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Rover 1 w/ scoop

#1

Hey everybody

Over the past weekend i have been adding to my Rover 1

it now has a scoop with goes up and down (obviously)

the scoop itself is made of some sheet metal soldered together i made back in 6th grade (it was actually a pencil holder), the lifting mechanism consists of a home machined pan and tilt, the tilt servo lifts the bucket a little bit and the pan servo pulls the buckt so its like a basket

the servos it attacheted to the bucket via a brake rod from my surplus of R/C goodies and a spring from a VCR, the two are connected to create a universal joint and let a little flex happen in the spring

heres the video:
media.putfile.com/Rover-video

tomorrow im going to home depot to get some sheet metal for a new scoop

-Jared

P.S. does anyone know if you can synchronize 2 servos? splice them together to have them work on a single pin? :confused:

#2

Yes you can run two servos from the same signal. The thing to watch out for is to insure that there is some mechanical compliance in the linkages so they’re not fighting each other.

Yay for scoops, salvaged parts, and robots that move!

#3

i totally agree

now for the 2 servos running on the same pin and signal, would you have to slice the servos wires?

#4

I’m pretty sure there are “Y” cables that will allow this without splicing.

Absent the “Y” cable splicing is the thing to do.

#5

You could, indeed splice the wires together, but that would be messier.

There indeed is a “Y” cable on the site.

Be careful, though, once you stick them together, they won’t be able to go in opposite directions or at different speeds, even though they’ll want to a bit.

If you stick a servo saver on one or both of them, that should take care of it.

#6

Servo “Y” Adapter Cable

:wink:

#7

ok, ill look into that

now, considering the fact im a little bit behind on robot gadgets, could someone tell me wat a servo saver is? :blush:

#8

A servo saver is a servo horn that has a spring inside to allow the servo horn to move without moving the servo shaft. Like a cars suspension, it would allow the servo horn to absorb a hit from an out side force to some degree.

#9

o0o0o, ok, thanks mike

but would that rob the servo of any power that could b used to lift the scoop?

#10

That’s a good question, I have not used these types of servo horns so I really couldn’t tell you about how they perform. Servocity.com sells these Perhaps they have some info on the performance?

#11

well, i looked at servocity and they stok them but all that servocity says is

so im not really sure

#12

Yeah, I don’t know either. If your scoop has a load of dirt, it may compress the spring to the point of no added protection. I’m not sure how strong the spring is.

#13

I think the idea is to act like a clutch so if, on a rc plane, you crash and a rudder gets twisted when it hits the ground, the servosaver slips instead of destroying the geartrain.
To put it into context, if you drop something too heavy onto your scoop (like, say, a foot) and:
1)the servo doesnt have enought torque to hold it up +
2)the object is so heavy it forces the scoop down very quickly
the gear train might not be able to withstand such a sudden movement at such high speed. the servosaver slips, the scoop lowers and the gear train doesnt move at all.
At least I’m pretty sure that’s what happens :confused:, I’ve only seen one brand firsthand, others may be different.
I don’t know if they come with different “ratings”, where the clutch has different properties – if you’re using heavy duty servos the clutch might slip before the servo reaches its max holding power.
Anyway, if you’re thinking of putting two servo shafts in parallel having one of these on one shaft might be a good idea, so if one servo comes out of alignment they won’t end up fighting each other.

#14

Most servo savers are stiff enough to allow normal servo operation over most normal loads. Does your particular use qualify as “normal”? Hard to say, without just slapping a saver on the servo spline and trying it. I doubt you’ll find actual ratings on how much torque it takes before the spring begins to compress, though. As mentioned above, servo savers are typically used in applications such as the steering mechanisms of R/C cars (where I used to use them when I used to race the trucks), and “stiff enough to allow you to steer, while being light enough to keep from stripping out the servo’s teeth” is about as precise a “rating” as I’ve ever seen for them. If you’re really concerned about stripping your servos, I can only recommend trying one and seeing if it will work for you. If the spring is heavier than necessary, consider it a servo horn with an added margin of safety. If lighter than you need, you can use it in another project, or consider yourself out just a couple of bucks, and raid the spaces between the sofa cushions to recoup your investment.

I’d be surprised if your bot’s scoop would encounter enough force to really warrant a servo saver on the servo that drives it, but it certainly can’t hurt if you want that extra margin of protection.

#15

I should also add that because of the extra room occupied by the spring mechanism at the hub of the servo saver, you’ll have fewer choices of where to connect to the output. If your current attachment point is out at the end of the servo horn, you may need to use a large servo saver or an extension to get to the same distance out, or if you’re connected close to the center, you may need to use a small saver, adjust your servo throws, and/or get creative with mounting the connection point.

My current thinking on the use of servo savers in my projects is that I’ll build without them, then if I strip out a servo’s teeth, I’ll get a replacement gear set, rebuild it, and install a servo saver after the fact - it’s a simple enough operation to perform, and replacement gearsets are cheap and plentiful. If I were planning a project where I expected a servo to experience sudden jolts, and could accept a little bit of play in the joint when it happened, I’d probably design one in.

#16

thanks for all the input guys

ok, today i went and got some hardware from Home Depot; a nice big sheet of sheet metal for the new scoop, some threaded rod for connecting the ball link from the servos to the bucket, some rod for a new connector for the scoop to the lexan and some screws and bolts for connecting it all together

img338.imageshack.us/img338/1332/newscoopdesign9up.th.png

that is what i am thinking to do for the new scoop, with 2 servos on either side of the rover, i am trying to figure out a way to b able to dump the scoop, so far, however, im stumped, i was thing of having some sort of sliding slot for the bolts on the scoop, then having a micro servo push it up and down

:confused: not very clear, ill see if i can get get a picture up of my digrams up so that its more clear

if any of you guys have any ideas, feel free to speak up :laughing:

-Jared

#17

ok, heres my diagram of how i would get the scoop to dump

img367.imageshack.us/img367/493/pics0017ww.th.jpg This is the image of how the mechanics would work

also, i would some how make the rods spring loaded so the whole system would work and not push and stuff, i hope you know what i mean, i cant really put it into words

img367.imageshack.us/img367/905/pics0036ys.th.jpg
This is what it would look like from the outside

the slide slot would carry the whole scoop so i would have to strengthen the lexan of the slot somehow

Id be much obliged if you guys looked it over and see if there is any faults
-Jared

#18

[img=http://img112.imageshack.us/img112/9803/pics0046im.th.jpg]Side View
[img=http://img112.imageshack.us/img112/8898/pics0055vj.th.jpg]Front View
[img=http://img47.imageshack.us/img47/3329/pics0068bx.th.jpg]Front Iso View

ok, here it is, my bot with the new scoop and the new lifting system, note i haven’t yet put in the slide slot for it to be able to dump

it has come to my attention, as i was about to test the lifting mechanism, that spliced servos move in opposite directions :imp:

does anyone know how i can fix this very large problem? cause, its bad if i dont, my whole project will go down the drain :cry:

o yea, and if you look at my previous post could u look at my slide slot mechanism? id be much pleased if you could tell me if anything is wrog with it

o yea, the servos and brackets are temporary, im planning on upgrading both with some HS-645MG Standard sercos and some E-Z servo brackets to hold those things down, o yea, finally a pan and tilt w/ a camera in the future

-Jared

#19

Nope… spliced servos run in precisely the same direction. Look at them from the top down and see if they both turn CW or CCW. You’ve got them oriented such that if they both turn CW at the same time, they are fighting each other. If you can’t solve it mechanically by turning one around, the easiest thing would be to use another servo channel.

#20

andy ur right but i have them fighting each other, but i want one to go CCW and the other to go CW, is there anyway to switch the wires around to switch the direction of the servo? so i wont need to hold 2 buttons down at the same time and possibly mess up the lift system