by Tony » Sat Oct 11, 2008 12:56 am
The speed/load control system for my Telma is entirely home made. It is designed so it can control either one Telma retarder or two (for four wheel drive). Although I only have one roller frame and one retarder for it at this stage.
All the parts of the whole system have been prototyped, and all parts tested, but I now have to build it up properly to test it as a complete system. I believe my methjod of doing this is fairly unique, but it all works extremely well.
The basic idea, is that there is a central master oscillator, the frequency of which sets the desired road speed.
Each dyno has a slotted wheel fitted to the rollers, and this outputs a frequency proportional to roller speed. The phase/frequency of the roller output frequency is compared to the master oscillator frequency, and retarder load is adjusted with a PID controller to hold the rollers to the speed set by the master oscillator.
So you could have four wheel drive, or even six wheel drive, each dyno speed locks onto the master oscillator frequency. The dynos do not try to lock onto each others speed.
This controls the power to each retarder independently. While everyone else uses a phase controlled rectifier to supply the high dc current to the retarder windings, I prefer to use high frequency pulse width modulation from a high voltage dc supply. This responds much faster, and controls significantly better than mains phase control. I have done a lot of work on this part of it, and am pretty pleased with the dynamic response of the retarder.
That is the grand plan.
Also known as the infamous "Warpspeed" on some other Forums.