555 timer regulator

I have a robot with a 12 volt and 5 volt supply. I bought some automotive relays that use 6 volts. The relays don't work on 5 volts. I was going to give the relays PWM with the arduino but didn't want to waste and processing power. Is it possible to use a 555 timer to make PWM and then amplify it with a transistor or MOSFET?

Yes, you can use a transistor or mosfet to to drive a relay from the 555 output in exactly the same way you would drive a relay from an Arduino pin. BTW the hardware PWM on the Arduino doesn't consume processing power once it is set up.

A simpler but less efficient way to run a 6V relay coil from 12V is to put a resistor in series with it.

An Arduino pin shouldn't be used to power a relay directly anyway...so use the 12V supply with a suitable drop-down resistor and a transistor to switch it.

How much current does the relay winding take at 6V?

MarkT:
How much current does the relay winding take at 6V?

Depends on the relay…that’s what datasheets are for.

automotive relays that use 6 volts. The relays don't work on 5 volts.

Unless it is some odd-ball relays, they will work at 5v. Most relays will work down to 1/3 of their rated voltages. Many "relay savers" will actually insert a resistor in their once the relay has been activated, effectively reducing the voltage applied to the relay. So if your relay is rated at 6v, chances are that it will work at 5v, and even lower.

I was going to give the relays PWM with the arduino but didn't want to waste and processing power. Is it possible to use a 555 timer to make PWM and then amplify it with a transistor or MOSFET?

Yes.