Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: rcdooley on January 25, 2007, 10:24:31 AM

Title: Relay Help
Post by: rcdooley on January 25, 2007, 10:24:31 AM

Using

 4 AA Alkaline Batteries (internal resistance of .4 ohms)
 Tamiya 10168 motor gearbox    http://www.pololu.com/products/tamiya/0114/
 
I need to be able to control the motors to operate seperatley and go in reverse
I am planning on using a spdt relay ( for off and on ) and a dpdt relay (for high speed and low speed)
I do not know what size relay to use or how to wire them.

If I run all the AA batteries together I will have a max of six Volts but three Volts for each motor therefore I need a relay less than 3 Volts to make sure the relay will come on?

Thanks,
 
 

Title: Re: Relay Help
Post by: Admin on January 25, 2007, 10:34:21 AM

how do you plan to control the relays? if you plan to use a microcontroller, using MOSFETs are better than relays. for the el-cheapo motors in that tamiya product, you can use a simple H-bridge IC or cheap motor driver - this would be the route I would go.

but if you were going to use relays . . .

to operate a single motor in both forward and reverse directions, you will need two dpdt relays wired in a configuration similar to that of an H-bridge:
http://www.societyofrobots.com/schematics_h-bridgedes.shtml

since the motors are small and wont draw much power, just get a really small cheap relay. if you wire 6V to both motors, then both motors will still receive 6V. the current will divide by two, not voltage :P

Title: Re: Relay Help
Post by: rcdooley on January 26, 2007, 10:26:35 AM

Then making a transistor H bridge is better, but more complicated so what do i need to do for it to work for my parameters.
Two NPNs and Two PNP, I know how an H bridge is set up but do not know what to get.

I thought Mabuchi motors where good?
I have 6V total but need two motors too run at once and need a High torque, is there a better motor that i could swap out in the dual motot gearbox.

Title: Re: Relay Help
Post by: Admin on January 26, 2007, 10:40:58 AM

If you want to make an H-bridge, go to Digikey.com and do a search for 'MOSFET'

in the Packaging/Case section, select all that have TO-220. This gives you a package that you can easily work with on your circuit board, and heat sink too.

Then select your current and voltage that you need.

But I think making an H-bridge is the hard way. I recommend instead searching for 'motor driver' in Digikey. This will give you a simple one package solution.

If you require higher current for your motors, try http://www.dimensionengineering.com/ for larger motor drivers.