Ok thanks , seems I misunderstood. I've read so much stuff in a short time . That's why I said I'm not sure.

The sensor wheel on mine is a thin disc with holes in it ,  so looks like i need to make a wheel too.

Just to confirm , my rollers will top out at 3000 rpm max so that's  3000 divided by 60   makes 50 rpm sec.

So minimum 4 slots, I suppose 6 would be a good number then .

Am i getting this right ?

Yes you're on the right track, 4 slots × 50 RPS = 200 PPS is minimum but i would increase that to a high number , read this link  http://yourdyno.com/the-trigger-wheel/

Quote from "  http://yourdyno.com/the-trigger-wheel/

Brake control performance is reduced when the update rate is below 20 pulses per second. 

More teeth is better up to a certain point. If you have say 2000 pulses per second, YourDyno will make an average of 10 samples per calculation, which automatically filters noise without any downside to accuracy.

There is no hard limit to the maximum number of pulses per second, but it is recommended to stay below 6000. " .

Because you RPM of the rollers is slow compared to my engine dyno you can go high in the number of teeth in the trigger wheel so 2000 Pulses Per Second ÷ 50 Revs Per Second = 40 teeth trigger wheel . You can even consider a 60 tooth trigger wheel which equals 3000 PPS and is still within yourdynos limits of 6000 PPS. 

How small are your chassis rollers diameter ???

Is your chassis dyno a interia type or electric brake ( retarder ) style chassis dyno?

Have a look at Walter's build  titled " My Hub Dyno Build"  very nice example. 

Chassis dyno with Taylor waterbrake . All just parts gathered not going.

The rollers are an old rolling road that had pneumatic disc brakes.

Yeah i like the idea of hub dyno , takes up less space. I do have two identical retarders but they are big heavy units and I've never seen hub done, with water. I don't think it's really an option with pumps , hoses etc ,and if control is good enough to match wheel speeds.

Just letting you know if you don't already , I'm no expert on any of this . So please check on anything i say.

Hi , wasn't suggesting going to a Hub dyno  just merely his setup in general. The reason I ask about the roller diameter is you quoted max roller RPM at 3000RPM sounds a bit low. But then again there are other facts shaft and bearings and so on plus even the  Taylor water_brake dyno power curve.  Taylor Dynos certainly make some robust engine and chassis water_brake dynos.

What are the roller diameter  measurements ?

What sort of control valve is on the Taylor water_brake dyno??

Do you have any pictures to post?

Big horsepower vehicles will sometimes have to be tested in higher gears not 2nd gear but 3rd gear and possible in 4th sometimes which means great roller speeds. I don't know what type of vehicles you will be testing just merely stating some trivial information if its any good to you.

You will need a disc_rotor on the dyno also to get off the rollers to lock the front rollers up so you can drive off the vehicles being tested. Or do you have a Pneumatics over Hydraulics platform that sits between the rollers  raise the vehicle up to drive of the rollers.

Love some of the Taylor Dynamometer  , here is a truck Taylor TD-24 Chassis Dynamometer picture.

Rollers a bit over 8", just worked from kmh to diameter of rollers.

Brakes are from 1100 hp semi truck dyno , I'm planing on using one.

 I'm making the valve now , questions asked in another topic i started today

The rollers had a pneumatic disc before as a loading device , I plan on using that.

 CM 51 is the dyno the brakes are off , from what I'm told

https://www.youtube.com/watch?v=pyzu56Z-ToU

I plan on using one of these and modified ball valve

https://www.youtube.com/watch?v=X3d0pbFhNTM&t=49s

Showing speed , he sets a bit too fast in part, but doesn't have time to get full travel, and still doesn't get lost . That's why I chose these rather than a stepper , and they are cheap too.

These are huge power so If it is a bit slow I'll change the ratio of levers. Could double servo arm to valve and double speed. I think resolution would be good enough still. The valve I'm making should help too, nice slow change of opening size. Again though It's all theory till i make and test , I'm no expert just jack of all trades. It's going to take a while. I'm considering making a dyno room to keep noise down, job keeps getting bigger.

The ASME servo controller uses feedback for position referencing just a bigger version of the smaller RC servos. They are also DC brush motor construction with geared torque multiplication.  Nice units

Don't know what torque/rpm the Taylor CM51 hydraulic water brake can handle and what water supply is required?

Do you have a power curve map for the CM51 ?

At 8inch(203.2mm) roller diameter last thing you want to do is overspeed the dyno if directly coupled.

I spoke t a guy from taylor long time back when i first got the brakes. Std rating is 130 kmh on a 20" roller. So yes i will be over speeding, but he said they have margin in it. He said try to stay under 100kmh and it should be ok. I did think of using a step down gearbox but it seems messy and much bigger job.

Do you have any pictures of waterbrake valves internally ?

http://www.taylordyno.com/products/chassis-dynamometers/water-brake/cm-series/

I would like to reduce rpm 2-1 , but on the cheap I only thought of using a differential and can't find low enough ratio , or it won't have braking power till too high in kmh.

You got me thinking and I can get ford 273 to 1 diffs cheap,  they would be strong enough. It  would make the rpm much better , but will add complexity. I'll look into the possibility.

I did a quick calculation and with 20 inches roller diameter and maximum road speed of 130km/h the rollers are spinning at 1358 RPM. But with 8 inch rollers at 130km/h the rollers will be 3396 RPM. 

I know you said yor are going stay max at 100km/h. I would be checking the power curve torque/rpm.

There are plenty good V-grove ball manufacturers out there. Have you dismantled the valves on you Taylor water brake dyno. You say they have two valves on them at  one inch diameter ??? Where are the valves located on the dyno ?

I haven't yet removed to inspect my H&F GB4 valve as i want to first get up and running YourDyno hardware in manual mode before introducing another alteration to the system.

Easiest way is to make cylindrical V valves as opposed to spherical V groved valves.  There is nothing stopping you modifying a normal ball valves by inserting material into the hole and pinning it and make a V grove or slot into the ball valve.

Waterbrakes have two 1" inlets not actual valves. I was only able to get brakes and load cells.

I feel it's easier to modify the ball valve. I was going to go to great trouble to get more than 45 degrees rotation,  but now decided it's easier just to go big , so the opening can be reformed into a nice long V,  that could change. I would love to have some dimensional views of different waterbrake valves . The only one i found showing inside was from here, with no dimensions or hp capacity.

The CM dyno actually shows 90mph on the graph contradicting the kmh speed, but still agree much faster, although the rep said 100kph would be ok . That limits me so much I should gear it down, so i can use top gear to limit wheelspin.