Blastoff (FW) Build Diary

[Liftoff]

Time to start a new build, one which I'm determined to finish and come over with next year (or there about!). Now that I've settled a bit I started fresh plans for a new build. ( "settled" being a wild assumption as with a four month daughter around I'm left with next to no time of my own!)

Those who followed my Liftoff build will instantly notice the resemblance in shape of the new Blastoff build (CAD drawings will follow soon ) - it's a shape I very much like, a bit like a tank, a bit stealthy.

Biggest change in the shape will be its size, where as the first version of Liftoff had a base of 500x500mm and weighed about 17kg,
Blastoff will measure 300 by 480 base by 130mm tall - still on the larger side compared with other feather weights, but much smaller than it's predecessor.

It will still be track driven, powered by a pair of NTM3548 housed inside the drive wheels and coupled to a custom gearbox.

Weapon will be a FP pneumatically armed, spring powered flipper. Springs rated at 1000kg each, more on how it will work later - will give a detailed description of the concept. (no idea if it has ever been attempted before)
All pneumatics will be custom built including valvetry and rams, so a lot of testing will be required but the concept should work, then of course any advice and suggestions from the experts will be very much appreciated !

Chassis will be totally bolt on 10mm aluminium, will be trying to source 7075T6 alloy for maximum strength and lowest weight.

Armour will be all titanium, again for weight reduction, 4mm sloped at the front, and 6mm vertical on the sides.

Unlike the previous build, where I could build most of it using hand tools etc, this one will require a great deal of machining so a lathe/mill is a must. The first thing I need to do is to set up a properly equipped workshop - that's works in progress

Most probably will start building it mid May on wards, will be having plenty of free time then, given I have three months off work (working in aviation has it's benefits!)

[Liftoff]

Let's start posting some CAD pictures:

Overall appearance
blastoff1.jpg
Chassis: I'm aiming for 10mm bolted aluminium alloy, preferibly 7075 series. Will have to be strong enough to contain a pair of springs each capable of 1000kg.
blastoff2.jpg
Drive train and cross section view. The motor is housed in a hub inside the drive wheel, with a reduction gearbox outside. A fair amount of machining will be involved but I think it's doable.
For tracks I'm going to use a poly V belt 45mm wide. The drive pulley will be machined to match the groves in the belt - I have high hopes this will be a final solution to solve the track alignment problems on previous builds
blastoff3.jpg blastoff4.jpg
Weapon system:
Main supply is Co2 from a paintball bottle (9oz for now - might get larger). From the bottle through a custom FP valve which will mount directly onto the bottle pin valve.
It consists of an on/off valve and a 2 position 2 way valve, solenoid operated normally closed. When energized air will pass through the valve to a QEV mounted on the ram inlet and retracts the ram, which in turn compress the spring.
When the valve is de energized air is exhausted through the QEV and the spring forces the flipper arm up.
blastoff5.jpg blastoff6.jpg

[Runsler]

Sounds like a really interesting design.
Only So far i found 3 possible weak points, but i guess you know them and either it's worth to have them (most likely) or you didn't find a way to build around them. Well, at least i have questions about why you build it that way^^

1. Motor inside the wheel:
Sure saves a lot of space (and some weight) but from what i have seen the wheels are amongst the most often damaged parts.
Putting something as valuable (well, depends on the motor, but i count all the machining need in here) to a place that likely to get hit sounds like a risky option. Might be worth it, if you can machine it yourself, and the motors aren't too expensive/if you are willing and able to have enough spares around.

2. Springs tend to loose a bit when keeping them under pressure.
Heavily depends on the kind of spring you use, and i doubt the effect would be noticeable in our short "active" periods. Just maybe something to keep in mind.

3. Springs for the actual flip, and pneumatics to compress them again. Interesting Idea to design it that way round, but you'll need a lot of air to get those compressed (but you can do it a bit slower than the air is used normally, so less valve freezing).
Possible problem i see here: if anything in your pneumatics get damaged, you'll stay there with the flipper wide open, possibly showing all your inside vulnerable. Others might still work as wedge without their pneumatics, you won't.

[firefly]

Looks great! But also won't the flipper be stuck in the open position once all the gas is expended or will there be some kind of locking mechanism to keep it wedge shaped.

[Liftoff]

Looks great! But also won't the flipper be stuck in the open position once all the gas is expended or will there be some kind of locking mechanism to keep it wedge shaped.

The short answer is yes....gas finished the flipper will remain open, and for that reason I will have to estimate the number of times I can fire it and not exceed

[Liftoff]

1. Motor inside the wheel:
Sure saves a lot of space (and some weight) but from what i have seen the wheels are amongst the most often damaged parts.
Putting something as valuable (well, depends on the motor, but i count all the machining need in here) to a place that likely to get hit sounds like a risky option. Might be worth it, if you can machine it yourself, and the motors aren't too expensive/if you are willing and able to have enough spares around.

Maybe it was not clear from the drawings - the wheels are totally encased by 10mm aluminium and 6mm titanium on the sides and 10mm HDPE on the top, so I'm thinking they will be pretty safe there - the only exposed part will be point of contact with the floor which is inevitable, I opted for motor inside wheel actually to protect the motor; being an outrunner I'd rather have it tucked away from anything loose which could end up a tangled mess.

2. Springs tend to loose a bit when keeping them under pressure.
Heavily depends on the kind of spring you use, and i doubt the effect would be noticeable in our short "active" periods. Just maybe something to keep in mind.

Yes I agree with you on this, I'm using die springs rated at 1000kg when compressed 25% of their length. At this 25% compression the travel is 38mm and I can get approx service life of 150000 cycles without the spring setting. All this info of course is from the spring manufacturer not myself!

3. Springs for the actual flip, and pneumatics to compress them again. Interesting Idea to design it that way round, but you'll need a lot of air to get those compressed (but you can do it a bit slower than the air is used normally, so less valve freezing).
Possible problem i see here: if anything in your pneumatics get damaged, you'll stay there with the flipper wide open, possibly showing all your inside vulnerable. Others might still work as wedge without their pneumatics, you won't.

As one spring is rated at 1000kg I figured a 51mm bore ram at 55bar will be capable of compressing the spring. The valve I plan to build is not a high flow valve and gas will flow through 1mm orifices. The QEV through which the gas flows to compress the ram has also a 1mm orifice. This should help prevent the pneumatics getting frozen, but only prototyping and testing can really determine the outcome.

As you correctly pointed out, my biggest concern is the flipper remaining open if the pneumatics malfunction. In actual fact the system is very simple, in that it comprises of a solenoid valve and a couple of QEV's, so if it's well designed and tested very little can go wrong.

[Runsler]

I see, sleepy me didn't find anything you didn't think of before^^

Suggestion for the problem with staying open after a number of flips:
maybe it's possible to get the amount of gas needed to compress the springs again estimated (or tested). thus you can try to build a digital manometer in, and only allow flipping when you got more than a certain amount of pressure (and gas) left, maybe except you press an "override" button for desperate needs? I don't know much about pneumatics (the little i know comes from softair guns a few years ago, so...), but if there is a good way to do this, it could be an option.
Gas needed will vary by temperature, so measuring pressure could be more reliable than just counting flips.
From one of my softair the range for how long a tank of gas works is from "barely the 20 rounds in the magazin" when firing fast up to "no problem shooting three magazins in a row if every shot is taken with care"

[Liftoff]

I get your idea Jan, I could calculate the minimum pressure required to compress the springs and then install and adjust a pressure switch to that pressure. The pressure switch will keep the solenoid valve on when pressure falls to the minimum value so the flipper remains closed even if I try to fire it.
Will need an override then to dump residual pressure from the rams in order to disarm it safely.
If any of the event organizers or tech checkers read through this build I would need some help from their side to make sure I'm within the rules.

[mattsdragons]

Just running a quick google calculation, you should come up with roughly double the power than if you were using the pneumatic system in the conventional way. Really like the idea of this build, I'll be keen to see how it works in a real world scenario

[Liftoff]

I'll be happier with less Matt

A couple of schematics for the pneumatics:
valve 2.jpg
The first shows the system deployed. This is also the initial condition of the robot before it's powered up. So the flipper will be in the open position, gas is off, power is off.

valve 1.jpg
Next is to turn on the on/off valve which opens the pin-valve on the main tank - gas is supplied to the solenoid valve now, still nothing happens as the robot has no elec power yet. Switch the elec power on (link) and select flipper switch to on - solenoid is energized and valve opens - gas flows through QEV into the ram and piston retracts, compressing the main spring
Select flipper switch off - solenoid is de-energized, gas exhausted from the 3/2 valve, QEV opens and gas exhausts from the ram - Main spring extends flipper goes up. In this position it is also the position to deactivate the robot.
As the rams are empty and the flipper arm is open there is no danger of getting hit, remove the link and the robot is dead.