MAC FAB Bomber build, TAKE 2

[MAC FAB]

Bringing this back to life again because it found a pulse yesterday. I was going to strip it for parts and build something else with them. I didn't care for the way those Summit diffs were working, too flexi-flyer in my bulkhead. Upper shock mounts...........Seemed it was always 1 step forward, 8 steps back. Lucky for it, the front arms aren't long enough to be used in another class 1/1500 buggy or this would be shelved. Annoyed at that, that got me looking at the thing again and here we go, hence the "take 2". Front now cycles about 3-3/4", I don't think I have to reinvent half the world now. Steering is next hurdle, made that in my sleep last night, a few different ways. Dream technology? Not sure if I trust the plastic cage either. Anyhow, here is quick look at the front IFS "progression" (if that is the right word) from the beginning to now. "Action!"

20170523_195751 by MAC FAB, on Flickr

20170523_195514 by MAC FAB, on Flickr

20171012_193810 by MAC FAB, on Flickr

20180114_155439 by MAC FAB, on Flickr

[terrible]

That's a lot of travel! I like it.

[Bliss_RC]

pretty interesting. are those 1.9's? they look a bit on the small side...

[MasteroFlego]

Originally Posted by Bliss_RC

pretty interesting. are those 1.9's? they look a bit on the small side...

IIRC those are yeti scores wheels and tires.

Sent from my Nexus 5 using Tapatalk

[JatoTheRipper]

Very cool project!

[generalee7]

Cool hood! Where did you get it? Also, build a chassis out of 4130, its not TOOOO much more than A513

[MAC FAB]

Yes, those are SCORE TT wheels and tires, short course to miss all the steering, driveline....... If they end up being too small, and the rig really works, I'll cut up my KR2 2.2s to fit SC wheels. If not, it should be easy to regear it for speed and go run with the Baja Reys.

Generalee7, I built the hood, and will one day get to building a scratch Bomber like you.

[MAC FAB]

Probably getting the cart before the horse, but trying to give it a different look. What cha think?

Scan0003 by MAC FAB, on Flickr

[JatoTheRipper]

Looks good. It reminds me of a new U4 racer chassis that I believe is from UC Fab. I saw it on Facebook.

[durok]

Has a Penhall look to it...

[TheLetterJ]

With a heavy dose of Jconcepts BAJR body. I can dig it.

[MAC FAB]

Yes and no I suppose on the body idea. Yes with Penhall/Jimco..... style wheel wells up front, so I can close it up. Unlike the Bajr, a lot of shape (compound curve) will go into this sucker, with the exception of the roof. I conquered my next obstacle for completion this eve, the steering. I have been looking for Clod rod ends everywhere, so I could actually see them in my hot sweaty hands, per DavidH's suggestion. Nope. Necessity is the mother of invention, so I invented! Unorthodox, yes, but it works with only a couple degrees of bump steer, toe in, at full droop in the ~3-3/4" it cycles. This has been such a PITA to figure out. Sad thing is there is no adjustment for toe, fixed length, so I gotta get them right. So what is the desirable crawler set up, some toe in, pretty much straight, or toe out? I'll make the curved/dogleg shaped tie rods Thurs evening. Oh happy day! Fab the rear bulkhead/diff mount, weld on shock mounts where required on the arms, mount the trans and drive shafts, add electronics and then its test drive time!!! Its looking like the battery should go in the factory location as well. Forward progress, for a change.

20180123_185924 by MAC FAB, on Flickr

[DavidH]

I would aim for zero toe and zero Ackermann, as you would typically get in a solid axle bomber. More steering angle.

[MAC FAB]

Zero toe it is, can't do anything for the ackerman, hopefully its a good thing. I think 2wd Slash bell cranks get somewhere around 5-10*, I'll live with whatever it is. Camber in slightly negative at droop, positive at full bump so the tires won't hit the body/chassis at full lock. Upper link mounts are easy enough to change if it needs to be different. Rear sees about 10* camber change overall, positive to negative at full bump. Works in the buggies so it should here as well. Quite a bit of engineering in this "toy".

[DavidH]

I am not familiar enough with traxxas suspension to know what options you have here.

Ackermann is what makes the outside wheel turn less than the inside wheel in a corner, and is better for high traction surfaces; a small bit of toe-in can give you back that steering angle at the cost of some drag in a straight line.

[MAC FAB]

I understand Ackerman. I can actually change how much I get over stock OEM ( proper angle) by changing the spacing of the mounts, which I do on the buggy builds for a tad bit more. The only way to get around it would be 2 steering servos, so there wouldn't be the bar that ties them together generating the Ackerman. I'm also beginning to think that I will need to run 2.2 for ground clearance.

[PoorManRC]

There's some fabrication skills going on here that I haven't seen in quite a while!! Definitely something to follow. Part of me is dying to see how you get the front end geometry sorted.
While I'm going in the complete opposite direction (Wraith Rock Bouncer), I can see valuable things to learn here!! :thumbup:

[DavidH]

Originally Posted by MAC FAB

I understand Ackerman. I can actually change how much I get over stock OEM ( proper angle) by changing the spacing of the mounts, which I do on the buggy builds for a tad bit more. The only way to get around it would be 2 steering servos, so there wouldn't be the bar that ties them together generating the Ackerman.

As I understand it, what you would need are knuckles that place the tie rod pivot the same distance out as the kingpin, as can be done on the AR60 axles. But the dual-servo steering does have geek appeal.



But, I would go with your plan of expecting the Ackermann to be on the low side, and simply live with it.

I'm also beginning to think that I will need to run 2.2 for ground clearance.

Somewhat ironic to use taller tires for ground clearance on a vehicle with so much suspension travel.

[MAC FAB]

Originally Posted by DavidH

As I understand it, what you would need are knuckles that place the tie rod pivot the same distance out as the kingpin, as can be done on the AR60 axles. But the dual-servo steering does have geek appeal.



But, I would go with your plan of expecting the Ackermann to be on the low side, and simply live with it.


Somewhat ironic to use taller tires for ground clearance on a vehicle with so much suspension travel.

Tie rods are about 1-1/4", ~20* off of square compared to your picture, rearward, (making bump steer go away a headach) so I'm stuck until I build my own steering stuff. With the tires, I have a 13" wide track width. If the suspension is set up as a stink bug, all is good for ground clearance as a climbing crawler (based on where I will take it out first), the width perhaps being my enemy. Its perfect for a go fast rig if set up as seen, with the reasonable ride height, being mid stroke on the shocks. I'm hoping the "extra reach" through the wheel travel will be a crawling aid, for traction. I need figure out a plan B battery location option for go fast mode, rig needs a 40/60 weight bias f/r to work best.
Great feedback Nice to have another set of eyes when you make something.

[MAC FAB]

Originally Posted by PoorManRC

There's some fabrication skills going on here that I haven't seen in quite a while!! Definitely something to follow. Part of me is dying to see how yoU get the front end geometry sorted.
While I'm going in the complete opposite direction (Wraith Rock Bouncer), I can see valuable things to learn here!! :thumbup:

Thank you for the kind words. If I were going to pull a Mulligan on this thing it would be the Summit diffs. Figuring the mounting on those sucked hard. Instead, I would have used Slash 4x/XO-1 diffs, and would already be driving it. Maybe a V2??? Geometry isn't the hard part in reality, its all part of the scratch build process, for me anyhow. Finding parts that fit or can be made to work in the design criteria is the battle. Having tie rods that have crazy articulation was the other stumbling block. Mine are not "scale", I don't care, neither is my rig for that matter. Now for the rock bouncer, I personally don't understand the appearant death wish those guys seem to have, all while considering the cage lines. Surprisingly the roofs don't cave in. No rides for me, thank you. The same is probably said for going 100+ mph thru the desert. I'm perfectly fine with that.

To end this novel, let it be known that this is my first crawler/4×4 rig besides a SC truck I had. I'm more than open to suggestions so I only have to make stuff once.