Yep, 567 grams of gas on the spreadsheet - I'm glad to have the spare weight to play around with but it feels weird and wrong after every other bot struggling to make the weight limit.

Another idea to use the weight are some 'keep away sticks' around the back of the bot. If they are above 25mm and parallel to the floor, I think they comply with the rules and can't be called spatulas or wedges.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Here is a better view of the bungee and pulleys:



The cord is 1 metre long at the moment- probably needs a couple of cm cut off to give it some tension when the flipper arm is fully closed.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Looking epic
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Miles Blow - Julie Pitts
www.mulesfilm.com.au
www.wombokforest.com.au

-Pickasso- Vivid Sportsman champion 2015

you for sure want a bunch of force at the end, you still need to get the gas out and it sucks when you are driving around with the flipper 2 inches off the ground
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Mechanical engineers build weapons, civil engineers build targets

Agreed, it really sucks when the arm doesn't retract. The ram has experimental quick exhaust ports at the top of the piston stroke, which should let most of the CO2 escape, making the bungee's work easier. I also built in an adjustable exhaust port at the bottom of the ram.

Today's mini prototype:



The bungee skips over it's mounting point on the arm fairly easily and the tension should keep it there without having the cord squeezed flat - one less point where it might break.



To add weight and strength, the side panels on the arm are now taller and the cross section is less 'U' shaped nad more 'I' shaped. Its not a large change as there isn't room on the Ti sheet for more.

All up, I added 204 grams and Mr T is now a massive 11.153 Kg
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

With the whole 2.5kg spare, you could make it 4WD to make it super easy to drive
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More drive is a good idea.

What is your favourite drive from all of your robots for power and control?
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So even the rain that falls isn't actually going to fill our dams and our river systems

Four wheel drive is in the too hard basket - the T shape would have to change to more of a square and that won't fit on the Ti sheets I have. Thinking back, my very first bot was the only 4WD I ever made; since then I have always gone for weapon power over controllability. The next sportsman will probably be my fave for control; the massive tank tracks and solid lifter mechanism almost guarantee that .

Picking drive motors for that bot might be a challenge; it will take much more torque to spin the the tracks compared to wheels. There are plenty of out-runners with the power but they could overheat easily. I might go back to 700 motors and a Ragebrige.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Its all looking pretty damn swish Nick!

775 and a ragebridge would be awesome. I'd put a chunk of any spare weight into a counterweight at the back, doesn't have to be useless mass could be more armour

Looking at it now, without a grunty drive system behind it it looks like it it will move like arseholes. Get some power in there and suddenly you've got your badass weapon and a badass way of transporting it to people

Might be worth getting a gyro in there too?
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For my stuff
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Ha Ha, those tiny little motors will surprise you! They are capable of 250W continuous (not Hobbyking peak power for one second pretendo watts) and with a 38:1 gearbox the torque should be pretty good too. They are sensored, so the torque will be there even a low speeds.

The hold-up today is finding a frigging soldering iron! I got out all the wire & connectors to do the wiring loom last night and all three of the large soldering irons are hidden in a box somewhere.

I was thinking about the 775 motors and Ragebridge for the tracked sportsman; one thing that small brushless ESCs can't do well is current limiting. The Ragebridge's current limiting should save the motors when the tank tracks stall.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

So what type of motor and ESC would you choose for a belt driven four wheel drive feather?
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So even the rain that falls isn't actually going to fill our dams and our river systems

How many pages do you want me to fill up?

A 4WD belt drive bot probably needs extra power & torque compared to 2WD as it has more floor contact and will be skid steering (assuming you have reasonably grippy wheels).

You only need two motors with belt drive, making it more economical to go brushless and the extra reduction available in the belt drive opens up more gearbox ratio options. Most out-runners with enough power have at least a 5mm shaft, making the P60 gearbox one of the few options. I like to have a large reduction for brushless motors so the bot has better low speed control and torque.

With a belt reduction between 2:1 and 3:1 and either the 11:1 or 13:1 P60, you can find many higher Kv out-runners in the 500 helicopter class that will deliver the goods at the right wheel RPM. The added bonus of a final belt drive reduction is less shock transmitted back to the gearboxes.

Option B might be a pair of DeWut gearboxes and motors. I don't like the weight or the stock ratios but with extra belt reduction the high speed GB setting would be more usable.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

You most definitely have a large build thread. Imagine going through it all to find a particular post.

My initial thought was to directly drive a wheel from a P60 and belt drive off that. The robot would still drive if a belt broke. Your idea to reduce the shock to the drives by not attaching the wheels to the gearbox is valid in a spinner rich competition.

Is there a clear difference in performance between brushed and brushless motors in your opinion?
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So even the rain that falls isn't actually going to fill our dams and our river systems

Difference between brushed and brushless.


As Nick mentioned, go for decent KV brushless outrunners and large gearratios and you get a way better power to weight and control ratio compared to old style brushed.
Reflashed esc with SimonK or simular software and you won't lack control or low speed grunt.

Also, brushless is getting cheaper by the day.

Its a good point about reliability and still having one wheel turning if a belt fails; my smart-arse answer is to not select a belt that will not break . More seriously, drive belts seldom snap, they usually strip the teeth and that can be avoided by having a wider belt, larger pulleys so more teeth are engaged and good belt tension. You can't always get the perfect belt set-up, but 2 out of 3 of the above should prevent most belt problems.

After using 550 brushed motors, small (100W) sensored in-runners and medium sized sensored out-runners, I still think that a good brushed motor has an edge over brushless at very low speed. The thing is, you don't want to be crawling around the arena slowly - that just makes you a target! As long as the motor set-up has good control from about 25% throttle, that's good enough. The only time low speed control might be really useful is navigating around an arena pit.

The other way to get good control with brushless motors is to have stupidly over powered models (anything over 500W in my opinion). When a powerful & large diameter motor tries to start, it only needs a fraction of it's maximum torque to get going and once it has generated a some positioning info for the ESC (less than one revolution) then the ESC can ramp up the current and really accelerate the bot.

Another side effect of large gear reduction is that there is usually more slop or backlash in the system. This helps the motor to get going as there is effectively no load on the motor for the fist few degrees of rotation.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion