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Author Topic: Mounting a Wheel to the DC Motor  (Read 2260 times)
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I initially purchased the Arduino Starter Kit (the one from the site, not some other companies version). I went through the projects and have moved on to trying to make my own stuff. I'm working on making the basic "drive, avoid walls" bot. I have two DC motors I bought at Radioshack. Forewarning - I come from a programming background. So I can handle the code stuff better than the hands on parts.

How do I mount a wheel to the motors? All I've got is this little nub that barely fits anything. Right now my robot is being made out of cardboard. I'm a college student and I've already spent a couple hundred on various electronics (the starter kit, motors, wires, solder. I've purchased a toy and dismantled it and they had plastic gears on their motors and they created some little gearing system inside of it (which would be tough for my shaky hands). What do you guys do for making the body parts as well? I found myself at Lowes finding absolutely nothing useful for building the body. I may end up just getting a bunch of thin pieces of wood. I can't cut the aluminum they did have...
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Look here:
http://www.robotshop.com/ca/contact-us.html
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Most model shops sell a selection of brass tubing of different diameters. It should be possible to get a piece into which the motor shaft fits snugly and the outside diameter (O/D) may suit your wheel. If not you may need a second piece of tube that fits over the first etc. etc. You would cut the tube to the length you want and glue it in place on the motor shaft with epoxy.

If you can drive a small rod (the size of the motor shaft) into the open end of the tube it should be possible to push the motor out if you need to remove it. On no account try to pull the motor out - you will break it.

...R
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How do I mount a wheel to the motors? All I've got is this little nub that barely fits anything. Right now my robot is being made out of cardboard.

If you want to make a simple fast start bot, you may want to skip the motors with their shaft issues and use modified servos to drive the wheels. The below is very simple and inexpensive servo to modify for continuous rotation, and wheels can be hot glued to the servos (easy to apply and remove). Bottom is a simple bot test setup I made and used plastic jar lids for wheels (from dry roasted peanut jars, mmm... good!) hot glued to the servo horns. 

http://www.hobbyking.com/hobbyking/store/__3743__HXT_6_9kg_39_2g_16sec_Twin_bearing_servo.html

http://www.lynxmotion.net/viewtopic.php?f=20&t=6343
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A photo of what you have would be worth perhaps not a thousand but possibly a few hundred words!
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A photo of what you have would be worth perhaps not a thousand but possibly a few hundred words!

A photo might be worth a few hundred laughs as well... You asked for it. smiley-wink

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A photo might be worth a few hundred laughs as well... You asked for it. smiley-wink

I'm sorry to be the party-pooper here - but that ain't going to work at all.

Discounting the duct tape and cardboard construction (and honestly, you would want the motors on the -other- side; on the "bottom" of the cardboard platform), the main reason it won't work is because those motors aren't gear motors; they won't have enough torque to move anything. You need to gear a DC motor down in order to generate enough torque to move. If those motors had some gearboxes on them, they'd work OK, most likely.

For a table-top robot - you want a gearmotor with an output speed of around 100 RPM.

You could attempt to build your own "gearing" with your setup. For instance, make a wheel with a jar lid, put a rubber band around it and the motor's drive shaft. You may need to hunt down something to use as a pulley on the drive shaft - a pencil eraser, perhaps? That might turn fast, but it would likely have enough torque then to move. You would also need to figure out a way to keep the rubber band on the pulley and on the jar lid; all doable, of course.

Make that cardboard about half as wide as well - maybe about 6-8 inches wide, and about as long. Mount your wheels (jar lids) in the center; figure out an axle for them. Cut a ping-pong ball in half, stick one half on each end (on the bottom of the platform) - you may need a spacer of some sort - to act as a primitive "caster" wheel.

Instead of cardboard, you may want to try foam-core board. Instead of duct tape - use hot glue.

Also - I second the suggestion of using continuous rotation servos instead of gear-motors; just easier to work with, likely cheaper, too!
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What do you guys do for making the body parts as well?

1. I design a frame and have a welder make it from me.

2. I make a design on inkscape and have it laser cut.

3. I buy a pre made kit.
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What do you guys do for making the body parts as well? I found myself at Lowes finding absolutely nothing useful for building the body. I may end up just getting a bunch of thin pieces of wood. I can't cut the aluminum they did have...

Go back to Lowes and get a 2'x2' piece of 5.2mm lauan plywood (~$3, make sure it is flat), a full sized hot glue gun, and a small saw. You should be able to make a simple and strong bot frame with this. Wood is cheap and easy to work with using common inexpensive tools. 
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A photo might be worth a few hundred laughs as well... You asked for it. smiley-wink

I'm sorry to be the party-pooper here - but that ain't going to work at all.

Discounting the duct tape and cardboard construction (and honestly, you would want the motors on the -other- side; on the "bottom" of the cardboard platform), the main reason it won't work is because those motors aren't gear motors; they won't have enough torque to move anything. You need to gear a DC motor down in order to generate enough torque to move. If those motors had some gearboxes on them, they'd work OK, most likely.

For a table-top robot - you want a gearmotor with an output speed of around 100 RPM.

You could attempt to build your own "gearing" with your setup. For instance, make a wheel with a jar lid, put a rubber band around it and the motor's drive shaft. You may need to hunt down something to use as a pulley on the drive shaft - a pencil eraser, perhaps? That might turn fast, but it would likely have enough torque then to move. You would also need to figure out a way to keep the rubber band on the pulley and on the jar lid; all doable, of course.

Make that cardboard about half as wide as well - maybe about 6-8 inches wide, and about as long. Mount your wheels (jar lids) in the center; figure out an axle for them. Cut a ping-pong ball in half, stick one half on each end (on the bottom of the platform) - you may need a spacer of some sort - to act as a primitive "caster" wheel.

Instead of cardboard, you may want to try foam-core board. Instead of duct tape - use hot glue.

Also - I second the suggestion of using continuous rotation servos instead of gear-motors; just easier to work with, likely cheaper, too!

Obviously, this is not the end design goal. This is a stepping platform to ensure that I am able to make stuff connect and function (ie program it to do stuff). The point of cardboard is that I can move stuff around. Right now I can just reposition stuff as needed. Also, duck tape can hit up to 80 lbs per wrap. Just because it's not pretty and poorly done in the picture, doesn't mean it wouldn't work. Never underestimate the power of duck tape. I bought a robot kit that came in the mail today and it has some elbow shaped motors that have the edges on the drives trimmed down to be non-circular. Some people at work suggested filing them as well.
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Obviously, this is not the end design goal. This is a stepping platform to ensure that I am able to make stuff connect and function (ie program it to do stuff).

I kinda figured that.

The point of cardboard is that I can move stuff around. Right now I can just reposition stuff as needed.

I think cardboard is a fine material to prototype with; heck, you can even build the final with it, if you wanted to (for extra stiffness, fiberglass over it). Still, you might want to try playing with foam-core board; it tends to be lighter weight (for the same thickness), and has greater bend resistance.

Also, duck tape can hit up to 80 lbs per wrap. Just because it's not pretty and poorly done in the picture, doesn't mean it wouldn't work. Never underestimate the power of duck tape.

Nothing wrong with duct tape, when used properly; I wasn't actually harping on the construction, just that it seemed you expected the motors, with some wheels attached, to move the platform (with the weight of the Arduino, motor shield, batteries, etc). It was that part I was more concerned about, because we have had a ton of newbies in the past trying to build essentially the same kind of platform, and wondering why they can't get it to move.

I bought a robot kit that came in the mail today and it has some elbow shaped motors that have the edges on the drives trimmed down to be non-circular. Some people at work suggested filing them as well.

I'm not sure what you mean here, unless you are meaning a "D" or crescent shaft profile? Typically those are used when the part you are attaching has a similar hole profile, and/or also has a setscrew which can be tightened against the "flat" of the shaft. You may or may not find it easy to flatten the shaft of your small motors; it can be difficult to do unless you can remove the armature from the motor, and clamp it in a vice. Those small motors are meant to be taken apart in that fashion. Plus, while this could be used to keep the shaft from "spinning" inside the wheel (or gear), it's not ideal for such a small motor.

Most of the time, such gears or wheels are fixed to small diameter shafts with a friction fit. Sometimes, the shaft end will be knurled (and the part to go on the end will be plastic with a slightly undersized hole; the knurling grips the plastic, and bites in - kinda a cheap spline fit). Otherwise, a drop of superglue, loctite blue, or some epoxy is a better solution to affixing a wheel or a gear to a small shaft. If it's a metal gear, you could do an interference fit by freezing the rotor (and shaft), and heating the gear (that has a slightly smaller bore) - to expand it; fit it over quickly, and when everything comes to room temp, just about nothing will budge the gear off the shaft.
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A lightweight and versatile sheet material I often use for projects is foam pvc board available at a sign materials supplier. It's pretty strong, easy to cut and can be assembled with pvc cement. Many thicknesses are available. It's pretty expensive though with a 4' x 8' 6mm sheet going for over $50. - Scotty
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The elbow motor I'm guessing is some kind of geared motor. But the part that connects to the wheel is sort of oval shaped rather than circular. Kind of like a D, but more like []. I've got this thing all assembled now and it seems to be working ok. My major problem right now is that the motors seem really weak. Maybe the robot is too heavy (it now is made of metal, a motor shield, a sensor shield, the uno, a breadboard, and the PING))) sensor. It has no problem going forward, but when it gets close to a wall, it stops, backs up, then is suppose to turn. This thing really struggles to turn. I originally had the wheels reverse for the turn, but I switched it to go forward for a second, then just reduce power on one side.

So the pattern looks like this:
Forward (All Forward) -> Sensor Too Close -> Backup (All Backward)
then Forward for a split second to start the momentum -> reduce power on right to 25% for short time, then all forward.

Any ideas why the motors might be struggling this much? Maybe I'm doing something or maybe they just aren't strong enough for it.

This is the kit I purchased: http://www.amazon.com/dp/B00AJGM4H2/ref=pe_385040_30332190_pe_175190_21431760_M3T1_ST1_dp_1

It's basically their setup (which I want to rip apart and make my own soon, but it was a good starter project.) There is a motor on each wheel, but the left rear and left front is paired with each other, as is the right side.
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This thing really struggles to turn.

To understand what is going on, you're going to need to have (and give us) some information:

1) What is voltage requirements of one of the motors?
2) What is the current requirements (stall current) of one of the motors?
3) How are the motors connected to the motor shield?
4) How are you powering the motors (type of batteries, number, voltage, mAh, etc)?
5) How are you powering everything else (type of batteries, number, voltage, mAh, etc)?

Pictures of how things are assembled would help as well.
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Note that the h-bridge that comes with the bot may have a significant voltage drop across it.
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