Build Diary - Plastic Fantastic - FW

Hi everyone, after finishing the upgrades to Pressure Point and with plenty of time remaining until the events start up again, I have decided it’s time to build another featherweight. I have been working on it sporadically over the winter has time as allowed and decided I better get a build diary up before I forget what I did.

The aim for this one is to be fairly simple, I want something that I can throw into the arena, hopefully come out still working, charge the batteries and then throw it back in for the next fight without too much other work. I also have not fought any spinners yet and this will allow me to see what works and what doesn't before committing too much. Therefore I’m going with a 4wd ram bot, this should keep the design and internals fairly straightforward. It’s going to be constructed out of 1 type of material, HDPE which should keep costs down as I can make all the parts myself. The fixings will be kept all identical where possible to further aid with this. Motive power will come from 4 of the mighty Argos value drill motors, each one directly driving a wheel and each side pair of motors driven off 1 TZ85A flashed to brushed motor operation. Voltage will be as 5s as it gives a good speed/power boost to the motors and they seem to handle it without too many complaints.

With the above in mind, I set about coming up with a design on Fusion 360, its a fairly standard invertible 4wd ram bot type design. The chassis bulkheads are all 20mm HDPE witht the mounts for the motors milled directly into them. Side and rear armour is also 20mm HDPE, while the top and bottom are 15mm. The front wedge is 30mm thick but I think I might end up needing a small steel running strip along the sharp end of the wedge as the HDPE won’t hold the edge, but that should be the only non HDPE part. Fusion puts the weight in at around 11.7kg, so hopefully a bit of scope for it inevitably weighing more than you expect. The name of the machine shall be Plastic Fantastic since it is built out of the stuff.

The HDPE came from Direct Plastics, all natural white as I’ll come up with some sort of decoration scheme when it’s done. Fusion 360 spits out g-code from its CAM module that I can send straight to my CNC router so it wasn’t too long before the first part was made. It’s one of the main bulkheads that surrounds the battery compartment, and here it is before it was cleaned up.

Attachment 7545

A couple more parts later and there is the other battery compartment bulkhead along with one internal side. You can see the mounts for the front of the motors in it. Apologies for the poor picture but its the only one I have of it at this stage.

Attachment 7546

More to come soon.

Fancy giving us a image of the CAD ?

Also what CNC router do you have? personal or work?

Looks good so far - reminds me of the FW version of Limpet from the description.

Quote:

---

Originally Posted by Maxamuslead

Fancy giving us a image of the CAD ?

Also what CNC router do you have? personal or work?

---

Here is a quick look at the cad, sans nuts and bolts which I never seem to put in. The side tippers which stop it balancing on its side are still up in the air. I’ll see what dimensions they need to be once it is built and I can test it. The battery lives in the centre compartment, ESCs are in the front and the link is in the back. My router is a personal one, a Chinese 6040 off eBay. The consensus seems to be that the machines are ok for the money but the electronics and wiring are junk. As it happens I’ve already replaced a faulty connector on it and the PSU died over Christmas, so I’ve replaced that too. I’m going to replace the stepper drivers and all the wiring/connectors as things allow but otherwise I’ve not had any problems with the machine itself.

Attachment 7575

cool which ebay listing did you get as I am looking at 4030 version and from what i have read the older one had better quality control boxes.

I cant find the exact listing right now, but mine is over a year old and if it has a 'better quality' control box then I'd hate to see one of the newer ones! Mine has the generic blue control box, here's a picture of it.

Attachment 7576

As I said earlier the boards inside are not great designs are built down to eliminate every bit of cost they can. This control box also has the PC interface and stepper drivers as an all in one board (I know some others have them separate) so when a part on that board inevitably fails too it will mean replacing the whole board.

Another point to note about the older control boxes is that they are nearly all parallel port connectors and require a PC (not laptop) with a native parallel port, not one on an add in card. There are lots of old PCs going cheap on eBay with parallel ports but its another expense and hassle to bear in mind. Some of the newer control boxes reckon to be USB connections which would be much easier but I don't know how that would work with whatever software you plan on using to control it with.

Having said all that, don't let it put you off. I got mine to play around with and try and learn something along they way. I had no knowledge of any of this when I started and I'm starting to make some passable parts for my robots for now. For woods, plastics and soft metals (within reason) these machines seem good for getting started on, just keep their limitations in mind.

that stuff with the parallel board is a load of bull, but it is good to here that the blue control boxes better then some people are making out.

This is the one I am planning to buy but if the blue control boxes are fine i could get a "cheaper" one.

sorry for the thread hijack but what spindle are you using and did you cut Presser Point's crusher assembly (arm and frame) with it ?

I didn't cut Pressure Point's arm and frame on it as they were made before I had the machine and so were water-jetted instead. Any new bits I attempt for it I'll do on the machine though, but from the aluminium I have tried on it, don't expect quick cuts.

Looking at the one you have linked, the machine itself looks virtually identical. The steppers are smaller and the spindle on it is 230w, I have the 600W air cooled spindle on mine. I don't know if that would hinder your ability to cut soft metals on it or how fast you could cut them but someone with more knowledge may be able to comment. The ER11 collect limits you to around a 6mm bit, but I don't think you'd want to be pushing a much bigger tool around with it anyway.

Continuing with the build diary, the next parts made were the left side, its spacer and the left hand rear motor mounts, plus all their respective mirrored parts for the right hand side. I fitted a couple of motors with their wheels and assembled what I had of the bot so far:

Attachment 7586

Only 2 motors are shown in the picture as back when that was taken there seemed to be a national shortage of the 12V Argos Value drills, and I couldn’t get hold of any more. Thankfully this situation seems to have sorted itself out and I have some more and the drills are back in stock. At this stage the chassis was starting to get some rigidity to it which was encouraging. There is a fairly large gap between the wheels and the chassis to allow for a bit of chassis deflection but also for wider tires should I need in future.

Next piece to be made was the back, in the same style as the rest and here it is fitted, along with the other 2 motors and wheels. At this stage I now had something I could roll around the workbench.

Attachment 7587

The final part to complete the chassis was the front wedge and it was also the longest part to make, a combination of being the thickest piece and having an angle to cut on it (unlike all the previous parts which where all straight sided cuts). Here it is at the start of the cut, at the end and the finished piece.


Attachment 7588Attachment 7589Attachment 7590

Looking great - super chunky and sturdy! Should be very difficult to KO.

Update time – First up the front wedge, shown in the last post, was fitted and bolted on. I was a bit worried that if I had any alignment problems, it wouldn’t meet up with all 6 chassis / side pieces, but thankfully it was fine. With the being the last main piece of the body (except the top), it meant I could now do the wiring, which is mainly what has happened since the last update. The first wiring job was to flash the TZ85As for brushed operation and then make and solder on some splitters, since each one will drive 2 motors.

Attachment 7694

The ESCs will tuck down between the front wedge and front motors, supported with some foam. It’s a bit tight, but they do squeeze in. They connect to the 125A main fuse via ring terminals, along with 2 feeds for power lights. The bolts holding them on will be cut down flush to the nuts and covered in 2 layers of adhesive lined heat shrink to stop them coming undone, the same as I used on Pressure Point. The cables are on the long side, but fit into the space ok.

Attachment 7695Attachment 7696

Next job was to figure out a way to hold the link, which goes in at the back. In the end I decided on a 10mm plate of HDPE with a chamfered hole cut in it for a connector. It is offset to the side slightly to allow the link cable to be tucked away safely inside the robot but still be easy to remove at the end of the fight.

Attachment 7697

To hold the connector in place I have melted some plastic and moulded it on and around both halves of the connector. This holds it securely in place but as a secondary safety measure I have then bolted the 2 plastic mouldings through the HDPE plate. This has also had the side effect of acting as a guide for the mating half of the connector that forms the link to make it a bit easier to plug in. For some reason I don’t have a picture of this yet, so I’ll grab one for the next update.

After a quick test to make sure everything was functioning, the final wiring job was the power LEDs. One feed runs 2 LEDs at the back, one either side of the link. The second feed runs the 2 side LEDs, one in the left, one in the right. The LEDs are fixed into holes from the inside of the robot with a step at the bottom so the LED can’t go all the way through and stays recessed about 13mm from the outside of the robot for protection.

Attachment 7698

That’s it for now, next will be neatening the wiring and making the side/rear tippers and the top.

looks really nice

That is some beautiful CNC work there. The only negative of this build will be seeing all of the dents on it after several fights...

Quote:

---

Originally Posted by Shooty

That is some beautiful CNC work there. The only negative of this build will be seeing all of the dents on it after several fights...

---

Thanks, but I wouldn't worry about that, it's already got a number of dents in it before it has even had a fight! ;)

Mini update time, which gets the Robot pretty much completed.

Following on from the last update, a quick neatening of the wiring was in order. Most if it is clipped in position where possible and the ESC’s, Rx and Battery are all cushioned with sponge.

Attachment 7888

The last large part to be made was the top, it’s almost a mirror of the bottom, just slightly shortened to allow for the wedge. The top and bottom are both tapered at the back to give the robot a chance to drive off another robot’s wedge before the wheels come off the ground. The cut outs in them for the wheels are also filleted on the inside to allow for larger diameter and wider wheels to be fitted when an increase in ground clearance is required.

Attachment 7889Attachment 7890

Next up, there is the only non-plastic structural part. (Boo!) I have put a 5mm thick mild steel strip along the bottom of the front wedge to hopefully stop it getting bent under itself on impacts. The metal strip is recessed into the wedge to help absorb any big hits.

Attachment 7891Attachment 7892

Last are the tippers which stop the bot being able to balance on its side or rear. I’m not too sure on these yet, I think the side ones may end up getting caught on other things and cause a problem, so I’m contemplating adding a couple of triangles in front of the leading side tippers to push things past them rather than into them. I’ll give them a try and see how they go.

Other than that, I have had a quick drive to check everything works and that the fail-safes are working. Also, I’ve put it on the scales to check the weight. Almost bang on 12kg which is not too far from what I was predicting.

Attachment 7893

All that leaves me now is the cradle, the bigger wheels and the visuals. I might even get chance to make a few spares!

looks like a beauty, your going to take to Manchester ?

Looks niiiiccceee, can't wait to see it in action.

Quote:

---

Originally Posted by Maxamuslead

looks like a beauty, your going to take to Manchester ?

---

Yep, I'll be there with both of them.

Quick update following a fantastic weekend at Manchester. Other than one very annoying and recurring problem, I’m pretty happy with how Plastic performed at the event.


Melee 1 – I started with my colson wheels that give me about 5mm of ground clearance. These are fantastically grippy, but I got hung up a few times on the seams between the arena floor panels and had to sit there until someone hit me off them so I could get going again. Now a good portion of this was down to my poor driving and could defiantly be minimised but I decided I would swap wheels after the fight to be safe. When I wasn’t stuck on the seams I was able to get stuck in and mix it up a bit. Lots of speed and pushing power from the bot which I was pleased to see.....and then it just stopped. Power lights still on but no movement from it. Resetting the transmitted did nothing either.


Back in the pits with Plastic on it’s cradle, I put the link in and it worked fine, wheels turning but under no actual load. Nothing felt too hot in there and although its a good 10 minutes from the robot stopping to getting it to back to the pits and taking the top off, I would have thought if something were overheating it would be obvious. Damage suffered to the top from Shrekt, but nothing else other than the usual bumps and scratches.

Attachment 8014


Melee 2 – Bigger wheels fitted which give 10-12mm ground clearance. They were homemade HDPE wheels with bike tires screwed on the outsides. Not as grippy as the colsons, but no more issues crossing or stopping on the arena seams. Also the grip did seem to improve as the newness was scrubbed off the tires. I don’t remember much about this fight, but the same problem happened again with the robot just stopping after a couple of minutes.


Back to the pits again, same diagnosis again. At this point I was wondering about voltage sag from the Lipo not being at its best in some way, and maybe this was causing the ESCs to cut out due to low voltage. However having no way of reading the voltage during the fight I’m only guessing. The battery voltage still showed fine after the fight (under no load of course) and each fight was only taking about 1000mAh out of what should be a 4250mAh battery. The charger was happy to charge it each time too. Neither of these rule out voltage sag from a loaded battery though.


I decided at this point I would switch to Pressure Point’s battery for the next fight, its smaller (but still ample) capacity and the same voltage at 5s. I took a nice hit from Binky in the fight, a gouge out of the side and some bending of the top panel above it. The top panel was sorted with the heat gun and some brute force but I think it’s a bit of a design flaw. The vertical spinners will always want to rip the edges of the top panel up and bend it out of shape like in this case. I think in a future re-design I'll extend the sides to where the top panel currently is and the top panel will sit recessed inside them instead of on top of them to minimise the chances of this happening more. The fact that the sides of the robot have taken all the hits while the front wedge is essentially unscathed speaks volumes about my driving!

Attachment 8015


Melee 3 – AKA the 5 spinners of doom. Some serious damage flying around in this one, somehow I manage to miss the worst of it. However the same issue happened again which was getting frustrating.


Since there was only one more fight left for the weekend, I decided I would remove the sponge that the ESCs have around them just in case they were getting too hot, though there were not much more than warm each time I had checked them.


Melee 4 – Not a lot to say other than the same thing happening after the same amount of time, capping off a promising but ultimately frustrating start for the bot.


Now I am considering the possibility I have knackered both my batteries. I didn’t storage charge either of them over the winter and they were left in my shed. Maybe it got too cold in there and the 2 things combined has somehow damaged the cells. I have ordered a new battery to test this out. I have also already swapped the Rx and checked all wiring as a precaution but this made no difference. If this doesn’t work, then unless both ESCs are somehow failing/stopping at the same point I don’t see what else it can be.


Anyway, that’s enough rabble, sort this problem out, a couple of other minor tweaks and off to Portsmouth in a few weeks time.

but didnt Pressure Points battery work fine in The feather fun time match ? ( has anyone got a video as that was really fun)

Quote:

---

Originally Posted by Maxamuslead

but didnt Pressure Points battery work fine in The feather fun time match ? ( has anyone got a video as that was really fun)

---

It did but the bot didn't run for very long before I stopped due to the wheel problem and also the current draw in Pressure Point is generally lower then on Plastic. Therefore if it was going to do the same thing it didn't really get the chance. I'll be looking to test this battery too if putting the new one in Plastic fixes the problem.

Tough little robot you’ve got there, did the most amount of damage to Shrekt it’s taken so far. After watching the first fight back it seems that the slice in your lid wasn’t caused by Shrekt bouncing off the wall, it hit another robot and managed to backflip several times, over the top of PF.
Attachment 8021

Quote:

---

Originally Posted by mrsam

Tough little robot you’ve got there, did the most amount of damage to Shrekt it’s taken so far. After watching the first fight back it seems that the slice in your lid wasn’t caused by Shrekt bouncing off the wall, it hit another robot and managed to backflip several times, over the top of PF.

---

Oh yeah, nice catch. I haven't had chance to watch the vids yet that have been posted, going to view them this evening. 10/10 on style from the judges for the backflip!

Update time following a weekend of rumbles at Portsmouth and my attempt to fix the ongoing issues I was suffering at Manchester.

As detailed earlier in the thread, I was having problems with the robot stopping after about 2 minutes of battle. Power was still on to the robot and worked fine once it was back on the bench. I had already done a few things to try fixing it at Manchester including swapping batteries and Rx. I still felt the batteries were probably the culprit as they had been left in a cold, outside shed over the winter in a full state of charge. Maybe this had hurt them somehow?

I went into the first fight with the new Rx, a brand new battery from Overlander and a new main wiring loom. I checked the loom over between events and while there were no issues, the main feed from the battery to the link to the ESC's was clearly getting warmer than I would like, so this was increased to 10AWG size cable fromt 12 AWG. The robot performed fine at the start and then after about 2 minutes, the same problem occurred again, very frustrating.

Back in the pits there was only one thing left to try and that was to swap the ESCs. I removed the TZ85s and swapped them for a pair of single channel feather 2s. The wiring was a bit of a bodge as I only had the few bits I had with me but it was enough to get them in and working.

Attachment 8121

Into rumble 2 and it was apparent that these ESCs were driving the motors harder than the TZ85a's. Maybe its better components or different programming but there was a noticeable difference. However them main thing was the the robot finally did the whole 3 minutes flawlessly! Zipping round the arena, slamming into things and shoving the other bots into the walls and what not. I can only assume that I was pushing the TZ85a's too hard and that they were getting too hot and shutting themselves down even though they were cool when I got back to the pits.

Speaking of the pits, after doing the full fight I was able to check things over and I found a couple of things out:

1. A charge of the batteries shows I took a shade under 3Ah out of them. That means over 3 minutes my average current draw was about 58A. Certainly higher than I was expecting and that explains point 2.
2. The robot gets hot. Really hot. Like starting to melt itself hot. :D The areas around the motors showed that tell tale sign of the dull, rough, cloudy texture of HDPE where it has been melty. A couple of bits were still clear and the HDPE soft.

In hindsight its probably a combination of a couple of things. The first been that running the Argos drill motors on 5s is really pushing them. 4s is fine and if such a thing as 4.5s existed it would probably be a better limit. Also with the robot being made from plastic and the motor enclosures sealed in, there is no where for either the heat to vent away to or sink in to. In isolation I would probably get away with these but together its probably a bit much. I could help things by making some vent holes in the base and lid but I'm still on the fence about if I actually want to.

Anyway, this wasn't effecting the performance of the robot to any significant degree so I left as it and ran it for the rest of the weekend. For rumbles 3 and 4 I wasn't driving so I can't say much about those. The only issue happened in Rumble 4 where the driver felt like one side of the drive wasn't right, so stopped as a precaution. Having stripped it down today I found one of the motors was a bit off. Unfortunately I damaged the motor when removing it so I can't be sure what exactly was wrong. I have put a spare motor in, then I have the wiring to the ESCs to neaten up and it will be off to the next event.

good to see that you fixed that issue, although i want a pushing match now 2 775 at 6s vs 4 550 at 4/5s. XD

I think you would win that fairly easily as it seems I have spent most of the fights so far turning my tires into bits of rubber left all over the arena. Only 8 fights the bike tires are almost worn smooth. Got some fresh ones to put on for the next event.