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Grove TM9120 Outrigger Design.

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1) Vertical Ram Design:

The real TM9120's rams allow for 1.5 inches of vertical travel, at 9.2:1 scale. My solution was to use large diameter Exacto shafts for the rams, and a block and tackle type 4:1 pulley system to get a 4x mechanical advantage. 80lb breaking strain Dacron fishing line (that's to John Hornsby for suggesting the Dacron) is therefore pulled over a 6 inch movement to achieve the required ram movement. The design goal was for each ram to be able of lifting 50lb with ease (1/4 of 200lb, the estimated weight of the finished model).

	The vertical lift ram and 'foot'. In the final implementation, I will add pressure sensors inside each foot, electrically connected back to the microprocessor in each ram, so that true vertical lift can be achieved without excessive stress on the chassis. Electronic components will supply feedback on the tilt of the chassis compared to gravity and hence with computer control it should be possible to auto level the truck, and hence the turntable.
	The vertical lift ram fully retracted.
	And fully extended. 1.5" of movement.
	Taking the top cover off reveals the winding pulley system for torque reduction. You can see the return spring as well. The pulley scheme gives a symmetrical downward pull on the Exacto large diameter rod (piston), preventing bending forces being applied.
	And from the other direction....
	The ram assembly and middle jacket separated.

2) Outrigger Extension Arm Design:

A rack and pinion scheme is used to drive the arm in and out of the outrigger box. Two electrical connections are provided, plus the arm's metal acting as electrical ground. All power to the vertical and horizontal drive motors will be passed through thee connections, as well as a digital control signal to the microprocessor that will be used in each outrigger arm.

	The vertical lift ram is attached to the Outrigger arm. The motor shown (from Geoff Wright's MW models shop ~10 years ago) elevates the stabilizer arm. Part of the Outrigger arm box structure (one of the L girders is removed to show detail in the following photographs).
	Initial pinion gear reduction followed by worm and pinion drive to the winding drum. There is no power fed through a rod - every drive gear is mechanically linked to the next part of the gear train, so that it cannot come undone.
	The vertical lift ram shown from the top of the Outrigger arm, showing the lift cable path.
	And from the underside, showing the rack and pinion drive pinion (bottom left end of arm).
	The horizontal drive motor. The motor is heavily geared internally, so all I need is a contrate drive to some 19 tooth pinions, to get the motive power to the rack's drive pinion.
	The electrical contact arms, at the rear of the outrigger arm. These are sprung, and allow for some small amount of angular freedom in all 3 degrees of movement, to ensure both contacts (brass collars) touch their respective contact strips. At this point in time, no electronics is built, so wires hang from this, the first of the 4 Outrigger arms.

3) Outrigger Box Design:

Not actually built yet, but the Solidworks 3D CAD model shows it should work....

	CAD model showing the front Outrigger unit, with outriggers fully retracted.
	CAD model showing the front Outrigger unit, with outriggers fully extended.
	the inside 'guts' of the Outrigger Box. Rack strips are attached to the topside and insulated contact strips to the bottom side. in theory, it all works!
	The dual insulated narrow strip contact strips, mounted to the Outrigger box by assemblies comprising 260f brackets, 260d plastic pins and 59b soft plastic collars.

Last Updated: February 18, 2010