Roomba motor Soft Start circuit

[Bakafish]

This is my first time posting, so be gentle! Love watching the channel, and will be depending on you guys to help me ramp up my skills.

There is a flaw with the 800 series Roomba where the main controller board will randomly kick a small voltage spike into the vacuum motor causing it to click randomly every few minutes 24/7. It is super annoying, like a dripping water faucet. Anyway, some nice individual not only identified the root cause, but he created a "Soft Start" compensation circuit that is supposed to delay the motor spinning up so that these random discharges no longer cause this annoyance. The circuit is quite simple, with one N-type MOSFET, two resistors and a capacitor. I will include his diagram.

I built this circuit substituting the MOSFET with an STU13N65M2 n-channel MOSFET (which matched the specifications he said were important), A Panasonic 10uF 50v cap, and nice 1W 100K ohm resistors. The voltage of the motor circuit is 7.2V from NiMH batteries. The MOSFET he used was a BUK663R7-75C, which seems to have a lower Vgs(th) than the one I am using, and I am thinking this may be the problem, but I don't really have much of a clue. Can someone take a look and let me know how to debug this? I have a scope, multimeter and power supply.

[macboy]

It looks like the run on 14.4 v battery packs. The two 100k resistors in that design effectively form a voltage divider at the MOSFET gate, so the maximum voltage is no more than 7.2 V, assuming the drive signal (grey wire) is at 14.4 V when the motor is on. That is a big assumption. You need over 6 V, more like 7 V to drive the MOSFET into saturation and pass high current, refer to figure 7 in the datasheet, not simply Vgsth. You probably aren't getting that voltage. Reduce R2 by half and/or double R1. This will also change the on/off switching delays, but those aren't critical anyway.

[Bakafish]

I tried various divider ratio's and kept getting odder and odder output results, then went back and looked at his physical example and realized I didn't understand the mosfet's pinout correctly. After correctly wiring the circuit with the indicated values it works fine. Thanks for taking a look.