Looking for tracks, cog wheels and motors

[Progrezz]

Hey, we are making a robot at school.
Since we are 17 year old electronic student we don't know much about mechanics and stuff.
We are making a robot controlled by micro controller and rs232 trough the internet.
We want to let it drive on tracks.
Easyest would be if we could get motors that work on 5volts and only use about 20mA.
What would you suggest on using (what sort of motors) and do you know some stores where we can buy this.

Thanks in advance.

[Admin]

How much $$ are you willing spend?

What rpm and torque do you need?

20mA is an extremely small amount for any motor (unless you are building a microrobot) . . . expect 200mA at least.

I recommend using a servo . . .
http://www.societyofrobots.com/actuators_servos.shtml

[Progrezz]

The problem is that we are going to use a micro controller to control the motors.
The micro controller wont be able to send a 200mA signal. Should we use a relay or something?

Thanks in advance.

[Admin]

Yea, you should never power a motor directly from a microcontroller (it will fry the microcontroller). The microcontroller just outputs a signal, then you must use that signal as an on/off switch to a much larger power source.

You also cant use it to control a relay, as a relay is high current too.

Instead, you should use one of these options:

servo (has its own circuitry built in)
http://www.societyofrobots.com/actuators_servos.shtml

motor driver IC, or motor controller
http://www.societyofrobots.com/robot_parts_list_electronics.shtml

H-bridge (using mosfets) - the homemade method
http://www.societyofrobots.com/schematics_h-bridgedes.shtml

[Progrezz]

Ok, thanks will discuss that and see what we will use.

Also i need some tracks and cog wheels. The length of the driving part should be about10-15cm, so i guess the cog wheels should be about 3-4cm diameter.

If anyone knows some webstores in europe that sell this, that would be nice.

[polar bear6]

i think tamiyia make tracks, maybe towerhobbies has some?
you should check.

[T.bag]

hey,

i think this store http://www.conrad.com/ should be able to help you out, you can pick your country when you get there and then look at the "model"(not sure on the english) making section for all kinds of little wheels and things... also motors... cogs or gears too

this place http://www.farnell.nl (or .com, and pick a flag) has more advanced stuff, relays, controllers and everything, but they suck for motors

[ilovetabasco]

Don't know if you've already found anything yet, but you might consider hacking this guy:
http://toyeast.com/v3/pdtdetail.asp?pdt_id=A02100339

Its a 1:24 scale tank (they have others as well, seeing as you are from europe you might be interested in the Leopard?). So it will have a complete chassis, body, motors, tracks, wheels, etc. all in a nice little package for US $89.99. Realistically, you could simply hack the remote and you'd be good to go, but that might take too much of the fun out of it.

Personally I'd scrap most internal electronics to get rid of the stupid toyish stuff (recoling action, digital firing sounds), throw a web cam on it and go.

[Handmixer.com]

You should try making your own tracks . Use a strip of wetsuit material the right width and cut diagonally from one corner of each end to about four centimetres down the opposite side. do a mirror image on the other end, then glue it together with an appropriate glue.

[sdk32285]

Ive never used wetsuit material. In the past i have made tracks from cloth. the thing to watch is that cloth stretches in different angles so you need to layer it to try countering the stretch. Also its easy to put grommets in the cloth for better traction.

[Admin]

Ive used both conveyor belt material, and timing belts, as good tread material.

[ilovetabasco]

What type of conveyer material? I am currently planning to try plastic conveyer like this guy:
http://www.rctankcombat.com/tanks/T010/

Using the tool from their website, however, told me that I would be operating WAY outside the specs for this stuff. But then again, they probably weren't planning on conveyers running at 15 MPH.

I like the fact that its positive drive, and I can easily attach some rubber pads to the surface to increase traction. If you know of any better ideas I would love to hear them. My last resort is going in and custom machining tracks out of aluminum and rubber, something like the real deal:
http://www.army-technology.com/contractors/tracks/blair_catton/blair_catton1.html

But that will make for some REALLY long days in the shop.

The other interesting problem I have is that I have a suspension system, so I can't make the tread fit really tight.

[Progrezz]

ok, whe are going to buy some servo motors

we would like to use some cheap positioning servos for arms and stuff, 90° and 180° and they are 3.5kg/cm, the cost about 7 euro
is that powerfull enough

we also need some continious rotation servos (2) for the the wheels, with tracks, where we can mount cogg wheels on


the main frame of the motor is about 15cm long and 10cm wide
i think in the end it will be about 25-30cm high and will way about 4 to 5kg
maybe this can give a better idea how strong the servos need to be

also one thing, the servos for the wheels need to be 100% the same torque and speed, otherwise the robot wont be able to drive 100% straight

edit: thanks for the reply's we are currently using the tracks from some kind of meccano toy box and are building the frame with that, works quit well
maybe in a further stage we could use better materials

[Admin]

This post talks about how to calculate how strong a servo needs to be for a robot arm:
http://www.societyofrobots.com/robotforum/index.php?topic=91.0

And this tutorial will help too for robot arms:
http://www.societyofrobots.com/mechanics_statics.shtml

And this one should help with calculating how strong the servos need to be for the wheels:
http://www.societyofrobots.com/mechanics_dynamics.shtml

Its a little math heavy, but its the only way to answer your question . . .

[Progrezz]

This post talks about how to calculate how strong a servo needs to be for a robot arm:
http://www.societyofrobots.com/robotforum/index.php?topic=91.0

And this tutorial will help too for robot arms:
http://www.societyofrobots.com/mechanics_statics.shtml

And this one should help with calculating how strong the servos need to be for the wheels:
http://www.societyofrobots.com/mechanics_dynamics.shtml

Its a little math heavy, but its the only way to answer your question . . .

so this formule for the arm
Moment = can_weight * arm_length + arm_weight * 1/2 * arm_length

but i don't really understant how to calculate the torque for the wheels in the last link