DIY Engine dyno

Hi all

I am in the planning of making an Engine dyno, it has to fit two strokes up to 20HP. As i see it i have several options. and picked the ones below to invistigate futher

  1. Inertia flywheel, there is several good guides on the net, one norwigian has a very good working one and really good instructions to build it.

  2. Use a Hydraulic pump as a brake, and a loadcell to calculate the power. This setup should be smaller and the Hardware will have a smaller "footprint".

The first option i have all info on how to build it, and the software it avalible.

The second i´m in the dark a bit. Can Arduino handle this and how can i make it calculate the output power? The hardware part of it is easy, but i have no clue how to get Arduino to calculate output power.

any advice, or some one that have done this before

Quite a bit of good info here and some free downloads as well.

https://www.sportdevices.com/download.php

Another older writeup here.....
http://www.modelenginenews.org/techniques/testing.html

Bai7200:
...Use a Hydraulic pump as a brake, and a loadcell to calculate the power. This setup should be smaller and the Hardware will have a smaller "footprint".

The second i´m in the dark a bit. Can Arduino handle this and how can i make it calculate the output power? The hardware part of it is easy, but i have no clue how to get Arduino to calculate output power.

As I understand it, you will use the engine to directly drive a hydraulic pump, and in restricting the flow-rate of the pumped oil you will brake the engine to the required engine speed. The reaction to this will be measured with a load-cell, and it's output will be scaled an read as torque.
There is a relationship between torque and power, but I can't remember what it is!
Remember that using this method will put most of this power into the oil as heat, think how you will keep the oil temperature stable.

Measuring the engine speed (rpm) should be easy with an optical or magnetic pick-up. I'm afraid I'm not fully up to speed with the coding for this, but I suggest something like:

  1. Take a reading of millis() when the pickup is sensed, and set the revcount to 1.
  2. Next revolution revcount = revcount + 1 (assuming one revolution per pickup pulse)
  3. Read millis() when it revcount = 100.
  4. Time taken to do 100 revs is millis-now minus millis-then.
  5. Engine speed is 60 divided by time taken for 100 revs, times 100,000 in revs per minute.

The reason that I suggest taking the time for 100 revs is that an engine operating at 6000 rpm does 100 revs per second, or 1 rev per 10 milliseconds. Given that millis() returns the number of milliseconds since the last reset, the resolution will be +/- 600rpm if you tried to read it every revolution. This way the average of 100 revs gives an update once per second at 6000 rpm, but at a resolution of about +/- 6rpm.
That said, 6000 rpm is relatively sedate for a high performance two-stroke... 100cc kart engines typically peak at 18-20,000 rpm!

Measuring the torque, and then on to power should be straightforward. The load-cell will be a set distance in metres from the centre of rotation, and it will output relative to the force applied to it (say in killogram). The torque will be Force in Newtons (kg x 9.81) x distance from centre in metres .... unit is Newton-metre (Nm).

Despite my cop-out over conversion from torque to power, I seem to remember that 1 hp is defined as 33,000 foot-pounds per minute, so I suppose you can substitute the imperial equivalents (feet and pounds) into this equation to get power in hp, or indeed use the metric figures to calculate kW. My brain won't let me do this at the moment.

Hope that helps, an that I haven't gone off at a tangent.

GM

s I understand it, you will use the engine to directly drive a hydraulic pump, and in restricting the flow-rate of the pumped oil you will brake the engine to the required engine speed. The reaction to this will be measured with a load-cell, and it's output will be scaled an read as torque.
There is a relationship between torque and power, but I can't remember what it is!
Remember that using this method will put most of this power into the oil as heat, think how you will keep the oil temperature stable.

The plan is make a frame with an axle mounted to a pump, a valve to restrict the flow and a loadcell to read the force. I was planning to either preheat the oil to a given temp or cool it down, to heat it i only need a heater and a thermostate to control it. The issue must be to have an even tempeture to get good readings.
I was hoping to be able to accelerated the engine from Idle(2000Rpm) to full speed in say 10sec or so and get a power curve.

he reason that I suggest taking the time for 100 revs is that an engine operating at 6000 rpm does 100 revs per second, or 1 rev per 10 milliseconds. Given that millis() returns the number of milliseconds since the last reset, the resolution will be +/- 600rpm if you tried to read it every revolution. This way the average of 100 revs gives an update once per second at 6000 rpm, but at a resolution of about +/- 6rpm.
That said, 6000 rpm is relatively sedate for a high performance two-stroke... 100cc kart engines typically peak at 18-20,000 rpm!

The engines we use and that we are going to test is "only" reving to 14000 and is 60cc and is putting out 12hp or so, could it be possible to read the RPM with just a wire around the Sparkplug wire, just like our Laptimer do?

For data collection i was thinking of using makerplot software, looks like it could suit me fine. But i am kind of new in this Arduino thing, and cant seem to find the correct board that can read the loadcell and a RPM signal

The thing is im not that interested in knowing the precise power output, it´s more impotant to know that the things we try works or not, its less exspensive to test in garage, and we dont loose tracktime testing ignition timing and carb adjustments.

An other option is to make a inertia dyno like this one https://ardyno.weebly.com/ the benifit would be that i know it works and not much can go wrong, all info is ready, the downside is that need to get a flywheel made up and that the thing gets kind of bulky.

WRT the 20 HP worth of heat to remove I'd suggest a water brake. It scales neatly up to hundreds of HP.
Also see wikipedia "Dynamometer".

Glorymill:
There is a relationship between torque and power, but I can't remember what it is!

Torque is the turning reaction Lb/ft(pound foot) wheras work is ft/lbf (foot pound force) and hp is the rate of doing the previous work.
Other equations also need to be introduced ( atmospheric pressure, temperature and wet bulb relative humidity) as they all have an effect on the outcome.

Might be useful for the Op to take a look at a Google search for "rc engine dyno.pdf".
A LOT of info there including build platforms and free download software.

Still have the charts on my workshop cupboard from the unit I built about 30 years ago.
Sadly the 2013 flood took the machine itself and all other associated paperwork/instructions but I did see the old original magazine somewhere online.

You wrote: " I was hoping to be able to accelerated the engine from Idle(2000Rpm) to full speed in say 10sec or so and get a power curve.".

How do you intend to stop cavitation in the oil pump? That is a super fast acceleration for a gear pump, or do you have some other type of a pump in mind?

Paul

I am working on the same project. I have an old hydraulic dyno I want to add some electronics to. Have you made any progress? Where are you located? Check out the following link. It is how I am running mine right now. BUILDING A HYDRAULIC DYNO

Ken