Q&A Forum
Hi,
I have build me a hydraulic brake dyno with a 19 teeths trigger wheel and about 2000 pump rpm at max.
I have a RC servo (6 revolutions sail winch) for automatic brake control. I've connected the servo axle and the flow control valve axle directly, head to head. And that's what the question is about... When applying brake, it do the opposite, the valve opens, and vice versa.. I've tried to check the invert box in the software, but the servo then stalls. Any idea how to get around this without rebuilding the brake control rig?
Regards,
Geir
Yes, maybe I should make that more clear in the software.
Click "Invert signal" and set minimum pulse width to 100% - 11% = 89% and maximum pulse width to 100% - 4% = 96%.
You can reduce this range (89% to 96%) if you don't need the full travel of your servo. Note that sail winches are quite slow, indeed for this servo it is a good idea to reduce the range as much as possible so you only cover the valve max/min you really need.
Cheers,
Jostein
Thanks!
It worked perfectly.
Yes, the sail winch is slow.. I'm afraid it's to slow, but we'll see. I done some tests today, it worked good, but had some oscillation. Have to play with the PID setings and hope the sail winch can handle the job.
Regards,
Geir
An alternative is to go for a stepper motor, but I would search for a faster servo first.
With a slow servo you need a long flat part in the beginning of the brake curve. You increase RPM until it hits the start RPM, the servo will start to turn the brake valve and you continue to increase throttle just fast enough so the servo can cope, all while holding more or less the same RPM. When you reach 100% throttle, your flat curve can stop and the RPM curve can start the ramp.