O-ring Drive Belts vs Rubber Bands

For a long time I considered ‘o-ring’ to be the proper terminology for a drive belt in little DIY (do it yourself) animatronic projects. But when trying to purchase some o-ring drive belts, I discovered that the term ‘o-ring’ by itself is technically wrong. O-rings are for sealing things (like valves).

Better terminology when using them to drive things (transfer power from one location to another) is ‘o-ring drive belt’, or even ‘urethane belt’, which most o-ring drive belts are made from. (Rubber bands are made from, well, rubber). (So if you’re searching Google or YouTube for information on o-ring drive belts, you’ll have much better results using the full term instead of just searching for o-rings).

Rubber bands are for holding things together.

Rubber bands do not make great o-ring drive belt replacements, but they can work OK in simple applications.

How to quickly tell the difference between o-rings and rubber bands: O-ring cross-sections are typically round and they stretch some, but not as much or as easily as rubber bands. Rubber bands typically have rectangular cross sections and stretch easily.

Imagine that you have a little hobby toy your are playing with and you are trying to rotate a shaft that is located a few inches away from your drive motor.

If you use a rubber band as the drive belt, the rubber band can ‘store’ energy as it stretches, and then it will finally transfer the power (rotate the shaft) after it has stretched to a certain point. This can make for a very uneven rotation, or it might just slip on the drive or driven shaft before ‘giving up’ its energy and result in complete failure to rotate the shaft at all.

The o-ring drive belt doesn’t stretch like the rubber band so rotation is much smoother. It also maintains its integrity much, much longer than rubber bands, which loose their strength and elasticity fairly soon.

White rubber band, black o-ring shown below.

 

Here’s a little video I made to show the difference in drive smoothness:

Here’s a page with some good information: http://www.applerubber.com/seal-design-guide/special-elastomer-applications/drive-belt.cfm

And here: http://www.durabelt.com/rubber-band-belts.php

 

Buying resistors

If you’re going to purchase resistors, don’t get these blue ones. The color bands that show the values don’t show up well enough against the blue background. They’re fine if you only use a single value, but if you regularly need to read different values they’re very difficult to read — at least for me, and I got a refund because they were so hard to read.

Get the ‘normal’ ones with a brown background

These used to be standard until, like too many things, manufacturers got cheap and started to use lesser quality.

And watch out for the ones that have extremely thin leads. All of the blue ones and some of the brown ones that I’ve purchased from China via eBay have had very thin leads that are difficult to handle and they bend way too easily which means they kind of crumple when you try to insert them into test boards.

I found resistors from a US supplier that have the brown background and the ‘normal’ fatter leads at a very good price. Here is their ebay store: http://stores.ebay.com/E-Projects-Electronics

Of course you can get them from other sources, too. I found them at www.newark.com and www.microcenter.com too.

All about the L298N H-bridge motor controller module

Oh boy, was I confused about this module at first! I found a fair amount of bits and pieces about it, but could not find the complete info that I was looking for. So I decided to create this tutorial for others who want to understand it better. I’m not an expert, but I have figured it out well enough to make what I think is a very clear and complete basic ‘primer’ on this device. Whether it’s right for your project is up to you to determine, but here’s info about the module itself, and especially about the mysterious jumpers (at least they were the biggest mystery to me).

What is it?

This module is a very inexpensive and convenient package based on the L298 dual full-bridge rectifier chip made by ST Microelectronics. It can be used to drive speed and direction for one servo or two standard DC motors, and drive other inductive loads like relays and solenoids. It can be controlled by microcontrollers like the Arduino.

Here is the description of the chip (not the module) from ST: The L298 is an integrated monolithic circuit in a 15-lead Multiwatt and PowerSO20 packages. It is a high voltage, high current dual full-bridge driver designed to accept standard TTL logic levels and drive inductive loads such as relays, solenoids, DC and stepping motors.

You can see the data sheet on their website here: http://www.st.com/en/motor-drivers/l298.html .

You could just purchase the chip and component parts and wire up your own parts, but this complete module is probably cheaper than the combined parts, and it’s certainly more convenient. As of January, 2017, the modules are selling on ebay for under $2.00! At this price they’re from China of course, but you can purchase them at higher prices in the United States if you can’t wait for the long shipping times from China.

I’ve read in forums that the L298 chip is about 15 or 20 years old, so there are better(?) chips available now. People seem to like the Pololu A4988 https://www.pololu.com/product/1182 .  Stepper motor current limiting is apparently one of the big improvements, but none of the current-limiting chips come in this neat module format that I’m aware of. So this L298N module is fun and handy, certainly great for testing and little projects, but be careful if you need current-limiting features when driving stepper motors.

How to use it

If you buy from the auctions on Ebay you get the typical Chinese-translated-to-English descriptions that are neither complete nor understandable. And searching for other resources on the internet or YouTube results in some great information, I was not able to find any one source that was all-inclusive like I’m hoping this one is (for a basic primer anyway).

So here’s how you use this little beauty to control the speed and direction of a simple dc motor.

You can use only this module and a power supply to control the motor direction and have it run at either full speed or stop completely. You need a micro controller like an Arduino if you want to control the speed of your motor anywhere between full speed and off. I’ll assume you are familiar with an Arduino. If not, you’ll need to learn that first.

Powering the module —

It runs on from 5 to 35V. That means you can run your motors, servos, or other objects anywhere in that range. Click the photo for a larger version.

The module itself needs 5V for its internal logic and can generate the 5V through its own regulator if you input from 7 to 12V. If you run your motors under 7V or over 12V, the internal regulator will not function and you will need to apply your own external 5V to the module.

There is a jumper that applies your input voltage to the internal 5V regulator on the module. You must not use that jumper if you input less than 7V or more than 12V. Less than 7V and the regulator can’t do its thing to create a regulated 5V. More than 12V and you will burn out the 5V regulator.

A red LED will light when the internal 5V is active.

 

So you use PWM (pulse width modulation) to control the speed of the motor, and two ‘enable’ pins to control the direction.

…More coming soon…

My new CD is available now!

cd-art-tear-downs

cauldron                    junction box

Learn About Halloween
Animatronics!

And other animated gadgets and props!

Get 17 videos and close-up photos!

CD mailed to you — or download right now!

Click here to see the complete ‘Witch’s Legs in Cauldron’ video on youtube

Click Here to Learn More and Order!

 

Ways to Lift Lids (as in opening coffin lids for Halloween props)

I thought I would offer some ideas on different ways to open box lids. My main motivation has been finding a good way for lifting the lid of small Halloween coffin props, but the techniques can be used for many other applications as well.

I love to play around making these things as a hobby, but I need to make smaller versions of these because I don’t have enough room for full-sized ones. Here’s an example of a nice full-sized one by MrTmartindale on YouTube.

Seeing as I was recently playing around with pulleys I thought I would start with probably the most basic way to lift a lid — with a string!

open2a            open3a

There are a lot of potential problems with this arrangement:

It’s visible.

You need to reverse the polarity on the motor for up and down directions.

It takes up a lot of space.

It needs a lot of parts: string, string pulley, pulley support, motor, motor pulley, motor mount, and some way to reverse the motor direction.

More ideas and videos coming soon…