Electromechanical Horse Racing

This is a game where the win depends on the player’s skill. It’s obvious that the electromechanical ‘horse’ would run; could it behave otherwise, when the power is ‘on’?The question is how it would run. You, as the jockey, decide.

The game described here is a game for two, but it can also be extended for more players, you only have to make more lanes.

Materials

For the mechanical part

Thick (8…20 mm) plywood of wooden board

Transparent plastic 2 mm thick

Cardboard 1 mm thick

Elastic cord 0.6 mm diameter

Fishing line 0.8 mm diameter

Thin plastic (0.5 mm)

Tin plate (0.5 mm)

Thin wooden sticks (2 mm diameter)

Copper clad textolite pads

Two small rollers

Two screws M3 with nuts and plastic washers

Aluminum angles

Wooden stock diameter 20mm

Small screws for wood

Paper

For the electrical part

Two small motors like those used in walkmans

Two end microswitches SPDT (see explanation in the text)

Two transistors 2N3904 or similar

Two resistors 1K

Two electrolytic capacitors 22 microfarad x 10 volts

Plug to connect power adapter

Power adapter with 4.5 volts output

Cables

Tools

Saw for wood

Saw for metal

Fretsaw

Electric drill with bits

Long nose pliers

Screwdriver

Exacto knife

Soldering gun with solder

Scissors for paper

Scissors for metal

File for metal

Sandpaper

There are two figures that represent a horse with a jockey, each figure being attached to an elastic cord. Each cord forms a loop between the sheave of an electric motor and an idle roller, and transforms rotation of the sheave into linear movement of the figure. The tension of the cord should be such that the cord do not slide on the sheave. Each player can press or release the button of a switch; when the button is pressed, the figure moves for a certain distance. The goal of each player is to achieve the finish before the rival does it.

There are two identical circuits driving the two motors; the circuits are connected in parallel and powered by a DC adapter connected through a plug. The nominal voltage of the motors is 6 volts, but I used 4.5 volts as power voltage to reduce rotational speed.

The switch used is an SPDT (single pole, double throw) switch. When the switch is in its left position (the button released), the capacitor charges from the power source. When the button is pressed, the switch passes to its right position, the capacitor begins discharging through the resistor R1 to the base of the transistor T1. The transistor opens and remains opened until the capacitor voltage is sufficient to keep the transistor opened. During this time the motor is energized, and the ‘horse’ moves to a certain distance. When the transistor closes, the motor, and, consequently, the ‘horse’ stop.

After the ‘horse’ stops, you release the button to allow the capacitor to recharge. You are interested to release your button quicker than your rival does, to be the first to begin recharging his capacitor. Are you interested to press your button before the rival does the same? I suppose the temptation would be big, but it’s necessary to be moderate and allow the capacitor to charge sufficiently; thus, the next run of your horse would be quite significant. (Don’t forget that your rival thinks the same.)

The diode D1 protects the transistors against reverse current from the motor that is produced when the motor gets OFF.

The motors should have identical nominal voltages and revolutions to ensure that the linear speeds of both cords are the same.

I mounted the mechanical elements on a piece of 20 mm thick plywood that I had available; the dimensions are 700 x 140 mm; the base is painted in white.

The motors and idle rollers are fixed on aluminum angles profiles. The size of the angles depends on the diameter of motors. In my case, the diameter of the motor is 24 mm and its height is 14 mm. The angles are fixed to the base using small wood screws. In fact, I cut these profiles out of an aluminum piece that was available in my workshop; it’s also possible to ply these angles from sheet aluminum.

I used an M3 screw as the axe for the idle roller; however, I blunted the threads that were supposed to be under the roller. (I held that part of the screw quite tightly with long nose pliers and turned the screw using a screwdriver.) As to the roller itself, I took it from the tuning mechanism of an old radio; any small metal or plastic roller could serve here. The screw is fit into a threaded hole in the angle, an M3 nut locks the screw.

The elastic cord forms a loop between the sheave of the motor and the idle roller. The tension of the cord should be sufficient to prevent the cord from sliding on the sheave, but not too big. The cords in both lanes should have the same tension. When I discovered during preliminary tests that a cord was slightly sliding on its respective sheave, I put a small amount of resin on the cord to increase friction, after which the sliding disappeared.

It’s very important that the diameters of the sheaves be identical to ensure the identical speeds of the cords in both lanes - this would equal the chances of the players.

That’s how I made the ‘horse with jockey’:

- printed and cut out the attached images of the horse with jockey

- glued them on both sides of a piece of transparent plastic

- cut the figure using a fretsaw

- made the holes necessary to fix the cord

- refined the figure’s contour using a file and sandpaper

- painted the figure using felt pens and varnished it

An elastic cord (diameter 0.6mm) is passed into the holes in the figure and fixed. To reduce lateral rocking of the horse a transversal piece is fixed to the base of the figure; a guide made of fishing line (diameter 0.8mm) passes through the hole in the piece.

When I tested the design, I realized that the horse still rocked too much; therefore, I made an additional support to the horse’s base; this support is made of thin plastic.

The length of the figure from the nose to the end of the horse’s tail is 70 mm.

A jockey is supposed to hold a whip in his/her hand; that’s why I mounted the switches in pieces of a wooden stick of round cross section (diameter 20mm, length 120mm). Thus, you hold the ‘whip’s handle’ in your hand and press the switch with your thumb. The switches used are roller lever SPDT microswitches.

The switch is fixed in its place with 2 thin sticks of hardwood (I used pieces of a toothpick).

I made the elements of the enclosure of 1 mm thick cardboard and painted them grass green. The side and middle elements are glued to the base; the front and back elements are fixed with small wood screws. Thus, your can take these elements off to get access to the motors and idle rollers.

The height of the game with the enclosures installed is 50 mm.

A flag is placed at the end of every lane to indicate the horse’s arrival. The flags and their bases are made of tin plate; I used pieces of a pin to make the pivots for the flags. When the ‘horse’ touches the flag, it falls and shows who the winner is.