hey guys, I just got a set of 2" tracks and the small 2" sprockets and have a bit of a problem. it seems to me that the sprockets roll along with a up down hop and i cant figure out how to eliminate this. Im thinking maybe the test chassis i built has the sprockets too close together and thus not tensioning the track enough but im not too sure. it seems no matter what i wuld do they will hop. this creates a bg problem for me because i am building a sumo robot and my tracks are very small (3-4 links contact area depending or the tracks orientation as it rolls). with the hop i mentioned I lose my even weight distribution on the pads.
does anyone know what the ideal distance from hub center to hub center is? granted everyone uses a different amount of links (i assume even number or links) but there must be a way of determining the hub to hub length given a certain number or links.
does anyone have any advice on building thier own chassis for a tracked robot?
I don’t have my treads and sprockets handy to check with at the moment, but…
Are you sure that your sprockets are meshing properly with the treads? As I recall, there are two ways that they can mesh - one correct, with the large gaps between the teeth spanning over the joints between the tread link units, and one incorrect, with the small gap trying - and failing - to span the same joint. With the tread laying flat on the desktop, I seem to remember a very smooth action with hardly any little “hop” or variation as the sprockets traversed the links.
Try adjusting your mesh, and see if that helps. I’ll have a look at my tread and sprockets when I get home.
I’m pretty sure ive got it right, the large gap does come nto contact with the joint between 2 links. but the large gap and the 2 teeth that form it are raised about 2mm of the rest of the sprocket. so as it rolls over the link joint the whole hub center jumps up a little.
Are you running double sprockets? If so check all the pairs and be sure the teeth line up perfectly on both sprockets. Out of the 4 ways they can go together on the 4 bolt pattern, only 1 way lines all the teeth up on each sprocket.
There is no specific length better than another.
Are you running a motor on both the front and back sprockets? (4 motors in total?) If so that could be causing your problem. If both the front and back motors aren’t operating identical, which is unlikely, they will be fighting eachother and could cause a loose track to skip.
There is a small amount of play in side to side and front to back meshing, which makes these tracks great. You must have a sprocket not aligned with it’s partner or not meshing straight.
ive got then sprockets assembled fine, but hasnt anyone noticed when you roll a single sprocket along the mesh it goes bump bump?? when the teeth roll over the link junction the whole sprocket rises up about 2 or 3mm.
I am running 2 motors so thats fine, but i havent even gotten to that part because im not satisfied with how the tracks are rolling.
I deffinately noticed when I first got my tracks that they are not a smooth ride on tile/hardwood or any hard surface for that matter. The best results I have had are when driving on very “forgiving” or soft terraine such as carpet and grass becuase it acts as a spring when driving over it, absorbing a lot of the bumps. I even have idlers in between the 5" gap between both sprockets (2 idlers!). With this bumpy ride my little pinhole camera’s image and signal are messed up.
I’m not complaining about this becuase A) Something could be wrong with my setup (so I am designing and building a new one proffessionally by using CAD and a CAM CNC mill and milling the parts out so that everything is precise. And B) I know nothing can be perfect, and what I have is alright for now, until I come up with a solution.
My sprocket teeth are lined up perfectly and I have even enlarged (widened) my sprockets so that one sprocket is on one side of the track and the other sprocket is on the other side so that I have a larger “footprint” on the tracks giving my robot a smoother ride…
Basically I don’t think Ive done anything wrong and the tracks are running fine, but I am still reinventing my design and adding shocks or something to counter the bumpyness.
So your not alone, you just need some crazy shock absorbers!
P.S. In these pictures, only one sprocket is in place. Just image the second one coming out into the front of the sprocket
Jim has told me that using sprockets to support my bot off the ground is what is causing the “Whump, Whump, Whump” when driving…But how on earth don’t you use the sprockets to keep your bot off the ground? Ive looked at the totorials and can’t understand…
thats exactly it, usually i think the bot it supported by the nylon standoffs which have low friction roller sleeves over them so the endpoint sprockets are slightly higher and then the robot wouldnt go bump bump. But in my case my robot tracks are extemly small and i do not have room for a series of standoffs to prevent this. In fact, i only have room for one, so if i lower it signifigantly i just end up with a convex looking track… no good for sumo traction.
I have a few pics, but dont know how to post them… anyone??
I think what Jim might have meant is that you have nothing to support the tracks in between your sprockets. All the weight is riding on the sprockets themselves (Im assuming your setup is still similar to the pics you posted in that thread). You need rollers in between to distribute the weight.
My advice to you is to study exactly how Jim setup the tri-tracks in the guide here:
The tracks are made of hinged flat sections, and as such, probably cause bumping when wrapped around a round hub on which the bot rolls. For a given size track, the smaller the bot and the sprocket, the more pronounced the bumping will be. Close observation should reveal the source of the bumping.
yes it is very similar, but much smaller. i guess these aren’t supposed to be used in setups this small. I could upload some pictures if i knew how.
but to give you an idea, the distance from the center of my drive hub to the center of my iddler hub is only 3.2" so i only have room for one roller which doesent doo much good because the bumping lifts the roller off the track half the time…
this is what my setup looks like, so as you can see, theres no room to elimiinate the bump. im out of ideas, the only thing i can think of is maybee making my single central roller active with a spring keeping pressure on it somehow. If i move on without resolving this i feel like im giving up a lot of potential traction since half the time there wont be any uniform pressure on the tracks.
NOTE: this is a prototype and i just used to passive iiddlers for simplicity. http://i218.photobucket.com/albums/cc186/ruedorb/DSCF0240.jpg
Looks like the splines on the sprocket are not fitting properly into the spline slots in the track at certain points. I’d lay a track out flat and roll a detached sprocket along the track to see if it fits the slots properly without bumping. If two sprockets are combined to make a hub, the there maybe a potential for some misalignment. There could be some design issues with the small sprockets fitting well into the track.
they bump when a single sprocket is rolled alone and equally when assembled along a the track layed flat. it seems llike the sprockets design is flawed, but i guess there is a reason for all this. im almost 100% sure they are fitting fine.
