Update: 3/2/04
Added new page of dyno graphs and results.
Update 3/10/03: I have now got Performance trends Datamite up and running on the dyno, and a damn fine thing it is too. More on this when I get some time to update the piccies.
Introduction
The following page will cover some of the things I have found out while designing and making my own rolling road dynamometer for motorcycles. In theory, much of it will apply to a car dyno as well, but due to the higher horsepower requirements, cost and size will increase substantially.
Excuse some of the fuzzy photos. I have just got an old digital camera, and they take a bit of getting used to.
Is it worth it?
Think carefully before you embark on this voyage, lest you to become bald like me. It has it's frustrations, and it is not cheap. A large drum or flywheel is expensive, and so are the rest of the parts. I did it because
My total (not including my fabrication labour) for this project so far is around $NZ5-6000 over 8 years, or $US3500 or so. Cheap if you are serious about development, but an expensive toy if you don't use it.
First step: Read Blair's SAE article and the TDK karts page before you start.
I have had a hankering to make an inertia type dyno for a long time, and this is the cumulation of a lot of work and contributions from all over the world. i have had advice from the US, UK, Spain, Australia, New Zealand and a lot of other places I have no doubt forgotten. I would like to thank all those who have helped me with this project. In fact, it is a testament to the power of the Internet, as it couldn't have happened without it.
The original idea came from John Fitzgerald of Thunderbike Engineering in 1996 when he described to me via e-mail how his home brew dyno worked. In his case, he had modified a waterbrake to inertia type by adding a large flywheel and disconnecting the water pump. I went called in to see him later that year and he showed it to me and how it worked, and did a couple of runs (on a Triumph triple IIRC). The idea got canned for a couple of years after that, as I went back to university, and hence had no time or money. I still kept an eye open for ideas, and was trying to find a cheap and elegant way to collect the data.
Towards the end of 1997, I finally got things underway, by ordering the timer and a copy of the dyno software card from Andy Cree at Canterbury University, which he had originally written for John. While in theory, the computer program and data acquisition are easy, according to the experts, I have trouble programming my VCR. The computer side is the key to a successful inertia dyno and it is what you really pay for when you buy a Dynojet, etc. Fortunately, with the decreasing cost of computer hardware, the availability of general PICs like the BasicStamp, and more people who can program the black box, the prices are dropping.
Mechanically, fabricating the dyno has been relatively trivial. I subcontracted out the fabrication of the drum and dynamic balancing to Titan Marine Engineering, Railside Ave in Henderson, Auckland, New Zealand. If you use a chain or direct drive with a flywheel, then this job is a lot easier and cheaper. The problem I had was finding a workshop with sufficient capacity to turn the drum after they had welded it together - there was no way it would fit in my Colchester. With a flywheel, then it can be done in a smaller lathe with a gap bed. The welding, fabrication and painting of the frame took a couple of weekends.
One of the objectives of the design of this dyno is that it had to be reasonable portable. At the very least, it had to be able to disassemble so that I could pack it away in a corner when it wasn't in use, as I am rapidly running out of space in the workshop. I have done this by making the frame that supports the front of the bike unbolt from the drum assembly. The carriage that the front wheel straps onto to lock it into place also unbolts, as does the front support frame. The dyno drum unit is on wheels so I can roll it away.
The dyno drum is fabricated from 500mm steel pipe with a 75mm shaft through the centre. I have found this is a little light for 70hp+, so I added a flywheel to one end to increase the inertia. In your case, I suggest making the end plates of the drum from thicker material (eg 100mm) to achieve the same end.
The frame of the dyno powerhead is 75*75 RHS mounted on wheels. The frame could actually be smaller and lighter, but I wanted to overbuild it, as having the frame collapse as the drum is doing 1700rpm would really ruin your day. The wheels aren't fitted to the front of the dyno frame at the time the picture was taken.
The front frame is 50*50 RHS with 100*100 angle to provide a guide for the front wheel to run in up to the carriage, which also slides back and forwards in it.
The carriage has a screw adjustment, but you could do it by undoing bolts and sliding it to suit. The screw adjuster (pics below) makes it a lot easier to set up by yourself, as you can strap the bike down and crank the bike along to suit on top of the drum. An electric motor would be nice here, as there is a a lot of cranking to get the carriage from one end to the other. I didn't put one on due to increasing weight (semi portable remember!) but if you had a permanent setup, it would be easy to do, by using a motor and gearbox instead of the crank handle.
Below: RD350LC with Cycleworks chambers. Bought originally for spares, I decided it was to good to wreck so it is back on the road. Coming up for new pistons, rings and gearbox work soon due to old age.
Left: My old nail Suzuki GSX400X Impulse. My first racebike and with under 38hp,
it has one sick motor. The motor has been sitting for 5 years in a shed, so the
rings may be stuck or worse. The seat subframe has been modified to take Keihn
CR28 Special smoothbores on a custom manifold. While this setup worked on other
Impulses, I could never get it to go. One problem is the Disney designed Aisan
carbs which are a twin throat twin carb setup. This means you can't bolt on a
set of 4 carb bodies to the head, so the intake length is very long. Later
GSX/GSXR/Bandit motors used the same bottom end with a new head and conventional
Mikuni CVs. In the picture is the current setup, with the stock carbs and no
airbox. It requires new pilot jets and drilling the main jet to #118-120.
Daytona used to sell jet kits for these but they have not been available for
years. The jets are non-standard and solid unobtainium.
Drum dimensions
The picture below is the plan for my drum
As noted above, I suggest you make it heavier / more inertia by increasing the size of the drum and/or having a flywheel or thicker endplates. Dynamic balancing after machining is a MUST - it will take off on you otherwise. My drum has no vibration at all at full speed. It has 2 weights welded onto the endplates to balance it.
I have added a 560*75mm flywheel (below) onto the end, which
has made a huge difference to the inertia (currently around 12kg.m^2).
This was a press fit over the shaft and welded to the drum. I
didn't have to rebalance the assembly after welding thanks to
careful fabrication.
Other changes...
Aside from a motor to wind the crank (not actually much on an issue), the other changes I would make for a permanent installation include a starter motor (for race bikes with no starter) and a brake. The starter is almost a must have if you are doing a lot of race bikes, the brake is nice but not really an essential.
An important point with brakes is to make sure the pads don't drag on the disk or drum when it is running, or the extra drag will lead to strange results and incorrect data.
if I made another drum, I would make it solid steel. This would be easier to fabricate, and be a smaller diameter to make the dyno easier to load. The choice of the larger drum was to reduce tyre slippage. Changing from the grooved drum to a heavy knurl should reduce this in any case.
Besides the drum, this project is well within the reach of a good engineering shop. I used the following tools:
The data acquisition system is the key to the dyno, and is what you pay for with a commercial system. The drum speed is via a data acquisition card and a magnetic switch on the drum. The card also has a handheld trigger to start the run if you can't reach the keyboard
I originally bought a turnkey
card and software from Andy
Cree for $NZ800 (approx $US400). It is very basic but
workable. Importantly for me, it was a ready to go system - I
am no computer programmer. Main bugbear - it doesn't pick up engine
RPM directly, rather it calculates from the ratio that you enter
between drum speed and engine rpm. DOS based means the computer
hardware is cheap.
A few months ago, I bought the Performance Trends Datamite, (also used by TDK) with the inductive pickup and optical isolator. I recommend it as a good, well made package. It comes with an instruction manual which covers pretty much everything. A more dedicated review in due course.
Ontrack digital do a data acquisition that has been used on at least one dyno that I know of. it picks up the ignition pulses from the HT plug lead to measure the drum or engine rpm.
Factory Products sell retrofit kits for their eddy current dyno
Hyperpower also may be able to help.
Land and sea dynos
DynoSoft KD (Belgium)
Steve Muller's home made dyno in Australia - uses basicStamp
Odds and sods:
Read
