Sidneys1's Latest: A Rock Climber

[sidneys1]

Having been inspired by mattallen37's Rock Climber, I set out to build my own. Yesterday I started, blowing the six-ish months of dust off of my NXT parts bins, and got to work building the rear axle and differental. Things got off well, despite my rustiness at building and forgetting where I kept most of my parts, and I ended the day with a nice rear axle/diff setup.

Day 1 Progress Pictures


On day 2, I decided, this being a rock crawler, to not use too many gears, and instead achieve the needed torque by having two NXT motors power the differental in tandem. This worked out well, and after some minor changes to allow a body to be built off of it, I set about building the front suspension and steering mechanism. I wanted to use the same "crossed beam" suspension style mattallen37 used in these pictures, but slightly improved to use Lego spring pistons. This I did, and I then focused on attaching the front and back axles securely. Then, after some body detailing, I called it a day.

Day 2 Progress Pictures Note: may still need to be moderated before they're publicly visible.


Tomorrow I plan on figuring out how to get a motor in there to power the steering. Then I should be done

Have a nice day,
~Sidneys1

EDIT: Fixed multiple grammatical and formatting issues, as well as embedded the images.

[mattallen37]

Pretty cool looking!

I have a couple suggestions/ideas.

If you gear directly to a differential, 2 NXT motors have enough power to split the center differential gear (12 tooth). I recently learned that even gearing up 40:24 (for the old differential) it can still be broken by two motors, powered by the NXT battery pack. With your design, I believe you are gearing down about 3:2 (I am not sure the exact size of the new differential). If you connect NXT motors directly, you will have more than enough power to break the gear (one NXT motor on 9v might even do it). I use gearing after the differential to get the torque.

If you mount the motors on the drive axle assembly, it will not suffer from twisting, causing weird suspension issues. Another "fix" would be to have the drive shaft spinning really fast (gearing down a great deal at the axle assembly). The same holds somewhat true for the front, for the steering (since it is 2wd). Depending on your design, it might be to your advantage to mount the steering motor on the chassis, but you should consider trying to mount the steering motor on the front axle assembly.

Also, if you will be programming this in NXC, use the new APR functions for sure. It is so good for a rack and pinion style steering system. Before, I used to avoid this type of steering, because I never had a good way to control the position of the motor. Since the release of APR, I have yet to build a skid-steer.

[doc222]

Nice. But since it is a "Rock Crawler". You do NOT want a dif that slips. Nor would you want one even in most off road areas. It should be geared down alot so you can crawl up rocks. The stearing will need to have some power as well and be solid. Things like fully independent and such you can leave out if you just make the front pendular. Makes it simple and works well in the real world of micro crawlers. You may find that after you dump the difs that building the rear or even front axles for a 4x4 is easier as well and alot more power it can handel. I like the 4 point knob wheels for my solid axle directional change. also that new part that come with LA makes KILLER front hubs axle yokes and many other cool things like a axle tube .

I have broken even those knob wheels but with a motor that puts down more power than our Nxt servos and alot more rpm. But that motor runs on air and has broken many a Lego part.

Also the 12T gears are penny parts too. BUT those bigger bevels with axle hole are getting expensive and harder to find in bulk. Last i looked the only guy that had many(75 of them) for sale wanted 3:25$ EACH!<! I found one store that had 4 tan for 35 cents I thought i found gold.

You know I have heard the saying," a rolling rock never gathers moss" but what I did not know is they turn into PEARS!

[sidneys1]

Nice. But since it is a "Rock Crawler". You do NOT want a dif that slips. Nor would you want one even in most off road areas. It should be geared down alot so you can crawl up rocks...

...Also the 12T gears are penny parts too. BUT those bigger bevels with axle hole are getting expensive and harder to find in bulk. Last i looked the only guy that had many(75 of them) for sale wanted 3:25$ EACH!<! I found one store that had 4 tan for 35 cents I thought i found gold.

What do you suggest replacing the existing diff with?

Have a nice day,
~Sidneys1

[doc222]

Power to both wheels is needed off road at all times or one wheel may get high of center and just spin. I just use a long axle with the wheel knobs or a bevel set up. But for best results better to never change the powers direction the more 90 degree angles the greater the lose of power. This is why most cars are front wheel drive. In a sytem with axles that have the changes like a rear wheeled car about15-20% lose of power depending on what you are workinh about and a front wheel drive car lose is only 5-10%. This would put our lego motors side ways and then you can just gear it staight too.

But now we have Hy tech cars that some have the motor in the wheel, we can do this too in Lego but each wheel needs it own motor mounted right on thetire. this has the best of all ratio of power use since is direct.

One thing though about locked or straight axles in an area where there is alot of traction it will bind when you stear, if the front is locked its much wosre and could even cause binding. Thas why they have Difs that can lock or unlock with a button or a PC tells it when to on some very advanced sytems, even in Lego.