PC Plod Build/Upgrade Log

This is a build/upgrade log for the heavyweight robot PC Plod which I just purchased from the previous owner for £45. That's a full chassis, armour, drive motors, wheels, weapon motor and most of the electronics for a, currently, 67kg robot for £45. Bargain!
I will be starting simple by just adding a transmitter/receiver and replacing the dead batteries in order to get it driving again. Then the team and I will begin work on adding an active weapon, as the old spinning disk shattered in a battle in 2000, when the robot was last used.
As this is the teams first ever attempt at work on a combat robot I will be documenting any and all changes or advancements I make here. All feedback and advice for a new guy is appreciated.

Turns out that they're still making the same type of battery that was put into the robot 16 years ago, YUASA NP Series NP 12-12. Since the team has no practical experience with combat robotics we've decided the safest bet for now is to just use the same type of batteries that were used before.

Integrated Robot Controller Document I was given with the robot.
Photo Album for PC Plod
Robot Wars Wiki for PC Plod
NP 12-12 Datasheet

What do you have in mind for the bot? Bearing in mind that the electronics, batteries, weapon, probably armour etc are all very old school tech and unlikely to do much in the modern arena.

What drive motors does it use?

Quite honestly right now I haven't much more in mind than to get it functioning properly. I doubt I'll be happy enough to have it entered into a competition for a year or two, this will be a long ongoing project for me.
Once it's working again I'll start work on replacing parts to upgrade it to a modern standard.
The drive motors are two 24V wheelchair motors. According to the previous owner they will do about 6mph.

I've been looking into different 2.4ghz transmitter/receiver pairs over the past few days and I've come to realise that I lack the ability to realise which controllers would work with PC Plod. The robot works off of effectively tank controls, both wheels forward to go forward, both back for backwards and one each way to turn, so both motors can spin both clockwise and counter-clockwise. I know we'll need at least 4 channels, possibly 6, one for each wheel motor and one for the weapon. Plus one spare left over, probably to be added to a srimech when we eventually add one.

So my question to all those with knowledge is this, what sort of things should I be looking for in a transmitter/receiver? Will any of the ones listed below actually work for my needs?

1) Radiolink 2.4GHz T4EU 4 Channel Transmitter Radio & Receiver
2) Radiolink T6EHP-E 2.4G 6CH Transmitter w/ R7EH Receiver
3) FlySky FS-i6 6CH Transmitter + iA6B 2.4GHz 6CH Receiver with Telemetry

If you need me to give more information let me know, I'll give what limited information I can.

You can run all the motors on one side from the same (side of a, for dual channel* controllers) speed controller, so you don't need a separate radio channel for each motor! The speed controller will drive the motors forwards and backwards from just one radio channel, so the bare minimum you'll need is three - two channels for drive and one for weapon. The drive channels are often 'mixed' to give forwards/backwards/left/right control on one joystick; this function can be done in the radio transmitter, in most dual channel speed controllers, or a separate device known as a 'mixer' in the robot between the radio reciever and speed controller(s).

All the sets you linked will work; the key thing for combat robotics is that the reciever failsafes properly (to avoid a runaway robot). I use odd radio gear myself, so I'll leave specific recommendations up to others, but it can come largely down to personal preference, and it's not something you need to worry too much about committing to too heavily as it's completely swappable.

*try not to get too confused between 'channels' on speed controllers and radio gear. it does happen. :P

Thanks, you've saved me from spending another hour or two reading everything I can find about transmitters unnecessarily and stressing over it all.

The old integrated speed controller has been entirely removed, cutting the circuitry down to the bear minimum needed to test all the motors. Batteries, through the safety key switch, into the drive motors.
Both the drive motors and the weapon motor appear to be fully functioning. So, with a Sabertooth speed controller ordered and on its way, I'm hoping for a first drive test within the next two weeks.

There is a jumper on the sabertooth that let's you tune the sensitivity at different throttle inputs. I've done loads of testing with a sabertooth and wheel chair motors and the middle of the road settings all worked the nicest. If you read the instructions when you get it you'll see what I mean

Thanks for the advice, you've probably just saved me hours of playing around with different settings.

You may want to upgrade from a sabertooth for actual combat. Dimension engineering products are a bit shit at the best of times now it seems and the boards are super delicate. Maybes something like tz85 or ragebridge for an upgrade :)

I agree, I intend to upgrade before putting PC Plod back into combat. Thanks for the recommendations.

The Sabertooth will likely be moved into a prototype featherweight as and when it gets designed and built.

Looking at the way the front of the robot is designed, the weapon would be entirely ineffective in combat with the bots being so close to the ground. So, we've decided, in an attempt in avoid having to redesign the chassis, to redesign the front plate setup. This should reduce the ground clearance and provide a ramp to force the opposing bot into the spinner.
This is how it looks in a first draft out of scrap metal:
Attachment 6494
And here's a drive test with the draft front:
https://www.facebook.com/TeamTheScra...88734953835798

After attaching the weapon motor/weapon mount, we're struggling to see how the old cutting disk was mounted. Our original guess was that the holes in the front of the mount were where the disk was mounted and it was belt driven.
However, the largest disk that could fit (it's against the bottom plate) barely shows out of the front panel. Meaning that it's useless as a weapon, unless an opponent drives all the way up the front, and even then it would barely scratch the bottom of the opposition.
Any ideas?
Attachment 6661Attachment 6662Attachment 6663

So, we have absolutely no idea how to mount the weapon. As I said before, the biggest disk that would fit only extends out the front of the bot by a few millimetres. Explained in this video:
https://www.facebook.com/TeamTheScra...0165626710589/
So we're either going to have to change the weapon mounting system entirely, or change the weapon into something different entirely. And considering my personal preference of 'control weapons' such as clamps, crushers or lifters. It looks like we're going that route.

PC Plod's current weapon system is useless. So we're going to design a new one. Which weapon systems should we make designs for?
http://www.strawpoll.me/12980979

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.
Attachment 6714

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.

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:
Attachment 6721
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.

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.

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

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: Attachment 6722

Extra supports added to the redesigned chassis.
Attachment 6723

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?

Attachment 7491

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.

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.

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.

https://youtu.be/zYXeJgXcpDg

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:
https://www.youtube.com/watch?v=LGI91MMHBL0&index=9&list=PLsnBzw0E hMnIgm3A CG-mDQOY0TKAPtYjv

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.

Quote:

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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

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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).

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.

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

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)

Quote:

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Originally Posted by Theo

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

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The drive right now is pretty much the same as it before I bought it. 2 scooter motors powering, going through some custom gearing to drive the wheels. I have simplified all the wiring, and I'm planning to change the gears so I can actually have replacement parts instead of hoping the current set up never breaks.

Quote:

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Originally Posted by 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)

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Completely ignore my diagram from before, I'd have to put the CAM above the axe arm. The CAM would push the bar down, raising the axe up and stretching the spring, then the spring being used to pull the axe down with something more than the force of gravity.

I'll probably use a scooter motor to power the CAM, with high torque gearing. If not a more powerful motor like an Ampflow.

I've found an actual example of the CAM driven axe system I was looking for:
https://www.facebook.com/harley.wolf...ater&ifg=1

Now I have a proof of concept to work from, and a basic idea of how to build a working model. Just need to find a way to upscale it.