I have never seen a track segment that small before so you are going to have to be even more sure that everything is perfect.
OK, I just laid out some track and ran a small sprocket across it in my fingers. And yes, the sprocket does rise off the track about 1/16" at every joint. Then rides with the large surface of the sprocket flush again until the next joint.
This is due to the small diameter of the sprocket. If the concave sections between the teeth, destined for the track joints, was deeper the teeth would grab the track after the joint. I tried filing the groove deeper but it makes the teeth stick.
The small sprocket is obviously just the absolute smallest that this type of tooth arrangement will work with. The larger sprockets do not rise up when they pass over the joints.
I have 8 small sprockets sitting here but I’ve never actually used then for a project so I didn’t notice this until I tried right now. The problem you are having is that your hub to hub distance is so small, there is no room for the track to absorb the change.
In my opinion, you options are this: switch over to large sprockets, extend the distance between your hubs, or add a spring tensioner of some kind to the top of track at the idler.
I think you best bet is to extend the length as much as possible. Even if it means raising your idler so your track is more triangle shaped and spring load the idler.
The sprockets both large and small do the bump thing. It’s required to keep the tension on the track even as it goes around the sprockets. This is not a flaw but just how it works. You must use idlers to support the weight of the robot. Idlers will provide a smooth ride.
Just dug out and checked my tracks and sprockets (must get caught up so I can play with these wonderful toys!), and I guess I was remembering incorrectly. As others have stated, they do indeed hop as they roll over the sprockets. Also as others have stated though, when used with idlers, this action should be minimized.
Looking at your photos, you don’t have a whole lot of space in between your sprockets, but you might still be able to work out some sort of idler, or even a pressure plate sort of system, to keep as much of the track in flat contact with the ground as possible. Pressure plates often need grooves or rails to keep a track from drifting sideways, but between the short run between the sprockets, the deep teeth on them, and the relative rigidity of the track units, I doubt that this would be much of a problem for your design.
If the sprocket is what supports the bot on the track, then I don’t see how an idler will remove the bumping. Perhaps riding the bot on smooth bogies would help instead of riding on the sprockets, but the small size would be an issue for this.
At the risk of sounding ike a jerk, and I hope I don’t, but I do not see the point of a track assembly that is so short. I would just use a wheel for such a small diameter…
Well, IF you can reliably keep the entire length in flat contact with the running surface (a pretty big “if”), I can see how the increased contact patch would give you plenty of traction, as opposed to a couple of spots provided by wheels. Of course, as soon as the tread unit begins to deviate from flat contact, your contact patch shrinks very quickly, so the rest of the design has to work to ensure that you maintain that flat attitude. It seems that the molded-in “nubs” would help a bit, in that they add some compliance and provide some grab, but yeah, a good tacky set of rear-mounted wheels with a bit of compliance to flatten them out a little bit (and provide a larger contact patch) would probably give more traction over a wider range of angles, and require less space and mass dedicated to the drive systems. But…
This is about the tread-hop thing, so yeah. I’d say maybe a flat pressure plate - sprung, if you can get the mechanism wedged in between the drive plates - would be my bet for maintaining as much contact with the drive surface as possible, and minimizing “sprocket hop”. I’d guess that your ideal plate placement would be even with, or just the tiniest hair below, the level of the sprockets during their “hop” phase, so that you have consistent pressure and ride, with the least amount of bowing of the tread path.
Some time back I did some research on tracks, and they are used for a lot of very different reasons. I’d assume maximum surface traction in this instance, although a center bogie keeping some weight on the center of the track would be needed to improve performance over wheels (wheels would probably require a “skid steer” setup). As to fixing the bumping, I’d try placing something thin like a piece of flat toothpick, cardboard, etc., on the sprocket hub between the splines where the sprockets drop into the track. This would have the effect of keeping the sprocket riding somewhat high on the track all the time, but should help minimize the sprocket bumping. For a quick check, thin rubberbands could be wrapped across the hub low spots between the splines to check the effect of the increased outward spacing.
Personally I think there needs to be a minimum of 5 full links between sprockets so as one link begins to pull up on the rear sprocket, it’s movement will not influence the other links between the sprockets.
I agree. I think the big reason you are having problem is the links are too big for your setup so when the sprockets are moving they jump becuase that extra 1/2 inch of track has no where to go but up.
Your situation is quite different than mine, but you can see how much I have learned by being involved in this thread. I now know I need to find a way to have idlers support my track and sprockets to mainly just drive the track forward rather than having them do this and support my bot’s chassis at the same time. Looks like a new modified body is in order
For a little added traction, I’d look at adding small bogie/idler for the bottom of the track. A small foam airplane wheel there between the sprockets positioned where it could supply some downward bot weight force on the track between the sprockets would increase the track friction area with the surface being operated on. Might be as simple as putting the foam wheels on a coat hanger wire and glueing it to the bottom of the bot. I’d also look at coating the outside of each track section with some rubber cement (the type that when dry and rubbed, it rolls up and comes off). It should add a lot of traction for flat smooth surfaces.
Or use some scotch tape, Elmer’s glue, and Popsicle sticks to construct the idler tension system and you can cut out strips of metal from a used ravioli can for springs for the idler.
its too late for a change, to make things run a little smoother i added 2 more links to the tracks and a pressure plate.I will make a hinged wedge that dops down when the game starts. to keep within the 20 cm limit. I chose tracks for the added surface contact and these things have amazing traction i find. and mostly because tracks are bad ass.
