Project: supercrawler

[z3_2drive]

This will be my topic for a hopefully successful project. After my 4 L motor project failed badly, I'm giving it another shot after seeing the performance of my test crawler, so this will have 2 buggy motors, my 10 volt batteries and stronger design currently stuck with trying to find a way to acquire a second buggy motor(donations welcome ), but I have already finished front axle connection(always start with front axle) with triangulated 4 link, and made a simple start to a chassis. I tested the geometry, and measured wheel space, so I will be buying the 1.9 Rok Lox tires This crawler will have long wheelbase, good ground clearance, wheel speed and power. Will post WIP pictures later today, wish me luck

And for those who have not yet seen, heres my test crawler:

http://www.youtube.com/watch?v=xjvZiD9pV_I&feature=plcp

so hopefully project Supercrawler will have similar to better performance.

[Alasdair Ryan]

Oh I have two buggy motors but they are not really the things would would want to give away for fee.

[Kronos]

You could always buy one from this guy...

http://www.bricklink.com/store.asp?p=ToyBrickBrigade&itemID=37362614

I've seen worse prices...

[z3_2drive]

Oh I have two buggy motors but they are not really the things would would want to give away for fee.

oh I can understand its just I cant find any on bricklink in the U.S. 20-30$ is a fair price in my opinion

edit: didnt see that one, but 45$ seems too pricey, meh, guess i'll get one

Edited October 14, 2012 by z3_2drive

[z3_2drive]

WIP pics from couple days ago, now theres more but dont feel like uploading btw have bought motor, wire, and tires, hopefully everything comes by Friday, so I can build and finish on weekend heres pics:

^long wheelbase as i said, and got nice leather/rubber type mat to put on table, great for building/pics :thumbup:

^closeup-sorry for fuzziness, took them fast

^front axle, strong with offset servo for easy placement, and I have lengthened the axle 2 studs since this picture to give bit more room for those giant Rok Lox tires

^closeup of suspension-everything triangulated and thought out, so U-Joints never pop out looks realistic, huh?

^definitely room for big tires, although may rub a bit when suspension compressed to one side while turning...

^simple two level chassis(now three level with battery cage)

^from the top

^showing all linkages, and i've measured that with Rok Lox, it will have about 8 centimeters(little over 3 inches) of ground clearance in the middle of the chassis and 2 inches(5 cm) under the axles wish me luck!

[timslegos]

Suspension looks pretty flexible, I look forward to the video.

tim

[Alasdair Ryan]

For off road vehicles like this I would reinforce the U-joints ether with bull joints found on the crawler or making my own.

[AndyCW]

I like the updated pictures and am planning something very similiar. Good luck. It is interesting to see the little ways that our vehicles differ. My crawlers share many of the same design elements and I see some points where you might run into issues further along.

1) The 7 stud beam on the axles between the lower link mounts can separate from the axle during abrupt maneuvers.

2) The servo may not have enough torque to handle larger wheels and obstacles.

3) Lower link mounts on chasis may create a point for the vehicle to get "hung up" on obstacles.

4) You can add caster angle by slightly changing the geometry of the links. This will help with the steering effort.

5) 9:1 axles + large tires works great on 7.2v, but you are running higher voltage. You may want to look into changing the axle ratios. Philo's page shows the difference in torque between 7.2 and 9+ volts.

It looks like you will enjoy yourself creating this project.

v/r

Andy

[z3_2drive]

I like the updated pictures and am planning something very similiar. Good luck. It is interesting to see the little ways that our vehicles differ. My crawlers share many of the same design elements and I see some points where you might run into issues further along.

1) The 7 stud beam on the axles between the lower link mounts can separate from the axle during abrupt maneuvers.

2) The servo may not have enough torque to handle larger wheels and obstacles.

3) Lower link mounts on chasis may create a point for the vehicle to get "hung up" on obstacles.

4) You can add caster angle by slightly changing the geometry of the links. This will help with the steering effort.

5) 9:1 axles + large tires works great on 7.2v, but you are running higher voltage. You may want to look into changing the axle ratios. Philo's page shows the difference in torque between 7.2 and 9+ volts.

It looks like you will enjoy yourself creating this project.

v/r

Andy

thanks! yes, I realize the issue of the lower link mounts-its happened before so I will try to do something about it, caster angle-most likely will not implement it, servo is quite strong but you cant steer against an obstacle while moving-but you wouldnt want to do that anyway, and about ratio, are you implying gearing it down more? if so I might possibly do this but it would increase weight/complexity and I'm hoping its enough power using two motors. And you are right! it is fun, as I tested it (built the rear axle connections and hooked everything up) with one motor I have and it was decent but of course stalls easy with large size. I am thinking that with the doubled power without doubled weight will be sufficient power my goal is for the front axle to be able to lift itself up the wall without stalling. Was your crawler with 2 buggy motors able to do this?

Edited October 17, 2012 by z3_2drive

[AndyCW]

My two buggy motor crawler could climb walls with unimog tires.

My crawler was 9:1 and used 7.2 volts. It could spin the PP tires on occasion. According to Philo's page, on 7.2 volts the motors output about 7.5 Ncm of torque. We then multiply this by the 9:1 axles and we end up with 67.5 Ncm of torque at the wheels. 67.5 Ncm of torque was plenty for my crawler. You have somewhere north of 9.5 Ncm of torque at the motor because of your increased voltage. If you are looking for similiar torque at the wheels, then we take 67.5 and divide it by 9.5 and we arrive at an approximate gear ratio of 7.1:1. I am suggesting that you you can make do with less gearing and in doing so increase your wheel speed. One of the trial truck tips is to never gear the truck down more than you need.

http://www.philohome.com/pfrec/pfcurves.htm

v/r

Andrew

[z3_2drive]

My two buggy motor crawler could climb walls with unimog tires.

My crawler was 9:1 and used 7.2 volts. It could spin the PP tires on occasion. According to Philo's page, on 7.2 volts the motors output about 7.5 Ncm of torque. We then multiply this by the 9:1 axles and we end up with 67.5 Ncm of torque at the wheels. 67.5 Ncm of torque was plenty for my crawler. You have somewhere north of 9.5 Ncm of torque at the motor because of your increased voltage. If you are looking for similiar torque at the wheels, then we take 67.5 and divide it by 9.5 and we arrive at an approximate gear ratio of 7.1:1. I am suggesting that you you can make do with less gearing and in doing so increase your wheel speed. One of the trial truck tips is to never gear the truck down more than you need.

http://www.philohome...ec/pfcurves.htm

v/r

Andrew

thank you! well I hope i'll need less gearing, so it will be crazy fast! and heres an update for you, fixing some problems you mentioned

^battery cage and one motor i already have(guy with overpriced motor was slow with my order so might come Monday )

^You mentioned weakness of steering? well this pretty much fixes that, replacing weak link with rack/pinion :thumbup:

^bottom view(gears never slip in steering )

^You mentioned possible separation of bottom link mount? Well, not anymore

^rear axle

^bottom view(missing link mount reinforcements because I thought of it between pictures )

good so far!

[AndyCW]

Looks better. Can't wait to see it in action. I am currently away from home on business travel and don't have access to my Lego. I need to live vicariously through you guys during these trips.

[pint14]

Nice crawler, cant wait to see the bodywork and video!

[z3_2drive]

Another update: no motor yet but tires arrived yesterday and today made some nice bodywork heres pics:

^shock braces to keep them from popping out

^on front axle

^liftarm above top links in chassis so they dont pop out easily

^hopefully will be able to climb this (60-65 degree)

And now for bodywork!

^Looks awesome, doesn't it?

^looks pretty scale with these tires

^little bars/lights for detail

^doesn't look like a lot of ground clearance because of sheer size of crawler , but it's actually pretty decent!

^nice articulation

^ weight with everything and two batteries (only one motor) is 1,378 grams now just wait for motor to come...

[pint14]

I think that the bodywork should be maybe 2-6 studs longer, but thats my opinion.

[z3_2drive]

I think that the bodywork should be maybe 2-6 studs longer, but thats my opinion.

I think it looks good and im trying to save weight, and any reason for double posts?

[pint14]

Its some sort a issue what i m having, i dont know what to do.(i klick 1 time, still double posts come) :S

[DLuders]

@ z3_2drive: I like those Rok Lox 1.9 Comp Tires on your Supercrawler! Those tires are sure sticky to handle a 60-65 degree slope. I have some of those tires too, and like how they are compatible with the Lego 44772 wheel.

[z3_2drive]

thats how I feel right now, when I realized a big but simple mistake... lately was noticing the driveshaft going into the rear axle was a bit wiggly, so today I took a closer look, and was shocked with what I saw and the smell of burnt plastic-heres what it looked like:

^friction completely melted this side of the hole

^Other side is fine

^Plastic melted and wove around the axle

^with some tugging with clamps I pulled it out of the u-joint...

^what it looks like - apparently something was pushing the driveshaft into the hole, causing large amounts of friction...

^but the front axle was fine except for a little dust...

THE PROBLEM: one top link was a stud off, causing inequalities in the geometry, most likely causing the driveshaft to be pushed into the rear axle, and it was like this for a day or two...ruined part because of a simple mistake but I replaced the 5x7 frame and moved the link and there seems to be no more friction problems motor hopefully arrives tomorrow

[DLuders]

@ z3_2drive: I wouldn't sweat the loss/destruction of a few Lego Technic parts -- they only cost a few dollars total. The most important thing is that you're HAVING FUN.

[Alasdair Ryan]

@ z3_2drive: I wouldn't sweat the loss/destruction of a few Lego Technic parts -- they only cost a few dollars total. The most important thing is that you're HAVING FUN.

.........While braking parts.

like I said above I would of used the ball joints found in the crawler and the unimog.

[z3_2drive]

.........While braking parts.

like I said above I would of used the ball joints found in the crawler and the unimog.

instead of 4-link? no way this is way more realistic and no negative caster, we'll see how strong it is...

[Alasdair Ryan]

No these:

You can have the U joint go through the middle which would be stronger than what you have done.

Edited October 21, 2012 by Alasdair Ryan

[AndyCW]

I have used the telescoping driveshafts to cope with the issue. The downside is that they provide another failure point. It takes a much closer tolerance on geometry to make fixed length driveshafts work with a triangulated four link. One of the key elements is to get the driveshaft equal in length to the links and parallel to the links. Adjusting caster angle by changing link geometry can also be used to fine tune the driveshaft length requirements.

Do you have problems with the pinion gear trying to "walk up" the ring gear. The bearing surface is only 1 stud deep. On my 9:1 axles i had a double bearing on the pinion gear. One behind and one infront of the pinion gear. This put the pinion shaft in double shear when it tried to walk up the ring. This approach might reinforce your center section and make a repeat situation less damaging. I think that the GM 14 bolt axle uses a similiar pinion bearing structure.

http://www.brickshelf.com/cgi-bin/gallery.cgi?i=5588763

I also think using the ball joint setup from 9398 is not as much fun.

v/r

Andy

[z3_2drive]

I have used the telescoping driveshafts to cope with the issue. The downside is that they provide another failure point. It takes a much closer tolerance on geometry to make fixed length driveshafts work with a triangulated four link. One of the key elements is to get the driveshaft equal in length to the links and parallel to the links. Adjusting caster angle by changing link geometry can also be used to fine tune the driveshaft length requirements.

Do you have problems with the pinion gear trying to "walk up" the ring gear. The bearing surface is only 1 stud deep. On my 9:1 axles i had a double bearing on the pinion gear. One behind and one infront of the pinion gear. This put the pinion shaft in double shear when it tried to walk up the ring. This approach might reinforce your center section and make a repeat situation less damaging. I think that the GM 14 bolt axle uses a similiar pinion bearing structure.

http://www.brickshel...y.cgi?i=5588763

I also think using the ball joint setup from 9398 is not as much fun.

v/r

Andy

well it doesnt do that with just one motor, but i'm sure it will with 2, will try something like that! thanks for the tip!