Small motor Dyno?

[doug odom]

Anyone know how to build a small dyno for about 10 horsepower 1/4 midget motors?  I really don't have to know what the torque is just be able to compare with another motor. Grandson is starting 1/4 midgets and Papa is getting dragged into it.

    Doug Odom in big Ditch

[Peter Jack]

Doug, some time ago around here there were several successful dynos built using a disk brake, an arm to restrict it's rotation and a scale to measure the force on the end of the arm. These were being used for full sized vehicles so scaling the principle down for a small engine shouldn't be that difficult for someone who builds lsr stuff.

Good Luck,
Pete

[doug odom]

Pete, Thanks for the reply. That is kind of what I had in mind. I was hoping someone had built one or had pictures or drawings so I didn't try and reinvent the wheel. Yea, I know I'm lazy.

Doug in big ditch where it is 78* today

[NathanStewart]

Connect the engine to a DC electric motor and put a variable load on the system that'll take 8kW of power.  Measure the power with a wattmeter.  1kW = 1.34 hp.  Done.

[Peter Jack]

That was a nasty dig Doug! We're expecting another foot of snow on the weekend even though we've lost most of what we had

Pete

[Freud]

Peter, does Bob Harris have electricity or a snow blower?

FREUD

[Interested Observer]

Doug,
Any type of “brake” dynamometer, be it electric, hydraulic, or mechanical requires a considerable amount of instrumentation, servocontrols, software etc. to operate successfully and maintain adequate control over what is happening.  While watching a “pull” on an installed commercial dyno seems pretty straightforward, behind the scenes there is a lot of automatic electronic controlling going on to make it work properly.  It is doubtful that it could be done manually and produce any useful data or even avoid damaging the engine or dyno.

I would suggest that you investigate using an inertia dyno.  These are commonly used for low horsepower engines and are relatively simple to operate.  As you may know, the engine drives into an appropriately sized flywheel through a clutch or overrunning coupling.  By recording the RPM as a function of time (a fairly simple instrumentation and data acquisition task) and consequently the change in RPM per unit time, the torque and horsepower can be calculated or, you can simply compare the slopes of the curves for the baseline and test engines to see which accelerates harder.  It would probably be best to do the calcs and generate the torque and power curves to really see what and where the differences are.  This would be easy to do on a spreadsheet using the rpm data.

[SPARKY]

Now this is the recall of a 69 Year young mind with CRS from  '69  speedweek 42 years ago----the "EGG" had a combo starter dyno using a generator to power the rollers for start and a resistance load to make the generator load up the "torque arm"bath to push against the bathroom scales for comparison.

[wobblywalrus]

Itsy bitsy dynos are mentioned in Harold Bettes' and Bill Hancock's "Dyno Testing and Tuning" ISBN-13 978-1-932494-49-5.  They say in the Eddy Current Dynamometer section "Sizes in field applications vary from tiny fractional horsepower electric motors to huge braking devices on drilling rigs and cranes."  "Some very small eddy currents are supplied by Dyno-mite, allowing testing of small radio-controlled racecars and aircraft engines."

The address etc. for Dyno-mite is in the book, too.  It is Dyno-Mite Dynamometers, Land and Sea Dynamometers, 138 Route 111, Hampstead, New Hampshire, 03841, (603) 329-5645, www.land-and-sea.com

[Peter Jack]

Electricity for sure Freud (he needs it for the anodizing) but I'm not sure whether he uses power or manual methods to remove the snow. Knowing Bob he probably has something mechanical although it may be home brewed.

Pete

[johnneilson]

What motors ar ethe Quarter midgets running these days? Are they using the OHV yet?

Years ago my son ran 5hp Briggs on alky, we had 2 dynos for testing.

I had a hydraulic manual dyno and then built a inertia dyno. The numbers off each are very different but will show gains or loss if used consistantly.

For the inertial dyno, make sure the flywheel has removable segments or rings to adjust for the power measured. I worked with Kevin at Performance trends to have a package and SW tailored to suit me.

http://performancetrends.com/dtm-dyno.htm

John

[John Burk]

If you use a brake rotor to load the engine be sure it's steel . A good ductile iron rotor explodes at 4700 rpm .

How about a complete rear with brakes  mounted so it pivots on the pinion axis and a bathroom scale under the housing . Apply the brakes hydraulically or by the emergency brake cables . Limited slip would be good to avoid a drum or rotor explosion in case the brakes stopped one side and the spider gears over-reved the other .

[McRat]

If you don't really have to know the exact HP, but need relative numbers, here's a thought.

You need to dissipate the HP in a way that doesn't change over time.

If you are on a budget, get a water pump off a V8.  This will take the RPM and HP no problemo.

Then you need to pump the water straight up against gravity.  The longer the pipe the better.  Kiddy swimming pool might make a good reservoir.

Get a flow meter (cheap) do the math and see how many lb of water you push up per second.  550? pounds of water, up one foot, in one second is a HP, IIRC.

If it doesn't work, at least you'll put on a great show for the kids and neighbors as it throws water way into the sky as the motor screams.  And it's fairly safe compared to other options.

It was 30+ years ago that I ran a Stuka? water dyno for VW engines.  Seems I had to play with a water knob and the throttle handle to try and balance the tach, then read the TQ and do the math?  Dunno.  Didn't make a career out of it.

[pookie]

  Doug, try TDK Motorsports Inertia Dyno Testing, or www.1 cedar-rapids.net/tdkmotor .  They show step by step how to build a Inertia dyno, and how it was used, materials then about 7 pages of Q 7A..All at no charge, and about 200 have been built across the nation..    Mike R.

[NathanStewart]

Doug,
Any type of “brake” dynamometer, be it electric, hydraulic, or mechanical requires a considerable amount of instrumentation, servocontrols, software etc. to operate successfully and maintain adequate control over what is happening.  While watching a “pull” on an installed commercial dyno seems pretty straightforward, behind the scenes there is a lot of automatic electronic controlling going on to make it work properly.  It is doubtful that it could be done manually and produce any useful data or even avoid damaging the engine or dyno.

I would suggest that you investigate using an inertia dyno.  These are commonly used for low horsepower engines and are relatively simple to operate.  As you may know, the engine drives into an appropriately sized flywheel through a clutch or overrunning coupling.  By recording the RPM as a function of time (a fairly simple instrumentation and data acquisition task) and consequently the change in RPM per unit time, the torque and horsepower can be calculated or, you can simply compare the slopes of the curves for the baseline and test engines to see which accelerates harder.  It would probably be best to do the calcs and generate the torque and power curves to really see what and where the differences are.  This would be easy to do on a spreadsheet using the rpm data.

^^^ Excellent information however I would like to remind you that dyno's existed long before computers ever did.  If all he is doing is measuring max power or torque output to compare with a different engine then you don't need any kind of complex controls or data recorders or anything like that.  The application of load was manually controlled on those old dynos.  All they did was look at a torque reading at a certain rpm and from that they calculated hp at that point.  I really don't think a 10 hp engine needs a full dyno plot across the full rpm range. 

Just my $.02.