Control Engineering

Paul Grayson

Electric Power
May 14, 2008

HUNTING AGV TECHNOLOGY
The promise of this column was that you would get to look over my shoulder as I chopped my way through the jungle of technical information searching for examples of useful Automated Vehicle technology. Here is an update on what leads I have been investigating the past few days. I have been looking at two companies that have interesting bits of technology in their products that look promising and may point toward useful technology for Automated Vehicles. The first is Jacobsen who is producing a golf course greens mower that is all electric. The second is E-Z-Go which is producing a golf car that is driven by an AC motor.  Both of these stand out as remarkable departures from the traditional way of dong things in the golf industry. Other break through innovations are promised in 2009 such as hybrid drive and alternative fuel capability.

JACOBSEN E-Plex II Electric Greens Mower 88117 - Power Steering, EC
• Motors
Drive Motor . . . . . . . .. 48 volt DC, 3.5 hp (2.6kW)
Reel Motors . . . . . . . . 48 volt DC, 0.5 hp (0.4 kW) 
Steering Motor . . . . . . 48 volt DC, 0.5 hp (0.4 kW)
• Speed (maximum):
Transport . . . . . . . . . . . . . . . . . . 7.5 mph (12 km/h)
Mowing . . . . . . . . . . . . . .. . . . . . . 4 mph (6.4 km/h)
• Dimensions:
Width Of Cut . . . . . . . . . . . . . . . .  . . 62", (1.6 m)
Overall Width (w/reels) . . . . . . . . . . . 75", (1.9 m)
Overall Length (w/reels & catchers). 102", (2.6 m)
Height . . . . . . . . . . . . . . . . . . . . .  . . 55", (1.4 m)
Wheel Base . . . . . . . . . . . . . . . . .  . . 54", (1.37 m)
Wheel Tread (width) . . . . . . . . . .  . 51.6", (1.3 m)
Weight w/reels . . . . . . . . . . .  . 1,706 lbs., (773 kg) 
Eight Trojan T-145 Batteries . . .  576 lbs., (264 kg)
• Battery Requirements . . . . . . . eight golf car type,
deep cycle lead-acid 6–volt, with minimum 217 Amp Hour rating
• Max. Battery Size:
Height (including posts) . . . . . . . . 11-5/8", (295mm)
Width . . . . . . . . . . . . . . . . . . . .  7- 3/16", (183mm)
Length . . . . . . . .  . . . . . . . . . . . . 10-3/8", (264mm)
• Tires: . . . . . . . 20 x 10.00–10, 2–ply, smooth tread

ELECTRONIC TRACTION CONTROL SYSTEM
The E–Plex II is equipped with an electronic closed loop traction control system which utilizes a microprocessor and software to regulate speed and optimize the drive ability of the unit.  A speed sensor in the drive motor reports the exact vehicle speed to the controller which electronically controls the drive motor to maintain a smooth and constant speed whether the unit is going uphill or downhill.  When the direction/speed pedal is returned to neutral, the controller electrically brakes the motor to bring the unit to a stop.  If the unit begins to over–speed, the controller uses regenerative braking by turning the drive motor into a generator and putting energy back into the battery pack.  The traction control system also provides holding torque to prevent the unit from coasting down hill, even if the operator is not in the seat.  However, using the traction control system to creep down a long steep hill may overheat and/or shorten the life of the drive motor.  There is a parking brake to set before leaving the unit.  The traction system controller is fully programmable, by utilizing a hand-held programmer.  Functions such as acceleration, deceleration, throttle response, speed limits, etc. may be adjusted to the operator’s preferences.  

ELECTRIC  POWER STEERING
The power steering on the E-PLEX II 88117 model is a marine grade gear motor turning a sprocket which is linked to the much larger sprocket on the guide wheel by #40 roller chain.  A sensor follows steering wheel movement and through a controller, controls the movement of the steering motor.  Electric steering and electric drive are simplify the problems of adapting the machine for control by a computer.



E-Z-Go FREEDOM RXV Golf Car/Neighborhood Vehicle http://www.ezgo.com/rxv/
Chassis & Frame: Welded steel with DuraShield™ epoxy coating
Body Injection Molded TPO 
Standard Color Forest Green/Ivory
Overall Length 94.5 in (240 cm)
Overall Width 47.0 in (119 cm)
Overall Height with canopy: 68.5 in (174 cm) (top of sun canopy)
Wheel Base 65.7 in (167 cm)
Front Wheel Track 35.5 in (90 cm)
Rear Wheel Track 38.0 in (97 cm)
Ground Clearance (at differential) 4.5 in (11 cm)
PowerPower Source 48-volt DC
Motor Type 48-volt AC
Horsepower (kW) 4.4 hp (3.3 kW) continuous
Electric System 48-volt
Batteries (qty/type) Four, 12-volt deep cycle
Battery Charger 48 V PowerWise QE high frequency, UL and CSA
Speed Controller 235 amp AC controller
Drive Train Motor shaft direct drive
Transaxle Limited slip differential
Gear Selection Key Switch
Rear Axle Ratio 16.99:1
Performance Seating Capacity 2-person
Curb Weight 935 lb (425 kg)
Vehicle Load Capacity 800 lb (360 kg)
Outside Clearance Circle 19.2 ft (5.8 m)
Ground Speed level ground 17.5-19.5 mph (28-31 kph)
Towing Capacity 3 golf cars with approved permanent tow bar 

OBSERVATIONS
The AC electric drive is 30% more efficient than previous all-DC models of E-Z-GO golf cars and utility vehicles. The improved efficiency can be used to extend battery range, or to use smaller batteries, which would reduce weight and cost. Each 18 hole golf course has about 100 golf cars so any savings are multiplied. While electric carts are already very economical, a 30% improvement puts them even farther ahead of gasoline powered golf cars. There are no brakes in the wheels... the service brake is the spring/magnetic motor brake, dynamic braking, and regenerative braking. The motor brake serves also as the parking brake. Overall the vehicle now has 350 fewer parts making it that much less expensive to manufacture. List price is $6,550 which is typical for a golf car / community vehicle.

GO ROBOTS !

Paul F. Grayson - Chief Engineer
AMERICAN INDUSTRIAL MAGIC, LLC
Racing to build technology that saves soldier's lives.
390 4-Mile Rd. S.
Traverse City, MI 49686-8411
(231) 946-0187, (231) 883-4463 Cell
pgrayson@aimagic.org
AIM: http://aimagic.org
Robot Club: http://tech.groups.yahoo.com/group/robotcluboftraversecitymi/
CE Magazine: http://www.controleng.com/blog/1180000318.html

Posted by Paul Grayson on May 14, 2008 | Comments (0)