How to Set-Up an 18-Cell Monohull for 4 Minute Offshore & Sprint Oval Racing Using the FDM Turbo Transmission

Transcription

1 How to Set-Up an 18-Cell Monohull for 4 Minute Offshore & Sprint Oval Racing Using the FDM Turbo Transmission By Ralph von Eppinghoven Metro Marine Modelers Toronto, Canada Offshore style, Fast Electric radio control, boat racing, where RC boats race for 4 minutes around a course that has both left and right turns, is becoming very popular in a number of different classes. One class that combines speed and large model boat size is the 18-cell or Q classes. These 18-cell boats run in either the 4-minute offshore races or the 5-lap sprint oval races that only last approximately 1 minute. Since the offshore and sprint races have such different duration, they require very different set ups which normally means two different boats, motors and speed controls. One way to avoid the problem and costs of having 2 different boats for sprint and offshore racing is to use a transmission with different gear ratios to optimize a single 18- cell boat and motor set up for both sprint and offshore racing. This article shows how to install and set-up the Fine Design Marine (FDM) Turbo Transmission in an 18-cell monohull that can be used in either sprint or offshore races. Photo 1: The finished 18 Cell Monohull The El Lobo 4 1: BOAT DESCRIPTION: 1.1 Boat Specifications: Hull: 30 Deep-Vee Monohull such as Bandit El Lobo 4, MHz Lizard, or H&M No Step 3 Motor: Hacker 8XL, 9XL, or 10XL Transmission: Fine Design Turbo Transmission Gears: 41T, 45T, 64T and 78T, all 48 pitch: 41/78 for 4 min; 45/64 for 5 laps Speed Control: Hacker Master 77 Hardware: Fine Design EGSRA all in one strut and rudder Shaft: Octura flex Propeller: Octura X445 for 4 min offshore, X648 for 5 lap sprint Radio System: Hitec Lynx FM Power: 18 NiMH GP3300s 1.2 Project Description: The objective of this project was to build a Fast Electric (FE), radio controlled, 18-cell, monohull that could be used to race in both a 4 minute offshore and 5 lap oval race with the same brushless motor and speed control. To do this, the FE boat was built using the FDM transmission and different gear ratios were used with different props to allow the boat to run reliably and competitively in both of these classes. All of the parts and materials used to build this FE boat are available from Fine Design Marine ( 1

2 2: INSTALLING THE FDM TURBO TRANSMISSION: 2.1 Rear Transmission Mount Installation: The FDM Turbo Transmission will be screwed into the hull using front and rear aluminium mounting brackets. Use of mounting brackets, instead of gluing the transmission into the hull, allows the transmission position to be adjusted within the hull for proper shaft alignment, and the transmission to be easily removed for cleaning and lubrication. In this example, the transmission is mounted with the bow end higher than the stern end so that a smooth curved stuffing tube can be used. Some builders prefer to keep the transmission level in the hull and use an S-shaped stuffing tube. The configuration is the builder s choice and the installation process is the same in either case. The rear tranny bracket is fastened to a 1-1/2 X 2-1/2 plywood sheet (with pre-installed 6-32 blind nuts) that is glued into the hull using medium CA glue. The sheet is installed 5 from the transom as shown in Photo 2. The blind nuts are spaced 1-1/4 apart on the sheet to allow an aluminium mounting bracket to be screwed to the wood sheet. Photo 2: Rear transmission mount base and stuffing tube installed The rear tranny mounting bracket is simply a 1-3/4 X 2-1/4 rectangular sheet of.064 aluminium that is cut and filed to fit the end of the turbo tranny. The rear mounting bracket is shown in Photo 3. Test fit the mounting bracket on the end of the tranny and bend the bracket so that the tranny is sitting as low as possible in the bottom of the hull. In this case, the bracket is 1 high and has a 1-1/4 long base and is 1-3/4 wide. The bracket has been bent to an angle of approximately 80 degrees to accommodate the smooth curve of the stuffing tube. The tranny is fastened to the rear bracket using the two existing 6-32 screws in the end plates and two additional 6-32 screws and nylock nuts that are installed in the pre-drilled mounting holes in the tranny. Lastly, the rear mounting bracket is fastened into the hull by drilling holes in the bottom portion of the mounting bracket to match the blind nuts in the wood sheet, and then screwing the bracket onto the sheet that has been glued into the hull. It will be necessary to cut the 6-32 cap head screws to a short length so they do not protrude too far below the wood base and damage the fiberglass hull. Flat washers and lock washers are used with the cap head screws. Test fit the transmission often in the hull while the rear mounting plate is being fabricated to ensure the tranny will end up low in the hull and the shaft will be at a shallow angle to accommodate a stuffing tube with a nice smooth bend. Photo 4 shows the transmission installed in the hull. 2

3 Photo 3: Detail of rear transmission mount Photo 4: Rear transmission mount fastened to base 2.2 Front Transmission Mount Installation: The front end of the transmission is fastened to the hull using two ¾ square wood bases and two right angle aluminium brackets. The right angle brackets are fabricated from.064 thick sheet aluminium sheet. The brackets in this example are ¾ wide and 1-3/4 long. Bend the bottom of the brackets to fit the ¾ plywood bases. The plywood bases are made from ¼ aircraft plywood and a 6-32 blind nut is installed on the underside of each base. Do not glue the wood bases into the hull at this time. Drill a hole in the aluminium brackets to match the blind nut in the wood base and screw the brackets to the wood base using a short 6-32 cap head screw. The screw must not protrude below the wood base otherwise it will damage the hull when the base is glued onto the bottom of the hull. Now test fit the two brackets on the front of the tranny and determine the correct tranny height and angle to have the shaft on a shallow slope towards the transom. Mark the lower tranny endplate holes on the aluminium brackets and drill the holes to accommodate a 6-32 screw in each bracket and fasten the brackets and tranny using 6-32 screws and nylock nuts. Photo 5 shows the completed front mounts and the turbo tranny installed in the hull. Photo 5: Front transmission mounts fastened to small wood bases 3

4 Now test fit the transmission in the hull using the rear bracket and wood sheet, and the front mounting brackets - with the wood bases screwed onto the front brackets. Adjust the transmission position until it is perfectly straight in the hull and the shaft end is on a gentle angle that will be matched to the stuffing tube in the next step. The transmission can be adjusted in height at each end by slotting the holes in the aluminium mounting brackets. Once the correct location has been obtained, mark the outline of the front wood bases on the hull. Remove the tranny and unscrew the bases from the bracket and glue the wood bases into the hull at the marked locations using medium CA glue. It is important to unscrew the bases from the brackets when gluing them into the hull to avoid glue from getting on the blind nut threads and thus making it impossible to easily unscrew the transmission from the hull. The completed front mounting brackets are shown in Photo 5. The FDM turbo transmission can now be easily removed from the hull for maintenance simply by unscrewing the four 6-32 screws holding the rear and front brackets onto the wood bases. 2.3 Installing the Stuffing Tube The stuffing tube, made of ¼ K&S brass tubing, exits the hull at the bottom of the transom vee and has a gentle bend to line up with the transmission coupler. Drill a ¼ hole in the bottom of the transom vee at the center line and 5/16 (to the hole center) above the bottom of the hull. Make sure the hole is exactly aligned with the transmission shaft when looking down from above the hull. In this example, the ¼ brass tube is 4-3/4 long and is installed as shown in Photo 2. There should be a gap of approximately ½ between the end of the brass tube and the motor coupler when the final installation is complete. Do a final test fit of the tube, teflon liner, flex shaft, and motor and glue the brass tube in place in the hull transom using medium CA glue. Glue the stuffing tube from both the inside and outside of the transom to ensure a good waterproof seal. Once the CA has dried, it may be helpful to apply epoxy glue to the stuffing tube and transom joint on the inside of the hull. This additional layer of glue will provide additional waterproofing on this critical joint. It is prudent to provide support to the stuffing tube inside the hull. This is done by gluing a small block of wood between the brass tube and the hull bottom as shown in Photo Coupler and Flex Shaft Installation: The hex coupler should be installed onto the transmission shaft prior to installing the tranny in the hull. It should be noted that in this case an Octura 5mm to.150 Flex Hex is used. The FDM turbo tranny can be ordered with the end of the drive shaft machined down to 5mm to accommodate the smaller flex hex couplers. The smaller couplers are easier to work on in the small space in a boat hull. Test fit the coupler on the shaft, and grind or file a flat spot on the shaft where the coupler set screw will contact the shaft. Slide the coupler onto the shaft such that the end of the coupler touches the aluminium sleeve that is over the shaft and tighten the coupler set screw in place. The shaft sleeve is supplied so that it fits over the shaft and rests against the tranny bearing (see Photo 4) and the coupler is meant to rest against the sleeve edge. When the boat is in operation, the thrust of the prop is transmitted along the shaft and coupler and the thrust is taken at the transmission bearing since the coupler is pushing against the sleeve which pushes against the bearing. This is ideal as the bearing can take this load better and with less friction than the strut or other parts of the boat. 3: INSTALLING THE FDM 21 EGSRA HARDWARE AND TRIM TABS AND TURN FINS: 3.1 Bracket, Strut and Rudder Installation: Assemble the all in one FDM Strut/Rudder Assembly as shown in Photos 6, 7 and 8. The height of the strut is adjustable so that the angle of thrust of the propeller can be adjusted upwards, level, or downwards to change the ride of the boat. In this case the strut angle is kept level to the hull bottom, at 0 degrees angle. 4

5 Photo 6: Hardware installed (back view) Photo 7: Hardware installed (side view) Note - Neutral strut angle (0º) Photo 8: Hardware installed (top view) Note dual turn fins for Offshore racing 5

6 The EGSRA rudder has a kick up feature to protect against boat damage in the event of the rudder hitting anything. Make sure the socket head screws are tight enough to hold the rudder in place during normal operation, but will allow the rudder to hinge up during impact. Also care must be taken to file a flat spot on the rudder hinge post and the small set screw at the back of the rudder must be securely tightened. Check this set screw periodically as it may become loose during boat operation. 3.2 Trim Tab and Turn Fin Installation: The two trim tabs and dual turn fins are installed as shown in Photos 6, 7 and 8. In this example the trim tabs are 1-3/4 wide and 1 deep (this is the ride area that touches the water) and the inside edge of the trim tabs are installed 1-1/4 up from the centre line of the transom. As a starting point, the right tab should be 90º and level with the hull bottom while the left tab should be bent upwards about 1/16. This should result in the hull running level (across the beam) when viewing the boat as it is going away from you. If is it desired to have the boat running looser on the water, it is recommended to shorten the length of the trim tabs behind the transom (3/4 deep). The two turn fins brackets (right angle aluminium pieces) are screwed to the transom, and them the turn fins are fastened to the brackets using 6-32 stainless steels crews and nylock nuts. The separate fin and bracket assembly allows the fin to be angled deeper or shallower in the water depending on the boat set up. The higher speeds of the sprint oval set up requires as deeper right turn fin than the 4 minute offshore set up. 3.3 Flex Shaft Installation: Insert the flex shaft through the strut bullet and stuffing tube (with teflon liner) into the transmission coupler. The flex shaft needs to be reduced in length such that the end of the flex shaft will be securely clamped in the hex coupler and a 1/16 gap exists between the back of the strut bullet and the front face of the drive dog. This gap is required since the flex shaft will shorten when it is spinning at high speed and will create excessive friction at the drive dog if there is no gap. The gap at the strut also ensures the thrust from the prop will be taken at the tranny rear bearing as described in section 2.4. Test fit the flex shaft and measure the required length that has to be removed in order to achieve the correct fit described above. Be extra careful to get the length correct it is better to cut off too little than too much of the shaft since it is impossible to add material to the shaft but it is easy to remove unwanted material. The easiest way to cut the flex shaft is to use a Dremel tool with a cutting wheel to slice through the cable. Once the cable has been cut, the cut end needs to be soldered to prevent the strands of the flex shaft from unravelling. Make sure enough solder is used to cover the cut end but not too much so that the end thickens and cannot be properly gripped by the flex hex coupler. Use of soldering paste or flux will greatly improve the quality of the solder work. 4: LAYOUT OF THE SPEED CONTROL, RECEIVER, SERVO AND BATTERIES 4.1 Component Installation: Photos 9 and 10 show the layout of the RC components in the hull. The components have been placed so that the Centre of Gravity (C.G.) of the hull is 30% of it s length, measured from the transom. In this case the hull is 30-1/2 long and the hull balances out at 9-1/8 from the transom. For reference, the rear edge of the FDM transmission is 6-1/2 from the transom, in this case. The rear edge of the battery packs are also 6-1/2 from the transom. As noted, this layout results in the required 30% CG for the hull. 6

7 Photo 9: Inside layout Left Side Photo 10: Inside layout Right Side As shown in Photo 9, the electronic speed control (ESC), and receiver are placed in the rear left side of the hull. The receiver is shown protected in a small rubber bag or balloon. A DuBro Kwik Switch Mount (Cat. No. 203) is used for easy transom mounting of the receiver on/off switch. Photo 11 shows the details of how to mount the receiver and Speed control. The receiver is held in place using a velcro strap that is inserted under two small ABS strips that are glued in the hull. The ABS strips are simply cut from thin plastic stock and glued in place using CA glue. The Speed control is held in place on a small rectangular balsa block. The purpose of the block is to raise the speed control off of the hull floor to minimize water contact in the event of a small amount of water sloshing in the hull. In this example, the balsa block is ¾ wide X 2 long and ½ high. The block has a ¾ wide shallow notch in the bottom that the velcro strap slides through. For additional support, velcro can be applied to the top of the block and the underside of the speed control. This will hold the ESC firmly in place. 7

8 Photo 10 shows the servo and small 5-cell receiver pack mounted in the rear right side of the hull. The receiver pack uses small rechargeable 300 mah cells. The details of the installation of the servo and receiver pack are shown in Photo 12. The servo is screwed onto a right angle aluminium bracket, and then this bracket is screwed onto the small plywood sheet that has been glued into the hull with blind nuts pre-installed under the sheet. This make the servo easy to install and service, yet provides a very strong and solid servo mount. A solid servo mount is absolutely necessary for offshore racing with larger 18-cell boats. A weak servo and poor mount will not stand up to the rigors of a 4-minute offshore race with choppy water and many turns in both directions. Photo 11: Wood block for ESC and velcro straps for receiver Photo 12: Servo and receiver battery As shown in the photos, the batteries are placed, as two 9-cell packs, on either side of the transmission. In this example, custom made fiberglas battery trays have been glued into the hull to hold the packs. These trays were supplied by a fellow racer at Metro Marine Modellers. Velcro is glued on the bottom of the battery trays to hold the packs in place. It is important to leave enough room to move the packs 1 forward or 1 rearward around the 30% CG point to accommodate water conditions and to adjust boat handling. 4.2 Water cooling of the Motor and ESC: As shown in Photos 6 and 7, the water cooling tube is fed from the rudder through the hull at the upper right side of the transom. A 2-3/4 long, 5/32 diameter, aluminium tube is glued through the hull at this point. The inner section of the tube is shown in Photo 12. The cooling tubing is run from here to the right side of the motor cooling coil. The left side of the motor coil is then connected with tubing to the ESC cooling tube and from there it is fed out the rear, left side of the hull as shown in Photo 9. The tubing used in this example is Aerotrend blueline silicone fuel line (#1005 Large). 5: ADJUSTING GEAR RATIOS & PROP SIZES 5.1 Motor Installation in the FDM Transmission: All motors are bolted into the two slots machined into the FDM transmission. In some cases, the mounting screws supplied with the motor will not be long enough to fit through the FDM tranny. The ideal mounting screws are 3MM X 8 socket head screws (DuBro Cat No. 2122) since they are long enough to be used with flat washers and lock washers, but no too long as to be screwed too far into the motor to hit the armature. It is also recommended to use these DuBro socket head screws for mounting the motor since they are the easiest to work with in a confined hull. Photos 9 and 13 show the motor installed it the transmission. It is recommended to use flat washers and lock washers due to the size of the motor mounting slots on the tranny. 8

9 5.2 Gearing Basics: Gears are used to reduce the loading on the motor to a point at which the correct size propeller can be used while operating the motor at proper efficiency and temperature. Gears change the ratio of the motor revolutions to propeller revolutions. For example, a 1.5:1 gear ratio means the motor shaft will rotate 1.5 times for each rotation of the propeller. Higher gear ratios (say 1.7:1) create less loading on the motor, but fewer prop revolutions. But the lower motor loading also means that a larger prop can be used. Conversely, lower gear ratios (say 1.2:1) create more loading on the motor, but higher prop revolutions. Since the motor has more loading, a smaller prop must be used. By adjusting gear ratios and props sizes, it is possible to trade off run-time, speed and prop size to come up with the ideal set up for any boat. Gear ratios are adjusted by varying the gear sizes on the motor (called the pinion gear) and the transmission drive shaft (called the spur gear). The gear sizes are commonly measured by the number of teeth on each gear. So a 1.5:1 gear ratio would have a pinion gear with say 40 teeth (T) and a spur gear with 60 teeth. Of course other gears such as 48T pinion and 72T spur would also provide the desired 1.5:1 gear ratio. Since there are many combinations of gear sizes for any given gear ratio, usually the exact gears to be used are determined by what gears the racer already has in his toolbox. Generally, for a given gear ratio, the smaller gear sizes are better as they reduce the mass of the gears and make them a bit easier to spin, and the smaller gears result in the motor being lower in the hull thereby making the boat more stable. The actual size of the teeth on the gears is measured by the pitch. Commonly 48 pitch teeth are used for FE applications. Smaller teeth do provide a finer adjustment of gear ratios, but for FE boats, very fine adjustments are not required. Typically, a 0.1 gear ratio change is the suggested minimum change for adjustments (i.e. go from say 1.5:1 to 1.6:1gear ratio) to a FE boat set up. Gear ratio changes of less than 0.1 have an almost imperceptible change on the boat s performance. Gears are made of either aluminum or Delron (a strong nylon material). Typically the pinion gear is made of aluminum and the spur gear is made of Delron. By having one metal and one nylon gear, wear and noise is minimized. Two Delron gears can also be used. It is not recommended to use two metal gears on a transmission due to heavy wear and increased friction. Gear lube or oil can be used to reduce friction on all gears, if desired. When installing the gears, it is important to make sure the gears are not too tight so as to create excessive friction. Adjust the fit of the gears so that there is a small amount of clearance between the teeth. One rule is that a sheet of copier paper should be able to be turned into the gears without the paper tearing. Always turn the gears by hand after installation to make sure they are turning freely with no binding. Also, double check that all set screws are tightened properly before operating the boat. 5.3 Offshore Racing Gearing: Offshore racing requires the boat to operate at top speed for 4 minutes. Since offshore racing has many turns, and varying speeds, a competitive boat must have good acceleration. This means the prop must be fairly large, at least 45 mm diameter. In this example, the 18-cell monohull is operating with a Hacker 8XL motor. For this set up, a gear ratio of 1.90:1, with an X445 propeller has proven to be successful. This gear ratio is achieved by using a 41T pinion gear and 78T spur gear. The gears are installed as shown in Photo 13. In this case the pinion gear is aluminum and the spur gear is Delron. 9

10 Photo 13: Offshore Gearing with 45mm prop for 4-minute run time Gear ratio: 78/41 = 1.90:1 5.4 Sprint Racing Gearing: Sprint racing requires the boat to operate at top speed for 5 or 6 laps around a standard oval. The run time is quite short, approximately 60 seconds. This short run time does allow for larger props and lower gear ratios. In this example - same 18-cell monohull with a Hacker 8XL motor - a gear ratio of 1.42:1, with an X448 propeller has proven to be successful. This gear ratio is achieved by using a 45T pinion gear and 64T spur gear. The gears are installed as shown in Photo 14. Again, the pinion gear is aluminium and the spur gear is Delron. Photo 14: Sprint Gearing with 48 mm prop for 5 or 6 laps run time Gear ratio: 64/45 = 1.42:1 10

11 6: SET UP & RUNNING TIPS Once the Fast Electric boat has been assembled and bathtub tested for leaks, there are several other final steps to be completed to ensure proper operation of the RC boat. 6.1 Flotation, Sloshing Water, and Visibility: Even the best built and raced FE boats can suffer impacts or damage during racing that causes the hull to leak and possibly sink. To avoid losing a boat if it gets filled with water, styrofoam or other flotation must be placed in the hull. The most common solution is to glue styrofoam pieces that have been sanded to shape under the bow as shown in Photo 15. Foam board adhesives, available from building supply stores, can be used to glue the styrofoam in place. Photo 15: Styrofoam Flotation Under Bow It is also likely that a small amount of water will enter the hull during operation. The water typically is drawn up the stuffing tube as the flex shaft spins in the tube. A small piece of silicone tubing can be placed around the stuffing tube and flex shaft to provide a seal. It is also prudent to place a small piece of kitchen sponge in the V of the hull, near the transom, to absorb any water that may get in the hull. Typically the small sponge is wedged in place under the stuffing tube near the transom. High visibility colours are critical to make the boat easily seen by fellow racers in case the boat becomes flipped or stranded during a heat. It is very important to make the bottom of the hull a bright colour since the most common reason for a disabled boat in the middle of the race course is flipping. As shown in Photo 16, the bottom of the boat has been left white for optimum visibility on the water. Photo 16: White Hull Bottom for Visibility 11

12 6.2 Set Up Tips: The boat, as configured in this example, will have a Centre of Gravity (CG) of approximately 9-1/8 measured from the back of the transom. This is the balance point that results in good speed and handling for this boat. The CG point can be determined easily by placing a round pencil (crossways) under the centre line of the V- hull when the boat is fully assembled and all components are in place. Roll the boat forward and backward, while gently supporting the boat, until the boat balances on the pencil. Measure the distance of the pencil to the back of the transom; this distance should be approximately 9-1/8. As mentioned in section 4.1, the CG can be adjusted easily by moving the battery packs forward or backward in the hull. For 4-minute Offshore racing, the boat is running slower than the Oval set up, so it can be run a bit looser with less hull touching the water when the boat is racing. This is achieved by moving the battery packs slightly rearward, which moves the CG rearward. The trim tabs can also be bent upwards slightly to raise the bow of the hull and have it running looser. For Oval racing, the boat is faster (since the short runtime allows a faster set up), so there is a risk of the hull blowing over on the straights. For this reason, the CG is moved forward, by moving the battery packs forward, on this set up. The trim tabs may also require slight downwards adjustment depending on the ride of the hull. The benefit of gearing is that it provides almost unlimited combinations of gear ratios and prop sizes. Experiment with different combinations to get the desired set up of run time and speed. Different brushless motors (say 10XL instead of 8XL) will all work well with gearing, but the ratios need to be adjusted for the different motors. Again, test out different gear and prop combinations for your motor and hull set up. 6.3 Reliable Running: In order to keep the RC boat running reliably, the following maintenance procedures should be followed: a) Use good grease, such as Prather Cable Grease (No.7145), to lubricate the flex shaft before each day s running. At the end of the day, remove the flex shaft, wipe it clean and dry it and leave it lying in the bottom of the hull for storage. b) Once a season, remove the FDM tranny and clean the bearings by spraying them with motor cleaner and re-oiling with light household oil. This easily done if the bearings are removed from the tranny housing. Simply remove the tranny shaft and then the bearings simply pop out when pushed from the inside. c) Keep the radio receiver dry at all times. The simplest way to do this is to place the receiver in a rubber receiver bag. Wet receivers are one of the most common causes of radio glitching and unreliable operation. d) Before each day s running, check all set screws on the tranny, hardware and pushrods are tight. A loose screw can mean a stranded boat. e) Rinse the hull and hardware after each day s running to prevent corrosion and maintain the paint finish. Photo 17: Finished Boat 12

13 7: SAFETY NOTES AND DISCLAIMER Warning! This fast electric RC boat is not a toy. Improper use may be hazardous to swimmers, boaters and the operator. This boat is capable of speeds of over 30 miles per hour. Always turn the transmitter on before connecting the batteries so that the boat will be under control at all times. This product is intended only for use by experienced model boaters. This product is not intended for use by children without close adult supervision. It is strongly recommended that the user be a member of a national model boating organization and that the user adhere to all safety rules of that organization. Since this boat is intended for use only by experienced model boaters, Fine Design Marine is not liable for any misuse of this product. Assembly or operation of this product implies acceptance of this policy. Photo 18: Enjoy Your Geared, Fast Electric, R.C. Boat 8. ACKNOWLEDGEMENTS: Many of the techniques used to build this Fast Electric radio controlled boat have been developed with tips and guidance from fellow FE racers at Metro Marine Modellers in Toronto, and other RC hobbiests. I wish to acknowledge and thank all those that have given me helpful suggestions and advice over the years. Thank you to Chris Fine of Fine Design Marine for posting this article, so others may build better Fast Electric boats. 13