Switch Activated Measuring Cup


Requested Project

We would like a measuring cup that will pour pre-measured ingrediants or dice into an appropriate place.  It should be at least 8 - 10 inches high and hold at least 1 cup of material.  It needs to have a switch connection for accessibility.We would like this as soon as you can do it.

kthompson@ccs.k12.ia.us

Design Notes

Design Information, Switch Activated Measuring Cup

A measuring cup that will dump into a bowl when activated by a switch has been completed and will be delivered to the client about March 15, 2007.

The switch activated measuring cup is comprised of a commercially available 2-cup plastic measuring cup that is attached to a shaft driven by a gearmotor.  The cup is suspended over a platform holding the mixing bowl and will dump its the contents into the bowl when activated by a switch.  Power for the gearmotor is supplied by a 9V transistor radio battery.  The shaft from the gearmotor contains a cam having a lobe so located that it will open the micro-switch supplying current to the gearmotor thus causing the cup to stop at its home position.  A standard single pole audio jack is provided to accept a plug from switches of the type generally used by client agencies.  The switch contact initiating cup rotation must persist for about two seconds to allow the cam to clear the micro-switch actuator and permit completion of the dump rotation.

It is highly desirable that the measuring cup be removable to facilitate clean-up of the cup.  That feature is provided by a cradle that conforms to the cup handle and a large rubber band that binds the cup to the  cradle.  The rubber band can be easily removed, thus freeing the cup.

Electrical Design:

The switch activated measuring cup uses an alkaline 9V transistor radio battery.  The motor requires about 20 ma current when the cup is lightly loaded and with a good battery will complete one cycle of dumping its contents and returning to home position in about 20 seconds. With this time and current profile it should complete well over 1000 cycles during the life of the battery.

The negative side of the battery is connected to the negative side of the motor (This is not marked on the motor, it is determined experimentally by choosing polarity to make the motor run in the desired direction.).  The positive side of the battery is connected to one terminal of the switch jack and to the common terminal of the micro-switch.  The positive terminal of the motor is connected to the normally closed contact of the micro-switch and to the remaining terminal of the switch jack.  For normal operation the switch connected to the switch jack is closed for a few seconds to activate the motor and allow the cam to move away from the actuator of the micro-switch.  The closed micro-switch will then supply current to the motor until the contact is opened by the cam as the cup reaches home position.  Because of internal friction in the gear train and perhaps permanent magnet motor cogging the motor stops quickly when voltage is removed and a substantial torque can be applied to the motor output shaft without causing rotation.

Parts used the construct the unit are as follows:

Supporting Platform:  Formica covered particle board, approximately 12? X 16? about 3/4? thick.  The bottom of this platform is fitted in each corner with plastic foot pads so there is space beneath the platform to accommodate mounting the angle bracket that supports the mechanism.  These foot pads are a standard hardware item and attach to the platform with screws.

Gear Motor:  Surplus Chrysler product vent actuator, 4 RPM, operable over the 3-12 V range.  Obtained from American Science and Surplus, P/N 37244, $7.95.  The output shaft of the motor is prepared for use after fabrication of the cup support and drive shaft.  Once the hole is bored in the drive shaft it can be placed over the motor shaft at the hole drilled through the motor shaft.  In order for the hole in the motor output shaft to be aligned with the hole in each side of the tube, it is best to drill halfway through from both sides and then run the bit completely through and out the hole on the opposite side of the tube.  The outside diameter of the motor shaft has molded cogs so it is most convenient to drill the through hole between these cogs.

Angle Bracket used to support apparatus:  Fabricated from the angle bracket of a 16? shelf support modified by removing an angular brace between legs of the right-angle bracket and shortening the long side of the bracket to about 13?.  The angle bracket is further modified with holes for motor mounting, a hole for the motor output shaft to pass through, holes to mount the bearing support angle bracket and countersinks on the existing holes on the short end of the bracket to accept the heads of #10 flathead screws (which are used to mount the bracket to the base platform.

Angle Bracket used to suspend the cup, battery, jack and shaft bearing:  Standard Hardware angle bracket with 6? legs, 1 1/8 wide, 3/16? thick.  One leg is trimmed to 4?, see pictures for additional modifications required to mount the outer support bearing, the battery holder and the switch jack.

Cup Support and drive shaft:  This shaft is fabricated from two pieces of seamless tubing having an OD of 5/8? and ID of about 1/2?.  The respective length of the two pieces is about 4 3/8? and 3 1/4?.  The two pieces are joined by a pitman arm providing a 2? offset between the centers of the two tubes.  The pitman arm is fabricated from 3/32? galvanized strap iron 1? wide.  At each end a hole is bored that will provide a snug fit to the outside diameter of the tubes.  One end of each tube is inserted into one of the holes (with the free ends pointing opposite directions) and the joints are brazed.  The purpose of this offset arm is to permit the cup to rotate about the center of extremities such as the pouring spout and the handle cradle.  At the motor end of the shaft a 3/32? hole is bored along a diameter to accept a cotter key used when attaching to the motor output shaft.  On the cup end the shaft is drilled along a diameter and tapped for a #6-32 screw used to secure the cup cradle to the shaft.  This hole is located about 1? from the outer end of the shaft.  (See the cup cradle description for additional direction on the location of this hole.)

Outer Cup Support Bearing:  This bearing is fabricated from 3/4? polypropylene.  The physical size of the block is about 1 3/4? X 1 7/16?.  The block is provided with a 5/8? diameter hole to accept the cup drive shaft, mounting holes threaded for #6-32 screws, and micro-switch mounting holes threaded for #2-56 screws.  See pictures for the physical setup of these items.

Micro-switch:  Omron SS-5T  NO/NC contacts, approximately $2 on surplus market.  This switch is mounted to the shaft bearing block so that the actuator is fully depressed when in contact with the highest point on the cam.

Cam:  Machined from 1? brass rod, finished length of 3/4? plus about 1? to hold with the chuck during machining.  The rod is center-drilled to provide a 5/8? hole for the shaft.  The collar of the cam is 1/2? in length, a lobe extends axially 1/4? from this collar.  This lobe is an integral part of the original rod and is machined by chucking the collar in a 4-jaw chuck such that the center is about a point on the diameter of the 5/8? hole.  The lobe is then machined to a 3/8? diameter, 1/4? long.  Part of the 3/8? diameter will have been previously removed in providing the shaft hole.  The collar is drilled with two holes spaced 90 degrees along the circumference of the collar and centered axially, threaded for #6-32 socket-head set screws 3/16? long.  The cam is positioned on the shaft such that the micro-switch switches the normally closed contact to open when the cup arrives in a level home position.

Switch connector jack:  Radio Shack #274-251 1/8? mono phono jack. Cost: $3.99 for package of 3.  A mounting bracket for the jack is fabricated from a 1 1/4? X 1 3/8? rectangle of 1/16? aluminum sheet stock.

Battery Holder:  Commercially available molded plastic 9V transistor radio batter holder with integral molded-in battery connection terminals, and external connection tabs (originally configured for PC board mounting).  Salvaged from equipment, vendor unknown.

Measuring cup:  Commercially available molded plastic, 2 cup capacity with cup and metric measurement markings.  Obtained at Theisen?s, item #75290612, $2.19

Cup Cradle:  Cut from maple block about 3?X4?X 1 1/2?.  Contours to nest the cup handle are bored with 1? Forstner bit.  A 5/8? diameter hole is drilled to accept the cup drive/support shaft.  When the cradle is mounted to the support shaft the hole for the #6-32 mounting screw is simultaneously bored through the cradle and the shaft using a #36 drill.  The shaft is then removed and tapped for the #6-32 screw, and the hole in the cradle is then enlarged to a clearance hole for the screw.  A countersink is also provided in the cradle for the screw head.  A detail drawing of these operations can be provided upon request.

Rubber band for securing the cup:  The band used was a 2 1/2?  diameter O-ring having a cross-section diameter of about 1/8?.

Miscellaneous Hardware:

Item      Quantity Application
? -20 hex head machine screw, 1 1/4? long 2 motor mounting
#2-56 flat head machine screw, 3/4? long 2 micro-switch mount
#8-32 socket head set screw, 3/16? long 2 secure cam to shaft
#4-40 flat head machine screw, 1/4? long 2 mount battery case
1/4-20 flat head machine screw, 1/2? long 1 connect angle brackets
1/4-20 hex nuts 4 motor mounting
1/4? toothed washers 4 motor mounting
#6-32 flat head machine screw, 1 1/2? long 1 mount cup cradle
#10 flat head wood screws, 3/4? long 3 attach bracket to platform
hook-up wire, red and black 16? electrical connections

RCRV designer is Russell Schuchmann, and was requested by Prairie Crest Elementary College Commnity Schools, Katie Thompson 848-5280, cell 573-5100. The project was begun Mar 12, 2007 and completed Mar 14, 2007.



Switch activated measuring cup system



Cup mount detail



Mechanical system detail


2021 RCRV