liam.mccaffrey
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| posted on 27/2/04 at 01:46 PM |
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DIY dyno?
I would like to start playing with bike engines, (I'm an engineer) tuning and the like. I don't mean high power engines as in BEC's
but smaller single and twin cylinder fourstrokes. I don't want to start a business and have no interest in any financial gain, this is just an
interest of mine.
What I want to ask is, does anybody know of a "locost" way to obtain power or torque figures for engines, allowing evalution of
tuning/modifications.
I have a lathe and access to a mahine shop. I am open to any sugesstions including computer data logging and mechanical means.
Cheers
Liam
[Edited on 27/2/04 by liam.mccaffrey]
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MikeR
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| posted on 27/2/04 at 02:12 PM |
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have you done a web search, i'm sure i've seen something somewhere!!! (like that helps you!)
isn't the principle the engines ability to overcome a known amount of friction + some fancy maths.
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thebutler
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| posted on 27/2/04 at 02:20 PM |
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Could ask the Burgerman, he built his own. As well as all sorts of other crazy sh!t
http://www.diy-nitrous.fsnet.co.uk/nitrous-kits-designer.htm
Steve
[Edited on 27/2/04 by thebutler]
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liam.mccaffrey
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| posted on 27/2/04 at 02:23 PM |
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DIY dyno
I have been looking into various ways including known friction method. I know you can make an air brake dyno but I don't have any info on it.
Software estimators aren't much good as I am looking at fly wheel figures and they depend on 0-60 times.
I had thought about rigging up a pump and measuring the volume pumped or the pressure created at varying rpm, this could be callibrated to give a
power curve.
Any thoughts anyone?
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Mk-Ninja
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| posted on 27/2/04 at 03:02 PM |
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Couldnt you use a generator loaded against a known resistor bank. That would give you a direct power output with some simple maths.
Might be talking boll*ks though.
Gordon
I'm sure I've got one, just don't know where I've put it
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sebastiaan
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| posted on 27/2/04 at 03:23 PM |
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have a look at some gokart sites. Some guys seem to be making their own (flywheel based though....)
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PioneerX
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| posted on 27/2/04 at 04:00 PM |
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Did a web search too, found a electrical based one (looks like ti was designed from the R/C ones I found bu scaled up)
http://www.innovatia.com/Design_Center/dyno_project.htm
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liam.mccaffrey
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| posted on 1/3/04 at 03:04 PM |
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I have now have enough info to build my own dyno. I think!
I admit that it is simply measures from the flywheel but this is what I want it for!
Will post my ideas if anyone is interested.
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timf
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| posted on 1/3/04 at 03:12 PM |
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along similar lines
url on how to build your own flowbench
http://www.ag.auburn.edu/users/gparmer/articles/flowbench2/
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liam.mccaffrey
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| posted on 1/3/04 at 03:18 PM |
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brilliant i think this sort of thing is very much in the locost spirit
good thing is dyno will cost less than £100 quid this is for all equipment including sensors AND data aquisition hardware!
[Edited on 1/3/04 by liam.mccaffrey]
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greggors84
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| posted on 1/3/04 at 08:17 PM |
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Let us know how you get on liam
Chris
The Magnificent 7!
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racer56
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| posted on 2/3/04 at 06:29 PM |
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Liam
I am very interested to see your plans for a dyno for less than £100!! I have been looking at this for some time (although looking for someting that
would take higher power) and although I know in principle how it can be done, I have not come accross anywhere to get the gear for that sort of money.
If you are talking small bike engines (say to 12hp ie. 9kW, then you need 3 good fan heaters to absorb that kind of power!) I am looking for something
more like 70kW. Electric brake this means some kind of driveline retarder ("Telma" and they are pretty expensive, otherwise get into
water brake etc - also expensive to get the pumps etc. The trouble with accelerating a mass (inertia roll) is that you cant run a steady speed point,
so it make comparison a bit more tricky. Keen to find out how you are doing it to see if it could work for me
Cheers
Phil
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racer56
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| posted on 2/3/04 at 06:30 PM |
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by the way, sorry about the smiley, wasn't thinking when I put punctuation into the thread!!!
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liam.mccaffrey
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| posted on 12/3/04 at 01:43 PM |
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in reply to racer's comment,
would you ellaborate on the
"can't run a steady speed point"
I am not really sure what you mean.
by the way my plans for a dyno were along the lines of a rotating inertia accelerating and data logging software.
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Bob C
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| posted on 12/3/04 at 02:55 PM |
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You can use a car disc brake and a mechanical (handbrake) caliper to load a small motor. Measure torque by mounting the whole thing on concentric
bearings - you can then measure reaction torque with a lever arm & spring balance( feet and lbs - couldn't be easier)
Easiest to drive with a Vbelt but losses are unknown - cam type belt is better. All good fun
Bob C
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paulf
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| posted on 12/3/04 at 10:28 PM |
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I was thinking along similiar lines to this but thought of using a tourque converter with the output anchored to the fixed chassis.My concern was how
do you know how much energy is being absorbed and lost by the brake or torque converter?
Would it have to be calibrated from a known power source?
However just as a means of measuing power before and after mods it should work well.Maybe suspension springs with a known poundage could be used and
the reading taken from a scale calibrated in inches.
Paul.
quote:
Originally posted by Bob C
You can use a car disc brake and a mechanical (handbrake) caliper to load a small motor. Measure torque by mounting the whole thing on concentric
bearings - you can then measure reaction torque with a lever arm & spring balance( feet and lbs - couldn't be easier)
Easiest to drive with a Vbelt but losses are unknown - cam type belt is better. All good fun
Bob C
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Bob C
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| posted on 13/3/04 at 07:15 PM |
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If you mount on concentric bearings the torque reaction from the brake IS the load torque. The spring balance gives you this torque exactly (you know
how long the arm is & are measuring the lbs). To derive power from torque you need to know the rpm then
power = torque * rpm / 5250
if the torque is in ft lbs the power is in horsepower.
Note any dyno like this ALL the motor power becomes heat in the brake somewhere, whether you use electric, water, a disc brake, whatever - a 3hp motor
is like 2 electric fire bars. So blow a fan on the disc brake & it'll warm up the garage...
Cheers
Bob C
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sacem1
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| posted on 14/3/04 at 02:52 AM |
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liam
I'm really interested in knowing more about your design and equipment as I would like to have a dyno around to tune my engines (dune buggy 1.6L
aircooled VW's and now my Celica 2.0L S7 project car engine)
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liam.mccaffrey
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| posted on 14/3/04 at 09:48 PM |
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basically al I planned to do was to rig up a balanced flywheel, quite heavy (in terms of inertia) with respect to the engine.
then by making the engine accelerate the flywheel from tickover to redline and measuring, with some data aquisition software and a suitable proximity
sensor, the time interval between voltage spikes caused by points of known angular distance (ie teeth on a gear) passing the proximity sensor. This
will give a series of time values separated by a known angular displacement.
Now by taking 2 consecutive time points and multiplying the difference in the times by the known angular displacement gives an average angular
velocity between the 2 data points. repeated for all consecutive measured points.
A similar approach is taken to find the average accelerations between the newly aquired rotational velocity data points using the formula V=U+at
rotationally.
Finally now we have a series of instantaneous angular velocities and angular accelerations and the time at which they occured,
using newtons second law for rotation
torque=inertia x angula acceleration
we can calculate instantaneous torques for all the angular accelerations which will allow a graph of torque against angular velocity to be drawn.
In order to do this you must be able to obtain the moment of inertia of your flywheel. An interesting pursuit in itself.
I am no expert and I am quite prepared to be ripped to bits on this but at the moment it looks ok to me, comments/ideas/adaptations/improvements all
welcome
[Edited on 14/3/04 by liam.mccaffrey]
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Bob C
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| posted on 14/3/04 at 11:53 PM |
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liam, you can do all that, you'll need something fancy to measure & store the timings, Excel will do the rest. - Oh yeah - the point; moment
of intertia - your best bet is physical measurement. Moment of a disc is 0.5Mr^2 & your flywheel will probably be a disc. With r in metres your in
SI units to make the sums easy using w and Nm.
You then have to stop a bl00dy big flywheel doing a zillion rpm - probably best just to leave it while you sleep or have dinner....
cheers
Bob
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liam.mccaffrey
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| posted on 15/3/04 at 08:33 AM |
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I agree to some extent, whilst it shouldn't be too difficult getting moment of inertia from physical dims another way is to model the flywheel
assembly in CAD (very easy) and let the cad program give you its moment of inertia,
I have found some possibly suitable data logging equipment for very little money and yes excel will do the rest, the software that comes with the data
logging kit will actually dump all your data into an allready prepared excell sheet. I will investigate further and post any conclusions
As for braking, why cant the flywheel be braked using a disc and caliper, I don't mean jam on the brakes as hard as you can but the forces
present when used moderately can't be that much higher than when a car brakes to standstill
Liam
[Edited on 15/3/04 by liam.mccaffrey]
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