ME3200Practice Questions 5.(15 pts) esign an active low-pass filter with a gain of 5 and a time constant of 50 msec. Use realistic values as were used in lab. 6. (8 pts) A pressure sensor is made by gluing four strain gauges on a steel diaphragm. As the diaphragm deflects under pressure, the strain is sensed by the gauges configured in a full Wheatstone bridge. The pressure sensor has been working fine with an output of 2 mv for full pressure. The sensor sat on the shelve for a year and then was tested again. This time the sensor had an offset of 8 mv (before it was balanced) and the sensitivity was reduced. What do you think happened to the pressure sensor? 4. (15 pts) Find the relationship between Vout and V1 and V2. (Solve for Vout.) R1 = 10 KΩ R2 = 20 KΩ R2 R1 V1 V2 - + Vout R1 R2
4. rive the relationship for the output as a function of the input for the following operational amplifier circuit. R2 Vin R1-2 Vout + 2. Write the equation relating Vout to Vin. R3 Vin R2 R1 - + Vout
3. What is the angular velocity of gear? The angular velocity of gear A is 1000 rpm clockwise. NA= 30, N= 20, N= 26, NF= 70. Gears and F are ring gears. 4. What is the output speed and direction of gear J? Gear A is the input at a speed of 10,000 rpm clockwise as seen from the left. A and are spur gears, and are helical gears, E and F are bevel gears, G and H are chain sprockets, I and J are worm gears. The number of teeth for each are indicated. 40 18 F 36 3 I Output Input 20 A 48 18 E 36 J 20 G 48 H
7. A differential can be treated in the same manner as a planetary gear train (they are kinematically the same). For the differential shown, what is the angular velocity of gear if the velocity of gear A is 30 rpm cw as seen from the left and the velocity of shaft,, is 40 rpm ccw? NA = N = 32, N = 24 A 3. (15 pts) What is the angular velocity of gear? The angular velocity of the input, planet carrier, A, is 1000 rpm clockwise as seen from the left (arrow). N= 20, N= 26, NF= 70. The two ring gears, F, are the same size and are rigidly connected and rotate at 200 rpm counter clockwise. Input Output
4. (10 pts) The gearing of a bicycle is described in terms of the size of an equivalent single wheel directly connected to the pedals. This is a carryover from the old bigwheeled bicycles called ordinaries or penny-farthings that you may have seen in old pictures where the pedals were directly attached to the wheel without any chains or gearing. Modern bicycles with chain drives enable smaller wheels to be used. However, the gear ratios of modern bicycles is still given in terms of the old direct drive bicycles. A modern bicycle set at a gearing of 70 inches would travel the same distance as an oldfashioned bicycle with a single 70 inch diameter wheel for each revolution of the pedals. Here is the problem to solve: a human-powered-vehicle (HPV) has a compound gearing shown below. It consists of two stages of chain drives. The first cog has 52 teeth and is attached to the pedals. It drives a cog of 42 teeth which is attached to a cog of 52 teeth. That cog drives a 12 tooth cog that is attached to the 26 inch diameter wheel. What is the equivalent single wheel diameter for this gearing? If the rider were pedaling at a rate of 100 revolutions per minute (cadence of 100), how fast would the bicycle be traveling? The front wheel, seat, and rider are not shown. Pedals 26 in dia 42T 52T 52T 12T
3. (20 pts) For the planetary gear train shown, find the angular velocity of carrier. The angular velocity of the input, A, is 2000 rpm clockwise. N= 20, N= 100. The ring gear,, rotates at 500 rpm counter clockwise. The drawing is not to scale. A If gear A is a 24 pitch gear, What will the center-to-center distances be for gears A,, and? There is a problem with this design. What is it and how would you fix it?
4. (15 pts) What is the speed and direction of the output shaft for the gearing system shown? NA= 20, N= 50, N= 30, N= 15, NE= 40, NF= 25, NG= 48, NH= 64, NI= 2, NJ= 50, ωa = 1000 rpm cw Indicate on the drawing the direction that any thrust bearings must apply force ON the gears or shafts. Output Gear and pulley on a common shaft Toothed elt evel gears H I J Worm Gear F G Helical Gears Spur Gears E A Input 7. (10 pts) What motor(s) would you choose to power an electric automobile. Explain your choice. 4. It is desired to have a maximum lift of 1 inch of the follower when a cam is made a 180 rotation. No other specifications are given. escribe the follower lift profile that you would use and justify your design. Make any sketches required to explain your design. 4. (25 pts) It is desired to use a load cell to measure the tension is a cable. A piece of aluminum (E = 10x10 6 psi) with a cross sectional area of.1 in 2 is used and is placed so that it is in tension on the cable. There is room to place two strain gages on the loadcell. If the gages are nominally 120Ω, gage factor of 2, the excitation voltage is 5V, and the output of the bridge is.5 mv, what is the tension in the cable? How can the sensitivity (voltage output as a function of tension) be increased? Give at least one advantage and one disadvantage for your method of increasing the sensitivity.
1. A dynamometer such as the one that you built in the laboratory has the outputs shown. The speed was measured with a tachometer whose gain is 2V/1000rpm. The torque was measured with a cantilever-type load cell of dimensions 5 mm thick by 10 mm wide by 100 mm long (from strain gauges to load application) made of 6061T6 aluminum (E=70GPa). The moment arm of the brake-to-load application point is 100 mm. Two strain gauges were used, one on the top and one on the bottom. Each has a gauge factor of 2 and a resistance of 120 Ω. The Wheatstone bridge was completed with 120 Ω resistors and had a 5 V excitation. The resulting torque-speed curve is shown. Note that the torque is given as the voltage output from the bridge and the speed is given as the voltage from the tachometer. Vtorque 0.214 mv 0 0 3.0 V Vtach Answer the following questions: What is the stall torque? What is the no-load speed? Is the load cell temperature compensated?
What is the motor power at half of the no-load speed? What all of the types of motors could produce this torque-speed curve?