I haven't been able to test any of your suggestions yet, but it was another problem at the same time as decreased speed. Vdd was at the time 12 or 15v but i was measuring outputs of my decoder going to the gate with respect to ground, which were a little under 6.2v.

I used a square wave generator with a 0-5 Vpp. frequency was around 1 Hz

 

Well, you will need to match the logic levels of the CMOS IC's, or drop the voltage down on the CMOS logic to 5v.

That's a big problem with these Instructibles, they aren't very well designed to begin with, and they don't mention you'll have problems if you don't match the logic levels.

Those IC's your using don't have Schmitt-trigger inputs. If your inputs are slow-rising, or the logic levels don't quite match up, you'll wind up in the indeterminate zone, which is a bad place to be.

Do you have 0.1uF caps across the Vdd/GND terminals of those logic ICs? If not, that will cause problems. Every logic or linear IC that you use should have a minimum of one 0.1uF (100nF) capacitor across its' power supply, as close to the IC as possible. Metal poly film is preferred, but ceramics are OK. Tantalums are OK too, if you don't mind having one explode every now and then.

 

it's amazing how two little caps can much such a big difference. after removing the slow diodes and adding the caps I can get the motor to run smoothly with a 3kHZ clock, much faster than i should ever need. thanks for the help.

 

Well, glad you got it working better.

Sorry I didn't bring up the 0.1uF/100nF bypass caps earlier, as that should be one of the first things you learn about when using IC's of virtually any type. When you've been working with this stuff for awhile, it becomes so 2nd nature that one tends to forget to mention it, as their requirement is a given .