Liftoff (FW) build diary

A couple of short clips - final stages of flipper testing

http://i8.photobucket.com/albums/a49...d/th_00008.jpg


http://i8.photobucket.com/albums/a49...d/th_00012.jpg

We were testing that at around midnight as we were quite tight on time, at one point we wanted to throw something in the air just to have an idea if the throw was strong enough. So I set the regulator at 6bar, took the machine out in the front garden and put a 2L water bottle on the flipper edge... and gave it a go... that threw the bottle one storey in the air and almost over to our neighbour's balcony! :o


Monday will try to find time to open up one side where the drive system stays, take a couple of pics and post a description of how we got it set up. It was a real pain to get it working, and we ended up with an emergency set up - it worked but I'm not happy with it, so it will be modified for sure - or totally eliminated and replaced by wheels...

Found some time this morn to open one side of the track drive and took some photos of the internals as promised - Any questions or suggestions for improvement are welcome :wink:

I took quite a lot of photos as they speak much more than words and makes it much simpler to explain.
A quick description of what we used and how it works:

General view of the bottom sides with all parts assembled

http://i8.photobucket.com/albums/a49...d/P1070419.jpg


First to go is the titanium armour plate, this plate also acts as and end plate for the forward roller pin..


http://i8.photobucket.com/albums/a49...d/P1070420.jpg


Next to go is the HDPE side - the hole at the forward side holds the shaft of the forward roller. The hole in the middle was the hole for the tensioner, but that was later discarded.


http://i8.photobucket.com/albums/a49...d/P1070422.jpg


This is a view of how it looks from inside - pretty much simple, the large wheel connected directly to the drive motor, turning the tracks around the forward roller, the track slides along the bottom face of the machine which ensures even and full contact between the floor and the tracks. This eliminates the need of complicated rollers and other stuff you normally see in a tank drive.


http://i8.photobucket.com/albums/a49...d/P1070423.jpg


It was not all plain sailing though, we started off by machining a pair of drive wheels out of Alu. The outer surface was knurled for better grip, but we found out it was not enough in testing phase. It slipped of the thread - most probably bec the knurling used was not coarse enough, so we coated them with a material similar to the threads themselves and that was one problem solved.


http://i8.photobucket.com/albums/a49...d/P1070425.jpg


View of the coated drive roller. It was a pain in itself to machine it in 2 parts to save from machining time and material costs. Its hollow from the other side so that part of the motor can fit inside the wheel, that saved about 10cm from the overall with of the machine


http://i8.photobucket.com/albums/a49...d/P1070428.jpg


This is the HDPE side plate which holds the forward roller in place and pretty much also holds everything in place :roll:
It took quite a beating, infact from the photo you can see that the threads ate away into the sides and sliced a groove. The problem here was that we did not allow for adjustment of the rollers, and without any precision method of drilling perfectly aligned holes for the rollers, the thread is bound to move to one side or the other :cry:


http://i8.photobucket.com/albums/a49...d/P1070424.jpg


The solution had to be a quick fix one as time was running out (we did that 2 days before the event!)
I milled about 1.5mm of the hdpe sides with a router and inserted those two pieces of stainless plates, hoping the threads will slide against them. It worked, but from the photo its visibly polished where the belt was rubbing.


http://i8.photobucket.com/albums/a49...d/P1070435.jpg

This is the thread, its quite durable, having been used for these last four events and survived is a remarkable feat!
We had it made at a local shop which sells conveyor belts, it is sort of got two layers, one canvas at the bottom which looks like bonded in some way, and then a rubber coating is moulded externally.
We always debate between us which is best to have for better grip - a thread with a grooved rugged surface (like we have) or a flat smooth surface? We never came to a conclusion as we tend to accept only physical evidence not theory! :lol:


http://i8.photobucket.com/albums/a49...d/P1070432.jpg

The forward roller...

http://i8.photobucket.com/albums/a49...d/P1070426.jpg


Another issue is the amount of tension to put on the thread. The more you tension the more current the motors will draw. On no load with nothing attached the motor was drawing about 5A. When we put the belt on and tensioned the thing first time, it was drawing about 20A :shock: - that is free wheeling back side up without touching the floor! After reducing the tension and fixing the sides for better slipping of the tracks the current dropped to about 11A.

http://i8.photobucket.com/albums/a49...d/P1070433.jpg


So thats it, if you had to ask me is it worth using tracks I'd say - not really, they're good for looks and for the sake of having a tank like machine but otherwise I think its a hassle, I don't really see an advantage.
Having said that I still do like the track drive, and before giving up on it I want to give it another try - this time I'll make the fwd roller tensionable, and adjustable so that I can adjust the tension and align the belt with the same mechanism...already got a plan for that, but its still in my brains...need to put it on paper and then on to metal! :wink:

Sorry for the long post - hope you find it interesting

That is brilliant! I have wanted to run tracks on a machine for ages and all I could come up with was using double sided timing belts which are horrendously expensive.
That has given me some great ideas for machines!
An idea that might help to tension the belts is this...
http://www.popsci.com/files/imagecache/ ... iagram.jpg
http://www.popsci.com/invention
The machine uses a moving front pulley to keep the tracks in tension so even when the suspension compresses it stays on. Its basically sprung and runs in a grove. That could easily be implemented on your machine with the space you have.

I would't say we spent a lot on the tracks, can't remember off hand.
Re spring tensioning its a really good idea - we had thought about it but couldn't figure out how to do it in at the time...it has to be something compact as even tho space looks abundant, its still tight.
I had thought of using a gas dampers as a tensioner like this... they are 150N each, think they'll work?

http://i8.photobucket.com/albums/a49...d/P1070440.jpg

Next step in this build is to go lighter and get it in-line (as much as possible to FRA rules)
This means that from 17kg Liftoff must shed at least 3.6kg (quite a lot!)
The single heaviest part of the machine is the flipper arm, then the motors, and then the pneumatics...
The motors weigh 1kg each - if I get to replace them by two Gimson GR02 I'd save more than 1 kg.
The flipper arm is a problem, at the moment its 1 square section 1.2mm thick, its quite heavy...don't really have much options, never seen titanium square section, so next option is aluminium.
Think I'll use alu square section 1 by 3.2mm thick 6082T6 but not sure if its strong enough as I need to put some welds to it as well :? And besides I have to calculate the weight lost bec if it's not too much it might not be worth while...
Any advice re aluminium flipper arm?

Right, its shopping time again! :D

Plans for the re-design in the final stages - mainly to do with weight reduction, believe me its not so simple eh!
I wouldn't like to order the wrong parts so my question : I'm downsizing the 5/2 valve from 1/2 to something smaller, will any size do? I'm looking at a 1/8 port size valve - like this
http://www.ebay.co.uk/itm/DC-12V-2-P...item53f148c741
Will it be suitable, I mean what else apart from taking longer to fill up the buffer tank should I expect?

As long it doesn't get liquid CO2 , it should work fine for a while.

And I'm sorry, for that amound of £ that seller asks, I can't even ship you one of the dozen Festo's I have here.

Yeah I know...its dirt cheap! :D in fact I just bought it yesterday
The 1/2 one I have was of a similar make and similar pricing and it worked fine...up till now.
It's not worth spending too much money on something you might end up changing just after a season!

I also got my self a replacement QEV. The one I have installed is a 1/2 but quite bulky and heavy (I think its brass or steel) Found this on ebay, its smaller and lighter and still 1/2 - might need to modify the outlet though as it looks like its 3/8
http://www.ebay.co.uk/itm/160930294213

I have got the latest version of liftoff drawings in the final stages before the mods start taking place - parts started arriving as well, got the GR02's from Ewan, really compact compared the the Makitas I had before!

The basic design remains very similar, and I'm using the same platform - what's changing apart from the motors and pneumatic parts is the orientation or the ram. It will now be in a horizontal position rather than vertical. I've added a self-righting mechanism as I have moved the flipper hinge forward and I'm afraid it lost this ability it had before. I'm still a bit sceptic if the mechanism will work - if anyone could look into it from these pics and see something wrong or any place for improvement, I'm all ears!


General views : Front side.

http://i8.photobucket.com/albums/a49...ps65b32c1f.jpg

Back side. Back cover I'm thinking about a polycarbonate panel, it would look really nice I think!

http://i8.photobucket.com/albums/a49...ps8fa5a42b.jpg

Top panels off - self righter linkage will be a nightmare I think :cry:

http://i8.photobucket.com/albums/a49...ps2a295733.jpg

Flipper and self-righting mechanism in action...

http://i8.photobucket.com/albums/a49...ps905e07b3.jpg

Internal components layout

http://i8.photobucket.com/albums/a49...psf101c5ee.jpg

I'm not an expert but I reckon that will work.

A few things I would change if it was me...

-Use a solid triangle for the ram to push against rather than the L shaped piece
-Give yourself 4WD by running a belt to the front, otherwise the weight out front will act like a massive pendulum making it difficult to steer
-Don't use the Sabertooth 50A [Unless you already have it] and go for TZ85A from Botbitz... Sabertooth's have a bad history in combat (But some people have never had an issue) Its hit and miss...

Besides that it looks superb! Its got this kind of cool angular look to it and has the guts to match!