Intro: A Practical Robot
I call it a practical robot for a number of reasons. It can be make using every day tools that most people who do work around the house would have. By using many surplus items the cost is kept down. The robot's arm can lift over a 2 lb. object from the floor to 3 ft. 4 in. in the air, so the arm can put objects onto tables. So if you are tired of reading about robots that can only lift a ping pong ball a few inchs in the air then read on. In this tutorial I hope to give you tips that can be used on other robot projects as well.
Most of the parts used in this robot came from the "Lentek" robotic vac. This vac was a gold mine of robotic parts. I got a 14.4 volt battery, motors with gearbox, drive wheels, power transformer, remote control, H bridges, I.R. leds, photo transistors and etc.
Step 1: Testing the Vac
The goals of the robot was to be able to pick up objects weighing up to 2 lbs. from the floor and put them on a table by remote control and autonomously.
The first thing I did was to see if the "Lentek" vac was
strong enough for the robot I wanted to build. I put a 5 lb
weight on the vac and see if it could run and turn on a rug; it did.
Some notes here; even without a weight the vac could not go from the floor surface to the rug so don't try to build upon the base of the vac itself.
When I give wood measurements in the rest of this tutorial
they will be real measurements and not store measurements.
For example I will be using a 4" by 1" piece of wood in many places in this project. Real measurements are 3 3/4" by 3/4".
Step 2: Let's Look Inside the Motor
Take the vac apart and pull out the drive motors. By looking at them you can see there is no optical encoder wheel. What an optical encoder wheel does is to break a light beam as the motor turns there by giving X amount of pulses for 1 turn of the wheel. Lets build one for the motor.
The encoder wheel is made from cardboard. Cardboard will be used in many places in this project. Where did I get the cardboard from? Cereal boxes. The shaft of the encoder wheel is a "panel nail" the type of nail that is use to put up wood panels in a house. The length used here is 1 5/8".
I used a compass to trace out a circle on the cardboard that is a little smaller than the width of the body of the motor case. I used a paper hole punch tool to put the holes in the wheel. Use the small hole that is made by the tip of the compass to find the center of the wheel to put the shaft (nail) thru. Put a little glue on the head of the nail to hold on the encoder wheel, let it dry.
The shaft will go into the center hole of the worm gear. First file off a little of the motor case wall so that the shaft does not touch the motor case walls. Put a little glue on the tip of the encoder wheel's shaft (nail) and push it into the center hole of the worm gear. Let dry and put the case back on the motor.
I will not go into details about the electric part of the robot in this tutorial. I will say that we will use the I.R. led and photo transistors found in the vac as the light beam and that we will feed the output to the comparator input on a "PIC" chip. I will make more tutorials as time goes by. Drop by my web site at: http://robotics.scienceontheweb.net
You will have to make the change to 2 motors. One modified motor will be used in the robot's base and the other in it's arm. This means you will need to buy 2 vacs. and you will have a spare battery and remote as well as other types of motors.
Step 3: Making the Main Base and Motor Base of the Robot
I made the base from plywood. I used plywood because it is easy to work with and you can sink the head of a screw into to it so that it will be flat with the wood surface. Many times pieces of plywood may have a hole in one of the layers from a knot in the wood. I use a hot glue gun to fill the hole. If you don't have a hot glue gun you should buy one. They are great at holding down wires, filling gaps, etc. You can get them at many dollar type stores. The same stores will sell the glue sticks for as low as 25 sticks per dollar.
When making the base you want the size to be small enough to fit thru doorways and be able to turn in hallways. Remember that the arm will also be sticking out over the base; so you don't want the base so small that it will tip over. So I made the base 11 3/4" by 17 3/4". Why not an even 12" you ask? Well the plywood surface will be covered by cardboard. Yes you guessed it, cardboard from a cereal box. A note here, I didn't use contact paper over the cardboard but there is no reason you can't. So if you want to dress him up more go ahead.
To mount the motors to the main base you will need to make a small motor base. Each motor base was made from two 1/2" thick pieces of wood. With the size wheel caster I used I needed the motor 1 inch high from the main base. So if you have a 1" thick piece of wood then you only need to cut one piece of wood per base motor. The motor's base size is 2 1/4" by 4" I used a 5/8" drill bit for the hole in the motor's base. The round hole to square hole is about 1 19/32" center hole to center hole. The longer hole was made by drilling holes and then using a file to shape them. A better way would be to use a saw blade to shape the long hole.
Step 4: Working on the Bottom of the Main Base
Remember the main base will hold one modified motor and one unchanged motor. In the photo the motor with the small box next to it is the modified motor. The box is used to cover the encoder wheel, I.R. led and photo transistor. Nail and glue the motor base to the main base. Again I used 1 5/8 in. panel nails. On the other side of the main base cut off the end of the nails that stick out.
I know in most robots the rear caster wheel is a small little thing that may not even swivel. DO NOT USE THAT TYPE! I am all for saving money when building a robot but do not do it on this part. The robot will not be able to go from wood floor surface to the rug. It will not turn well and will take more power. I used a 3 in. swivel ball bearing caster. Mount the caster so that when the caster wheel turns it will not go pass the rear of the base. I mounted mine 1 6/16 in. from the rear. The type of screw I used was a #6 "drywall screw". Again cut off the end of the screws that stick out.
Step 5: Working on the Top of the Main Base
Now it is the time to glue the cardboard to the top of the main base. Cut open the large cereal box and glue the glossy side down using "Contact Cement". Wait until dry then trim.
Check to see if your large cereal box matches the size cereal box I am using if not then you will have to use some other materials. The small side of the box is 3 1/4" wide, the large side is 11 10/16" long.
PLEASE SEE PHOTOS BEFORE STARTING THIS PART.
Cut open two large cereal boxes. Cut off the bottom and top flaps on the cereal boxes. Cut along the seams of one cereal box. Glue those pieces on to the other cereal box glossy side facing glossy side. Wait to dry before using.
Cut 2 pieces of 3/4" thick wood 8 3/16" by 3 2/16". We will use this wood as the 2 walls to the box we are building on the top of the main base. Place and glue one piece in the middle of the base, 14/16" from the rear of the base. The 2nd piece goes 10 2/16" from the 1st piece. This is going to form the box which is 10 2/16" long on the inside. When the glue is dry nail the 2 pieces of wood in place from the bottom of the base using "Panel nails". I like to drill a small pilot for the nail 1st.
Now take the cardboard we glued together and used that as the long walls and top of the box. Glue one side to the ends of the two pieces of wood and to the main base. The other side needs to be trim so that it can fold to make the other side of the long box wall. DO NOT GLUE THIS SIDE.
Step 6: How the Arm Works
This arm doesn't work like most robotic arms. It works more like a forklift. The hand will ride up and down on a wooden rail. This will allow the robot to lift an object 3' 4" off the floor using little torque.
For a normal robotic arm to lift an object 40" off the floor the arm would have to be 20" long. A 2 lb. object would take 640 oz. in. of torque to lift.
Using a 1" wheel to lift the 2 lb. object would only take 16 oz. in. of torque.
The math used to find the object in 3-D space is also easier.
Step 7: Mounting the Rail to the Main Base
The wood used for the rail is call a furring strip. In Lowe's it would be listed as: 1" by 2" by 8' treated furring #201999. It is about 1 5/16" wide and about 9/16 thick. I used this type of wood because it seems to have the least amount of warp and bow. Cut a 48" long piece. Cut a 1 1/2" thick piece a wood 3 3/16" by 3 3/16" You can cut a notch into the wood to hold the rail in place and then drill a hole thru the rail and the block of wood. Use a drywall # 6 screw to hold the rail in place. If you do not want to make the notch in the wood block then you will have to use 2 more screws to both sides of the rail to hold it in place.
Place the block so that the rail is in the middle of the base and the block of wood is 1/2" from the front of the base. From the bottom side of the base use two drywall screws to hold the block of wood to the main base.
Step 8: Working on the Arm
Unscrew the rail from the base, we will be using it in this step.
Using a 1 1/2" circler hole blade cut a hole in a 3/4" thick piece of wood. Take out the wood (see photo) from the blade. This will be used as a roller. Make four of these rollers. A "5D 2 inch common" nail will become the shaft of the roller.
Cut two 3/4" thick pieces of wood 3 1/2" by 5 7/16". Place a roller near the back top of the wood but do not let the roller go pass the edge of the wood. Hammer the nail in the center of the roller but not too far in because you will be pulling them out later. Place the rail on the wood, make sure the rail is straight and tight against the 1st roller (see photo). Place the rest of the rollers tight against the rail and nail in place.
Remove the rail and then remove the four nails from the wood. Using the nail holes as a guide drill four pilot holes in the wood. Take the 2nd piece of wood you cut and clamp it over the 1st piece. Now drill the four holes thru the 2nd piece of wood as well.
Nail the four 5D common nails into the four holes in one piece of wood. Now you want to drill four pilot holes in the path of the rail. Screw in four # 6 drywall screws but leave the heads about 2/16" above the wood. You will need to adjust them later. Put the four rollers and rail back in place. The four screws will let you adjust for any bow in the wood. Adjust the four screws so that the rail is even with the top of the four rollers. The screws may be needed to be adjusted again later. Take the 2nd piece of wood and
hammer it in place over the 1st piece of wood. You will have to play with the 2nd piece of wood a little until it is close to the rollers but yet the rollers can spin freely. You may also have to adjust the four screws so that the rail is not too tight against the side of the wood. Slide out the rail.
Cut another 3/4" thick piece of wood 3 1/2" by 9". Nail the roller section to the top middle of this piece of wood. Cut another piece of wood (about 3 1/2" by 2 1/4")that will cover the other side of the roller section and nail in place. Now cut off all the screw and nail ends that are sticking out.
Slide the rail back into the roller section. There will be spots that will bind against either the rollers or the screw heads. Using sandpaper (best if the sandpaper is mounted to a block of wood) sand down the spots on the wooden rail where it is binding.
Step 9: Making the Reel
Using a 2" circler hole blade, cut a hole in a 1/2" thick piece of wood. Take out the wood from the blade. This will become part of a reel. Make another one. Clamp the two wheels together. Drill four pilot holes around the wheels. Unclamp the wheels and make the four pilot holes in one wheel .140" big so that the 2" # 6 drywall screw can fit thru the hole. Open up and square out the wheel's center holes so that they can fit on the motor's square shaft. Using the four 2" # 6 drywall screws, screw the two wheels together so that there is a 13/16" gap between the two wheels. Tie a 54" long monofilament (weed eater trimmer line) line to one of the screws.
Step 10: Mounting the Motors to the Rail
Cut a 3/4" thick piece of wood 4 11/16" by 3 14/16" I used a 5/8" drill bit for the holes in the motor's base. The longer hole was made by drilling holes then using a file to shape them. A better way would be to use a saw blade to shape the hole. The round holes are apart 3 2/16" center hole to center hole. The round hole to square hole is about 1 19/32" center hole to center hole.
Attach the reel to the motors (one motor is modified) and the motors to the motor base. Wired the motors (remember to reverse the leads to one motor) to a 6 volt battery just to test everything is working. Now take the reel and motors off the motor's base. Next cut a 1 1/2" thick piece of wood 3 3/16" by 3 14/16". Using two # 6 drywall screws attach the wood block to the under side on the motor base 1/2" from the left edge. Drill two pilot holes thru the rail into the block. Attach the rail to the block using two # 6 drywall screws. Now put the reel and motors back but this time glue the motors to the motor's base.
Take the monofilament line and make sure that the line runs in front of the reel. Pull it down straight to the roller assembly that is on the rail. Where the line touch the roller assembly drill a hole thru the side and screw in a 2" # 6 drywall screw. Tie the line to this screw.
Step 11: Making the Hand
Anyone who has a "VEX" set will recognize these parts. I do not believe it would pay to buy VEX parts just to build this hand. This hand is only one of many protypes that I have been working on. I will give details of other hands on my web site at: http://robotics.scienceontheweb.net over the coming months. Here comes the but. But if you already have the VEX parts, give it a try.
You can use any gearbox motor if you can get the vex gear to stay on the motor's shaft. The motor I used here was left over from another project. A note you need to know about this motor is the brown cap gets screw down to the plate on the motor which the motor turns.
Drill a center hole thru the cap so that a #8-32 by 1 3/4" screw will fit. Take the screw's head and grind down the two sides a little so that the head is now a rectangle with two curves ends. This makes it harder for the screw to break loose when glued in. Put the screw thru the cap with head pointed towards the motor plate. Put the nut on and tighten.
Depending on the gearbox motor you use, the wood size my be deferent.
Cut two 3/4" thick piece of wood 7" by 2 2/16". One of these pieces will become the rail's base, the other the back plate of the hand's motor box. Cut two 3/4" thick pieces of wood 1 10/16 by 2 2/16" these will be the sides of the hand's motor box.
If you look in the photos you will see two L shaped brackets. They are 1 7/16" by 1 7/16" with one end shaped to fit the rack gear. These were made from an old bed frame. What can you find that will work? These were cut by using an saw with a cut off disc used for cutting metal. No fancy tools were used in making this robot.
Drill two holes thru the bracket and thru the side of the rack gear. Mount the bracket to the rack gear by using two screws with nuts.
The VEX metal parts must be cut. It's best to use a hack saw blade since a cut off disc takes too much metal with it. For the people who know nothing about VEX. The metal parts come with a little starter cut to show where you can cut. We will be using the smaller part, so cut that off. We will be using two. Using the screws that come with the rack gear, screw it into the metal slot using two screws with two metal washers. Now here comes a problem; if you tighten the screws all the way in, the rack gear can not move. If you do not tighten the screws, they will come loose in no time. The solution is; using everyday aluminum foil made tiny little balls and push them down the screw's holes. Take the rack gear, screw it back into the metal slot. If the rack gear still binds, repeat. When you get the rack gear to slide right, take out the screws and put a little glue into the screw's holes. Put the screws back in and let dry.
Take the rack gear assembly and screw it down onto the rail's base. I did NOT use drywall screws here. You want to use a screw with a flat head so that the rail assembly can be adjusted by a small amount. Take the other rail assembly and space it the width of the gear by putting the gear between the two rack gears. Now screw down the 2nd rack gear assembly. Take out the gear and side the rack gears in opposite directions. Put back the gear in the center and mark where the gear is.
Drill a hole large enough for the #8-32 by 1 3/4" screw to pass thru without binding. Take the rail assembly off the rail's base. Cut the rail's base from the top to the hole wide enough for the screw to side thru the slit.
Put the gear onto the screw. This is a very tight fit. I used a channel lock plier to hold the gear as I turned the screw. Turn the gear on the screw until the gear comes even to where the rack gear is with the cap close to the rail's base but not binding on it. When everything looks ok cut off what is not need from the #8-32 screw. Put glue on the head of the screw that is inside the cap and let dry. Put glue on the nut and around the base of the gear. When it is all dried screw the cap back on the motor. Side the motor gear assembly thru the slit until it hits the hole. Using a hot glue gun seal the slit. Put back the rail assembly.
Cut a 3/4" thick piece of wood 1 9/16 by 1 9/16. This will be the motor's base. Place the motor on to this base. See if the motor is parallel to the rail's base. If it looks good then screw the motor's base to the rail base. Glue the motor to the motor base. Nail the sides on to the rail's base. You will notice that the motor's rear shaft is sticking up. Mark and then drill this spot on the back plate so that the rear shaft has a place to go. Screw the back plate on.
The two fingers of the hand are made from two 3/4" thick piece of wood 3 1/16" by 1 11/16". You can cut a notch into the wood where it will be screwed into the bracket. Doing it this way lets the hand open a full 3" and you can cover the bracket and screw heads with cardboard. Drill two holes into each bracket that will allow the screws you are using to pass thru the bracket's holes. Mark and drill pilot holes on the fingers. Now mount the two fingers and screw them in place.
Using two 1 1/2" # 6 drywall screws attach this hand assembly to the bottom of the roller assembly.