Chaos Vehicle - RPM Issue

[eagletree]

Have a slightly different issue I’ve been fighting for a couple of days with the Chaos Vehicle Component and RPM. I have several vehicles set up and working well. I went to cut over our Tank Track controller (still a wheeled Vehicle) and have a bug. The RPM goes up to max but won’t fall off. The other vehicles all using the same parent BP, fall off as they should. The controller does fall off slightly, like at 5000 RPM when running full out, braking or backing off the throttle will let it drop to mid 4000s, but then it stays there until I jump out of the vehicle which does a CV reset.

I’ve tried using identical settings to the other vehicles but it does no good (including the torque curve I use elsewhere). The difference in the vehicle is that it has 16 wheels. 12 are all bogies and drive wheels spun with Chaos and I manually move the track spline around those, the track pieces are set on the spline. Beyond that, those are 12 wheels that do nothing. I then have 4 invisible wheels which actually do the locomotion of the vehicle. All this works other than this odd RPM issue.

Speed and gears seem to be fine, when I stop, speed is 0, gear goes to neutral, only the RPM stays way up a bit below the max RPM I set. I’ve played with fall off and it has no affect. Changing the torque, RPM and Idle only change where the problem occurs.

I’m sure it’s a config problem, but I’ve exhausted my testing options beyond just removing all the wheels. I didn’t think they could effect the RPM though. Has anyone struggled and conquered this sort of problem?

Edit: Since fighting with this problem for another day, I did find that somehow, the wheel set is having a direct impact on the RPM. Changing wheel sets to a jeep that I have working, cause the RPM to fall off as it should. I can’t think of any reason why the wheel sets would impact Engine Rotation Speed at all myself, yet alone to force the RPM to remain very high, perhaps someone else might conjecture on this. At present, it’s looking like a bug, at least in the way RPM is calculated in the plugin. It may have a relation to the number of wheels as the wheel set I replaced it with, had a more traditional 4 wheels. I do have another vehicle with 14 wheels that works. The failing one has 16.

The only engine version I’ve tested this on is 5.3.0.

[eagletree]

Found the issue. RPM is tied to wheelspin in the Chaos plugin. Any wheels not touching the ground will continue to spin causing a high percentage of the RPM as the returned RPM value.

In our case, since we were using the vehicle controller to spin all 16 tank wheels and 4 of them are in the air (the simulated front track Drivers and rear Idlers). These wheels held the engine rotation speed artificially high.

In testing, this can be made to happen even on a standard vehicle if it get’s on uneven ground and one wheel is elevated. Even after throttle is reduced and speed stopped, the elevated wheel will continue to spin and the engine rotation speed will remain partially high. This is true even if the vehicle specifies Rear Wheel Drive and the spinning wheel is not a drive wheel. It also occurs when the transmission is in neutral. Physically, this sounds like a bug, so I will file a report, they will know if it’s by intention.

The workaround is to turn elevated wheels separately from physics wheels. Easy in our case because it is a percentage of track/spline speed which we have to track separately and is derived from the rotation of the grounded wheels.