Let's Make Robots!

What to do with the big motor driver?

2.9.2010, past midnight

Lots of Ideas have been flying trough my mind since I got the motor driver ready.

(http://letsmakerobots.com/node/22363)

I am now thinking of making something like this, only a bit bigger.

This design involves having the wheels on each side connected to each other, so that they work almost as treads.

The big problem with this design is ofcourse obvious. When turning the wheels will have to slide and the motors must work against the friction. Most bots/rc cars with this design are very light for this particular reason. However there is some bigger devices that work with this principle. Bobcats.

http://www.youtube.com/watch?v=bVx1BYfEmXc ,  That is the problem I am going to face!

 

I'm thinking of using wheels from wheelbarrows, and motors from cordless drills.

For now I don't have anything to control my motors wirelessly, so I will have to look into that.

There will be many problems in my way, but I have just accepted the challenge created by myself, to make a big bot.

 

 

 

3.9.2010

So I bought four wheelbarrow- wheels from a cheap shop at 9 € each, two axis and bolts. This is what we got!

Tomorrow I will pay a visit to a local landfill and see what can find.

 

4.9.2010, just after the best show ever!

Today I went to a recycling station (not a landfill) and found some metal rods. A friendly guy cut them into 1.5 meter lengths so that they fitted into my friends car. They coasted me 20€ though :(.

I will have to sand them quite a bit before welding, since they are pretty rusty.

I experimented a little bit with the distance between the wheels on a temporary frame, and unfortunately it seems that the "bobcat-problem" is causing so much friction that my motors wont be able to make the damn thing turn if there is a heavy load.

I will probably use bicycle chains and sprockets but it ain't gonna be easy.

Hopefully my friend will bring me his MIG-welder tomorrow. My school is starting on Monday, so sadly I will have less time to build robots, but I give my best.

This is gonna be a tough one.

 

5.9.2010

I came across some old bicycle sprockets and I'm having a hard time figuring out how to connect them to the wheels.

 

The major problem is that the sprockets are divided into 5 sections and the wheels have 4 bolt holes. No matter how you turn the damn thing it is impossible to get it into place without some serious work. I am trying to remind myself "keep it simple, stupid", but it seems that my mind wont come up with a simple solution to this problem. I have also started to draw the parts in Solid Edge so that I can play with them when I'm not at my workshop.

This big sprocket has 46 teeth's and the smallest I have has 16 witch makes the relationship 1 : 2,875. I would like to find smaller sprockets than these 16. Today I will probably start playing with the MIG welder I borrowed. :)

 

9.9.2010, The show must go on!

I now have access to a MIG-welder, but really need to work on my skills with that thing.  And I have solved the problem "how to attach my sprockets to the wheels?".

I made bought some extension bolts and made custom adapter thingies by grinding and welding.

--->

 

Adapter- "thing" ready! :D

It would probably have been much easier to just buy thick metal sheets and start from there, but that would have coasted me alot more and I would have missed all the training with the MIG. :)

My next phase is to make the prototype frame move, so that I can test the gear ratio and torque. For this I really needed to radio control the motors, so I found a toy I bought for 10€ a while ago that has been laying around my house, and "hacked" the receiver.

It has only four buttons witch can either be on or off, so I had to make some nifty programming to be able to change the speed and direction of the motors and have the ability to "KILL" both motors instantly.

Cheap RC-toy                                                                                        Receiver, at 40 MHz          

 

So here is my professional radio control system for the thing that I'm making. A picaxe 28x1 is used to take in the signals from the receiver, indicate whats happening and provide the motordriver with PWM/froward/reverse- signals.

Action Video at:

http://www.youtube.com/watch?v=8Fnin4H6iC4

 

I have been looking around for some information about connecting Xbees to Picaxe, and I might be asking stupid questions about how it is done in the forum. I can't really find any good tutorials for this without purchasing a Connect Board. Have to find information if it is possible to use the Xbees without programming them (changing braudrate) and what kind of breakout-boards there is that would take care of the 3.3V signal wire regulation, or if 'im capable of producing one myself.

Have to save money and read about Xbees!

So until the future is now...

 

 

20.9.2010, my birthday!!

I have ordered Xbee modules (for radio-control) from sparkfun among with much other useful stuff. The model is  XBee Pro 50mW Series 2.5 RPSMA with antennas that I hope will fit. I did a first tes-trun of the frame with only one motor and decided that the gear ratio needs to be changed. Speed is not a priority. If I want this thing to be able to turn like a bobcat it needs allot more torque. I will try to change the small sprockets down from 16 to 11 and observe the difference. In worst case I will have to buy better motors.

 

The motors I am using now are from 10€ cordless drills from a cheap shop.

 

Here is a short video from the first test-run:   http://www.youtube.com/watch?v=ty91ZLM-yAY

The problem I'm struggling with right now is how to attach the small 11-teeth sprockets to the motor. These are the smallest sprockets that I have managed to find that will work with a standard bicycle chain.

 

If only money was not an issue, you could just buy parts that would just fit together, but whats the fun in that?

...to be continued

 

26.9.2010, Very very happy!

My XBee modules have arrived and after some major problems and help from members of this community I got them to work! :)

Today I did a quick range test and I'm pleased. About 1 km is more than suitable for my needs. (had not more open space to test than that).

People was looking a little bit scared when they saw a guy walking around with a breadboard with wires sticking out in every direction and a LCD witch was counting something. :) I actually had to explain to a guy that this was not a bomb.

So my goal is to construct a remote with two thumb joysticks, a graphical LCD and some pushbuttons.

 

Another thing I have done is configuring my drill motors so that they are more suitable for my purpose. I removed the moment lock from them by opening them and figure out how they worked. I made custom screws and screwed them tight into place.

I am getting close to figure out the sprocket problem.

 

26.10.2010, Hard to find time

Yes I have had hard to find time to work on this project, but have not been lasy. I have been working on the controller that will control this crazy project.

I have planned and etched the main brain circuit. It will use a picaxe 28x2 and external 512 EEprom. The controller will have dual vibrating motors (one for each side), a graphical LCD, piezo for sound, two thumb joysticks with center-buttons, three panel buttons, one 5V regulator for brain and XBee, one 6V regulator for the screen, programming jack, and a indication LED.

The sides are from oak with a intarsia inlay. The top and bottom from 5mm aluminium sheets and they work as heatsink. The front and back -panels are from 3mm white polystyrene.

 

The vibrating motors are taken from old mobile phones.

 

Now I am trying to program the controller and it seems to be working. I have had quite some problems with the readings from the analog thumb-joysticks, but I hope to fix it soon. One downside is that the LCD seems to be a bit slow. When I am sending readings from the joystick over XBee to another picaxe with a regular 2x16 char LCD I see the readings change on the receiving LCD faster than on the sending one.

I am a little bit dissapointed that I decided to buy v2.5 PRO XBees, instead of regular. I tought that they should work better as they are newer, but I was wrong. They don't work straight out of the box, you will have to configure them the right way, and I have not been able to get two-way communication with them yet. (but I havn't given up, when I have more time I will try this)

Well that's whats new for now.

Peace out

 

 

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I have considered using drill motors as well. I'm always keeping my eyes open for a pair of matched cordless drills at garage sales, etc.

Could  you post higher resolution pictures and more detailed explanation of how you configured your drill motors? You can upload the higher resolution pictures and them add them as links from your smaller pictures in the body of the post.

I'm not quite sure if higher resolution pictures will help you with this, but I can take some when i configure the other motor. It will take some time though, cause it is still attached to the drill I'm using to build this thing :).

The BIG question that needs to be answered first is probably:

WHY CONFIGURE YOUR DRILL MOTORS??

and the answer is this.

It will be much easier to attach the motors to any frame.

It is quite hard to explain how to do this, but it will be obvious when you open your own.

The gearbox has a plate with bumps. The holes you can see in the picture had steel balls in them and ontop of the holes was a spring-loaded plate. The springloaded plate was pushing against the balls in the holes witch pressed against the plate with bumps inside the gearbox. (I don't expect anyone to understand this, but you will when you open them). You were able to adjust the tension of the spring (adjusting the momentum lock) by rotating the big thing with numbers on it.

So what I did was I just removed the balls and screwed in screws in the holes so that they are pressing against the plate with the bumps, so that is could not move. I didn't use all 8 holes just 4 screws in 4 holes it should be enough.

 

Hope this didn't just confuse you! :D