The BULLY 2 steering thread (servo stalling solutions)

[Master Basher]

This thread is for the compilation of solutions for what I perceive to be the biggest issue with the new Bully 2 axles, the short steering knuckles.

This is a big advantage in several ways, the steering linkage almost never gets in the way of the rock crawling, and the tires have much less to get snagged on and rip open with. I'm also using a Hitec MS7990TH at 8volts. This is supposed to be giving my 660oz/in of torque. So I don't think the servo is to blame, as Rowdy said in another thread, the lack of mechanical advantage is at play here.

The problem for me is when I'm pulling up tight to a tall rock ledge to pull the front up tight to the rock with front wheel drive only. I have several "standard" rocks in which I can replicate this phenomenon repeatedly, every time. I have tried several solutions. One is extending the steering arms. Here is a picture of such:


I do not like this solution. I don't like the extra space out toward the tire, I've snagged and ripped tires 3 times in just a few weeks. I don't like adding anything on to the steering knuckles either. I have used aluminum for mine, I've seen cf (rmdesigns), stainless steel (rowdy), and g10(not sure who). I don't want to use any of this. I don't want to have arms that stick out close to my tires.

I have seen Joshs' drag link that goes to the opposite knuckle. I haven't tried this yet. It seems to be working for him, but I'm not sold on it until it passes my test rocks. I also use this area to mount my battery, and I'm not changing that soon, so I don't like this solution.

I recently went to this setup:
Here I need to lengthen the drag link a little so that it is perpendicular with the steering servo arm. THat will give me better movement with the short arm.



Using a 14mm eye to eye spacing on the holes in a very short servo arm. This solves my servo stalling problem completely, but it presents several other problems. First, is I don't have a tall offset mount servo arm, so my linkage has to go to the top of the servo arm. This is awkward and causes ball joints to be stressed a lot. Second, I'm going to have to mess with the drag link and it's length a good bit to get enough steering throw to take advantage of the bully 2 axles high amount of steering. You also lose a lot of control over the wheel at full right turn because of the steering arm is in line with the servo arm at full extension. I am happy with the steering link on top of the left knuckle, and then on bottom of the right knuckle. This give the most clearance for steering, and keeps the height of the stack on the right side down low to keep tires from snagging on it. I have tried this with the stock aluminum steering rod and then this tiny titanium rod. I ordered a 3/16" rod 160mm for use in the very near future.

Please feel free to add your solutions or pictures to this thread. I want to have a perfect set up, and I'm not there yet.

I feel like a servo arm that rises up from the servo would be ideal for this application so the drag link can go on the bottom of the servo arm. Anyone got any links for me?

[Brumle]

This is how i did it.


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[josh6575]

Master Basher can you take a video of your test rock. I would like to see if I can replicate the line you are trying to pull. I have plenty of rocks to stack to try and produce something similar.

[Master Basher]

^that is a great idea brumle. Im interested does your drag link pop off the ball ever?

[CrawlrKing]

Just tested your idea Basher and it seems to solve the stall I had on my 7950th, need some more time on the rocks to totally adopt it...


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[Master Basher]

Originally Posted by josh6575

Master Basher can you take a video of your test rock. I would like to see if I can replicate the line you are trying to pull. I have plenty of rocks to stack to try and produce something similar.

Yeah josh. I'll do it this afternoon. I might could get some video too, but don't hold your breath...

[Master Basher]

This rock is the vast majority (95%+) of my servo lock ups. It is representative of a particular type of crawl though.









Here is a photo representative of what happens when I turn the wheels to get a leg up on the rock and pull over. This stretches out the chassis links/compresses the springs and locks the servo up.





Here is another side of the rock that causes stall also, but not anymore:


And here is a top shot that shows where i need to make the drag link more perpendicular to the servo arm to get better servo throw.



I did get a video, but it is uploading and I won't be able to get to it for a bit.

[Brumle]

Originally Posted by Master Basher

^that is a great idea brumle. Im interested does your drag link pop off the ball ever?

No problems. I have run about 30 batteries with this setup.

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[Master Basher]

I'm trying to hold my phone and controller at the same time. Sorry for poor video.

This used to lock it up every time. I would still get over it, but my steering wasn't helping. Now I can move the steering as I get over it.

[ROWDY RACING]

Not matter the configuration the shortest horn you can use is the answer to the steering issue.

[josh6575]

I have always used the short horn and the long drag link does not make much difference other than not having to create some crazy looking drag link. I mostly like the long straight drag link because I know it will not bend or stress the servo. The 45 degree angle from the servo horn to the steering horn is pushing and pulling your servo up and down. Mine mostly side loads as intended making it more efficient.

[ROWDY RACING]

Originally Posted by josh6575

I have always used the short horn and the long drag link does not make much difference other than not having to create some crazy looking drag link. I mostly like the long straight drag link because I know it will not bend or stress the servo. The 45 degree angle from the servo horn to the steering horn is pushing and pulling your servo up and down. Mine mostly side loads as intended making it more efficient.

Not to mention huge batteries up high on the axle is not a good trade off for proper steering geo and low cog.

[Colgout]

Rowdy, how short is the servo horn you are using? I order one of these, would that be short enough?

OFNA CNC Machined Aluminum Single Arm Servo Horn (25T-Futaba/Orion/Savox/ACE) [OFN10776] | RC Cars & Trucks - A Main Hobbies

[ROWDY RACING]

1/2", info can be found in my thread. Josh uses one that's a little longer at 5/8" and it works for him.

[Master Basher]

Well I think I solved the problem to my satisfaction. I haven't gone with the short servo arm, although I have made several iterations that I like... I went with a medium foam (6.0") in size up front instead of the small soft that I had. Now the wheels don't suck down so hard and I rarely lock up the steering. My steering servo arm is actually longer, as the short arm I had before would even let me steer lock to lock without hitting my servo with the rod end.

This worked really well for me in the last comp, and I've tooled around with it for a bit, but I don't have a ton of wheel time with it to make sure that I like it enough to stay with it.

I made some really good crawls with blue voodoo's front and medium 6.0" foams in front as well, so I'm going to try this out for a bit.





By the way, I think if you are stacking the rod end for the steering link on top of the knuckle link and then on top of the knuckle arm, you are missing the boat. Placing one of these links below the steering knuckle arm leaves much more room for tire deformation and NOT snagging a tire on the stack of links above the steering knuckle.

If that wasn't clear, look at the link that connects my knuckles. It isn't horizontal. That is better than placing it on top of both knuckles imo.

[ROWDY RACING]

Zero steering problems for me since running the drag link to the long side, even with a 13/16" servo horn.

[josh6575]

Never had a problem here! MB how did you get those front tires to look like trexlers.

[rmdesignworks]

Along with my cf knuckle extensions I have made a new tie rod out of cf with a drag link mount near the long side...but I actually havent had any stalling issues either.

[ROWDY RACING]

Originally Posted by josh6575

Never had a problem here! MB how did you get those front tires to look like trexlers.

By over inflating them.

[Snatch]

I killed a Hitec 7950 and the second one always gets very hot.Now,since running many Lipos i´ve no more problems.I use the servo arm as short as possible and i made some longer steering arms.Looks not as nice as the Rowdy-Version,but it works: