheels. The 35Nm doesn't even include the gearing losses, rolling resistance, and bearing frictions, which would bump up the 35Nm to 42Nm.
At this point, there were only two options that could be taken, try and gear down the motor to the point it could turn, or use a larger motor with more power applied. Looking at gearing, there were a few different possibilities, worm gears, planetary gears, and simple gear chains. Worm gears were considered for a time considering the amount of torque they can convert given a limited space. Yet, the problem was that once the motor stopped turning, the wheels would completely lock in place due to the nature of worm gears, which would make braking difficult to do slowly. Using planetary gears would have the benefits of efficient motion conversion. Yet, due to the complex design, and need for specialty gears, it was not an option worth seeking. Finally, with conventional gears, the design is easy enough to create, but using this method to gear down a ratio of over 100:1 wound result in a large gear chain with similarly large gears.
Due to gearing being a rather difficult to produce, I started to look at using a different motor, possibly one that is 48 Volts instead of 24 volts and at a higher amperage, say 9 amps. Under those conditions a 400 watt motor can increase the stall torque to something more reasonable for this project.

Wednesday, October 5, 2016

October 5, 2016

Not much work done this week, had been busy writing a few papers and dealing with other classes.