Forced Articulation System
Overall Vehicle Measurements and Scale
|Front Track||6 3/8"|
|Rear Track||6 3/8"|
|Front Tire Height||24x43 - 3 5/16"|
|Rear Tire Height||24x43 - 3 5/16"|
|Skid height||2 1/4"|
|Break Over Angle||39 degrees|
9.1F / 9.3R
|Overall Motor-to-Wheel Gear Reduction||432 : 1|
|Power Source||9v Battery|
09/15/02 Built The First Forced
Last night Jason showed me his Lego Crawler and I thought it was way cool. I have a bunch of Legos from my earlier years, so today I started working on mine. I don't have all the gears, gear boxes and motors Jason has, so I'll have to work on that. For now, I began working on a "Forced Articulation" system. What that does is when one tire is forced up by an obstacle, it forces the other tire, on the same side of the vehicle, in the opposite direction. With a solid axle system, this links all four tires together. For example, when the front right tire is forced up, it forces the front left down, the rear right down, and the rear left up. It's tough to explain, so check out the pictures:
The object in the second picture that the tire is on is my first gear reduction system. So far I can only get 405:1 in the gear box and another 3:1 in the axles for a grand total of 1215:1. Jason had 5832:1 and the speed seemed perfect, so I know I have some work to do there.
I also have a video of the articulation system, check it out:
09/19/02 Ordered parts on ebay
Today I won two auctions for "Lego Crawler" parts. First I got an "Exploration Mars" kit for $31.50. This will give me more gears, axle couplers and most importantly the 24:1 diff housings. Next, I bought a 9v motor for $13. This should be all I need to get the power to the wheels and see how the forced articulation system works.
09/21/02 Redesigned the body
While I'm waiting for my parts to arrive from the ebay purchases, I decided to get to work building the main body of the crawler. What I had before was just a dummy block so I could get the FAS functioning. When my motor arrives, I'll be looking to get this crawler in motion, so I built the gear reduction system and made space for the 9v motor. I'm not sure where the battery will sit, but I'll just rubber band it on somewhere for now. I built the body with the engine and battery located at the front of the model. I think this weight differential will help the crawler climb. The gear reduction occurs for the entire length of the body with (5) 3:1 reductions. Then the power drops down to a lower point for the drive shafts. This is so the front drive shaft can run under the rest of the gear reduction. This works out nicely because the rear drive shaft is short. The rear does most of the heavy work and I believe it will be stronger this way. The body came out 3 lugs longer than it was originally, and the same width. Currently 19 long and 6 wide. The FAS sits on the outside of the body and is a total of 4 lugs wide. I also changed the upper part of the articulation arms. I'm using universal joints instead of the dual "Angle Connector #1" I used before. The u-joints take up less space and have a cleaner look to them. The last thing that I added was flex limiters. This way, when the FAS flexes WAY out, it will stop before the tires bind on the articulation arms.
09/24/02 Ordered another motor
No parts yet. Today I learned that the motor I bought on ebay (Lego P/N 5114) has a low torque rating. I've also heard that it's running RPM is either 4,000 or 1420. Either way, I'm geared WAY too low now. I found another Lego motor (P/N 5225) that has a much better torque rating and is already geared down to 375 RPM. Couple that with (2) 3:1 reductions and the final 24:1 worm gearbox and I'll spin a tire right around 30 seconds. Should be perfect. I found out that the "Hover-Sub with Motor" kit comes with the 5225 motor and costs less than $20. I found one at a website in Florida and submitted my order. I'm supposed to hear back from the guy who has it for sale to arrange payment. I guess the website is kind of like an ebay, but without the auction part.
09/25/02 We have motion
The FedEx guy delivered the first motor that I bought on ebay. I did a test with the motor and it spins at 3850 rpm with a 9v battery attached. Not quite 4,000, but close. With the 3:1 gears in the axles and the (6) 3:1 reductions in the main body, that gives me a total of 2187:1 to the wheels. The wheel takes 34 seconds to rotate.
I couldn't wait for my other parts to arrive so I made a few changes to get this sucker rolling under it's own power. I had the change the overall gearing to 1093:1 by changing an 8 tooth gear for a 16 tooth gear (on the motor). That's because I was 1 8 tooth gear short of getting 4WD functioning. Then I setup a few phone books and the video camera.
1 minute : 28 seconds
Now all I need is my "Expedition Mars" kit to arrive and I'll change out the axles for worm gear boxes, the u-joint underneath for an axle coupler, my homemade axle extensions for more axle couplers, etc.
09/27/02 Got the Expedition Mars kit
USPS delivered my "Exploration Mars" kit this afternoon. I immediately went to work changing the crawler. I changed out the axles, axle couplers, and I changes the body a bit. I moved the articulation arms down quite a bit since the new worm gear boxes raised the vehicle so much. I also made the articulation arms shorter so the axles can flex more without binding on the links. I then changed the gearing inside the crawler. I removed (1) 3:1 reduction since the axles will now be 24:1 instead of 3:1. Next I changed the gear on the motor. I was using a 16 tooth because I ran out of 8 tooth gears. The 16 tooth gear didn't align well with the 24 tooth. The 8 tooth lines up perfectly. The last change I made was bump stops. I had tried a bump stop system that was hidden from view, but it wasn't strong enough to keep the tires from binding on the body. The new body stops are on the outside, very visible and very effective.
Click the pictures for an 800x600 version in
a new window:
09/29/02 More "field" testing
Shot some video today on the dining room table. This one features the "Crawler CAM". Those familiar with my other hobby (Jeeps) might recognize this technology. It's a 12VDC "lipstick" camera. I rubber banded it to a couple Lego pieces and took the crawler for a spin on some of Natalie's rubber stamps. The crawler did so well it nearly climbed the wall at the end of the table. You have to watch the video to see the surprise ending though.
2 minutes : 22 seconds
10/07/02 Final changes before the
I received my 2nd motor that I ordered. This one is the geared down motor and supposedly only spins at 375. I didn't test it, but it's A LOT slower than the other motor and that's good enough for me. I was able to remove a bunch of gear sets so now I'm down to a 2:1, and (2) 3:1 reductions in the body totaling 18:1. Then the 24:1 at the axles making a grand total of 432:1. This spins the tire at 1 revolution in 80 seconds. Now that I think about it, the rules indicate the tire must rotate in less than 60 seconds, so I guess I'll be making more changes after all. Also, I guess the motor is spinning at 324 RPM. Anyway, here's today's pictures:
The first pic shows max articulation with the bump stops in place. The 2nd picture shows max with the bump stops removed. I need to run the bump stops to keep the tires from rubbing the articulation links under max compression. The 5th pic shows the power switch. It's the small 1 by 2 gray thing above the yellow gear box. The 6th & 7th pics show the inside battery box (right), motor (center) and a couple of the body mounted gear reductions (left). The last pic shows the under side of the crawler.
10/08/02 Final, final changes
I had to change the gear ratio to comply with the rules. I removed the 2:1 reduction, so the overall reduction is 216:1. This spins a tire at 1 revolution in 40 seconds. That's good enough.
06/06/03 Black gear boxes
Just for kicks, I ordered a couple black worm gear boxes from someone on BrickLink. Cost me all of $4.96 including shipping for two worm gear boxes and two grey worm gears. Now I'm 99.9% color coordinated. I still have one blue brick that's mostly hidden.