AndyCW

Thanks for the inspiration. v/r Andy

I you are more concerned with length than width of a gearbox, you could build the gear casing out of thin liftarms. This will shave a stud or two off of the length. v/r Andy

LDD file of the chassis. This is my first LDD experience and as such this file is rough, but it should help people build their own four speed crawlers. It is incomplete and not identical to the real deal, but the key structures are there. The axles are nothing special. The upper and lower towball mounts have an altered 3l bar between them. This helps locate the front gear brace and stops the towballs from backing out. Because of the models I used for the 5292 motor and the servo the instructions are a laugh. http://www.filedropper.com/4spdcrawler This is my first exposure to filedropper. v/r Andy

I like it. It is important to me to always have a list of improvements to make to our creations. I do the same thing and it allows me to continually push forward with concrete objectives. Are you going to remote control the whole assembly? Autovalves would help in this. v/r Andy

I don't have many pictures other than what is in the slideshow portion of the video. Are there any specifics people would like to see? The axles are pretty simple 8t to 24t portal hubs 12t to 36t spool four links 12t gear on rack for steering Transmission is this using the input shaft with the 24t gear on it instead of the 8t. The shifter linkage from servo to driving ring should be fairly straightforward from the video. Allanp provided this picture on a previous thread of the gear exchange used. v/r Andrew

Fourth gear is a little too weak for off road terrain. On flat level smooth surfaces it is fine, but it is hard to keep up with it using IR remote control. I am thinking about making a custom 9.6 Vdc battery pack. This would enable 4th gear to be used for much more, but make keeping up with it even harder. The lack of differentials cause it to bind and slow down significantly in fourth gear when turning. Using unimog tires may solve all of these problems. They have less grip, less diameter, and less mass. This makes them easier to turn. This might also solve what little gear popping remains in the driving rings. Another way to reinforce/fix u-joints is to wrap the end in string and then soak the string in superglue. Batteries were fully charged just before the video began. It should last longer than anyone will want to play with it. I have not had it run out of juice during testing. The math should be fairly easy to do. Max current allowed by IR rx and batteries combined with the capacity of the batteries. Ohms law and all that. v/r Andy

Wow!!! You sure are proliferous (sp?) I haven't built that much stuff in two years. v/r Andy

After my last truck with a two speed transmission and air lockers, I decided to try more gears in my transmission. I searched for transmission ideas and came across the regular four speed transmission. The common wisdom is that driving rings cannot handle any torque. This is accurate. I had to increase the gear reducton in the axles and step up the motor on the transmission input to reduce the torque that the transmission "felt". I also maded the linkage from the servo to the driving ring incapable of being backdriven. It still pops occasionally, but reengaging the driving rings with the servos clears it up. It also has a neutral gear and this allows it to roll after the throttle has been released. Eliminating any extra gear exchanges to improve efficiency, reducing weight, and maintaining a rigid structure for the transmission to operate within became critical. I tried to get rid of the knob gears connected to the rc buggy motors outputs, but was unsuccessful. 12t to 12t ground the gears down 20t to 20t also ground the gears down 24t to 24t crown would not fit. Caster angle on front axle is accomplished by less angle on the lower links. I tried a wider version of the LPE power unimog axle that has kingpin inclination. It worked and did not fall apart, but its turning radius was larger than a traditional steering axle and so it was discarded. It still is assembled, just not mounted on the truck. I made air lockers based off of the new 3 stud wide differential, but ended up discarding them because they added unnecessary complication. I killed several u joints on the driveshaft before I moved up to 9:1 reduction in the axle. The u joints that are installed have wax string wrapped around the ends and a small piece of heat shrink tube over that. This is a repair because all of my joints are now cracked. If a tire becomes blocked in first gear with the steering turned, this design can quickly destroy u joints in the axle. There are a couple of altered pieces. 3l bars have had a couple of mm ground off to secure the towballs on the chassis and there is a 4.5 stud axle going to the knob gear on the transmission input. Both elements could be done without. It would require some redesign though. Moving to a 9398 style suspension and increasing the wheelbase would eliminate both of these issues. I used 4l bars to secure the towballs in the axles. They fit into the back of the towball and prevent it from popping out of the lift arm. Questions, comments, concerns, relevant war stories???? v/r Andy

The power is stupendous. Considering the weight and complexity of the vehicle, its performance is remarkable.

I like the limited slip solution. It looks like 8:1 overall gearing from a PF XL. How are you going to locate the axles under the chassis? v/r Andy

I will make this quick to not derail someelses thread. Check out LPE Power's unimog front axle. It uses kingpin inclination to get what you want. It becomes simpler to build when you widen the track width by two studs.

That looks awesome. I am looking forward to the completed vehicle with that axle in it. It is going to be huge.

The upper third link mount (because it is being used as the centering device) will cause the suspension to rotate around the upper towball. A much more preferable point of rotation would be the drive shaft. It will function fine, but this approach will raise the roll center of the vehicle. This is the reason that I use triangulated four links. They create a roll center between the upper and lower links. I high roll center will cause instability while traversing slopes and create more stress on the springs. A portal axle with the fixed center third link will have a similiar roll center to your axle. v/r Andy

The new 8t and 24t gears will help some of your breakage problems. It looks like 3:1 gearing off of the NXT motor. The caster angle on the front axle looks a bit extreme.

Looks huge. The underside shots are good. Are those three links? Are those 9:1 axles? Are they air lockers or mechanical lockers? Can they be selected individually? What style of transmission did you use? Any parts breakage? Do you think that if you shed some weight and reduced it to a 4x4 it would perform significantly better? v/r Andrew v/r Andrew

Looks enormous. The third link mounted so high will create some interesting "motions" during articulation and significantly raise the roll center. v/r Andy

You may run into issues with your links so far out of plane with the horizontal. When encountering an obstacle, the front axle will try to tuck under the vehicle instead articulating. These forces could cause the links to easily pop off of the towballs or the towballs to pop out of the lift arms. It also causes the front axle to shift forward when compressing. This measn the suspension cycle will be going counter to the obstacle.

By limited differential do you mean a limited slip , a locker, or a spool? Most full scale crawlers have lockers, most performance cars have limited slips, most average cars have open differentials and crazy powerfull offroad vehicles (drag racers, hill climbers, pulling trucks, etc.) have spools. http://en.wikipedia.org/wiki/Locking_differential v/r Andy

Can't wait to see the delta in performance between this and my project due to the RC unit and its increased ability to supply the hungry motors. I have a lot of questions, but they will wait untill the rest of the pictures are posted. Hopefully we will also get to see a video of the performance. v/r Andy

No differentials on v2. The cost vs. benefit is not good enough for me. Every two speed I have tried did not manage to utilize the full power of twin rc buggy motors. Either the spacing between the two gears was too little or too much. Three speeds would be better, but the only three speed I tried failed. I have success right now with running a normal driving ring four speed shifted by a pair of servo motors. The key is a strong structure around the gears, increasing gearing in the axles, and reducing the gearing going into the transmission. This reduces the torque that the driving rings in the transmission experience. The axles would also try to walk out of the gearbox. I had to use axles with stops and create the casing so that the axles were trapped. A couple of non drivetrain parts are on order and I need to figure out how to make a better video. Hopefully between work, school, and family I will have the new project posted next week. v/r Andrew

Holy Necropost Batman!!!! The locking differentials never popped or slipped out of lock. It does not take much pressure to keep a driving ring engaged. The front axle used a straight connector to engage the driving ring on the differential lock and the rear one used a shift fork. The front solution created a fair amount of friction on the axle with the driving ring on it. The locks only see 1/3 of the forces that the wheel experiences. I never had any problems with the differential locking mechanism other than the isolated mention above in post number 7. I did have one of my shocks break at the top near the dogleg. I don't know how it happened. It could have been my little boy playing too rough with the truck. It was an easy fix. My son makes an excellent durability tester. I have been using the same four link and shock setup on my projects since this and have not had any further troubles. The four link mounting points allow me to put in caster when I want. Thanks for the interest and commendations. The follow up to this project is in the final testing phase. I moved to a four speed transmission. v/r Andrew

Bricklink is your friend. After all, it is only money. You can't take it with you. Have you ever seen a moving trailer towed behind a hearse? Somebody posted about how to "overvolt" the buggy motors to 18 vdc. This would provide stupid power in a crawler, but longevity of the motor will definitely be downgraded. It all depends on how far each one of us is willing to push it. v/r Andrew

They just came out this year. Bricklink or Lego Customer Direct will have them. http://www.bricklink...5&itemID=114206 Bricklink http://www.eurobrick...th#entry1481990 Discussion on how they help in the reduction hubs. v/r Andy

WOW. I have shattered some gears, chewed the teeth off of others, broken U joints and even made some custom half stud length axles, but never done something like that to a piece on purpose. It does seem to work though and that can't be argued. v/r Andy

You are going to want to go to the new 8t gears in your hubs they do make a lot of difference. The track width on that beast is considerable. This factor is most likely contributing to the strained pieces we are seeing in the second picture. The geometry of this suspension is "interesting". Again, those wheel caps are awesome. To embed Youtube videos I just paste the link for the video into the post. I look at the preview post option before committing. Extreme 4x4's episode this weekend was about a 1900 footpound mud buggy on 54 inch tires. It will be EPIC!!