regarding the drive, it seemed to drive okay, plenty of speed and power, went forwards/reverse instantly etc,

Only downside was the setup on the steering wheel tx (turn left- robot turns right and vice versa) which is a quick fix by reversing the channel on the TX should he wish to do so i'd imagine....

Also it doesn't spin on the spot (left wheel forwards, right wheel backwards) or it didn't seem too... Nick told me at the time though that's due to the weight being balanced on the front forks etc... so it tends to turn around the forks, like to turn left, only the right wheel turns and the left wheel stays still... not something id be happy with on one of my machines, but if it works for Nick then that's his call.

Hope you have a good trip home Nick.

Its not that I think those Trackstar ESCs are rubbish, I just think I have found an alternative that fits in my bots better. Aaron from BotBits has been happy with those ESCs and I didn't see them misbehave at the FRA event so they are not a bad choice if you want to use 6S motors.

Mr Mangle rebuild:

After sitting around in Heathrow for a couple of boring hours, I started looking at rebuilding Mr Mangle with all the useful ideas from Shiny - it might be possible by just milling off the hoop mounts and milling four short slots to mount the inverted drive wheels. I also like the idea of wider custom urethane wheels with more grip; I noticed that both bots wheel-spin quite a bit when turning in place, like you mention, Dave. The other thing I could try is to mill the underside of the forks so there is a smaller contact patch - does that sound like it would reduce friction?

Robogames:

For people who didn't pledge to the Kickstarter campaign, here is a very rough edit of one fight to show how the DVD is shaping up: http://robogames.net/2015.php . The 4K cameras and frech polycarb have made a huge difference!
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Australian 2015 Featherweight champion
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if anything i think a smaller contact patch would make it worse... as the front would have more grip from the weight pushing down on a point...

Probably worth making some nylon front test skids or mounting the the front of the robot on castors etc just as an experiment to see how it drives with minimal friction up front and go from there.

Sounds like a plan - i can make some UHMW 'shoes' to fit around the forks. The one time I did that on a much earlier bot, the plastic wore down pretty fast and the bot ended up riding on the screw heads holding the plastic on. Its still a good test though and easy to try.
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UK 2016 Gladiator champion

In theory the friction force is independent of the surface area. As the surface area reduces the force per unit area increases, keeping the friction the same.
Things like tyres have second order effects where they actually form into the shape of the mating surface giving larger surface areas more friction force.

If you can make it larger perhaps but shape it so its less likely to catch on scratches and the like in the floor it could solve your problem
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Mechanical engineers build weapons, civil engineers build targets

Good analysis Jake . I was thinking along the same lines - as long as the materials don't deform under the weight of the bot, the friction will stay fairly constant. To be effective, the forks need a sharp leading edge but there is no reason the sides of the forks cannot be bevelled so that sideways travel (IE turning) doesn't cause the forks to catch in irregularities in the floor.

The bots drive fairly well in forward and reverse but not so much when turning, so what's the difference? The contact area and weight over the forks must stay constant and the friction 'should' be constant too. The big difference is the length of the leading edge. In forwards, that's the width of the forks, under 20mm. When turning, the leading edge is the sides of the forks, around 60mm or three times as much. Unless there is something else going on, smoothing out or reducing the leading edges on the sides of the forks will help turning, at least a bit.

I can't test that directly until the bots are shipped back, but some sort of desktop experiment should help prove the theory. comments?
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Horizontal spinner:

After vegging out yesterday due to uber-jetlag, I am back in the workshop to start new projects. The motor rebuild for a new horizontal spinner will be complicated as the base motor has several issues. Opening up the motor was a challenge as every screw has threadlocker and the small ring screws had to be heated up with a soldering iron before they would come out:



The 24 pole, 72mm diameter stator is relatively small compared to the outside dimensions of the motor. The central tube looks like it is only held in with a circlip and has a double D flat to prevent it from rotating, so that's fairly easy to replicate. The single top bearing is a bit weedy and can be replaced with a needle roller bearing with far higher radial loading specs.



The base of the motor is where is gets complicated! The original base is a separate plate that bolts on to the centre tube with four totally inadequate M4 screws. I plan to replace the base with a large flange directly on the end of the tube, which will be wide enough for at least M6 screws. The existing tube is quite chunky but made of low-grade cast aluminium, so a machined 7075 replacement will be a huge improvement.

The winding on the motor is a complicated affair with every 2nd pole reverse wound. I really want to re-wind it with heavier gauge wire to get more power but perhaps just adding sensors to increase the start-up torque will be easier. There is plenty of room to mount the hall sensors and to run the wires down the gaps in the laminations.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

wrt experiment, dynamic friction is kinda hard to measure, you can probably fake it close enough though.
For a comparative test perhaps put a block on an inclined ramp, increase the angle until the block slips, then reduce the angle until when you give it a nudge it will just keep sliding down the ramp, not accelerating or stopping.
Then with that angle and surface fixed you can change your block and any difference in performance will manifest as the block moving at a different rate.

I reckon half the issue you are going to be getting is getting stuck in scratches and scrapes in the floor, but that's just a gut feel not backed by "science"

wrt your motor, why are you keeping the existing tube? the attachment from tube to base plate through that join is something I'd prefer to replace tbh.

That said, that is one dead sexy motor lol
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Mechanical engineers build weapons, civil engineers build targets

The tube is going as soon as I figure out how to press it out of the laminations without crushing any of the wires. Does anyone have advice on doing that? The circlip and tube have a coat of lacquer or very weak epoxy, which didn't stop the circlip from coming off but is preventing the tube from pushing out under hand pressure.

For friction testing, I was going to make up a jig that pressed the fork material down against a ball bearing. A long strip of floor material would be inserted horizontally between the fork material and the bearing and pulled thru with a small & sensitive spring gauge. The gauge should show friction differences between materials and surface areas if they are there. Its not a high priority but since all the bots and most of the hand tools are still over in the UK, I don't have much else to do.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

friction:
I dunno, ball bearings and stuff feels like a more complex setup perhaps prone to error.
The way we did it in physics was fix the floor piece and pull a test block along it (we used weights and a pulley with string to provide the slide force)

motor:
as glen saw, perhaps freeze it out? if the tube is Al it should shrink more than the steel laminations.
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Mechanical engineers build weapons, civil engineers build targets

Freezing sounds good - are we talking liquid nitrogen or just popping the motor in the freezer for a couple of hours?
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It's the same stator as I use in Catharsis, just thicker.

I got the central part out by using a tube as support of the stator, big enough to fit over the central boss but small enough not to hit any wires, and just use a press.

Did you get your stator out of one of the Rotomax motors, or from a multicopter motor like the ones in Mini Moth? Mine has that annoying shell support bearing in the way of using a tube to support the stator in a press. If freezing and a sharp blow from a hammer doesn't shift the motor tube, I will have to press off the bearing and then the tube. If I do screw up the windings, at least its a great excuse to try rewinding it
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The Rotomax 1.20, 72mm OD 10.5mm thick.

I think it goes 1.20 - 1.40 - 1.60 - 50cc, etc. All using the same stator laminations, just a thicker stack.

the 80cc - 100cc - 150cc rotomax use a larger OD stator, same trick.

Success!

Motor cryo-packed and at -18 deg.C:



After a small amount of hammering the tube popped right out; I don't know if the metals shrank apart of if the glue became brittle but the freezing worked well.



Now to measure and replicate the tube...
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UK 2016 Gladiator champion