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Giant Scale Amphibious Vehicle - 1/12/2004 8:28 AM   
brice_arnold


 

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From: Los Altos Hills, CA, USA
Status: offline 		Hello -
I am in the middle of a giant scale project my self. I'm building, I guess what one would call a 40% scale amphibious vehicle. When on land it is a four wheel driven vehicle and when on water the wheels pull up into the frame of the vehcle and it transforms into a hovercraft. The vehicle is of course radio controled but also uses several microcontrollers for the electronics and controls systems.

The vehicle uses 6" go cart wheels with 12.5" tires and a 56" wheel base. The vehicle will be powered by a single 7.5 hp two stroke twin cyclinder airplane engine with conversion for a liquid cooling system. The overall dimension are 96" in length, 52" wide, and about 59" tall (this includes the height of the rear thrust duct).

Thus far I have completed the frame, suspension, driveshafts, engine mounts, cooling system, and the various drivetrane components. I am in the process of making the drivetrane mounts for the frame and steering system. I hope to do a
test run in two weeks. My deadline for the entire project is the middle of may.

I am posting this because this is the first web site where I have found a forum of people interested in giant scale cars. I will post the progress of the project through the next five months for those who are interested. I would also like to hear peoples ideas, thoughts, and tips as this is my first attempt at a giant scale RC vehicle.

If anyone has experience in either hovercraft building and design, or cars of this scale and can offer advice please let me know. If you have any questions I would be happy to answer them.,

Below are pictures of the frame with uprights and suspension A-arms, front and rear uprights (rear ones are on top), one of three differentials with telescopic drive shafts, and the engine with the liquid cool conversion. The frame photo is a month old and there are several things that have been added since. The frame is 4130 chromolly 1/2" and 3/4" that has been TIG welded. The uprights are 6061-T6 alluminum that I machined in my shop. The engine conversion uses copper tubing wrapped around the engine heads. Fluid will be pumped in on one side and out on the other side. The fluid will than pass through a heat exchanger, resevoir, and back to the engine.

Enjoy and please give feedback

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< Message edited by brice_arnold -- 1/12/2004 4:17:10 PM >

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RE: Giant Scale Amphibious Vehicle - 1/12/2004 8:38 AM   
Mel Francis



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From: Oconomowoc , WI, USA
Status: offline 		Glad you were able to work out the photo sizing.

It looks almost large enough to support a full-size driver, at least on land.

Are you preparing a set of external body panels for it?

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RE: Giant Scale Amphibious Vehicle - 1/14/2004 12:12 AM   
brice_arnold


 

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From: Los Altos Hills, CA, USA
Status: offline 		Here are some more pictures

1. This is an updated picture of the project with the suspension, engine, and some of the drive train components

2. This is the engine mounted in the vehicle. The engine spins up at 9000 RPM so it's geared down to a more reasonable 3000 RPM. Power is distributed to verious parts of the drive train via electromagnetic clutches. Note the clutch to the right of the large gear.

3. This is the rear suspension. The right sided is extended and the left side is retracted (for hover craft mode). The actuation of the wheels is accomplished by using two 6" travel linear DC motors for each wheel. The shocks are cheap coil-over oil-filled go-kart shocks with a 700lb max compression load.

4. This is the right front suspension system. the left side has been dissasembled for work. The geometry of the suspension is somewhat visable in this picture.

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RE: Giant Scale Amphibious Vehicle - 1/14/2004 12:26 AM   
i8tweety



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Status: offline 		That's quite impressive! Please keep us informed on your progress.

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RE: Giant Scale Amphibious Vehicle - 1/17/2004 3:41 AM   
brice_arnold


 

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From: Los Altos Hills, CA, USA
Status: offline 		Here are some pictures of the drivetrain/transmission.

The design of the drivetrain is such that from the engine there is a 3:1 reduction to a main drive shaft. On this main drive shaft there are two clutches. One engages the both the lift and thrust fan for hovercraft mode and the second engages the wheels.

The powered wheel cluctch is adapted to a Torque-A-Verter which allows for an infinitly variable ratio which ranges from 5:1 to 0.8:1. This device delivers power to yet another drive shaft where there are two more clutches. One clutch engages forward drive and the other clutch engages reverse drive. The reverse drive also has a 2:1 ratio. Both of these clutches have sprokets/chain assemblies which deliver power to a front/rear differential.

The front/rear differential delivers power to both the front and rear differentials (a total of three diffs). Power is delivered via chain and sproket assemblies. There is an intermidiate drive shaft between the rear differential and the front/rear differential. This was necesary so as to work the drivetrain around the centralized lift duct for the hovercraft.

Here are the pics. In the pictures all of the chains have a lot of slack in them. I still have to make the chain tensioning assemblies

1.This is the powered wheel drivetrain assembly. From right to left: rear chain and sporcket, reverse clutch assembly, front/rear differential, forward clutch, front chain and sprocket.

2. This is the rear drivetrain assembly. Notice the intermidiate drive shaft. Also, the disc rotors can be seen on the rear drive shafts. Each wheel will use independant hydraulic disc brakes. with 6" rotors in the front and 8" rotors in the rear. In the background the pulleys used to drive the fans can be seen

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RE: Giant Scale Amphibious Vehicle - 1/19/2004 12:26 AM   
Savage_Dias



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Status: offline 		That's going to be awesome when it's finished. Actually, it's awesome as it is now that I think about it! lol Please keep the pics coming! BTW, how much does it weigh??

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RE: Giant Scale Amphibious Vehicle - 1/22/2004 10:07 AM   
brice_arnold


 

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From: Los Altos Hills, CA, USA
Status: offline 		More Pictures for the week

In response to Savage_Dias:
- Originally the vehicle was expected to weigh 250 lbs. However once we recieved all of our drive train components and had the frame 80% my new estimate shot up to 300 - 350lbs. Because of this I actually had to redesign the geometry of my suspension to accomidate for the extra 100lbs.

This vehicle is going to be a beast. Considering the size and weight of the vehicle I am a little concerned on whether or not the engine will be strong enough to move it. According to my calculations though I should have enough power in hovercraft mode and given the driven wheel transmission I should get 130 ft-lbs max to the wheels. However, neither of my calculations account for the inefficiencies of my drivetrain. If you think about SAE mini bajas or personal hovercrafts: including passenger, they are both heavier vehicles than mine. These vehicles also have engines that are roughly the same Hp as the one I'm using. I'm hoping this will verify my engine selection.

I've been spending the last couple of days fabricating and installing the hovercraft fan gear boxes. Both fans require power to be delivered via 90 degree offset gear boxes. These were machined in the shop. Both gear boxes have been machined and the lift fan was installed today. Hopefully I will be able to get the thrust fan installed within the next couple of days. The Pictures are as follows:

1. This is the thrust fan gear box. Both the input and output shaft are supported by a single bearing in the box and the other end of the shaft is supported by a bearing plate mounted to the frame. The gears are mounted to the shaft via splined shaft and retaining rings. Power is delivered from the box to the fan via v-belt and pulley assembly

2. This is the lift fan gear box with the fan mounted to the ouput shaft. This box was built larger and beefier than the thrust gear box because the box supports all of the loads caused by the lift fan. Also the output shaft is entirely supported by this part where-as on the thrust gear box the output shaft is supported by both the frame and box. The fan hub assembly actually uses a different shaft diameter than the rest of the drivetrain so a shaft was machined of two different diameters.

3. This is the lift fan assembly installed on the vehicle. notice the disc rotor. This will allow the fans to be stopped rapidly should the need arise.

4. This is an underbody shot of the lift fan assembly and the support members. Basically the lift fan gear box is sandwiched between two plates which are suppoted by members/struts.

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RE: Giant Scale Amphibious Vehicle - 1/22/2004 12:15 PM   
Dr.ArmoMaxx



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you are one luck guy to have a shop, bling, and skillz

Good luck with it

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RE: Giant Scale Amphibious Vehicle - 2/3/2004 7:09 AM   
brice_arnold


 

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From: Los Altos Hills, CA, USA
Status: offline 		Here are some more pictures of the project.

It's been busy what with school starting and all. However I've been able to get some work done on the thrust fan assembly and the steering assemble. Today I had a set back by cutting off the tip of my finger with the mill while machining parts for the steering asembly. After getting back from the hospital I was able to finish the parts. LOL, some people call me crazy. . . There may be some typographical errors due to my injury so just be warned. On with the pictures.

1. So on the thrust fan for the hovercraft the blades will have variable or collective pitch. The mechanics ar identical to that found on a radio controlled helicopter except for some custome components. My throst fan will use four helicopter plades. Instead of buying a multi-blade rotor head for $300+ I designed and machined one from scratch. The rotor head was designed to be used with X-Cell 60 blade holders and spindles. A typical swashplate is designed for either a 10 or 11 mm shaft. The Kyosho swashplates are boared out for 12 mm because they have an insert that slides on the ID of the swashplate and the 10mm OD of the drive shaft. With my setup I will be using the Kyosho 12mm swashplate on a 12mm shaft. The bigger the better. One would think that if you were using a fourbladed rotor head, the mechanics would be that much more coplicated. This is not so. With my setup there is no longer a need for any of the wash-out assembly or mixing linkages. The swashplate is driven by four servos. and the inner ring on the swashplat is directly linked to the blade holders on the rotorhead. So I've simplified the mechanics of this system but if I want to have collective pitch to aid in steering I may have made my servo mixing more complicated. Also i'm not too sure how effective my design will be until I test it.

2. This is a picture of the 90 degree offset gearbox mounted to the vehicle.

3. This is a picture of the thrust fan drive assembly. The main shaft (above) is adjustable to center the fan in the duct. Currently it is angle down because the belt is too short. I made an error in calculating my belt length and ordered the wrong belt.

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RE: Giant Scale Amphibious Vehicle - 2/3/2004 7:32 AM   
brice_arnold


 

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From: Los Altos Hills, CA, USA
Status: offline 		More pics for the same day.

From the beggining I've had several ideas for a steering assembly for this vehicle. At first I had picked up this large Bodine gear-head motor off ebay that had the torqu and speed of four 1/4 scale Hobbico servos. the only problem was that the motor alone weighed ten pounds. So then I thought I would just use four 1/4 scale servos to do the job but I thought that was kind of cheezy. Finally sometime in October '03 I was able to get a nice Maxon DC gearhead motor that had just as much torque if not more than the Bodine, was slightly faster, and about 20% the size of the Bodine motor. This would be my motor.

Now I needed an assembly. I found a really nice ultra precision track but this would be overkill and it also weighed too much. After putting some time into different designs and ideas I decided to make a self contained assembly that would hold all of the components into a nice little package. In doing this project I have come to love adjustable parts. They allow for fine tuning and minor chages down the way. I designed my assembly to not only fine tune the bearing positions of the track but also allow for a variety of pinnions to be used with the rack and pinnion setup. With the current rack and pinnion setup, both of which can easily be chaged to increase travel, speed, or force, has three inches of linear travel and 60 - 70 lbs of linear force.

The output from the motor shaft will be coupled to a potentiometer wich will provide the feedback to the control circuit. To control the motor I will use a 30 amp AMC servo amplifier. The whole setup is fairly simple. I've hacked a servo and removed both the motor and the potentiometer from the main board so that the onlything I'm using is the servo circuit. I then used the motor ouput as the input into the AMC servo amp. Then I hooked up the Maxon motor to servo amp, and the coupled pot to the pot input on the servo circuit board. Essentially I've created a giant super servo.

Enjoy the pictures.

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RE: Giant Scale Amphibious Vehicle - 2/11/2004 2:14 AM   
shawnskx100


 

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RE: Giant Scale Amphibious Vehicle - 2/21/2004 12:38 AM   
RobH



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Status: offline 		I hope it works out for you. You've put a load of time into it. The thread was surely entertaining to read.

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RE: Giant Scale Amphibious Vehicle - 2/23/2004 6:55 AM   
xyz



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From: alemeda, CA, USA
Status: offline 		wow that looks sweet cant wait to see itdone post somne vids too so we can see how it flies

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RE: Giant Scale Amphibious Vehicle - 2/23/2004 5:30 PM   
RobH



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Status: offline 		I just noticed his last post was 20 days ago. I hope he didn't cut some more vital than his finger.

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RE: Giant Scale Amphibious Vehicle - 3/2/2004 2:19 PM   
brice_arnold


 

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From: Los Altos Hills, CA, USA
Status: offline 		Hello it's been awhile school is demanding and so is the project.
Much progress has been made since the last post. Today the drive train was tested with the engine and it was actually able to move under it's own power. It really is quite amazing to see a 400 + lb vehicle move via radio control. Both forward and reverse work as planned. In addition to the drive train being completed the braking, steering, cooling, exhaust/intake system have made significant progress and will be completed by the end of the week. I will try to post as many pictures as possible. Here they are

The braking system uses hydraulic mountian bike disc brakes. The brakes are actuated by 1/4 servos which basically pull on the brake levers. The brake levers and servos are all mounted to a single assembly. wich is shown in the picture. The fifth lever is to actuate the brake for the fan system.

During the course of the last month I did a load test on the suspension by loading the vehicle with all of the components that would be going on after the final assembly. I learned a couple of things form this test. The first was the the final weight of the vehicle will be around 450lbs. The second is that the suspension can not handle this kind of weight. I imediatly went to the drawing board to improve upon my suspension design. My new design was a significant improvement over the original and multiple ways. Basically the new design incorporated the use of two shock absorbers for each wheel. The original shock is adjustuable via linear actuators (this allows the wheels to be pulled up into the vehicle. The disadvantage the original design is that when the wheels are pushed down from the vehicle the linear actuators do all the work to lift the vehicle. Also, when the vehicle is lowered as a funciton of land speed, (high speeds) the suspension has the same response as if the wheels were fully extended the would cause the vehicle to scrub on bumps and cornering. With the new design the second set of shocks are fixed to the frame on one end and mounted to the lower A-arm on the other end. With this design. the second set of shocks help raise the vehicle when wheels are extended. Also when the vehicle is lowered the suspension actually stiffens up as a function of the vehicle height. So the lower the vehicle the stiffer the suspension.
In the picture the original shocks have been removed. but the newly implimented design is visable.

After building the steering mechanism it was installed and tested. It works as expected though the control feedback system needs to be tweeked. The servo system acts like an underdamped system. However, the weight of the vehicle helps dampen the system.

Because the engine is isolated and the vehicle will encounter water percautions must be taken with the engine to allow it to function properly. An exhaust system and intake manifold were both fabricated from stainless steel tubing. The air intake was tricky because there is a choke flap which is right on the intake of the carbuerator. Clearance is needed between the carbuerator and the intake to allow the flap to move properly. The intake goes towards the front of the vehicle where is will mate up to a fiberglass air scoop molded into the body. The exhaust system is consist of two parts. the manifold and and the exaust pipes. To maximize the power of the engine there are no mufflers. just a manifold and straight pipes which go to the rear of the vehicle. Much like a smaller scale car the fuel tank is pressurized off of the exhaust. In the picture the intake goes up and to the left and the exhaust goes down and to the right.

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RE: Giant Scale Amphibious Vehicle - 3/2/2004 2:43 PM   
brice_arnold


 

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From: Los Altos Hills, CA, USA
Status: offline 		More pictures -

The clutches that are used on this vehicle are electromagnetic. The basically have three parts; the coil, the driven section and the powered section. The powered section is fixed to the drive shaft which is always rotating. When electricity is applied to the coil, the driven section is engauged to the powered section. The driven section originally is a pulley however for this project adaptors have been made that bolt up to the pulley. The thing with these clutches is that they opperate of 96v DC which isn't very popular. I came up with a power supply for these units but it's not very clean and it's heavy. I take 12v dc from one of my batteries. This powers an inverter which gives my 120v AC. I go from the inverter to a rehostat which allows me to adjust the voltage from 0 to 120. I set it to 96 v ac. I then go through a bridge rectifier to conver 96v AC to 96v DC. I don't like the system for two reasons. First, it's heavy. The rehostat alone weighs about 8 lbs. Second the whole system draws way too much current. With the inverter, rehostat, and coil. They draw 1.5 amps continuous which is a huge drain on my batteries. If someone knows a better way to do this let me know please. The clutch itself only draws 160 mA continuous @ 96v. This pictures is of my setup for testing. The control box is to start the motor with an emergency stop. Basically the big red button has to be held down for the engine to run.

This is the finished drivetrain clutch assembly from the bottom of the vehicle.

The bottom of the vehicle as it's being worked on.

The vehicle ready for testing, notice the flywheel, fueltank and exahust system. The green tubing is for the engine cooling system.

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RE: Giant Scale Amphibious Vehicle - 3/10/2004 8:11 PM   
spdfrek


 

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Status: offline 		Have you considered a mechanical clutch?Ive been looking at your setup and decided it might have almost been easier for you to pick up something like a cr80 engine with a tranny and clutch and all.Anyways,i remember my neighbor building a gocart using a simple clutch design.He had a belt that was a bit on the loose side and a tensioner pulling that would tighten it against the drive pully....The tensioner pull pivoted and was connected to a clutch pedal via a cable...My second thought would we using a centrifical clutch on the main drive so that when you throttle up it walways engaged...The use a slectable transmission to switch from wheel power to fan power.Either way good luck with it...looks like you have an awesome start..My first 1/5th scale project isnt gonna be nearly as complicated.

PS excuse spelling errors...My wireless keyboard is going dead...causes glitches

Joey

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RE: Giant Scale Amphibious Vehicle - 3/11/2004 11:31 PM   
brice_arnold


 

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Status: offline 		Originally I had considered a simple mechanical clutch with a three speed tranny but There would be the added complexity of developing actuators to engauge the clutch and shift gears. Also I would need to find something lighter than that of an ATV and heavier than that of a 1/5 scale vehicle. This is why I decided to use several electromagnetic clutches. On the powered wheel side of the drive train, I do actually have a pulley system which engauges once the RPM revs up to 1000. As of today I have conducted some test runs on the vehicle and the tranmission has performed well. I have run into some problems with the drivetrain components slipping on the shafts but I plan on resolving these issues by using keys and cutting keyways into the shafts and components. Currently I am in the process of building the mold for the body. I should be posting more pictures soon.

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RE: Giant Scale Amphibious Vehicle - 3/12/2004 12:51 AM   
paperclipracer


 

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RE: Giant Scale Amphibious Vehicle - 3/14/2004 10:09 AM   
spdfrek


 

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Status: offline 		Honda made a few motorcycles back in the day that were automatic clutches with a 3spd.So the only thing that you would have need was a shift lincage and throttle control...Coupled with a tranny that switched between the ground power and the hovercraft it would be pretty smooth...either way,awesome job on it...I wanna see some vids of this thing running

Joey

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RE: Giant Scale Amphibious Vehicle - 3/18/2004 10:56 PM   
brice_arnold


 

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Status: offline 		Here are some more pictures as promised. These are a little dark because they were taken around 10:30 at night when I finally got around to testing the vehicle.

The first picture shows some of the electronics used to test the vehicle. Essentially for the test, there was RC control for the throttle, choke, forward/reverse, steering, and brakes. The other stuff is power conversion/supply for either the brake servos or the electromagnetic clutches. There are also the electronics for the steering servo.

The second picture shows the vehicle driving around which I guess is not that obvious. At the time of testing I wasn't able to capture any video. Since the testing the vehicle has been stripped to make the body mold. I will get video footage the next time it's up and running.

To give you an idea of the size of the vehicle here I am pushing it around.

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RE: Giant Scale Amphibious Vehicle - 3/18/2004 11:20 PM   
brice_arnold


 

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Status: offline 		So I've been working on the body now for a little over a week. Basically the mold is made from a polystyrene based insulation foam. This is probably the worst stuff that I could have choosen to use for this purpose because A: it's pink and everything in the shop has become pink, B: it reacts with the resin and essentially melts, and C: it's just a pain ot work with. However the foam was readily availabe and free. The body for the vehicle will be created in panels and then fastened directly to the subframe. Each panel consists of three layers. The first layer is a polyester cloth Which is stretched tight over the mold. This is done to create natural contours of the frame transitions from one section to the next. the second layer is a matte fiberglass clothe and the third layer is an S-2 woven glass clothe. To prevent the mold from melting I am using 4 ml plastic drop clothe to create a barrier between the mold and glass resin.

This is a picture of the upper half of the rear duct. This will be a foam core part. It will also be removeable from the main frame for transportation purposes.

This is the completed main body mold. In this picture the upper rear half of the duct is white. This is because it was painted with Latex paint in an effort to seal the foam core from the resin. This didn't quit work, so I had to make a new core. I will either have to use more paint or use the plastic sheet to protect the core.

Here is a picture of the front two body panels ready to be prepped for painting. Notice the air scoop in the mid section. This is for the engine. The interal atmosphere of the vehicle will be pressurized due to the hovercraft fans. Because of this I decided to run a dedicated intake manifold for the engine to provide O2 at ambient conditions. The air intake will mate up to this scoop.

This is a picture of the lift fan spinner mold. Since the picture I have actually made the spinner part and am in the process of glassing and ballancing the lift fan.

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(in reply to brice_arnold)
       Post #: 22

RE: Giant Scale Amphibious Vehicle - 3/27/2004 1:44 PM   
tegwin



Posts: 431
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Joined: 10/28/2003
Last Login: 9/13/2011
From: malvern, UNITED KINGDOM
Status: offline 		Do you not think that it will be a bit heavy to hover?

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(in reply to brice_arnold)
       Post #: 23

RE: Giant Scale Amphibious Vehicle - 3/29/2004 5:44 AM   
brice_arnold


 

Posts: 491
Score: 120
Joined: 1/11/2004
Last Login: 7/25/2011
From: Los Altos Hills, CA, USA
Status: offline 		According to my calculations I am still within my weight limits for hovering, however, with the current state of things I think it will be too heavy to hover. If it does hover, then it probably will not have the necessary thrust to get it moving. Right now I am trying to focus on a school deadline of May 7th. This is my graduating senior project. Once I am finished with school and have a little more free time I have plans to either increase the engine size, or consider using multiple engines.

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(in reply to tegwin)
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RE: Giant Scale Amphibious Vehicle - 3/29/2004 6:13 PM   
tegwin



Posts: 431
Score: 100
Joined: 10/28/2003
Last Login: 9/13/2011
From: malvern, UNITED KINGDOM
Status: offline 		Could you not simply reduce the weight, buy building a fiberglass hull and bolting stuff to that rather than using a heavy welded frame?

Use a hovercraft desighn and make it drive on land rather than the other way around.

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(in reply to brice_arnold)
       Post #: 25



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