PC Plod Build/Upgrade Log

[callumhoy]

Finally got around to making a SketchUp model of PC Plod's chassis. As well as writing a physical list of the current planned upgrades.
PC Plod Chassis.jpg

Upgrades
1. Replace wheelchair motors.2. Replace lead acid batteries with LiPo packs.
3. Replace Sabertooth speed controller, possibly with BotBitz.
4. Increase armour holding bolts from M5, possibly to M10.
5. Replace current aluminium armour with Hardox.
6. Change the front wedge to a 35-40 degree angle.
7. Replace the current weapon system with a modular design.

If you can think of any more upgrades we might need to do, please do let us know.

[callumhoy]

Updated Upgrades Plan + Questions
1. New motors will be 2x Ampflow E30 - 150 Gearmotors. Does anyone have experience with these particular motors? Would we be better saving up the extra money and going for the Mid-Range or High-Performance motors?

2. Not having used LiPo packs before, we don't really know what we're looking for. The team Danby site says Foxic 3 runs off of 8s 10ah Lithium Polymer. Would something like this (https://hobbyking.com/en_us/turnigy-...lipo-pack.html) be similar/appropriate, ignoring the 5ah instead of 10ah? We're planning on using a separate battery for each side drive.

3. Botbitz – 30a Brushed ESCs are the planned replacement for the Sabertooth. Currently they're out of stock on ranglebox and have been for a while. Does anyone know if/when they'll be back in stock? Or will we have to ship them in direct from BotBitz?

4. Increasing the bolts from M5 to M10 is still the plan, providing they're not too wide and don't weaken the chassis too much.

5. Hardox seems to be the necessary armour in the modern arena, so that's what we're going with. We're going to go with thicker on the panels on the front half of the robot, slightly thinner on the back, top and bottom. How thick do people usually make their Hardox? And where is a reliable place to get it cut/machined?

6. The front wedge changes have been modelled in SketchUp:
New Wedge Chassis.png
We'll likely stick with the 25mm box steel that makes up the current chassis, meaning less changes have to be made to the rest of the chassis.

7. This is the most difficult one to do, because a modular design has to be relatively easy to switch out without taking the entire bot apart to do it. We'll happily take advice from anyone who has built or even considered building a modular system.

[Theo]

Last time I checked, Botbitz 30As aren't even enough for most featherweight. In fact, 85As will only just be enough for wheelchair motors, let alone ampflows.

[callumhoy]

We've also been looking at the RageBridge 2 and the Robot Power Vyper. Likely to go for the Vyper, depending on costs.

[TechAUmNu]

2) For working out how much LiPo capacity you need, best way is to figure out what your maximum draw will be and then get enough LiPo to run that for 5 min.

3) best to ask Ellis about that

4) M10 is a must, you can never have enough bolts. Also if you have the room then shock mounting your armour is a good idea, for example Beta is a good bot to look at regarding armour.

5) Even Hardox is getting torn to shreds by the likes of Carbide and Aftershock, but its the best price-weight-strength combination at the moment. Most people (including myself) get it waterjet cut by KCut https://k-cut.co.uk/

As for thickness I think most bots are running with 4-8mm depending on location, eg 4mm side and back, 6mm top, 8mm front wedge. But it really depends on your design.

6) I think you might want to put some cross beams in to support the bars on either side of the wedge like this: New Wedge Chassis.png

[callumhoy]

Extra supports added to the redesigned chassis.
New Wedge Chassis.png

[callumhoy]

So, I have a target for PC Plod's debut on the live circuit, 2019.
This will be the 1998 PC Plod upgraded enough to compete, just for us to have some fun with and get experience with heavyweights, not aiming to win a championship or anything serious.

Which leads me to my question for the day, a weapons system. Has anyone ever built a CAM driven axe for a heavyweight?
There's videos of flippers doing it, especially in lower classes, and one 'proof of concept' video for a heavy flipper. But nothing for an axe.

Here's a totally not to scale, 5 minute doodle in paint, is there any fundamental reason a system like this couldn't be done? Or is it purely the unnecessary effort to build and lack of power compared to a pneumatic axe?

Theoretical CAM Axe.jpg

[Ocracoke]

I am sure Mortis used a mechanical axe that may have been driven by a CAM mechanism - I've been re-watching the fight between Ghetto-Bot and Mortis from the War of Independence special in Series 4 and at one point, the angle of the camera shows the motor mechanism going around. I had planned to use something like that on The Honey Badger originally (adamclark also suggested another mechanical mechanism called a quick return mechanism that could potentially be used for something like this).

Reciprocating axe mechanisms like this are going to be weaker than pneumatic axes and even electric axes where you have to manually fire/retract the axe and there is the issue of keeping a complex-ish mechanism together during combat. The big advantage with reciprocating mechanisms like this though is the rate of fire.

[callumhoy]

I'm not too worried about it being weaker than a pneumatic axe. I'm probably putting a plastic (or inflatable) police truncheon on the end for the looks more than to be effective with a small hammer/axe part to do actual damage, at least for the first version.
The rapid fire rate looking impressive is part of the reason I looked at a CAM drive in the first place.

I also don't want to be learning pneumatics right now, I've not nowhere safe to test systems.

The mechanism breaking could be the biggest issue we'd face, although if we fix it in place with enough box steel it should survive most of the 3 minutes. Likely to chain or belt drive the CAM to stop any shocks being transferred into the motor.
Also slightly worried about the spring stretching over time if I spend most of the fight with the axe at top height, and the repeated quick expanding and contracting.

[Ocracoke]

I possibly would not bother with a spring... when I was prototyping a axe mechanism, I simply used a bit of metal with a slot on it, a motor and a hub with one screw in it and I'd imagine it is the screw that wins the contender of "most likely to break when shocked" award. This forms the basis of the Whitworth Quick Return mechanism I referred to earlier.

[callumhoy]

The Whitworth Quick Return does look far less likely to break down, although it does look far less powerful, because there's no actual force behind the downward swing

The spring appears to provide a decent amount of force, at least on a flipper:

[Ocracoke]

Hmm... certainly looks powerful but I would not want to be around it if that spring decides to break (might be worth fitting a blanking plate over where the spring is exposed.

The Whitworth Quick Return does look far less likely to break down, although it does look far less powerful, because there's no actual force behind the downward swing

Having watched my video again, I had the same concern but it depends on which way around the mechanism is turning I should think. For a axe mechanism, it looks to be that you'd want the motor turning clockwise and for lifting, run it anti-clockwise (from the angle that I shot the video at).

[callumhoy]

I have little faith in the setup used in that video, especially the spring being bent. That seems likely to be very unsafe.
The spring would definitely need to be contained in some kind of safety channel.

I think the Whitworth system looks like you'd definitely get a much higher fire rate, which would hopefully make up for the lower power.
I'll have to build smaller models of both and see how they run, probably run both in a FW before committing to one or the other.

[Theo]

Out of interest, what have you sorted with the drive?

[mattsdragons]

You would be better off with a scooter motor powered system I think. I'm all for different ideas but even using twin motors and a bloody huge solenoid would be easier!

But... if you want to go down the spring route, car springs would be a good shout. If you can compress them they should have a good amount of bounce and just add a bump stop to limit the travel (I work in parts supplies if you can't tell haha)