3.2 Steer Design. A. Concept Development & Selection Process. B. Configuration Summary

Transcription

1 3. Steer Deign A. Concept Development & Selection Proce The teering ytem for the RP1 motor module ha undergone ignificant deign improvement. The team elected to move forward with a timing belt drive ytem for teering a a reult of the concept development proce, the Concept Deign Review and related feedback. Thi deciion eliminated many concern brought forward in benchmarking pat iteration within the RP family, while maintaining critical cutomer requirement uch a ynchronou operation and the capability for infinite teering. At the ame time, however, everal iue and rik remain to be conidered. The current deign i depicted in Figure 3..1, with detail to follow. B. Configuration Summary Figure 3..1: Current Steering Sytem Deign The choen configuration incorporate a bearing-upported drive haft from the elevated teering motor to the driver timing pulley. The driven timing pulley i fixed to the lower yoke aembly, through the turntable, maintaining unobtructed belt operation during rotation. The turntable bearing provide upport and capability of rotation to the motor module upertructure

2 C. Rik Aement & Critical Deign Checkpoint What follow i an analyi of the teering ytem deign, in term of 4 rik area and potential roadblock. Alo included are critical deign checkpoint, which the team eek to reolve with input from the cutomer and Sytem Deign Review panel member. 1. Belt Tenioning The firt concern that reult from the deign deciion to ue a belt ytem i the iue of belt tenion. Figure 3..1 how the team propoed olution to thi problem. The Bearing Houing & Belt Tenion Sytem i attached to the platform uing two #6 crew, one of which ride in a lot machined into the platform urface. With the tationary crew looely in place, the belt can be put into poition on the two pulley, and the Tenion Sytem can then be rotated along the lot, and tightened into poition, with appropriate belt tenion. Thi deign i imple and effective, allowing rapid aembly/diaembly, though it doe introduce an extra degree of complexity. There are alo potential roadblock in requiring a lot in the platform for the both the crew and the leeve of the journal bearing. Thi could jeopardize the tructural integrity of the platform. A the deign mature, thee concern will be addreed through appropriate tre imulation. *!* Critical Steer Deign Checkpoint #1 *!* Belt Tenioning. Side Load Concern Directly related to the iue of belt tenioning i the reulting ide load that will be introduced to the teer motor drive haft. Though no manufacturer pecification wa identified, a bearing upport for the haft wa incorporated into the Bearing Houing & Belt Tenion Sytem previouly mentioned and hown in Figure 1. Calculation have yet to be performed that will etablih the amount of ide load that the motor haft will experience, though evaluating thi information once it i obtained remain in quetion. *!* Critical Steer Deign Checkpoint # *!* Side Load Concern 3. Driven Steer Pulley Connection A eriou deign concern i in the connection between the driven timing pulley and the lower yoke aembly. Currently, thi i planned to be done by machining a three-hole pattern in the face of the pulley hub, which will extend down through the center hole of the turntable (Figure 3..1). Screw will be ued with appropriate pacer to fix the pulley to the lower yoke plate, maintaining alignment with the driver pulley. Thi i a topic of interet that the team eek to gather input and feedback on poible direction. The concern exit in the integrity of the connection, in it capability to tranmit torque effectively from the motor to the lower yoke without interfering with the drive haft which will rotate independently inide the pulley. *!* Critical Steer Deign Checkpoint #3 *!* Driven Steer Pulley Connection - 9 -

3 4. Turntable The turntable remain a omewhat of an anomaly to the RP1 team. The team i not atified with the quality of the turntable that wa provided in the Baeline Kit. However, a wa dicued in the context of the Concept Deign Review, the next tep up cot omething like $800. The turntable eem to be a chief rik to the ucce of the RP1. Barring a product that the team ha not been able to locate (which would be welcome new), deign of a cutom-made turntable bearing of ort may need to be undertaken. At it wort, the turntable ha the potential to introduce ignificant lop to the mechanical ytem, affecting the robot linear travel, teering capability, and overall profeional appearance. At bet, the motor module deign may have the ability to aborb the lop of the bearing and it may erve it intended purpoe well. *!* Critical Steer Deign Checkpoint #4 *!* Turntable D. Calculation Several important calculation have been performed to characterize the behavior of the teering ytem, including crubbing torque, motor RP and torque baed on requirement at the wheel of RP1, a well a motor RP and torque baed on the motor provided in the Baeline Kit. a. Scrubbing Torque Scrubbing torque i one of the two chief contributor to the force that the teering motor mut be able to overcome in order to operate. The other i the friction in the turntable bearing, which ha been neglected for the purpoe of thi analyi. Scrubbing torque i defined a the torque required to twit a ingle wheel about it vertical axi 1. A more complete explanation can be found in the reference, which give Equation 1 hown below. The derivation i performed a hown, arriving at the final ueful form given by Equation 4. = 4µ B / b 0 0 x + y p( x) dxdy Equation 1.6RB B / b 0 0 x + y dxdy Equation Converting to polar coordinate: π b + ( B ).6 r drdθ RB Equation 3.6RB π 6 b + ( B ) Equation

4 Uing the crubbing torque expreion of Equation 4 and the parameter defined a in Table 3..1, the crubbing torque ha been predicted for a ingle RP1 motor module. Table 3..1: Parameter of Interet and Calculated Scrubbing Torque D wheel m R wheel m B (wheel width) 0.05 m b (contact patch) m β 0.3 Correction factor for even preure ditribution aumption µ 0.8 Coefficient of Friction (rubber to dry concrete) Total Platform a 9.18 kg Normal Force.5 N N-m b. otor analyi A per cutomer requet, calculation for torque and rpm delivered to the wheel for teering have been performed uing the motor indicated in the Baeline Kit, citing it maximum operating efficiency. A ummary of reult i hown in Table 3.. Table 3..: Drive Sytem Performance at aximum otor Efficiency η Gear train efficiency N 1:3 -- Gear Ratio T motor N-m RP motor RP T wheel N-m RP wheel rpm Angular peed deg/ Thee reult preent an additional critical deign conideration: the teering motor. It i clear from a comparion of Table 3..1 and 3.. that the teering motor of the Baeline Kit i vatly overpowered, and it i unlikely that it will ever be able to operate at it maximum efficiency, due to it intermittent ervice. Alo, the angular peed at the wheel will mot likely need to be down-regulated by the control oftware to mooth out the motor operation. Thi would ugget looking for a new teering motor, but a could be expected, budget conideration come into play. *!* Critical Steer Deign Checkpoint #5 *!* Steering otor

5 E. Preliminary Bill of aterial Table 3..3: Preliminary Bill of aterial Item Code Vendor Decription Unit Unit Price Qty/ Price/ Pulley K44 cater iniature xl Serie A Belt Pulley for 3/16" & Ea $ $9.60 Driver Width,.740" OD, T iniature xl Serie Alum -Belt Pulley Pulley K57 cater for 3/16" and 1/4" Driven Belt Width, OD, 60 Teeth Ea $ $13.95 Belt Steering otor 7887K75 GH-15 cater Lynxotion Turntable 6031K16 cater xl Serie Neoprene Rubber Belt.08" Pitch, 64 Trade Sz, 6.4" Outer Circle, 1/4" W 1vdc 30:1 00rpm (6mm haft) Corroion-Reitant Turntable Galvanized, 3" Square, 00 Pound Load Capacity Ea $.94 1 $.94 Ea $ $39.95 Ea $ $1.87 $