Electric stump cutter

Abstract

An electric stump cutter (100) including a base that is supported by and movable along the ground by a plurality of ground engagement members (106). A boom (108) is movably supported by the base (104) and configured for sweeping and tilting movements with respect to the base (104). A cutter wheel (102) supported at a distal end of the boom (108) and rotatable relative to the boom (108) to engage and reduce a stump. The plurality of ground engagement members (106) are electrically powered to move the base (104) along the ground, and wherein the cutter wheel (102) is electrically powered to rotate relative to the boom (108).

Description

ELECTRIC STUMP CUTTERCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to co-pending U.S. Provisional Patent Application No. 63 / 627,378, filed January 31, 2024, the entire contents of which are incorporated by reference herein.BACKGROUND

[0002] The present invention relates to machines for material reduction of tree stumps by cutting and / or grinding.

[0003] Conventional stump cutters are well known. These machines commonly include a rotating cutter wheel driven by a prime mover (e.g., a gas or diesel engine). The cutter wheel, while rotating, is advanced toward the stump and moved laterally across the face of the stump to reduce the stump material by cutting and / or grinding. Often, the cutter wheel is automatically advanced across the face of the stump in a sweeping motion. The cutter wheel is mounted to one end of a boom which is, in turn, pivotally mounted on a support frame. Hydraulic boom swing cylinders are used to pivot the boom about the pivot point to move the cutter wheel back and forth across the face of the stump to reduce it. Advancing the cutter wheel toward the stump is accomplished by separate hydraulic tilt cylinders that causes the boom to tilt within a vertical plane.

[0004] In some stump cutters, the engine is operably connected to the cutter wheel by belts that facilitate rotation of the cutter wheel. In other stump cutters, the engine powers a hydraulic pump that in turn drives a hydraulic motor coupled to the cutter wheel.SUMMARY

[0005] An electric stump cutter including a base that is supported by and movable along the ground by a plurality of ground engagement members. A boom is movably supported by the base and configured for sweeping and tilting movements with respect to the base. A cutter wheel supported at a distal end of the boom and rotatable relative to the boom to engage and reduce a stump. The plurality of ground engagement members are electrically powered to move the basealong the ground, and wherein the cutter wheel is electrically powered to rotate relative to the boom.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a left side elevation view of an electric stump cutter according to the present disclosure.

[0007] FIG. 2 is a front, top, right perspective view of the electric stump cutter of FIG. 1. A cover or housing is partially removed to illustrate an interior cavity.

[0008] FIG. 3 is a rear, right perspective view of the electric stump cutter of FIG. 1.

[0009] FIG. 4 is a rear, top, left perspective view of the electric stump cutter of FIG. 1.

[0010] FIG. 5 is a front, top, left perspective view of the electric stump cutter of FIG. 1. A cover or housing is partially removed to illustrate the interior cavity.

[0011] FIG. 6 is a top, left perspective view of the electric stump cutter of FIG. 1. A cover or housing is partially removed to illustrate the interior cavity.

[0012] FIG. 7 is a detail perspective view of a control panel of the electric stump cutter of FIG. 1.

[0013] FIG. 8 is detail perspective view of a of the electric stump cutter of FIG. 1. A cover or housing is partially removed to illustrate the interior cavity.

[0014] FIG. 9 is a graph representing an exemplary control scheme for an automatic sweep function of the electric stump cutter.

[0015] FIG. 9A is a graph representing an exemplary control scheme for an automatic sweep function of the electric stump cutter. FIG. 9A illustrates an example in which a threshold pump speed lies within the automatic sweep range, such that a variable relationship between pump speed and cutter wheel speed exists only in a first or upper control range.

[0016] FIG. 9B is a graph representing an exemplary control scheme for an automatic sweep function of the electric stump cutter. FIG. 9B illustrates an example in which the sweep speed during automatic sweep can be varied in relation to cutter wheel speed solely by proportional valve control within a hydraulic manifold, such that the pump runs at a fixed speed throughout the automatic sweep movements.DETAILED DESCRIPTION

[0017] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0018] Figs. 1 to 8 illustrate a stump cutter 100 for materially reducing tree stumps by cutting and / or grinding with a rotatable cutter wheel 102. The stump cutter 100 includes a base 104 that is supported by and movable along the ground by ground engagement members 106 (e.g., tracks). A boom 108 is movably supported by the base 104. In particular, one or more joints at a proximal end of the boom 108 can be configured for sweeping and tilting movements of the boom 108 with respect to the base 104. The cutter wheel 102 is supported at a distal end of the boom 108. As will be appreciated by one of ordinary skill in the art, tilting movements of the boom 108 are used to set the depth of engagement of the cutter wheel 102 with the stump, and sweeping movements of the boom 108 are used to move the cutter wheel 102 across the stump at a particular depth. In this way, the stump is gradually reduced through a plurality of horizontal sweeps or passes, between which the boom 108 is incrementally tilted farther downward. See for example, any of the constructions and boom movements included in U.S. Patent No. 11,612,115 or U.S. Patent No. 8,783,308, both to Vermeer Manufacturing Co., the entire contents of which are incorporated by reference herein. As shown in the drawings, the stump cutter 100 includes a sweep cylinder 128X and a tilt cylinder 128Y configured to, respectively, drive sweep and tilt movements of the boom 108. Each of the sweep and tilt cylinders 128X, 128Y can be a bi-directional hydraulic cylinder.

[0019] The stump cutter 100 can be entirely electrically powered, including one or more electric motors operable to directly or indirectly drive each respective mechanical function of the stump cutter 100. Although the stump cutter 100 may include a hydraulic system for one or more mechanical functions, the hydraulic system may be electrically powered as the stump cutter 100 may be provided without a combustion engine. Correspondingly, the stump cutter 100 can be provided without an on-board fossil fuel tank. A battery system 112 (or “primary” battery) is provided on-board the stump cutter 100. The primary battery 112 can be rechargeable and can supply electrical voltage (e.g., 48 V) for running all mechanical functions of the stump cutter 100. An additional or “secondary” battery 114 can also be provided on the stump cutter 100. The secondary battery 114 can be of lower voltage than the primary battery 112 (e.g., 12 V) and may be configured to power a control system, which may include any / all of: a main controller 150, operator input controls connected to the main controller 150, sensors connected to the main controller 150, indicators connected to the main controller 150, a display 152 connected to the main controller 150, etc. rather than running any mechanical functions of the stump cutter 100. The secondary battery 114 can be charged from the primary battery 112 through a DC-DC converter 164 (Fig. 2A).

[0020] The primary battery 112 can comprise one or a plurality of battery packs, e.g., in a parallel array. In some constructions, the primary battery 112 includes seven identical battery packs. Each battery pack includes a plurality of internal electrochemical cells. Individual battery packs of the primary battery 112 can be individually swappable. As shown in Fig. 1, the primary battery 112 can include a vertical stack of battery packs situated at a rear of the stump cutter 100, opposite the front end having the cutting wheel 102. In some constructions, the primary battery 112 is positioned entirely rearward of a drive axis A of a drive system that powers the ground engagement members 106. As illustrated, each one of the ground engagement members is drivably connected and selectively driven by a corresponding drive member 116 (e.g., sprocket) on the drive axis A. The respective drive members 116 are drivably connected and selectively driven by individually controlled hydraulic drive motors 118 (Figs. 5 and 8) centered on the drive axis A. The hydraulic drive motors 118 are powered by a hydraulic pump 120, which is in turn powered by an electric motor 122, which is in turn powered by the primary battery 112. The electric motor 122 that drives the hydraulic pump 120 may be referred to herein as the “hydraulics electric motor.” A motor controller 124 (e.g., inverter and associated processor) controls the powerdistribution from the primary battery 112 to the hydraulics electric motor 122 in response to the movements of a drive joystick 126. For example, the hydraulics electric motor 122 may be speed controlled by the motor controller 124 in relation to a scaled output on the amount of travel of the joystick 126. The power delivered by the hydraulic drive motors 118 is proportional to flow provided to them by the pump 120. In addition to controlling the pump 120, the flow to the hydraulic drive motors 118 is controlled by respective valves of a hydraulic manifold 130. In an alternate construction, the hydraulic drive motors 118 are replaced by electric drive motors, powered from the primary battery 112 through motor controllers such that the ground drive is allelectric. In such a construction, the hydraulic system may be limited to boom movement control - or the stump cutter 100 can be entirely electric powered by replacing the sweep and tilt cylinders 128X, 128Y with electric actuators (e.g., solenoids, motor and gear train, etc.).

[0021] A total available hydraulic flow is set by control of the hydraulics electric motor 122 (via the motor controller 124), and a portion of the flow is routed to the hydraulic drive motor 118, respectively, by selectively opening the valves of the hydraulic manifold 130 (i.e., separately controlled valves for forward and reverse of each of the separate motors 118). Thus, each of the hydraulic drive motors 118 is drivable at variable speed and reversible by different valve settings. As such, the drive joystick 126 is configured to control forward, rearward, left, and right movements of the ground engaging members 106, and various combinations thereof, at variable speeds within prescribed limits. The drive joystick 126 can include a presence sensor (e.g., capacitive touch sensor, pressure sensor, etc.) that selectively enables the ground drive system to be powered when the joystick 126 is grasped by the operator. A main controller 150 of the stump cutter 100 may also limit operation to exclusively one of the drive joystick 126 and a cutting joystick 132 at one time. The cutting joystick 132 can include a presence sensor (e.g., capacitive touch sensor, pressure sensor, etc.) that selectively enables its operation when the cutting joystick 132 is grasped by the operator. Drive and control of the cutter wheel 102 and the boom 108 are described further below.

[0022] An electric motor 134 is provided at the distal end of the boom 108 and configured to drive the cutter wheel 102 for rotation. The electric motor 134 that drives the cutter wheel 102 may be referred to herein as the “cutter wheel motor.” The cutter wheel motor 134 can have a central rotation axis B that is coaxial with a central rotation axis of the cutter wheel 102 so thatdrive power can be contained to a single axis. As such, drive power (referring to all the mechanical rotating parts, not the electrical power supply) is self-contained at the distal end of the boom 108. The output shaft of the cutter wheel motor 134 can be directly engaged with the cutter wheel 102 or indirectly engaged through one or more couplings, coaxial shafts, etc. In some constructions, at least one coaxial connector shaft is connected between the cutter wheel motor 134 and the cutter wheel 102. The connector shaft can be supported with respect to a bearing housing by one or more bearings external to the cutter wheel motor 134 (e.g., a pair of oppositely angled tapered rolling element bearings). Whether or not the output shaft of the cutter wheel motor 134 is directly or indirectly connected to the cutter wheel 102, the cutter wheel 102 is directly driven by the cutter wheel motor 134 in the sense that there is no mechanism (e.g., clutch) enabling the cutter wheel motor 134 and the cutter wheel 102 to rotate at different speeds. In other words, the running speed of the cutter wheel motor 134 matches the running speed of the cutter wheel 102 at all times. In other constructions, a clutch may be added between the cutter wheel motor 134 and the cutter wheel 102 to enable power interruption therebetween and the ability for the cutter wheel motor 134 and the cutter wheel 102 to have a speed differential.

[0023] In some constructions, not illustrated, the cutter wheel motor 134 can have a central rotation axis that is not coaxial with the cutter wheel 102. Such a construction may enable placement of the center of mass of the cutter wheel motor 134 further rearward on the boom 108. The output of the cutter wheel motor 134 can be parallel to the cutter wheel axis (e.g., offset rearward along the boom 108) or perpendicular to the cutter wheel axis (e.g., generally parallel to the boom 108). The cutter wheel motor 134 can be connected to drive the cutter wheel 102 through one or more gearboxes. As such, the desired orientation of the cutter wheel motor 134 can be selected separate from the position of the cutter wheel 102 on the boom 108. In some constructions, the cutter wheel motor 134 is connected to the cutter wheel 102 through a 90-degree gearbox. In some constructions, the cutter wheel motor 134 is supported on the base 104 rather than the boom 108. If one or more gearboxes or other power transmission devices are used, a drive ratio can be selected to achieve a desired speed / torque relationship between the cutter wheel motor 134 and the cutter wheel 102 so that the selection of the cutter wheel motor 134 is only indirectly dependent on the desired specifications of the cutter wheel 102. For example, the cutter wheel motor 134 can have a maximum speed in excess of the desired cutter wheel maximum speed, anda relatively low stall torque. The drivetrain between the cutter wheel motor 134 and the cutter wheel 102 can be configured to lower the speed and increase torque at the cutter wheel 102.

[0024] As shown in the drawings, the distal end of the boom 108 can include a receptacle or cradle 136 for at least partially receiving the cutter wheel motor 134. For example, the cradle 136 can open toward the bottom such that the cutter wheel motor 134 is assembled to the boom 108 in an upward direction and / or along the axis B. Additionally, a skid plate 138 (Fig. 3) can be provided below the cutter wheel motor 134 to shield the cutter wheel motor 134 from contact with the stump and / or surrounding ground. The skid plate 138 can also clear space when cutting below grade. The skid plate 138 can be constructed of steel or another suitable material, in one or more pieces. The skid plate 138 is separate from a chip skirt that extends downward from the boom 108 rearward of the cutter wheel 102 to contain chips released from the stump.

[0025] A motor controller 140, shown in Figs. 6 and 8, (e.g., inverter and associated processor) controls the power distribution from the primary battery 112 to the cutter wheel motor 134 in response to a cutter wheel engagement switch 142, shown in Fig. 7 (e.g., toggle, push-button, etc.). Running of the cutter wheel motor 134 and the cutter wheel 102 may be selectively enabled on the basis of the cutting joystick 132 being held by the operator. In some constructions, after the operator turns the stump cutter 100 on via a key switch 144, the operator then grasps the cutting joystick 132 and turns on the cutter wheel engagement switch 142 to begin running the cutter wheel 102 (e.g., at a predetermined or adjustable speed). A cutter wheel light 146 then illuminates in response. In some constructions, there is a light 168 (Fig. 7) on the control panel operable to illuminate selectively on the basis of whether or not the cutting joystick 132 detects the operator’s hand thereon. The hydraulics electric motor 122 is activated to a ready state, but may remain dormant (not rotating) until a demand for hydraulic function is received. The drive power to the cutter wheel motor 134 is stopped when either the cutter wheel engagement switch 142 is turned off or the operator lets go of the cutting joystick 132. In either case, the cutter wheel 102 may be braked by the cutter wheel motor 134. Braking may recharge the primary battery 112 through regeneration. Charging the battery 112 through regeneration may be dependent upon charge level and / or temperature of battery 112. In the absence of a clutch or brake between the cutter wheel motor 134 and the cutter wheel 102, overload protection may be provided electronically by the motor controller 140 (e.g., via a programmed amperage limit). A dedicated stop button 160 mayalso be provided in a conspicuous location at the rear of the stump cutter 100 as shown in Fig 2A. The dedicated stop button 160 may be configured to simply cut off all power from the primary battery 112. By cutting off all power from the primary battery 112, the cutter wheel motor 134 cannot be actively controlled and may run out naturally before coming to rest.

[0026] In addition to the primary battery 112 and the respective motor controllers 124, 140, the stump cutter 100 can include a power distribution unit (PDU) 162. In the illustrated construction, the PDU 162 is positioned on a right side of the stump cutter 100, forward of the primary battery 112. The PDU 162 contains two bus bars or “buses”: a first bus that connects the seven +48 V battery cables, and a second bus that connects the seven ground cables. Connected to the 48 V bus are two contactors, which are high amperage switches connected between the 48 V bus bar and each of the motor controllers 124, 140. Connected to the ground bus is a ground cable to each of the two motor controllers 124, 140.

[0027] The hydraulic system including the pump 120, the motor 122, the hydraulic manifold 130, and a hydraulic fluid tank 166 provides four separate hydraulic channels or circuits: left ground drive (left motor 118), right ground drive (right motor 118), sweep cylinder 128X, tilt cylinder 128Y. Two separate valves (e.g., solenoid controlled valves) of the manifold 130 are configured to control each one of the left and right drive motors 118 in response to the drive joystick 126, and two additional valves (e g., solenoid controlled valves) of the manifold 130 are configured to control each one of the sweep and tilt cylinders 128X, 128Y, respectively, in response to the cutting joystick 132. For any given input to either joystick 126, 132, the hydraulics electric motor 122 can be controlled by the motor controller 124 (as directed by the main controller 150) to run at a speed proportional to the joystick input. However, proportional control of the valves of the hydraulic manifold 130 (as directed by the main controller 150) may control the overall hydraulic flow (e.g., working in tandem with variable speed settings of the hydraulics electric motor 122, or proportional valve control at a fixed speed setting of the hydraulics electric motor 122). In some constructions, the valves of the hydraulic manifold can be exclusively set (by the main controller 150) to a 0% (fully closed) or 100% (fully open) flow setting, rather than a range of multiple open positions / settings - whereby the speed of the hydraulics electric motor 122 is exclusively responsible for varying the flow proportional to the movements of the joysticks 126, 132.

[0028] The drive joystick 126 allows free movement in forward, rearward, left, right, and combination directions. However, the cutting joystick 132 can be gated to exclusively allow movement in forward, rearward, left, and right directions. The gated configuration thus only provides four discrete functions, and only one function at any given time. Forward on the cutting joystick 132 can be configured to operate the hydraulics motor 122 and the manifold 130 to make the boom 108 tilt down or lower (e.g., tilt cylinder 128Y extend). Rearward on the cutting joystick 132 can be configured to operate the hydraulics motor 122 and the manifold 130 to make the boom 108 tilt up or raise (e.g., tilt cylinder 128Y retract). Left and right on the cutting joystick 132 can be configured to operate the hydraulics motor 122 and the manifold 130 to make the boom 108 sweep left and right, respectively (e.g., sweep cylinder 128X extend / retract accordingly). As noted above, the hydraulics electric motor 122 can be speed controlled proportional to the amount of movement of the cutting joystick 132. However, the cutting joystick 132 can also be used to engage an automatic sweep movement.

[0029] In response to a predetermined movement of the cutting joystick 132 (e.g., moved left or right at or beyond a predetermined position - such as 100% available travel, 50% available travel, or 25% available travel), the main controller 150 can be programmed to respond by enacting the automatic sweep movement (or “smart sweep” algorithm). See, for example, U.S. Patent No. 6,014,996 or U.S. Patent No. 11,326,655, both to Vermeer Manufacturing Co., the entire contents of which are incorporated by reference herein. As conventionally known, a stump cutter can control its own boom sweep speed in relation to a cutting load detected by the stump cutter - for example, observing the idle speed of the internal combustion engine fall during cutting, and then varying electrical current to a hydraulic valve in control of the sweep cylinder. This automatic speed control of the sweep movement is beneficial to keep the internal combustion engine in a predetermined operating range that maximizes efficiency and reduces premature wear on the cutter wheel 102. The stump cutter 100 of the present disclosure may achieve a similar performance in a different way. When the main controller 150 identifies speed of the cutter wheel motor 134 below a nominal (no load) speed, the main controller 150 can be programmed to direct the motor controller 124 to set a speed of the hydraulic pump 120 (by setting the speed of the hydraulics electric motor 122) in accordance with a stored relationship (i.e., a function or look-up table). An example is shown in Fig. 9. In the illustrated example, the nominal (no load) speed is 1100 rpm. The stored function is a linear function. The linear function covers a prescribed speed zone of thecutter wheel 102 (e.g., from 900 rpm to 1100 rpm). At the bottom boundary of the prescribed speed zone of the cutter wheel (e.g., 900 rpm), the hydraulic pump speed is zero - in other words, the boom 108 will not sweep due to lack of hydraulic flow to the sweep cylinder 128X. This may be in spite of the hydraulic circuit being opened by the corresponding valve of the manifold 130. Within the prescribed speed zone, the hydraulic pump speed is set in accordance with the actual cutter wheel speed resulting from engagement of the cutter wheel 102 on the stump. Maximum hydraulic pump speed (and resulting sweep speed) is achieved when there is effectively no cutting load, as indicated by the cutter wheel motor 134 operating at the nominal (no load) speed (e.g., 1100 rpm).

[0030] In some constructions, operation of the valves of the hydraulic manifold 130 may be dependent upon a fluid pressure of at least a threshold value (e g., 35 bar in order to supply adequate pilot pressure for valve actuation), and this corresponds to a threshold pump speed. In one example, the threshold pump speed may be about 1060 rpm. Fig. 9A illustrates an example in which the threshold pump speed of the hydraulic pump 120 (also speed of the hydraulics electric motor 122) lies within the automatic sweep range. As such, the variable relationship between pump speed and cutter wheel speed may exist only in a first or upper control range. In a second or lower control range, the pump speed may be maintained at or near the speed corresponding to the threshold fluid pressure value, while the sweep speed is further reduced, as needed based on cutter wheel speed, by proportional valve control within the hydraulic manifold 130.

[0031] In yet other constructions, as illustrated by Fig. 9B, the sweep speed during automatic sweep can be varied in relation to cutter wheel speed solely by proportional valve control within the hydraulic manifold 130. In other words, the hydraulics electric motor 122 may run the pump 120 at a fixed speed throughout the automatic sweep movements. The objective of reducing sweep speed for lower observed cutter wheel speeds is met by the main controller 150 identifying and setting a reduced (partially closed) valve setting for the valve of the hydraulic manifold 130 that controls the sweep movement. In the case that the cutter wheel speed does not fall from the nominal (no load) speed, the sweep valve remains at 100% open and the boom 108 sweeps at maximum speed. For cutter wheel speeds below the nominal speed and within the prescribed range, the illustrated relationship between observed cutter wheel speed and proportional sweep valve setting is a linear function similar to Fig. 9.

[0032] As noted above, the main controller 150 may be programmed with instructions for variably controlling the sweep valve of the hydraulic manifold 130 and / or the speed of the hydraulic pump 120. In some constructions, the relationships of Figs. 9, 9A, 9B between cutter wheel speed and the responsive sweep speed control parameter(s) is permanently fixed according to the stored function or table. In other constructions, the main controller 150 may enable the user to adjust the relationship, for example through interaction with operator control(s) (e.g., the display 152). Adjustment may allow the user to observe cutting performance (e.g., chips removed from the stump) during automatic sweep movement and change the relationship to alter the cutting performance. For example, the relationship can be changed by shifting or re-scaling values. In yet other constructions, torque sensing at the cutter wheel motor 134 may be used as a controlling variable for automatic sweep speed control. In a construction in which sweep movement is electrically driven, load sensing in the electric sweep drive line may be used as a controlling variable for automatic sweep speed control.

[0033] As a result of the stump cutter 100 having no internal combustion engine, there is no fuel tank. The absence of the internal combustion engine generally leaves space to be occupied by the primary battery 112 (e.g., at or near the rear end of the stump cutter 100). The absence of the fuel tank generally leaves space on the base 104 for a battery charger 154 and the hydraulics electric motor 122, both of which can be positioned on an exterior of the base 104. In addition to the primary battery 1 12, additional components (e.g., any / all of the hydraulic pump 120, the hydraulics electric motor 122, the motor controller 124, the hydraulic manifold 130, and the battery charger 154) may be positioned at least partially rearward of a vertical plane through the drive axis A.

[0034] Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.

Claims

CLAIMSWhat is claimed is:

1. An electric stump cutter comprising: a base that is supported by and movable along the ground by a plurality of ground engagement members; a boom movably supported by the base and configured for sweeping and tilting movements with respect to the base; and a cutter wheel supported at a distal end of the boom and rotatable relative to the boom to engage and reduce a stump; wherein the plurality of ground engagement members are electrically powered to move the base along the ground, and wherein the cutter wheel is electrically powered to rotate relative to the boom.

2. The electric stump cutter of claim 1, wherein the boom is movable with respect to the base for sweeping and tilting movements by a sweep cylinder and a tilt cylinder, respectfully, wherein the plurality of ground engagement members are driven by respective hydraulic drive motors, and wherein the sweep cylinder, the tilt cylinder, and the respective hydraulic drive motors are driven with hydraulic fluid from an electrically powered pump.

3. The electric stump cutter of claim 2, wherein the electrically powered pump is configured to remain dormant, without rotating, until a demand for hydraulic function is identified by a control system of the electric stump cutter.

4. The electric stump cutter of claim 1, further comprising an electric motor configured to drive rotation of the cutter wheel.

5. The electric stump cutter of claim 1, further comprising a battery, wherein the plurality of ground engagement members, the boom, and the cutter wheel are all powered, directly or indirectly, from the battery.

6. The electric stump cutter of claim 5, wherein the battery is a primary battery having a voltage greater than 12 V.

7. The electric stump cutter of claim 6, further comprising a a 12-volt control system.

8. The electric stump cutter of claim 7, further comprising a secondary 12 V battery powering the control system.

9. The electric stump cutter of claim 4, wherein the cutter wheel is directly driven by an electric motor.

10. The electric stump cutter of claim 4, wherein a rotation axis of the electric motor is coaxial with a rotation axis of the cutter wheel.

11. The electric stump cutter of claim 4, wherein a running speed of the electric motor matches a running speed of the cutter wheel at all times.

12. The electric stump cutter of claim 5, wherein the battery is configured to receive electrical recharging power through regenerative braking on the cutter wheel.

13. The electric stump cutter of claim 9, wherein overload protection is provided electronically by the electric motor.

14. The electric stump cutter of claim 1, further comprising a control system including an automatic sweep control function operable to sweep the boom at a speed in accordance with a cutting load on the cutter wheel.

15. The electric stump cutter of claim 14, wherein boom sweep speed is set by an operating speed of an electrically powered pump, and wherein the automatic sweep control function of the control system is programmed to adjust the operating speed according to a stored relationship based on speed of rotation of the cutter wheel during engagement with the stump.

16. The electric stump cutter of claim 15, wherein the stored relationship is a linear function.

17. The electric stump cutter of claim 16, wherein the linear function covers a prescribed speed zone of cutter wheel rotation speed.

18. The electric stump cutter of claim 14, wherein the cutter wheel is driven by an electric motor, and wherein the automatic sweep control function of the control system is programmed to adjust a sweep speed of the boom according to a stored relationship based on torque sensed at the electric motor during engagement with the stump.

19. The electric stump cutter of claim 1, further comprising a control system including an automatic sweep control function operable to sweep the boom at a maximum speed when the cutter wheel has no cutting load and operable to reduce sweep speed of the boom in accordance with an increased cutting load on the cutter wheel.

20. The electric stump cutter of claim 19, wherein boom sweep speed is set by an operating speed of an electrically powered pump, and wherein the automatic sweep control function of the control system is programmed to reduce the operating speed according to a stored relationship based on speed of rotation of the cutter wheel during engagement with the stump.

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