Gate 4 - Group 4

Revision as of 14:26, 25 November 2012

Gate 4: Product Explanation

Purpose

Nearing the end of our course project, the next step in our product-analyzing process is the reassembly of our drill. We documented each step as we put the product back together, and presented the steps in a way such that anybody could follow its directions to reassemble the drill. Afterwards we were able to make a few detailed conclusions about our product, including a discussion about a major mechanism found inside, and recommendations for design revisions at a system level.

Project Management: Critical Project Review

Cause for Corrective Action

Our goup management has not been confronted with any new, unexpected problems, in addition to those mentioned in previous gates. We have concluded how extremely difficult it is for all four members to meet together outside of class time, due to personal schedules, yet we have still succeeded in combining our efforts to complete project work. While keeping in close contact via email and text messaging, we have found it most beneficial to evenly distribute the work amongst the group members, by collectively determining who is best suited to complete certain tasks. While each member has had their schedules filled with other homework, exams, and working several days a week, careful planning and time management has proven beneficial for the completetion of gates thus far.

Product Archaeology: Reassembly

Step #	Descriptive Action	Tool Used (If Any)	Difficulty	Image Guide
1	Remove detachable support side handle from tool, by twisting handle in a counter-clockwise motion to loosen its grip.	none	1
2	Continue twisting the handle until it completely unscrews and seperates from the lag bolt/clamp.	none	1
3	Remove the 1/2" x 4" lag bolt from the circular clamp by simply sliding it out.	none	1
4	Remove three (3) screws from back of drill handle.	Torx t-15 screwdriver	3
5	Remove the rear casing from the back of the handle.	none	1
6	Remove front two (2) screws from the top of the gearbox casing. (front end of drill)	Torx t-15 screwdriver	3
7	Remove front screw from the bottom of the gearbox casing. (front end of drill)	Torx t-15 screwdriver	3
8	Slide the chuck* assembly and gearbox casing off from the front end, revealing the gearbox assembly.	none	2
9	Remove the gasket ("o-ring") from the gearbox assembly.	none	1
10	Remove relatively short-lengthed shaft (has two gears located on it) from the gearbox assembly.	none	1
11	Remove the single ball-bearing from the rear end of the shaft removed in the previous step. (step 10)	none	1
12	Slide the Hammer/Drill operation selector switch out from the top of the drill.	none	1
13	Remove two (2) screws from the rear end motor.	Torx t-10 screwdriver	4
14	Remove two (2) outside parts of the motor assembly.	none	2
15	Slide the trigger assembly/electrical power cord out from the handle casing.	none	1
16	Remove the positive (+) and negative (-) wires for the motor.	none	2
17	Remove the positive (+) and negative (-) wires for rear motor power terminals. (reverse)	none	2
18	Remove the trigger assembly/ electrical power cord from the entire assembly.	none	1
19	Slide the motor shaft out from the motor assembly.	none	2
20	Remove the black plastic collar from the frontside of the motor housing.	none	2
21	Remove the two (2) coarse-thread screws from the inside of the motor housing.	Torx t-10 screwdriver	3
22	Remove the outside of the motor from the casing.	none	2

Product Archaeology: Mechanisms

The gear system found inside our product is an important mechanism that plays a major role in the function of this drill. Its purpose is to transfer the rotational energy of the motor to the rotational energy of the chuck/bit, by changing the RPM. The motor produces the correct amount of power required for the drill, but the rotational speed needs to be changed to acquire the correct amount of torque. In Gate 3 we completed an analysis on the design of this gear train, which helped give us a better understanding of its functionality and purpose.

Assembly Drawings

n = number of teeth on gear

As the motor transfers electrical energy into mechanical energy, it rotates the armature at a very high RPM (near 30,000), much too fast for the chuck/drill bit to turn. Therefore, the use of a simple gear system is required to "step down" the input (armature) speed to the output (drill bit) speed. The typical drill bit speed of a hammerdrill ranges from 1100 to 3000 RPM, so the designers had to calculate the gear sizes required to accurately step down the motor speed to this range of output speeds.

This gear system works by changing the rotational speed from the armature, to a shaft, then to the output chuck. They are connected in order by meshing gears that contain different numbers of teeth. Going from a gear with a low number of teeth to a gear with a high number of teeth will decrease or "step down" the RPM's, because one full rotation of the first gear will result in only a fraction of a rotation in the second (dependent on the teeth ratio). The opposite is true for two gears that go from a high number of teeth to a lower number. In our case, the armature gives an input speed of approximately 30,000 RPM and has a gear with 5 teeth on it. This gear meshes with a gear of 31 teeth. With such a large gear tooth ratio, the rotational speed is stepped down to around 5,000 RPM. On the same shaft holding gear #2 is also a third gear, which roates at the same RPM despite having a different number of teeth. Therefore, we can mesh this third gear with a fourth gear (which is directly connected to the chuck assembly), giving a final step down to our output speed. Listed below are two equations required for the design of this mechanism:

• (w2)/(w1) = (n1)/(n2)

Where: w = the rotational speed in RPM

n = the number of teeth on the gear

• Overall Gear Ratio = (Output Rate)/(Input Rate)

Product Archaeology: Design Revisions