GRV-1 Turbotug Project 12/01/04

Posted on December 1, 2004

       The time has come for me to redesign the GR-5. There are a few changes I want to make on the engine that will improve it’s performance and ease of use. I wanted to get these changes completed  before I attempt to operate the GR-5 on the Turbotug. Although I am reluctant to change the current layout of the GR-5, These changes will make a big difference.

       The first modification to the GR-5 will be the drive train. Earlier I had added a automotive alternator and a jackshaft to the GR-5. The jackshaft was set up to allow me to use a go kart clutch to drive the rear wheels. I recently decided to add a two speed clutch system to the drivetrain. After finding a surplus clutch system, I made room for a second jackshaft that will carry the second speed clutch. The two speed clutch system uses a 2:1 and 1:1 ratio for shifting the drive after a certain speed is achieved. I am not sure on how well this will work but I am going to give it a try.
       The clutch system was made by Comet Industries years ago for mini bike applications. They do not make this system any longer but I was able to find one on eBay.

       After some minor modification to the secondary jackshaft, I was able to configure the two speed system to fit into the GR-5 engine frame. I installed a set of pillow block bearings onto the secondary jackshaft, preparing it for the layout of the bearing supports.

       The main clutch has a dual sprocket which uses two roller chains to drive two different sprockets. The larger sprocket (1st gear 2:1) is on a one-way roller bearing that will disengage when the second speed (1:1) clutch engages, increasing the shaft speed by 100%. I am sure the system will require some further adapting to the speed and torque of the GR-5 but for now I will complete the basic fabrication. I welded in the bearing supports for the secondary jack shaft and used flat washers as shims for alignment.

       The jackshaft output sprocket has 12 teeth on it and the axle drive sprocket has 84 teeth giving a ratio of 7:1. The transmission has a ratio of 2:1 in 1st gear and a 1:1 in second. The two systems together make a 14:1 in 1st gear and a 7:1 in second. To my calculations, the GRV-1 should have a top speed of about 25 MPH with the power turbine spinning 15,000 RPM. While the GR-5 was still in it’s operational state, I fired it up to test the alignment of the roller chains. By blocking up the Turbotug to allow the wheels to spin, I spooled up the engine and watched for any binding.
       After some testing, I concluded that the main clutch was not engaging at the right RPM so I disassembled it and stretched the clutch spring at increasing increments. After a few tests I had the right setup and the clutch engaged at 1200 RPM. I set the GRV-1 on the driveway and throttled her up to see if it was going to roll. I was surprised to see the kart push it’s way up my driveway which is on an incline. Well, not actually surprised, more like relieved as it would all be in vein if it did not work. I was very tempted to drive the Turbotug but had no way to safely control the throttle so I opted to wait till completion.

       The next modification to the GR-5 was to install a spooling blower. The spooling blower will act as a starter motor and allow the GR-5 to start itself without the use of external support equipment. I wanted to fit the blower into the existing GR-5 frame so I removed the old control panel, battery, throttle valve and ignition controller.

       With the battery removed, a great deal of space was gained. I now had an idea of how much room I could use for a spooling blower. Although, without a battery or control system, the engine could not run until the new ECU was built and installed. This made testing the blower system difficult so either it would work or it wouldn’t. I now was on the hunt for a lightweight 12 volt blower system that would be able to push enough air through the GR-5 to start it.
       I was able to find a awesome blower on eBay that filled the bill perfectly. I had purchased a 12 volt cordless Makita shop blower/vacuum (Cat# UB121DZ) that is very lightweight and powerful. The blower is advertised to have 18,000 RPM motor (no load) and exhaust air velocity at 179 MPH. These shop blowers are made for different voltages (battery configuration) and the 12 volt version was perfect for my application. I bought mine without the battery or charger which was fine as I would be modifying it anyway.
       I tested to see how much current the blower used and found that at startup, the blower draws over 23 amps. During normal operation, the Makita blower draws over 13.5 amps at 12.75 volts. After studying the blower design, I started hacking it up to suit my needs. I removed the handle part of the housing and smoothed out the intake with a Dremel tool for better draw.

       The next step in the spooling blower assembly was to create the blower valve. The blower valve will close during startup, allowing the blower to force air through the turbine. Once the engine is self sustaining, the blower valve will open allowing the turbine to normally aspirate. By using 1-1/2” EMT conduit, I was able to make a connection point to where the blower would be attached to the blower valve body.

       By welding the 1-1/2” EMT to a 2-1/2” piece, I was able to make the valve body that the butterfly valve will be housed in. I then cut a 16 gauge steel plate that will serve as the butterfly valve. After careful grinding, the valve fit tightly into the valve body.

       By using 1/4-20 rod couplings, I fabricated the hinge points for the valve. These rod couplings will allow me to remove the valve for service later by removing the valve retaining screws if needed. Notice the FOD screen I made for the blower and the plumbing coupler used to attach it to the valve.

       I now needed a way to mount the valve body to the inducer ring of the GR-5. To do this I machined a set of flanges that will be welded onto the inducer ring and valve body. I made the rings out of 3/32” steel plate and used the rotary table to space 12 holes evenly for flange bolts.

       I carefully welded a flange onto the inducer ring, cooling it in water as to prevent damage to the already installed fiber optic RPM sensor cables.

       I welded the second flange onto the valve body and then ground the two surfaces flat. A good belt sander can be a valuable tool in the work shop.

       I now needed a way to actuate the valve so I chose to use a pneumatic cylinder system. I installed a small cylinder with a spring return that would be later tied into the combustor plenum pressure. The theory was that when the combustor pressure was great enough, the cylinder would open the valve allowing the engine to normally aspirate. After I completed the assembly, I tested it with air pressure for proper operation.

       After I remounted the inducer ring, I bolted the valve body to it with 12 stainless steel fasteners. Yes, a little overkill but it looks cool doesn’t it? When you have cool tools you use things like this as an excuse to use them :0} I also made a mounting bracket for the blower so it could be mounted below the blower valve (not shown).

       I am now in shape to tackle my next job, creating the throttle valve. I had to design a throttle system that would connect the throttle pedal to a proportional fuel valve. The ball valve I was originally using was not set up for the linkage but was modified for propane use use so I reused the existing valve in the new system. I had originally modified the valve by carefully grinding the ball insert around the edges of the passthrough holes. By doing this, the valve acted less sensitive at the closed position making it more proportional.
       For this project I had to make a valve assembly that would accommodate a throttle cable linkage. In order to get started, I assembled my valve to the existing check valve and added a inline filter to the output.

       The check valve (on the right) is where the fuel enters the system. This is a very important item as it safeguards any pressure from flowing back into the fuel tanks which could be very bad. The ball valve (middle) will control fuel flow to the engine and the inline filter (left) keeps debris from clogging the fuel cutoff solenoid. I now could make the bracket that will hold the valve and allow for a throttle cable linkage.

       After some testing, I settled on this design. It has added feature that I wanted to try out. The cylinder on the top of the valve assembly is an idle-up booster. When the engine is to be started, the fuel level must be low or a small explosion will occur causing the car alarms on my block to go off. After the gas is ignited, more fuel is added to sustain an idle. This new throttle valve will hopefully solve the idle set point problem by using the combustor pressure to hold open the valve to a set idle. As you can see there are two set screws, the one on the left (closer) is the idle-up screw and the one on the right (farther) is the starting idle screw. I will later install a idle switch that will interlock with the ECU preventing the engine from firing if the throttle is open.

       After I checked all of the mounting positions on the new equipment, I was able to tear down the engine’s components so I could final weld the engine frame. This also allowed me to research how I was going to house the new ECU unit. To accommodate the new ECU (electronic control unit) I used a 8” x 8” x 4” pull box enclosure and mounted it under the power turbine. To shield the enclosure from excessive heat, I made a heat shield out of sheet steel.

       The new ECU enclosure will allow for easy access for future adjustments. With the box mounted, I was able to final weld the engine frame and paint it. After the paint was dry, I was able to get all of the parts off my garage floor and back into place.

       I bolted the painted engine frame onto the GRV-1 to start assembling the engine. I started with the drivetrain, installing the jackshafts and alternator system.

       Once the drivetrain was tuned up, I was able to install the hydraulic system including the oil tank, oil cooler, oil pump and oil pressure switch. I also installed the newly completed throttle valve.

       Now that the support equipment was in place, I could install the turbo, spooling blower and power turbine. You can barely see the spooling blower, I had painted it black to better match the engine.

       All of the systems are in place with the exception of the ECU. Unfortunately without the ECU, the engine can’t be tested. I really want to know if the blower is going to work but without hot-wiring every system, I cannot start the engine so I am going to wait for the ECU. So the next logical step is to design a ECU that will control the GR-5 throughout all of it’s operational stages. I will also have to create a control panel that will communicate with the GR-5’s ECU and also future ECU’s.
       Because I have changed the layout and function of the GR-5 engine, I will rename it the GR-5A (“A” for autostart). Hopefully it will function as I intend and be able to be completely self contained. For now, I have to get busy and design the electronic portion of this project.

Tune in again for the next episode...

Don Giandomenico


[Home] [What's New At RCDON] [Articles] [Aircraft Projects] [Aircraft Videos] [Aircraft Videos II] [Experimental Projects] [GR-1 Turbojet Engine Project] [GR-5 Turboshaft Engine Project] [GR-5A Turboshaft Engine] [GRV-1 Turbotug Project] [GR-7 Turbojet Engine Project] [GRV-2 Jet Bike Project] [GR-6 Turboshaft Engine Project] [GR Engine Series Q&A] [Readers Projects] [Experimental Projects II] [My Collection] [M.A.R.K.S. Club] [RC Links] [About Myself] [Contact RCDON]