2011 - Volume #35, Issue #4, Page #20[ Sample Stories From This Issue | List of All Stories In This Issue | Print this story | Read this issue]
Robotic Tug Can Pull Trailer, Power His House
"I like building things with multiple uses," says Visser. "When my teenage son and I decided to build a robotic tug, I wanted it to do more than just pull a trailer."
An older Coleman generator provides power for the tug. Driven by a 6.2 hp Briggs and Stratton engine, the generator puts out around 4.5 kW. Power is fed directly to two 1.0 hp, 220-volt AC motors.
"The motors are mechanical drive with high starting torque," says Visser. "They have so much torque that we had to increase our drive gear size and rebuild the boxes. We broke one of the gears in half."
Most of the frame is composed of 1-in. sq. tubing with some 1-in. round tubing and 10 and 11-gauge steel plate. The tug itself is only about 4 ft. by 3 1/2 ft. and about 4 ft. high, but weighs 550 lbs.
The main frame of the tug ties everything together. Drive wheels mount to the main frame with spindles from a 1979 Chevette. Front caster wheels, with their 600-lb. weight limit, are mounted to a collapsing spring. A kneel bar protects the caster wheels if the tug drops off an edge or if the tug is lifting something heavy.
"We drove the tug off a 6-in. drop and when it hit the sod, the kneel bar took out an 8-in. deep chunk in the lawn," says Visser. "The caster wheels had collapsed up and behind it."
The kneel bar is also needed if another structural element is put to use ű an armor-plated front end. The 10-gauge steel plate pivots on the lawn tractor's front axle. Visser designed it for dual purpose as well. Linkage allows it to be used like the blade on a bulldozer to slowly raise or lower the bottom edge of the plate up to 18 in. off the ground. Or it can be set to trigger with substantial force.
"It's articulated with a large suspension spring from a mid-sized car," explains Visser. "You can replace the linkage with flexible cable and a latch. Then if you strike the center of the blade, it springs loose. It can throw another robot through the air or would easily lift a car off the ground. We stretched a 3-ton rated ball joint with it."
The armor plate and its supports can be removed from the main frame as a single component. It alone accounts for 175 lbs. of the total weight.
The final structural element is the motor/generator sub frame. It's mounted to the main frame on rubber connectors. They protect the main frame from generator-produced vibrations.
Although Visser and his son built the tug largely for fun, it really is multi-purpose. He can plug power tools, a compressor or a welder into a pair of 110 or 220 outlets. If the tools are on wheels, the tug can pull them to the work site and then supply power. Visser also uses the tug as a drive unit when groups visit the farm.
"It can easily tow 10 adults at 2 1/2 mph on the trailer," he says.
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