roller dyno questions

[Belgian1979]

As some of you know I'm trying to build a roller dyno bench on the basis of a telma CC300 brake and an old brake test bench.

Since I'm trying to convert the brake bench I ran into a couple of issue for which I need some opinions:

1. I originally thought the rollers were drums that had an axle go through them to which the bearings were attached. This doesn't seem to be the case. I had to remove on of those axles as I need to have some things on it changed so I could attach the CC300 brake but the axle is made up out of axle stubs welded to the drums...Would this hold up. I mean the CC300 is capable of holding 3000 NM...
2. The connection I need to make between the drums on the left and the right has to go through has an end of about 30 mm with a keyway in it. I would have someone make a connecting axle that would slide over it. Would this be enough to hold the power?

[miniv8]

There are slide couplers available, I doubt they will hold anywhere near 3k.NM at 30mm diameter...

For an industrial application like this, IMO that's a Scania truck driveshaft territory.

[BCjohnny]

I need some opinions

Sorry but I think using an ordinary vehicle 'brake tester' (MOT type) as the basis for a rolling road is the wrong place to start, the design rpm and torque capability safety factor are well below what you'll be achieving, without being substantially re-engineered

Also the roller diameter is on the small side, and what will happen to the friction coating usually applied when you spin them up is anybody's guess

[Belgian1979]

Good points. I did some online calculations and seemingly the shaft would take it, but not confident enough in that. On the other hand the contact surface is the tire. So I would guess it would break loose before the axle can break, but not sure.
Bear in mind these are double rollers and wheel rpm is quite low. Contact area is double that of one roll. Using big rollers is obviously and advantage but makes the brake very big.
I mainly intend to tune partial load areas. The friction surface is actually quite good on these.

[BCjohnny]

Well as long as you’re aware of the limitations, a couple of pointers might help ……

Every rolling road I’ve owned had a flexible coupling of some sort between the rollers and the Telma

The biggest commonly available rubber ‘donut’ that’s available is off 500 + bhp Mercs, an ‘eight bolt’ design

It’s the one I’m using on each hub dyno I’m building, and originally fits between the gearbox and prop …… I’d suggest you use something similar as it will take the shock loading out of the rollertrain

Secondly, tapered lock collar type couplings are available that not only use the keyway but physically grab the shaft, like a collet, when tightened up …… this will increase the shafts ability to transfer the torque without snapping the key

Good luck with the build

[Belgian1979]

Well as long as you’re aware of the limitations, a couple of pointers might help ……

Every rolling road I’ve owned had a flexible coupling of some sort between the rollers and the Telma

The biggest commonly available rubber ‘donut’ that’s available is off 500 + bhp Mercs, an ‘eight bolt’ design

It’s the one I’m using on each hub dyno I’m building, and originally fits between the gearbox and prop …… I’d suggest you use something similar as it will take the shock loading out of the rollertrain

Secondly, tapered lock collar type couplings are available that not only use the keyway but physically grab the shaft, like a collet, when tightened up …… this will increase the shafts ability to transfer the torque without snapping the key

Good luck with the build

Do you have a couple of pictures of those dyno's Johnny?

[BCjohnny]

No, not yet ........ most of the effort currently is going into moving into the new workshop and setting up all the machines, old and new

It's all sketched out, it'll be next year probably before there's anything to see, but it will happen

I've got a couple of CC160s for the main set, and need to find another CC100 for the other axle set ..... all brakes will be set up 'tighter' to get the most out of them

I'll likely use the 'Your Dyno' controls when they've ironed out a few more bugs .....

[Belgian1979]

Was planning on using the same controls. What bugs?

[BCjohnny]

Been a while since I've been on the site, but in fairness it still seemed a bit of a work in progress, while fundamentally working users were reporting minor glitches here and there

Maybe that's mostly application specific ...... it's difficult to make an all things to all men system I guess ...... and it's certainly not put me off purchase, Jostein should be congratulated on what he's accomplished

I'm using IGBTs, buffer caps & optocouplers, all the main brake driver bridge components have been acquired .......although others have used Semikrons etc

But I'll prove the brakes manually first when it's finally assembled and prior to hooking up the electronics