Liftoff (FW) build diary

[Mouldy]

like it! the front wheel being used as a tracker/tensioner? If you have problems with it popping off... you could have it running in a U section at the top?

[Liftoff]

Yep, the front wheel is the tensioner, it does its job in keeping tension but not much in keeping the track on...

been doing some reading on flat belts etc and the strange thing about them is that they are supposed to be tolerant to a misalignment, cant understand how as in my case its completely opposite.

This afternoon had a go in driving it with just one track but just after a cople of seconds the track was off.
Very frustrating after all that work... will have to do some more research and a major redesign. ...if not scrapping the tracked design all together

[Mouldy]

look into true track belting... we use it at work, basically turn a grove into your drive roller and idle wheel.... then bond a bead into the centre of the belt... so it cant come out side to side... would probably be enough for your application.

[Liftoff]

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.

[Max]

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.

[Ellis]

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.

[Liftoff]

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.

[Liftoff]

Sadly I have to admit defeat!
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.

[Liftoff]

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!!

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 !

A couple of pics of the new simpler system.

track drive1.jpg

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.

track drive2.jpg

[Dan-27]

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.