Warner-Swasey HOPTO 900A EXCAVATOR

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Hopto 900A
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Of all Construction equipment, during the last 40 years, the excavator has come to to be the general purpose machine. When a thumb is installed (to provide opposition to the bucket) these machines will do almost anything, but there are a few things you shouldn't do with them, and the photos at the bottom of the page will show at least one such thing. As excavators go this is a fairly old model manufactured probably in the late 1960's. It is a transitional model in the sense that it is of a hybrid drive. You should bear in mind that the classic way to drive a machine like this on tracks is via a mechanical shaft down through the center and thence to bevel gears on cross shafts to sprockets and finally with chains to the drive sprocket. This machine is a hydraulic drive but still uses most of the classic drive train. The motors are in the front of the carbody and have a gear reduction on them. That in turn rotates a shaft that reaches in to the same bevel gear that was used in the center to pick up on the 'down the center' drive. Newer machines dumped all this Rube Goldberg linkages and put hydraulic motors directly on the drive sprocket. Also this machine uses low pressure hydraulics and has all manual hydraulic controls. This means that it works very smoothly, but requires a lot more physical effort on the part of the operator as the operator must pull a lever to crack the main spool valves instead of merely activation a servo control unit. This machine is powered by a relatively rare Detroit Diesel 8V53 engine. Many people have not even realized that Detroit made that engine configuration.

Excavator Design Evolution

The first excavator backhoe this writer ever saw was of the cable controlled variety. It was a backhoe front mounted on what was then a more or less standard track crane chassis which would take a lattice boom or a 'shovel front' equally well. The two cables customary of a crane were connected to the respective ends of the stick and controlled the extension and retraction of the stick. There was no bucket action. If the spoil was to be hauled off the dump truck driver had to be coordinated with the machine operator and drive forward as the stick was extended to catch the spoils as they fell free.

Block and skid steer, hook roll turntable, all cable control. It was only removed from being a 'steam shovel' in that it used a diesel engine instead of steam for power. Then innovation gradually lead this type of machine toward hydraulic controls from mechanical and cable controls. Some time later I saw a cable backhoe with a hydraulic bucket. This transitional design provided the bucket roll up action but still used cable control for the main functions. Understand that it takes 3 arms and 2 legs to operation one of these cable machines. One hand on each drive clutch for the respective winchers, one foot on each brake to hold the line once wound and your third arm on the swing lever to swing the machine, and all of this must be done in a coordinated fashion.

Warney-Swasey with their Hopto was one of the early adopters of using hydraulics. The hydraulic motors in the lower unit meant that only two hydraulic circuits had to pass the 'circle' and go downstairs. One circuit was provided for reach track and the brakes were spring set, hydraulic released so they needed no control. The same hydraulic pressure that turned the motors also backed off the brake bands. A two speed drive was provided by actually having 2 hydraulic motors on each drive unit. A lever on the lower unit would make the change. In 'low gear' oil was split and went through both motors, and in 'hi-gear' the calving was changed so that the oil went all into one motor and then to the second motor.

Systems today, of course, use a high pressure hydraulic system with the motor directly in the sprocket (or very near there with a gear reduction). For more on this see the article on the American 35.

Warner & Hopto H-900
Engine Detroit 8V-53 rated 235 HP @ 2400 RAM
Hydraulic System Triple Tandem 170 GAM @ 2400 RAM
Pressure 1600 PSI and 2400 PSI
Weight 76,780 lbs less bucket and fuel
digging depth 26 feet
Hopto 900

The boom is optimized in configuration for working inside of shoring. It is purposely built very close to the ground which is fine for digging holes and likewise it is particularly easy for the operator to get in and out of. It is most unsuitable for soft ground because with only about 10 inches of ground clearance it quickly mires down even with 30" pads (compare this to the CAT 330). The flat pad tracks are not suited for uneven ground and in summary, this machine is best used on hard flat surfaces. The thumb makes the machine very adept at digging stumps. Even stumps several feet in diameter can be dug loose and disposed of by pinching them between the bucket and the thumb.

I don't know what these things sold new for, but large excavators have gotten pricey. For example the sticker price on a Cat 325B LA which is a 52,000 lb machine (one size class smaller with a 177 hep engine and a 23 foot digging depth) is around $275,000. The new ones have, or course, added a lot of intelligence to them. The trend is to use variable displacement pumps and an interconnected throttle, so instead of pumping oil whether you need it or not, and setting an engine speed with a throttle, the operator sets a 'performance level' and logic in the variable displacement hydraulics throttles the engine as needed to provide the oil requirements, which saves fuel and wear and tear on things.

Although no longer made, the company who is successor to Warner-Swasey is the Badger Equipment Co.

What Not to Do

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This old machines didn't have the best brakes in the world. When parking it is best to leave the bucket in the hole, so if the brakes slip the machine can't get in the hole, but here the house was rotated so it would be easy to get out of it, and presto, when we came back the machine had migrated into the hole.

Here we recovered the machine by digging out on the uphill side with another backhoe. Then we put a cable on the excavator which went to a large dozer to stabalize the the machine. Next we started it up and it had oil pressure which was a good thing. From there it was possible to lift the boom and swing the boom around to the down side and level the machine by jacking it on the bucket. From there the machine was able to 'save itself.'

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