Engine Dyno Part #2

[rc_sjo]

So after consultation with the mighty RCG, I have changed my plans from creating a thrust rig to that of creating an engine dynamometer. I intend to make this suitable for testing plane and car engines, up to about 1.6ci in capacity.

I've pretty much got the design sorted in my head and will be paying my CAD guy a visit shortly to start laying it out. I've got my load and load control side of it designed and have found some 'cheap' inline rotary torque transducers and associated couplings (rather than build a comparatively complex load-carrier and associated torque arm for use with a tension/compression load cell).

The tricky bit now is figuring out how exactly i'm going to produce an engine mount that will cater for most engines. My second design problem right now is figuring out how I will connect the engine to the dyno. I'm thinking I should use two different materials for the pinion and spur gear (like how rc cars do it, metal pinion and nylon spur or whatever). It will be approx. 4:1 reduction gearing to suit the loads max rpm.

The problem is producing some kind of universal pinion that will bolt onto different engines, if at all even possible. OS told me they have a range of output shaft dimensions, so perhaps just different sleeves would suffice. The goal is to make it as simple and elegant as possible without getting a different flywhee/pinion assembly made for every different engine!

Another problem currently on-mind is a starting system :)


I'm keen to hear anyones previous experiences or thoughts on my few issues above.. it's always nice to hear someone elses view on how to tackle a problem! As well as the potential pitfalls..

Thanks,
Stu

[Tom Harper]

Stu,

Torque reaction is a lot easier. Use a plywood plate to accept the radial mounts you can buy at the hobby shop. Pick the one for the engine under test. Mount the plywood plate on a sleeve bearing - telescoping brass tubing with some powered graphite lube.

Set up a cross bar with a solenoid on one end and a counter balance on the other. Drive the solenoid from a current source with an R 2R ladder or a D/A with 8 - 12 switches on the inputs. Place an IR interrupter on the balance end of the arm. You need stops on the cross arm so that it only rotates a few thousandths of an inch. Just enough to open and close the IR beam.

When the engine runs it rotates the cross bar and interrupts the beam. An LED indicator lets you know. The solenoid is rigged to pull the arm back against torque. You then close the switches on the D/A as a seccessive approximation sequence. When you are done, read the switches to get torque.

It's easy to calibrate. Just hang a weight on the cross bar and go through the same process.

Shouldn't cost more than $20.

Tom

[rc_sjo]

Tom,

Thanks for your concise response. I already have the dyno design done (for how to measure torque), it's just the adjustable mount for the motor that i'm trying to figure out :)

I have considered using plane style mounts on a vertical board, but I think when fully loaded up they will twist too much and potentially cause a problem with my gear mesh clearances. I think solid mounts are the only proper way to do this!

[Tom Harper]

It's a problem. Usually ends up being the messiest part of an otherwise trim set up.

Tom