Tonight I tested the oil pump – it worked so well that the pressure blew off one of the plastic tubes I was using for testing and sneezed oil over everything. After I cleaned up the mess I connected it into the system and did another test run. The extra resistance of the oil passing through the turbo bearings caused the pump to stall out on the first attempt. The pump was originally designed to move air, so it’s not surprising that oil was too much of a load. To remedy this I made a new crankshaft for the pump on the lathe with as short of a ‘throw’ for the piston as possible. With the shorter throw, the pump is moving less oil per rev which reduces the load and prevented the motor stall. After this change it successfully ran continuously and held an average pressure in the system of about 75PSI, right about where it needs to be. To keep things simple I don’t have a bypass or pressure regulator in the system; because of this the pressure gauge flutters with each pump stroke but this doesn’t hurt functionality.
The motor draws about 5A, at 12V this is ‘only’ 60Watts and is about the same or even a bit less than when it was an inflator pump. Since it will now be running for longer time periods though I need to keep an eye on the motor temperature. I also need to protect the plastic gear from the (eventual) heat of the combustor above. To address both of these problems I’ll likely make a heat shield for this area as well as add a cooling fan.
This weekend I resumed work on the jet engine project. When I last left off I had just completed the frame and mounted the turbocharger/combustor. I had also fabricated an oil tank out of an old propane tank and mounted it under the turbo, but had hit a bit of a wall with what to do for an oil pump. There are electric oil pumps available, but basically all of them would be overkill for this application. Also, since this is a hobby I’d much rather put in the time to make something custom vs paying for parts. Turbocharger jet engines have been done by many others, my approach with this is to see how compact and well packaged I can make one – that doesn’t happen by bolting together a bunch of off-the-shelf parts.
I had considered using the bus’s old oil pump, but this created more problems than it solved (connection of inlet/output pipes would be a challenge as would driving it and selecting a motor). Today after a taking a fresh look at it I realized that an old 12V tire inflator pump that I had could be adapted to work. The plastic casing had broken, but the ‘guts’ were all metal and should hold up to oil pump duty. The only problem was that the cylinder head of the pump had no way of connecting an inlet pipe – being designed for air, it just drew in air from a small hole. To fix this, I made a new cylinder head on the lathe with one large hole in the center. A tee fitting screws into the head and I’ll put a check valve on each side. This larger single-hole head should also help compensate for the increased load of pumping oil, much thicker than air. Once I start running oil through it I may have to make some tweaks to avoid overload (lower voltage, thin oil, etc) but this at least gives a path forward for experimentation.
I also shortened the oil tank to make more room underneath for other support systems and made a threaded port on the lathe to weld into the tank to connect the oil pump. The welds aren’t the greatest looking, but are leak-free and that’s what matters – they should clean up OK after some grinding. For now the whole project is in fabrication mode, but once everything is in place and working I’ll go back and do body/paint work on all the parts to make it look nice too.
The rear VW emblem on the golf serves a number of purposes:
#1 – It’s an emblem.
#2 – It’s the latch and handle for opening the rear hatch. Pushing in at the top of the emblem causes the hatch to unlatch and the bottom of the emblem swings out to use as a handle for lifting.
#3 – (what this is all about) It’s a back-up camera. When in reverse, a small camera is pushed through a trap door behind the emblem causing the emblem to swivel up. The golf’s controller knows not to unlatch the hatch if it see the emblem swivel while in reverse (because it’s the camera that has swiveled the emblem, not a person).
Having a backup camera on a car that I can practically lean back and touch the rear windshield from the driver’s seat doesn’t make a lot of sense, most of the time. I have gotten used to it though – it’s great for towing and I have lines on the garage floor that allow for precision parking every time, maximizing usable garage space. A few weeks ago the camera stopped working; I investigated further and found that one of the arms of the extension mechanism had broken off. At that time I grafted a sheet metal strap onto the plastic mechanism and melted parts of it back together. This lasted a about a week, so this weekend I re-produced the entire plastic part completely with steel.
During the many cycles of assembly and dis-assembly of the camera mechanism I encountered a problem where any time it was put into reverse the hatch would open! This is kind of a funny outcome since it’s still fulfilling the purpose of more visibility when in reverse, just in a different way. This would be inconvenient, to say the least, so I tracked the problem down to some frayed wire connections. The shorted connections caused the hatch switch signal not to be ignored when the camera was deployed; re-terminating the wires fixed the problem completely.
Today I fabricated a cup holder basket. It’s made entirely out of the frame from one of those annoying corrugated plastic signs someone had planted in my yard, so it was basically free. There was an original accessory cupholder of a similar design that I got the idea from. The original was more in tune with 1960’s european beverage size sensibilities; I’ve created mine to work with 2010’s US sized cups.