Speed control help

Extreme Fighting Machines » Light and Middleweights » Some general tips please

i have decided, i contruct this circuit:
http://www.bugs.nl/media/source/projects/speedo/relay-layout.jpghttp://www.bugs.nl/media/source/proj...lay-layout.jpg

but I dont know the type of the rel¨, can you says me the type. thx

You are using wheel chair motors so you would need something like:
70amp SPDT relays (sometimes called 70amp SPCO relays)

Regards
Ian

The wheelchair motor generate 70amp at 24volt???

thx, what means SPCO?

SP means single pole, which means there is one moving contact in the relay. CO means change-over, which means the moving contact moves between two contacts. One is connected to the moving contact when the relay is off, the other is connected when the relay is on. You can also get SPNO relays in which you only get a contact when the relay is switched on. You really want the SPCO type if you want to build a motor controller.

ok, thx for the help.

I have a doubt, the microswitch resist at high amps (70 for example)???

In the picture you linked to, the microswitches only switch on the relays. The 70 amps required by the motors only flows through the relays, not the microswitches.

I would also recommend you ask about this circuit on a general eletronics forum or newsgroup where there are more Italian speakers. Were all happy to help but most of us here are limited to speaking English, and with these high currents it could be quite dangerous if a mistake in translation occurred. Please dont take this as an insult to your English skills, they are a lot better than my Italian :)

I designed a speed controller around the zn409 servo control IC for my first robot, Orac. The circuit is really simple and swaps a bank of FETs in where the servo would normally sit. To get reversing, there is an output from the chip that you can use to switch another FET in to operate a high powered changeover relay to reverse the motors. The ZN409 is now obsolete but I think you can still pick them up. Alternatively, I think you can redesign the circuit around the M51660L servo driver IC.

Have a search on google for ZN409 to see a few example circuits or search for ZN409 datasheet to get the full info.

It worked well driving the wheelchair motors on the robot. I used car relays for the reversing as I worked on a car producvtion line ;)

ok, i think that i ask in a italian forum for the elettrical question.

peter have you got an image of the circuit

http://www.roboterwelt.de/info/sheet/zn409.pdfhttp://www.roboterwelt.de/info/sheet/zn409.pdf

See figure 11


You need to beef up the output stage with lots of FETs though.