Electronics - Building a Robotic platform for my show! - Part 2

**GEEK ALERT!**

This post has a lot of "tech-talk". If you're not into electronics/robotics then you can skip this post! This is my contribution to the robotics community..

Building a robotic platform... Part 2!

To continue from my previous post, this prototype..

THIS WENT INTO THE TRASH!

I'm starting anew from scratch with a new idea!

Instead of servos, I'll be using geared motors. As the saying goes... With new motors, comes new motor mounts.. (not quite how the saying goes but..)

After a bit of researching, I decided on these.. These are 12v DC motors geared down to about 45rpm.

Nicely mounted to a piece of clear acrylic and testing it out with a direct drive from a battery.

 Using a geared motor instead of servos has its benefits. I can now use Li-ion battery instead of a Li-poly with a voltage regular. The geared motors draws much less current than a servo.

This time I'll be using a programmable motor driver instead. This is also from Pololu (I love Pololu!) This little board allows many adjustments. You can program the acceleration, the speed and even mix the signals across multiple boards. It even has built-in temperature sensors, over-current protection and fail-safe options!

Mine came as a kit, but you can buy them ready-made. I enjoy the "making" process and I wanna change a few pins connection method, so I'll solder my own board :-)

Testing out the controller over an RC receiver...

 Another great thing about this board is that it has a built-in voltage regulator. I can run this with a single 12v battery and it automatically regulates the voltage to power the board and the RC receiver, so no separate power is needed!

Once I got it working, time to add a second board!

Programming the drivers...

Testing it out!

If you notice, using a geared motor made it much more quieter (as compared to servo motors)

The final layout! (Yeah, lots of scotch tape  :-P )

Putting it to the test!

Having each driver drive 2 wheels each allows me to move them in the X & Y axis.. I still a rotating function to compensate for the little offsets while trying to travel in a straight line, also a need for it to rotate on the spot. I would need one motor driver for each wheel. I ordered some and now I'm waiting for it to arrive. 

Check back for new updates!

With love,

  - Kiki Tay

Electronics - Building a Robotic platform for my show! - Part 1

**GEEK ALERT!**

This post has a lot of "tech-talk". If you're not into electronics/robotics then you can skip this post! This is my contribution to the robotics community..

I started the idea of building a robotic platform for my EFX show. The big idea is to have a platform that I can put props or set on, and it will move to position on stage automatically! The final product should be a platform that is strong enough to have someone stand on (me). But that is further ahead... I should first start small.

The inspiration came when I first set my eyes on these!

Omni-directional wheels!

I was thinking of something easy to build, and strong enough to move at least a 10kg load. So I started this project using servos and some simple controllers.

I bought bunch of controllers and drivers from Pololu to experiment! (And a Wii Controller to mod! ;-)

Figuring out a way to attach the wheels to my servos

 The wheels weren't designed to be driven by servos, so I had to make some modifications. I'm not exactly proud of this solution.. :-P

 Servo horns held together with cable ties >.<

 

 Looks ugly, but hey it works!

I modified these servos for continuous rotation, see my previous post HERE

Mounting them directly to a cabinet... ?

Maybe not.. I've decided to build them on an acrylic board in case I change my mind, also makes it easy to do experiments on my desk..

Figuring a way to mount the servos... 

Not bad...

Success!

Testing it out!

 

I've decided to use a "Pololu servo controller" for this project. Not only is it tiny for its function, it is easy to use and you can expand it by adding your own codings! It also provides digital outputs to all its channels, which will come in useful in later parts of the project!

Connecting the servos and power supply to the board! I'm using a 3s Lipo battery and a voltage regulator UBEC 6V 3Amp to drive these.. 

Finally... Compiling the codes and getting it to work!

SUCCESS!!

Lastest update: This project ended up in my trash bin! Because of the frustration trying to get the servos to sync at the exact same speed, it is almost impossible to get it to run at a precise straight-line. Bad idea to drive this project using self-modified continuous servo. I've since figured out a new method... Look out for my next post!

Electronics - New way of modifying a continuous servo!

New way of modifying a continuous servo!

  This shall be the start of a new series of blog posts. I've been into electronics and robotics for quite a while now, being active in several electronics/LEDs/robotics forums. I thought, instead of posting my projects and ideas on the forum, it might reach out to more people if I post them on my blog instead. (Helps to drive traffic here as well! ;-) ) If you're not so into electronics, you can skip this post. (as well as all my other posts that begins with "Electronics -" If you're curious.. Read on!

  This first post shall be about modifying a standard servo into a continuous servo. While there are plenty of tutorials out there on how to accomplish this, my version has a new twist! I'm not sure if it's original, but I haven't seen anyone doing it this way before. The difference is leaving the pot (potentiometer) exposed instead of gluing it in place. The benefit of this is that you can always trim it to calibrate it if you need a few servos to sync in movement.

The old method posts several problems for me. Beside the fact that you only get one chance to glue the pot down, it is also almost impossible to modify all your servos to achieve the very exact precise trim. A big problem if you need to sync several servos like for a robotic projects. Sure you can code the differences in your programming but this step can possibly skip the hassles and make your code a little more compact.

The OLD method.

I won't be going into too much details here, if you want more details, google: "Modifying servo for continuous rotation" There are more than enough tutorials out there.

Open up the servo

Remove the pot gear and drill through it so that it no longer can turn the pot.

Locate the gear with a pin sticking out that prevents the gear from moving more than 180degrees.

Cut off the pin and file it down.

Cut away the potentiometer's core..

Trim it PRECISELY to ZERO, and glue it down with epoxy, make sure you use glue or epoxy that doesn't shrink when it dries.

I put it in front of a fan to speed up the drying process.

Put everything back and pray that your trimming stays!

Then test it!



The NEW Method!
Now for my version! Having the potentiometer exposed instead of gluing it down. Note: It should work with most servos (providing there are enough space inside to do this mod. You will get what I mean in a short while)

First, you open up the servo and do exactly the same as above, except this time you DON'T cut away the pot's trimming core!



The pot and circuit board of my servo were arranged like this (might differ from servos to servos)

Untwist it, bend it, or do whatever necessary to have it look like this!

Next, you will need to modify the casing as you probably won't be able to fit it back with this new arrangement..

Cutting, filing, bending etc. to make space.

More space now :-)

As the pot trimmer will be sticking out, you will need to drill a hole in the casing.. Make sure you align it with your pot's new position!

Nicely done...

Now the last part is to try and fit everything back with your pot's trimmer sticking out like this.

The final product!

Here is my contribution to the robotics community. Let me know what you think, or please share if you have any ideas to simplify or improve upon it! ;-)

With love,

   - Kiki Tay