Big Dave 3 Design & Build

[cmalton]

So, we've ignored advice from this fine community for at least a second time by trying out a HiFei speed controller rather than dropping £500 on an MGM.

So far, so good - I appreciate we haven't put much load on it yet (~15A) compared to what will be a considerably higher current when we have the weapons motor hooked up to the drum. You can view my testing at my flat in Southampton on our blog: https://www.arc-robotics.org.uk/2016...weapons-motor/

Next workshop weekend for us is 7th/8th January, so we'll see how far we can get. There's been a slight hiccup in the drum department - but I think Rob (emisnug) is on that to get it sorted asap. All being well, we'll be spinning everything up soon....

[cmalton]

Thanks to all you wonderful people on here with advice over the last few weeks, Rob's just been frantically redesigning the front end of Big Dave 3.

Here's what he had to say on the matter: https://www.arc-robotics.org.uk/2017...bout-bearings/

[typhoon_driver]

How are you preloading the taper roller bearings in the design?

[katch]

SKF are just over 300 meters from my workshop, if you want any advice on applications i can have a word for you.

They are very approachable in the factory.

Thanks to all you wonderful people on here with advice over the last few weeks, Rob's just been frantically redesigning the front end of Big Dave 3.

Here's what he had to say on the matter: https://www.arc-robotics.org.uk/2017...bout-bearings/

[emisnug]

Bearing preload wise, I'm leaning towards a beville washer running an ever-so-slight preload. However, preloads are something I have never, ever done before, and if you've got any experience with them, I'm all ears. Currently, they seems pretty straightforward, which normally means I'm missing something huge.

Katch, I may well take you up on that....

[emisnug]

Bear With Me.jpg

Taper rollers arrived today. They're scary levels of large.

[shakesc]

Needs a banana for scale

[emisnug]

Needs a banana for scale

Aye, but I ate it

[emisnug]

Big ol' bit of steel that will become our drum arrived today. Still a fair amount of material to take off and fun things to machine in (anyone know a good lathe person?), but it's big and heavy and deadly even in it's current state of being my footrest. Again, no banana for scale, because I needed a snack.

15976985_10211809992514954_4968922041205682775_n.jpg

[emisnug]

We did some more things last weekend, it's all over on the ARC Robotics blog:

https://www.arc-robotics.org.uk/2017...uary-update-1/

[shakesc]

I can see you have HiFei’s Fulcrum Pro 300A Controller for the weapon but what did you end up with for the drive?

[emisnug]

I can see you have HiFei’s Fulcrum Pro 300A Controller for the weapon but what did you end up with for the drive?

Chris chose the 180A Turnigy Marine ESCs I believe. As our motors draw 150A at stall, we're running an OK safety margin on them, but Chris is the guy for details on that (cmalton on here, I believe)

[cmalton]

Chris - we ended up on Turnigy's (supposedly) water-cooled 180A ESCs for the drive at the moment.

One of them doesn't like how much power we're pumping through it in extended tests - but we think that's actually a mechanical issue as the drive is much more reluctant to turn on one side.

Hopefully we'll fix that fairly quickly....

Was in the middle of replying - Rob beat me to it because I'm currently in the middle of a field running paintball/airsoft/laser tag events.....

[cmalton]

After a fairly short Saturday in the workshop, we now have an idea what this creation is going to look like...

The word "Yikes" sprung to mind when we managed to get things into a test fit for the first time.

16252160_1208147229302458_4099341607869864943_o.jpg

There's a (little) bit of milling work that needs to be done on the drum before we can mount that properly, but we're probably going to send that to one of our new-found machine shops (because they're proving infinitely more reliable than our previous choices).

We sent them the files for some parts on Sunday last week..... and I picked up the finished parts on Friday.

16388524_10155144758943738_1543384861_o.jpg

The price wasn't bad either for a 1-week turnaround.

We are so painfully close to the point where it's no longer "safe" for us to continue testing...... and when we get to that point.... we know we're onto something.

[emisnug]

Time for an update.

Things have changed. A lot. After a third attempt at getting on Robot Wars and some drivability problems with Big Dave 3, we sat down and had a little (almost complete) redesign with input from all three of us to design something that we're both proud of and is still the same levels of destructiveness...

Presenting Big Dave 3 (MK3)




And even then, it's somewhat changed from the CAD above - now with some more armour sections and a different tread pattern that I wasn't able to render because my computer is now 9 years out of date.

So - the drum, the taper roller bearings and the 100mm axle are all the same. Everything else is modular (because modular) - two drive pods and an electronics enclosure. The drive pods are exactly that - everything we need for the drive sections - two motors, 4 sets of gears, 4 belts and a couple of wheels and many bearings. Changes are as follows:

• We've changed from the Alien Power 8085 motors - we're now running quadruple Turnigy SK3 6374-192Kv motors and coupled them to an 8.75:1 gearing arrangement, allowing us to run at 16MPH with 16Kw/21Hp on the ground.
• The wheels are now cast with 50A Durometer rubber
• HTD Belts! (Because of an inhernent dislike for chains)
• Slightly longer impactors (249.31MPH mechanical tip speed)
• 44.4V (12s) throughout
• There's a wedge
• Polycarbonate top panel with flexinessâ„¢ to absorb hits
• We've decided on an Orange/Black colour scheme
• Marine anodising is happening for extra hardness
• Titanium impactors! We're fully aware that Ti isn't an ideal material for this, but white sparks!)

Our good friends over at GSD Tech in Southampton have started machining parts for us - we should hopefully have a fully working robot by the end of the year.