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The basic premise of this idea revolves arround track stands which are widely available from various manufacturers.
The device starts with a modular set of rollers placed underneath the rear wheel of a motorcycle while it sits perched on a rear-wheel stand [link]. These rollers can be adjusted
verticaly to sit firmly between the ground and the tyre. The modular roller package includes built-in data aquisition devices which connect to your PDA, laptop, or desktop computer via USB connection. (perhapse a bluetooth version sometime after development)
Next involved is an easily adapted modification to a rear wheel stand. Included is an additional set of supports to ensure the bike doesn't fall over mid test. Also included is a set of vibration dampening rubber 'feet' for the supports as added protection against a fall-over.
While this is by no means a professional, permanent dynamometer, the results could be off just slightly in comparison. But could prove very useful for having a quick track test of an engine without having to do rigorous guesswork to resolve a complication.
I've also linked to Dynamometers on trailers ... they are pretty cool, but this invention you could pack easily in a truck, trailer, or toolbox.
Trailer Dyno
http://www.sportdev.../gallery/index2.htm
[Letsbuildafort, Oct 04 2004, last modified Oct 05 2004]
Track Stand
https://www.oneidas...d=16284&cat=&page=1
OoOooh -- Suzuki! [Letsbuildafort, Oct 04 2004, last modified Oct 05 2004]
A bit about dyno's
http://www.pwrtst.com/what_is.htm
[half, Oct 04 2004, last modified Oct 05 2004]
Small Hydraulic Dynos
http://www.sportdev.../gallery/index5.htm
w00t [Letsbuildafort, Oct 04 2004, last modified Oct 05 2004]
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Secondly, the dyno requires a serious load, at least equal to the weight of the bike and a rider. how would you supply it? |
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The dyno brake itself must apply a load to the tire that simulates the resistance to movement experienced by the drive train when the bike is ridden. Small diameter rollers might suffer from slippage when trying to accelerate against the load.
This might be included in your idea and I just can't spot it, but what keeps the motorcycle from launching forward when the dyno brake does it's thing by basically attempting to stop the back wheel from turning? Is that part of the modification to the rear wheel track stand?
I guess some method of strapping the bike firmly to a _very_ stable stand might work. But it will have to provide a down force for traction and a backward force to keep the bike from smoking the tire down the driveway and across the street in to the neigbors yard. That shouldn't be too tough to do. I worry mostly about traction on the rollers.
Obviously this pocket dyno wouldn't have a big water brake on it. How compact and cheap is an eddy current dyno these days? |
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Perhapse having the roller assembly attached to the track stand and bracing it from there ... while having the roller assembly and stand as seperate parts ... just modify the stand to handle upwards of 400 lbs. of downward pressure, and you're set ... One thing I neglected to mention in the idea was that the rollers would be in effect free-spinning, and the data aquisition box would interpret the data for a specific bike for example, parameters for a '98 TL1000s would differ from that of a 2001 GSXR 750. The information would have to be filtered through bike-specific parameters to get even a rough calculation. |
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But thinking about your anno, [half], it might be possible to place the rollers at an alternate angle to the wheel that would offer a more stable platform for gathering data ... and you make a good point about securing the bike down ... you might need some specialized bracing equipment to add to your stand .. |
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Pardon my ignorance on these particulars...how well is the bike attached to the track stand? When the dyno brake is activated to actually measure the horsepower, what keeps the bike from taking off? There's more than downward force involved. Not that I'm saying it's not possible. I tend to try to build this stuff in my head and that's where the questions come from. (some people think I'm questioning when I'm actually just asking and I only ask when I'm interested)
Another engineering consideration is the amount of torque that must be applied to the back wheel and how that can be developed using a dyno brake that has a small diameter wheel (thinking compactness here). |
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Truthfully, the bike merely teeters on the stand ... its held on by small bobbins on the swingarm that sit in deep grooves on the stand ... an over-the-top lock can fix that problem ... a complete re-design of the stand would be best including a wide base, and features taht help support the roller box. |
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[thinks while eating lunch...]
how about a series of small eddy current brake/roller units that are linked together on a chain type of arrangement. One end of this "chain" (maybe 6-8" wide) could be affixed to the stand and the other end wrapped up around the tire and attached to some sort of binding mechanism also attached to the stand near floor level. This would tie the motorcycle to the roller stand to solve the launching issue, provide multiple rollers to help with the traction issue, provide several small brakes to generate torque and keep you from having to lug some large diameter brake around. You'd still need to provide significant fore-aft stability on the stand or it would try to rotate around with the wheel when the dyno applies a load. Of course, this scheme would do absolutely nothing to keep the cost/complexity down, but you never said it would be cheap. |
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Indeed, [half] ... thats a very nice idea indeed ... all I was seeking in this idea is something smaller than a trailer for dyno testing. Something a little more easy to set up and use, nevermind the cost ... |
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I just re-read some of your earlier annotations. I'm not sure now if I was really on the same page with you. As I'm familiar with them, a dyno must place some sort of load on the engine to measure the torque and calculate the horsepower. I suppose that for limited accuracy, you might somehow use a dyno brake-like mechanism with a fixed torque instead of the variable torque needed for more sophisticated measurement. Not sure about that.
I believe that there are also dyno's that interpret torque based on the engine's ability to accelerate the spin rate of a known mass. This would drastically reduce the complexity of the control system. I don't think that would work for you though since you'd ideally like to keep your mass/weight to a minimum.
NB: I'm not a mechanical engineer and I don't play one on TV. |
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perhaps an electric motor could be used as a variable load for the rear wheel. You still run into difficulties with stability and control. |
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A mechanical brake could be utilized as well, perhaps a ceramic disk with scintered pads... Heat dissapation would be tricky but not as much of a problem as with metal disks. The trick would be to accurately measure the load of the brake. |
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Unfortunately, I think you will rapidly approach the cost of a trailer mounted unit and storage thereof before you will be able to come up with a small portable unit that will be able to measure horsepower with any accuracy at all. |
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[half] your second statement is a good interpretation of what I wanted: |
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//dyno's that interpret torque based on the engine's ability to accelerate the spin rate of a known mass.// |
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thats pretty much what I was shooting for ... I understand that you would not have the more complex features of a fixed dyno, and the results may vary (though not dramaticaly) if you were to benchmark this idea with a static dyno ... just a smaller, easier to own/operate dyno for smaller applications ... I'm also linking to a small hydrolic dynamometer used for go-karts ... perhapse use a similar device for motorcycles |
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The strangest dyno test I've seen was using a "weed eater" head on a sub 1 hp motor. All that was needed was to determine relative improvement so the length of string that the motor could spin sufficed for a relative measurement. |
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I can imagine "Dyno-tuned Weed Wackers" being popular with those on the "Riding Lawn Mower Racing Circuit" ... hehe |
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Here's my contestant for the coolest dyno: I saw a test engineer where I worked set up a test for the drivetrain on a trencher using nothing but one hydraulic cylinder and a torque transducer. He hooked the cylinder up to the concrete slab, then up and forward to the frame. The tires spun on the concrete (this is a slow machine--maybe 2mph) and the load was controlled by pulling the frame down harder against the ground. The computer watched the torque transducer and controlled the cylinder via a solenoid valve. Entire test was thought up, set up, and run in a day or two. |
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This is why small companies can compete against big ones--John Deere would have spent $100,000 to do the same test in 6 weeks. |
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Why not integrate the dyno sensor into the drivetrain? You could get the reading while driving. I don't understand how dyno's work, but if necessary you could create a special gear N-sub-D for neutral-dyno. No need to spin your wheels... The dyno output could be displayed by dashboard instrumentation. |
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Because most commonly a horsepower reading is taken after you factor-in working load and gravity's effect on the wheel delivering power. Simply taking the HP reading at the countershaft is different than taking the HP from the rear wheel. |
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However I have seen some places that have a test rig where they remove the rear wheel and hook-up your chain directly to the dynamometer and through a computer that simluates gravity, etc. with algorythms. Perhaps if you have a properly mapped ECU and ignition, then at corresponding RPMs it would display your current HP, but it would only be translating table data, and not giving it an actual, active reading. |
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Maybe I missed something, but wouldn't it be cheaper just to take the bike to a speed shop with its own dyno?? |
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All our Dynos here at school are basic accelerometers. Now the trick is getting the bike to apply enough pressure on the measuring drum of the acceleromoter to simulate a realistic load. I think it would require some sort of rear wheel clamp using 3 symmetrically-opposing drums that can be tightened-down and otherwise adjusted to exert the appropriate pressure on the tire. Then just anchor and you can do light-load dynamic runs, second and third gear roll-ons. Can'd do steady-state runs or serious all-gear runs, but for quickly and cheaply diagnosing low and mid-range running conditions I think this could actually work-out. Oh yes, and lets not forget the Air-fuel-ratio meter being incorporated n there somehow. |
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OK, I've got an idea for you:
Put the test bike on a stand that holds it via a pivot at the front of the engine area. Support the back wheel off the ground with a small frame that has a load cell. The load cell will measure the weight of the back end.
Now use an old bike which has the back wheel and engine only, and reverse this bike so that it's back wheel pushes onto the back wheel of the test bike.
When the test bike is running, it will turn the wheel of the second bike in the correct direction. The old bike's engine doesn't have an ignition system or carburettor, but keep the water cooling system. |
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Now vary a restriction in the exhaust flow of the second bike to vary the load. The second bike acts as a compressor. |
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As the first bike gets loaded up, it will drive the back wheel downwards. This is the force at the circumference of the back wheel. Power, kW = radians per second x this force in Newtons. |
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Well, [ling] the only problem with that is there's a lot of extra equipment involved. if all you're thinking about is applying pressure and resistance to the rear wheel of the test vehicle, then how about just putting on a "compact" water-cooled brake that's in contact with the drive drum? The only thing that may throw-off readings is our limited ability to achieve the correct amount of resistance and friction incurred by the weight of a motorcycle and rider, then testing the dynamic running condition of the motorcycle's engine and driveline bits. |
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I'm thinking a clamp that you can place around the rear tire, and anchor to the swing arm or another steadily-mounted point, then just running the bike with the appropriate software. Now I know this won't provide the solid-reliable readings of a fixed dyno, but you can still diagnose running conditions simply and quickly. |
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I think the problem is getting rid of heat: if your bike makes 100+ hp, then heat will build up very quickly. I thought that an engine/compressor would be very cheap and most likely be able to run continuously. |
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Also, the expanded air from the compressor could be used to cool the first bike. |
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Your idea of using the dynamic response is similar to just freely accelerating the engine out of gear, but with extra load? Difficult for re-mapping, perhaps. |
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I'm not sure what you mean by dynamic response being similar to revving the engine out of gear. The technique of determining hp by ability to accelerate a known mass isn't in question, or shouldn't be (common technique, drum based dyno produces very repeatable results in my experience). I thought he was just proposing a different method, with several small drums instead of one large drum. Are you suggesting that the mass of those drums wouldn't be sufficient? (Or maybe I'm just not following the thread very well.) |
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At the limit, the known mass could be the engine and flywheel? If a small external mass is used, then the engine and flywheel inertia is still important: Something that LBAF touched on before.
By 'dynamic' I mean the time when acceleration is taking place, as opposed to when constant speed is maintained. If I remember correctly, the ignition timing and fuel injection is different when accelerating compared to steady speed.
So revving the engine will give a different response to steady state.
I just feel that it would be difficult to diagnose a particular problem at a particular rpm at full power, if one could only accelerate past that rpm. That's why I proposed a solution that could take care of continuous full power. |
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I guess it depends on what kind of diagnosis is required. |
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Now after being in the industry a while and working in a dyno testing and preformance shop, I now realize just how hair-brained and half-baked this really really is. |
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Damn I've grown up. *Whatta let-down. |
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