April 1, 2018

WLToys K989, new FPV indoor car

I saw this in an youtube ad from HobbyKing some time back and I was a bit intrigued by the features they had crammed into it. We have a few L939 fitted with FPV cameras at work but those cars are really not that fantastic. They have a stiff rear drive, bad handling and tends to flip over easily while turning.

Now, the K989 is something completely different. It is a bit bigger, I give it that but it has four wheel drive, rear and front differential and a low COG. It comes with a clumsier transmitter, but with a better feel to it.

The K989 is a real joy to drive, especially considering the price point compared to the alternatives in similar size and performance. I gave it two essential initial improvements, which owner should consider.

Improved front bumper

The stock "bumper" is just a piece of foam. It is good considering it will protect the chassis from damage on front impact. However, the front wheels and suspensions are not protected at all. And spare parts are still a bit hard to come by, at least if you can't stand monthly shipping delay from China. So, protecting the suspension is quite essential.

I made a new bumper which covers the front wheels, place right behind the edge of the body shell. It turned out it was quite important as I broke the first version after only a few minutes. So I improved the design a bit and printed it in ABS instead of PLA and I haven't managed to break it since.

The bumper model can be found on thingiverse.

K989 broken bumper

Lubricating the differentials

The diffs aren't that great. My specimen had a read diff that felt really bad out of the box, but the front was ok. I had to take a peek in the diffs to see if they were ok, which they were. But they needed oil. I gave them some 800cst silicone oil to work with. I didn't fill the diffs with oil as I suspected they would leak it out on the floor anyway. And they are leaky. But with at least some oil to work with, even the rear diff came to life and feels smooth now.

Oiling the diffs are probably the most important thing to do right away, they are dry on delivery and the planet gears are not of the best quality. To prevent the diff from eating itself you should probably lube it up right away.

FPV Mount

Mounting an FPV module on the car is quite easy. The stock receiver/ESC module is flat, positioned in the front of the chassis and makes for a perfect placement of a camera. The windscreen of the cover needs to be cut of course.

A colleague mounted the camera module simply with a rubber band and some hot glue. But I couldn't settle with that and I made a mount to 3D-print of course. The mount also holds a voltage regulator and I draw power from the main lead of the battery, since the battery is connected using the balance lead to the car itself.

WLToys K989 FPV mount