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Thanks Mouldy, did some reading on the subject trying to understand what I'm doing wrong and it seems like I missed a very important point in designing my wheels :?
The wheels should have had a "crown" for the track to stay centered, infact from a couple of vid clips I seen on youtube, the pulleys dont even have a raised edge to hold the belt, yet it stays on!
It will be a challenge to put a crown on the wheels, but I have to try.
http://www.youtube.com/watch?v=6sM0Qjumyro
From that video it looks like you could get away with only having a crown on one of the wheels, not both. You could try just putting one on the front wheel which looks easier than the back wheels. If that still doesn't work then you would have to our a crown in both wheels.
Fascinating concept, the crowned wheel, and it certainly seems to work reliably. But in a fighting robot the stresses a belt comes under are from all angles and far greater than simply starting a little off alignment. Imagine being pushed sideways by another machine, without some sort of guide, the belts will come off almost undoubtedly.
Point is I don't think it's as simple as just having a crowned pulley for this application. Crowned pulley with guides sounds good. Or the slotted pulley style as Mouldy mentioned sounds as likely to work.
Now that l've come this far I have to try all options before I give up on the tracked concept. The wheels are already flanged, will add the crown and see how it fares, if still not happy then I'll add the slot in the middle of the wheels.... if it still does not work then I'll put the tracks in the bin and put a couple of wheels, end of story! But I do really hope one of these solutions will cure this problem.
Sadly I have to admit defeat! :cry:
This morning I had a go with putting a crown on the wheels, it performed a bit better but still its not reliable enough to be used in combat. Bad design is the problem, the wheels and bearing support are attached to the base plate which is 5mm HDPE, the tension on the track is pulling every thing out of alignment. Even with the sides installed it still looks not right.
I sort of lost interest in this design now...
Think I'll start afresh...new tracked design but it must be a simple one.
Alright, so back from the drawing board with another design, hopefully should be functional now! The basic shape is still there, but materials will change from HDPE to aluminium... just hope I'll still be able to keep within the weight limits!! :o
Tracks will be mounted onto an aluminium cased, bolt on module complete with drive motors. The baseplate I'll change from 5mm HDPE to 3mm aluminium, trying to source some strong alloy though, was thinking 6061 or 2024... anyone knows where I can get hold of a 500x500x3mm piece? Preferably from within the EU, all I found on ebay were from the states - shipping costs are astronomical ! :evil:
A couple of pics of the new simpler system.
Attachment 3921
Tensioner is not included in the pic, but I'll use a roller on the top side of the belt for tensioning.
Will be adjustable by an eccentric shaft.
Attachment 3922
Might be worth sending this guy a message and see if he'll post out to you.
http://www.ebay.co.uk/itm/aluminium-...5f5031ccb#shId
Also I came across this article last year, it's not exactly what your doing but it might be some help. I was wondering if you could do something similar by running 2 bike gears on either end of the roller, 2 chains between the rollers and secure the belt onto the chains somehow. It would be loads heavier but wouldn't move sideways.
http://woodgears.ca/tracked_vehicle/
www.woodgears.ca is a great website to trawl through, his gear generator is particularly useful.
I'll check him out, don't know what type of alloy he has though, its listed as grade EN485, but that's not a grade I ever heard of...
Chains and sprocket is a good idea, as you mentioned weight will be an issue, but its an other option.
Bumped into this website by chance, dont know if anyone ever bought something from them, it looks interesting, they even have a complete track drive system, and its not expensive at all...my only concern is its plastic!
http://www.vexrobotics.com/vex/produ.../276-2168.html
Small update:
Got the armour cut and it's now back from the shop.
The large plate is the flipper arm, the other plates are the front and side armour. I opted for the front and side armour to be cut in small parts mainly for two reasons...
firstly, the material came for free :) but in the form of small pieces from which I could cut just one item....
second reason is that if a part is damaged I could easily replace it.
Also received some various thickness of hdpe to which the armour will be bolted.
I think 4mm titanium and 20mm hdpe should protect well against spinners...at least I hope so!
Have ordered some aluminium plate and box section for the chassis...still waiting for their delivery...and then back again to the waterjet shop to cut everything to size.
I've had to scrap the previous machine and build a completely new one from scratch as the old chassis was simply too flexible to work with. The shape will still remain the same though, only the name will change. Might start a new thread later on when I start to work on it...
Attachment 3964
Are you going to be bringing the weight down so that you can come and play with us at the Champs :-) That would be awesome!
The main thing that stands out for me is using lots of small pieces to construct your armour. There will be more things that could potentially break and if something does go mid fight then you are going to be very vulnerable as more can be ripped off from the resultant hole left in the armour. (This is assuming they are not welded into one single piece.)
Have you successfully resolved your track issues as well?