View Full Version : QuadCrawler help please

11-10-2007, 02:53 PM
Need some help please. I'm building the Quad Crawler, problem is that legs 1 and 4 do not
move correctly when put on floor. They all work right when on my test stand. Legs 3 and 2
move just fine. I have changed adjustments, but nothing happens. I've built 3 other robots,
all are good, but this one is driving me nuts.

11-12-2007, 09:01 AM
Hi Fred, welcome to the community:)

I moved your post to a new thread because I didn't want to see it get buried and unanswered.

What do you mean by they don't move correctly? Do the servos just not seem to have enough juice to move the robot when you place the robot on the ground?

11-12-2007, 06:04 PM
Legs 2 and 3 move back and forth just fine, but legs 1 and 4 just don't move at all.
But they all move fine on the test board with out any pressure on them.If I raise it
up just a little off the floor, they move fine. any pressure on 1 and 4, they don't
move at all.


11-13-2007, 12:26 PM
Do they lift up at all? It sounds like what's happening is that the legs aren't lifting off the ground like they're supposed to.

11-13-2007, 05:40 PM
That is correct. They don't lift up ,but legs 2 and 3 do lift up

11-13-2007, 10:07 PM
It sounds like the home position of the up/down servos on leg 1 and 4 aren't set up properly. I'd disconnect the horns from the bracket and check the startup positioning.

11-14-2007, 07:36 PM
Maybe its just me, but I'd double-check the wires. Excessive flex is a killer. I've never repaired the wires coming out of a servo, but if I had to I'd find some tough stuff. Not sure what, but something's got to be beter than the flimsy ones they come with.

11-21-2007, 05:36 PM
Just to let you know whats going on with my Crawler. First, I have a stripped gear on servo #2.
Next I've playing around with the vertical servo positions, and they seem to be doing well. But I
have to wait for my new servo. Have a good gooble day, I will keep you in the loop.

11-25-2007, 02:03 PM
I've done some changes on my Quad. Some seem to work better, but every so often all my legs
freeze up. And I get a humming sound coming from my servo controler. It does it when I change
the horz or vert constants.

11-25-2007, 03:16 PM
what type of servo(s) are you using?

11-26-2007, 10:24 AM
I'm using 8 HS-322 HD deluxe

11-26-2007, 03:31 PM
I must've misread your post right before this one.. You mentioned that you hear a humming sound coming from your controller, not your servos? What controller are you using? If it's not one that we carry, could you provide a link to a place that has some datasheets and documentation?

11-26-2007, 07:49 PM
Aren't the HS 322s a little on the weak side for a crawler? Granted, stronger is (almost) always better, and I know budgetary concerns DO figure in, but 322s (47 oz-in torque?) seem a tad anemic. If the servos hum but don't move under load...
And there's no binding at the pivot points?
Just tryin' to help.

11-27-2007, 10:37 AM
Thanks for the help kdwyer:D

That was my thought too, but Fred mentioned that his servo controller is the thing doing the humming:

I've done some changes on my Quad. Some seem to work better, but every so often all my legs
freeze up. And I get a humming sound coming from my servo controler. It does it when I change
the horz or vert constants.that's where I got confused. I don't know what would hum on a servo controller...

I agree though, the 322's are way weak, especially if the crawler has any additional weight on it. I'd be surprised that the servos would last long walking with only the weight of the crawler.

11-27-2007, 05:48 PM
I'm using the parallax servo controller serial, which is a new one. Kdwyer, I also was
wondering if those servos were weak. But that was sent to me in the kit. What would
be the best to use. I also noticed that when I tune the legs, one leg would shake until
I stop it. The humming might be comming from the servos

11-27-2007, 09:08 PM
Any standard size servo can work, there are several more powerful (ie. expensive) models around. I suppose the best would be one of the new digital servos, but that is a real financial ouch. As for the servo jitter... I think it comes back to an undersized servo unable to hold position under load. Upgrading 18 servos for a crawler IS a big chunk of change, but I don't see any way around it.
I've heard the HS 5995 digital servos are very good, and very strong, also NOT cheap. But they are all re-usable in the next bot... and being digital means they will be advanced enough for an advanced design.

11-28-2007, 02:37 PM
We've used the 645's in many lower-end crawlers:


I know they're a little over 3x's the cost of the 322's, but they should do the job.

On a side note though, if you're having troubles with basic operation of your kit though (ie. walking) and you haven't modified it, you should talk to the company you purchased the kit from. I think the kit you purchased was a Parallax specific kit. They're a really good company to work with, and they might have some better options than spending an extra roughly $600 on servos.

11-28-2007, 07:38 PM
Having you tried contacting CrustCralwer? They are the manufacturer of the QuadCrawler.