Liftoff (FW) build diary

[Liftoff]

A small update, been busy building the track drive these last days and finally most parts for it are ready, what remains to do is the tensioners holder and the tracks themselves. But before I order the tracks I want to get some different material samples to evaluate for best grip.

It was quite a headache to design and build, but it looks like this system will perform better than the old one...hope I can test it soon!
Here are some pictures of the progress so far.... questions and comments are welcome!

[Liftoff]

Been quite some time since last update and not much was happening either...was too busy at work...but now that I'm on holidays will try to give it a good push.So yesterday and today I spent the day on it trying to get the track drive in order.

And immediately bumped into the first problem! Put all the bits together, motors wheels track, and tensioners and tried to adjust the allignment, but the bearing on the motor gearbox is too flimsy! The motor shaft to which the drive wheel is mounted wobbles too much and as soon as I increased tension on the track, it jumped off the wheel and the gearbox jammed

I had the impression that the GR02 gearbox with the addional external bearing support would be up to the job, but it seems the wheel overhang is too much, even for this modification!

So had to go to the drawing board again to figure out a solution....and spent the morning filing and hacking at a new fitting to support the wheel at the far end... hopefully it will work, will see tomorrow!

[Liftoff]

Update: One of the track drives is almost finished and assembled, it looks promising as rotating the track by hand it feels free so I'm hoping allignment is fine...but only when I hook it to a battery will I know the real result!
It's late now so that's for tomorrow morning.... fingers crossed!

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[webby]

That looks great! Interested to see how it performs and how it grips/ slides, more inventive than wheels lol

[Liftoff]

more inventive than wheels lol

true, but its also a bigger headache than wheels!

So as planned this morning I rigged the motor to a 6v battery and gave it a go...and immediately it threw the track off the wheel! an hour later I managed to adjust the bloody thing to finally hold the track in place.

I'm not 100% convinced, I'm afraid that when both tracks are in place and try to steer the thing, it will throw the tracks off... the Hdpe base does not help much as it flexes a lot, installing the outer bulkhead should help stiffen the whole thing up, I hope!!

So this is how it looks while turning freely:

[Ellis]

Always liked this design, hopefully you can get it inside 13.6kg. Also, the video is set to private, can't see it!

[Liftoff]

Also, the video is set to private, can't see it!

should be fixed now, sorry about that!
I must get it in the 13.6kg limit Ellis, thats the aim at least! If all goes well you might be able to see it in person next year

[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.