Surfing the web for information on small inertial dynamometers, I found this wonderful website.

In my mind I had determined what my design should look like, and having found two photos of dyno's here that are extremely similar (the CMB 35 build and Spotlight on CC Racing), my overall design was confirmed and I have begun gathering the sources for materials and other hardware. I am looking for any input/suggestions from folks who have previously put one together.

I have done calculations for my flywheel, and am waiting on a fellow forumite who graciously offered to email me his spreadsheet for calculating ideal flywheel dimensions to confirm mine.
So far I have decided to use 4340HT for the wheel and shaft.
ABEC-3 bearings (maybe even spec 5), 7075 aluminum for the base-plate and bearing blocks.
For the wheel I am looking at 6" diameter by 5" thick running on a 1.5" shaft turned down to run 1" through the bearings. I haven't decided to have it dynamically balanced, or just do a static balance myself (after I build a balancing rig). Shipping up here is obscenely expensive.

So:
What software/hardware is everyone running? I have looked closely at the Performance Trends Data-Mite unit and this seems to be ideal for what I want; simple but with the ability to expand and upgrade.

Any suggestions and comments will be appreciated. I plan on having this up and running by the middle of July.

Thanks.

Sounds to me like you have things lined up pretty well and on your way to a successful dyno build!

I would go with the Performance Trends software...price is fair and it does indeed work well.

As for the material of the wheel, I'm not even certain what mine is made of ( I told the shop what it was for and let them make the selection). I know it was made from a "slice" in a rolled steel rod of the proper diameter, bored for the shaft, which was pressed in, and then the entire assembly was finish off on the lathe and checked for trueness. It was not balanced per say and has been used for several years now with no vibration issues doing runs up to the 20k RPM range.

Marc,

I was going to turn the outside diameter on my South Bend to clean it up and then drill the center, and finish slightly undersized with a finish reamer, heat the wheel and press in the shaft.

How do you clutch yours?

Mine is direct...in other words, the bell of the clutch is fixed to the shaft of the wheel. The shoes end of the clutch onto the motor and the two mated together when engine is mounted to the dyno. This has worked well for me. I am however considering modifying eventually (if I ever get the time) to us a Lovejoy coupler between the clutch and the engine. This would better isolate the engine. Most others that I have seen use the coupler method. The direct setup does work though.

If you plan to make the wheel on your Southbend lathe, then I would turn the O.D. and bore the I.D. without removing the part from the chuck. If you remove the part between ops, chances are good that you will not be able to hold concentricity and you'll have to have the wheel balanced before you can run it at high speed.

Another way would be to turn your shaft between centers, bore the wheel and heat shrink it on the shaft then turn the whole assembly between centers to assure concentricity. If you do it this way, be sure to turn and face both sides of the wheel.

Just trying to be helpful.

Steve

You are being helpful Steve, that is exactly what I was going to do. The materials are too expensive to make mistakes, so the old rule applies: measure twice, cut once.

Marc, then that is how I will do mine. Is there a specific clutch you would recommend? I need to go back and re-read and print some of these articles. I remember seeing a write-up on what appears to be a bulkhead mounted clutch which would work perfectly.

My wheel was done by a machine shop using the second method Steve posted. Thanks for the info Steve.

In all honesty, since you are building from scratch, I would go with the Lovejoy type coupler between the engine and the clutch to isolate the engine more. There are other good reasons for doing this, one being that you can setup an "airplane prop" test stand next to your dyno that uses the same Lovejoy coupler and swtich from one to the other very quickly. This is very good for doing warmup runs on the prop bench and getting the engine and pipe hot, then you quickly switch over to the dyno side and do your pulls. Engine performance is better and more accurate with everything warmed up to operating temps. Warming it all up on the dyno isn't so easy.

We use Performance Trends data logger and software. An article on our dynometer construction and use was published in Model Engine Builder issue 15 available at www.modelenginebuilder.com/issuefifteen.htm

Lohring Miller

Gentlemen,

With this level of help, I'll be able to accomplish this no problem.

Thanks!!!

Lohring, I had a feeling you would be posting on this thread! Is there any way we can actually see that article? I did not see a link to it on the site? Maybe a subscription is required. We would gladly put up that article here on MGB and share it with the boating community if that is a possibility. Anyway, thanks for posting and I am sure you have much you can add to help make this thread better. :drinks: