Using a lower pot value for motor bidirectional controller
Ordinarily you could just scale the resistors and capacitor and it would work, but 1K is about as low as you should go with R1. 

What you can do is to transfer some of the resistance in R3 into R1.

So, for example, to use 10K pots you could reduce R3 to zero (short), leave R1 at 1K, reduce R2 to 1K, and increase C1 to 1000uF.

For 20K pots, R3= 1K, R1 = 1K, R2 = 2K, C1 = 470uF.

...and so on. I woukd not suggest going much lower than 10K.



The reasoning behind this is that the capacitor charges through R1+R3+R5, but discharges through R2+R4. To keep the times similar to the original circuit you want the products of the total resistances and C1 to be the same as in the original circuit. You should be able to verify that my numbers are correct.