altezzaclub Posted September 4, 2017 Report Share Posted September 4, 2017 OK, one of the projects on my list is a dyno for Woolshed rallying. Either an engine dyno or a chassis dyno, each have their advantages, but a chassis dyno is handier for tuning a motor in use. An engine dyno is great for building a hand grenade for the future, but not as practical with a handful of KE70s being driven by mates around the town. So I found these guys- http://www.dtec.net.au/index.htm They make the electronics that help your home-built dyno make sense. Amongst their many handy downloads is a dyno designer for an inertial dyno. Basically you set up a roller, put a car on it and give it a power run. The inertia of the roller acts as a limiter on the motor as the car speeds the roller up. It turns out their calculator on "Inertial dyno design tools" says- Maximum speed for the roller set at 1500rpm Maximum car speed to test at set to 160kph Roller diameter 565mm.. or about a 175/75x13" size. Engine power to test set at 100KW Time for dyno run set at 8sec rpm of flywheel at start set to 600rpm (about 2400rpm on the engine) rpm of flywheel at end set to 1500rpm (about 6000rpm on the engine) Inertia required 85kg/m2 This equates to an equivalent vehicle mass of 1065kg, good enough for a KE70. Then it shows you how to calculate the inertia of a flywheel of almost any round shape, I'm thinking of some bulldozer drive wheels lying around... Once you have the roller on bearings it shows you how to measure the built-in inertia of the system. The one above needs a steel roller of 565mm OD, 450mm ID and 1800 long. Except it weighs 1300Kg! Not unexpected, you accelerate a car weighing 1000kg every day, so the roller has to weigh that much. The bearings would have to take that 1.3tons rotating at 1500rpm, about 160kph. Of course if we allow only 6seconds for the pull we only need an inertia of 58kg/m2, so a lighter roller but less accurate. The OD would stay at 565 but the ID goes up to 495. A 60mm thick solid steel tube 1.8M long.. 830Kg. So, not impossible, as an engineering project its straightforward... Anyone else keen? Maybe a brake dyno instead... Quote Link to comment Share on other sites More sharing options...
LittleRedSpirit Posted September 4, 2017 Report Share Posted September 4, 2017 While that's' all very interesting have you contacted dyno dynamics for a price on a basic unit? I remember a few years ago we looked and it was surprisingly affordable. That said you'd want to use it professionally to pay it off. How many mates need tuning on it? I think being limited to 6000 is a problem, I find the dyno is the best tool for testing the rpm where its hard to drive at on the road, so its going to fall short of its true requirements if its only spinning to 6000 to tune. Wheres the nearest dyno already installed in your area? Is it a viable opportunity? With the setup described above, can you do everything a dyno can? Can you vary the load, to allow testing at all points of load. Can you work at steady state, and keep it exactly where its at so you can isolate a cell? Its not a great tool if its not controllable. Quote Link to comment Share on other sites More sharing options...
ke70dave Posted September 5, 2017 Report Share Posted September 5, 2017 (edited) As Matt alluded to, having a way of braking the engine is great, but what you really need is the electronics to control the RPM and the electronics setup to measure it. Then to be successful in tuning you need a good O2 sensor setup, and probably more importantly for making power is a decent knock sensor or knock ears setup. Now all of this is doable. My idea was to get a water brake from a truck, god knows where you get one, but they exist. And i assume you could get one second hand from somewhere. Now the controlling the rpm i haven't looked too much into, but id guess the truck does this somewhere to regulate the braking, I am imagining. But realistically youd want to do this with precision. So you might need an electrically actuated globe valve attached to an arduino that takes the rpm signal from the engine and then you would need some kind of interface to tell the arduino what RPM to target. My dyno knowledge is limited, but if you want to do a full power pull, your ramp time of the brake comes into effect, how do you even design this? Now for actual measuring of torque of the engine this is quite "easy" however you mount your water brake, it needs to be restrained by something that you can attach a decent strain gauge. then you take that strain gauge, connect it to a strain gauge amplifier and connect it to another arduino. Then you can calibrate your strain gauge using a known torque value. Ie 10kg, on the end of a 1m bar = 98 newton meter. display that on an LCD screen, multiply it by the RPM within the electronics and you have power too. Arduino can data log relatively easy and you can even get yourself a curve. All of this arduino stuff is very do-able, i have done a fair bit of arduino work and im comfortable i could do the programming and electronics, with a fair bit of R & D and alot of trial and error. I suspect the majority of this is possible. But i suspect what you will end up is a machine that can measure relative torque and power. Ie you will know that what you did has increased or decreased torque, but i don't think the actual values can be used to compare against anything else. unless you calibrate it, but im unsure how good you can calibrate it. A water brake from a freakin truck might not be that repeatable. So the accuracy is very much in question. I would very much know how a water brake dyno works, but i guess thats why you pay big bucks for them. Side note, don't start tuning peoples engines without insurance, i would fear blowing up someone elses engine. Edited September 5, 2017 by ke70dave Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted September 5, 2017 Author Report Share Posted September 5, 2017 (edited) The inertial system is easy to calibrate, its just like driving the car on the road with the GPS dyno. You have accelerated a mass of Xkg to speed Ykph in Zsec, and you measure the resistance of the roller bearings with a string and pulley system. But that is all it does, one pull though the revs then slow it down for the next one. The brake dyno can hold the motor at any rpm, but you need either those electrical retarders or the water (or oil) ones, all off heavy vehicles. Mercedes offer water ones on their trucks here, the heated water goes into the radiator and around again. Telma make the electrical ones, but they're all worth a lot of money. I'll look at using a torque converter out of an auto box, its the same basic system. That will measure torque with a load cell OK, but you need to find out how much is lost in the drive. Maybe we can set this up on a roller for a chassis dyno- As for insurance on car work... Hahaha, these guys own KE70s, you don't expect us to get PAID do you?? Edited September 5, 2017 by altezzaclub 1 Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted September 6, 2017 Author Report Share Posted September 6, 2017 (edited) These guys supply plans if you buy their electronics. Some good tech articles. Seems even retarder chassis dynos need lots of inertia in the rollers, but their bhp figures are way way above what we are looking at. Anything that runs a 100KW 4AGE up to 160kph is great for rallying. https://www.dynomitedynamometer.com/dyno-tech-talk/dyno_hp_limits.htm and the sell the water brakes separately. https://www.dynomitedynamometer.com/absorber/dynamometer_water-brake_absorber.htm Edited September 6, 2017 by altezzaclub Quote Link to comment Share on other sites More sharing options...
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