We've had a look at some of the internal components that make up a basic rammer robot.  You've got a basic idea of what parts you want to use but now you need a chassis to mount them all onto.  In this post we are going to look at the design principles that were used traditionally for chassis construction and armour along with the modern principles that have evolved since.

Chassis design is a complex process that requires a good bit of trial and error.  The purpose of the chassis is to support all the parts of the robot and allow you to deliver your weapon to the opponent whilst being able to survive the resultant forces that will go back through your robot.  The requirements of a flipper differ to a crusher or spinner. 

Traditionally chassis design was a mixed affair.  The typical method was to construct an inner skeleton from steel box section.  Armour panels were bolted on the outside and brackets were welded on the inside to allow motors, gearboxes and weapons to be mounted. 

This technique was most famously used by Tornado.  You can see the red box section chassis with all components attached using various brackets.  Typical sizes for box section were around 25mm square with a 2mm wall. 

This is still a viable technique to build robots however there are a number of downsides.  The weakest point of your armour are the bolts holding it on.  You could weld the panels on but then this means that you are wasting weight with the box section chassis.  It can also take a great deal longer to create a box chassis and then cut all the panels for it. 

Formula one cars used to use the same manufacturing technique however they moved to a monocoque design.  So have modern robots.  A monocoque means that your armour and chassis are one and the same.

As you can see above, this is the technique we used with PP3D.  All the panels that form the robots body are both the armour and the chassis.  All the pieces were cut by a laser cutting company and designed to slot together with interlocking tabs.  These were then all welded together using our stick welder (we didn't have any gas available at the time for the TIG welder).

There are a number of advantages to this system.  It is much more weight efficient as you can make the panels at the front thicker than those at the rear to move the armour to where it's required.  You can make the shape much more efficient and it's much quicker to come together.  It also results in a far stronger structure.

The third method used is a bolted together bulkhead style design as shown with the insides of Pulsar above.  This method generally starts with a base onto which bulkheads are bolted.  These form an inner structure that the armour is then attached to.  Generally using this method the armour is made from as few pieces as possible to increase strength.  Another notable use of this technique is Terrorhurtz which survived an onslaught from Carbide with only a few scratches!  The resultant chassis is strong, not as strong as a welded chassis but you have the advantage that it can be taken apart and individual pieces replaced.

The majority of modern robots use a monocoque or bulkhead system of some variety with every robot that made it to the final 6 of Robot Wars 2016 using the techniques.  We would therefore recommend incorporating it into your own designs.

For this section we will look at each material available to you in turn and discuss where they have been used successfully and otherwise in the past.

Mild steel is a great material.  It comes in a whole range of shapes and profiles and easy to machine with handheld tools and a bit of patience.  You can also easily weld it with a cheap welder from Aldi or Lidl for around £40, some welding rods (ebay is a good source) and a bit of practice.  When using an arc welder, make sure that your rods are kept dry.  If they get wet being stored in the garage or shed an hour in the oven at 120 deg C will dry them out.  If you have access to MIG or TIG welding equipment then this can easily be welded with either.

It's very useful for making internal brackets for the robot.  We wouldn't advise using it for armour though as there are far better materials available for not much more in price. 

If you do a quick google search chances are you will find a number of suppliers relatively close to you and the majority will deliver.  We'd always advise getting a few quotations as prices can vary between suppliers.  We would also recommend giving any exposed mild steel a quick spray with some WD40 and a wipe down with a rag as even if it is stored inside in the garage or shed as it will gradually form surface rust. 

Stainless steel as the name says, doesn't stain or tarnish easily.  It won't rust up in the same way that mild steel will.  It is stronger than mild steel and requires a bit more patience to machine.  It is available in a more limited range of shapes and profile but can still be found in plate and sheet.  Due to the extra costs involved with stainless steel for a relatively soft material there isn't much we would recommend using it for.

These are the materials you will have heard all about from the latest series of Robot Wars and that's because they are the go to materials for a lot of robot builders.  They are all iron based like the steels mentioned previously however they are designed to be used as wear plates.  Wear plate materials are designed to be used in industrial applications where they are subjected to heavy wear such as JCB digger buckets and truck bodies used to transport stone in quarries. 

Hardox is the standard go to of these materials.  It is actually a trade name of the Swedish company SSAB and so other companies have equivalent products such as RAEX.  Weldox is a material from SSAB which as it's name suggests is better for welding.  In actual fact it is merely better at retaining it's properties during heavy welding processes.  Essentially all the wear plate materials begin to lose the material properties when subjected to high amounts of heat.  It is also not available in the same thin sheets thicknesses that hardox is available in.  Typical armour on a heavyweight is anywhere from 3mm to 10mm depending on the location on the robot.

Armox is the military grade equivalent that is used in armour for military vehicles.  Due to this it is far more expensive and more difficult to get a hold of than hardox and weldox.  It rarely makes sense to use it.

When ordering hardox you will see a number appear in the description.  This will be 400, 450, 500 or 600.  This refers to the brinell hardness of the material.  We'd recommend having a read up on this property via google to properly understand it but essentially the higher the number, the harder the material.  All grades of hardox will stand up to the majority of robot applications.  The higher grades are far more difficult to machine and are typically not available in the thinner thicknesses that we require.

When it comes to machining hardox, it can be welded with stick arc, TIG and MIG using standard filler material as you would with mild steel.  Cutting and shaping can be carried out with an angle grinder with a disc suitable for ferrous material.  Drilling can get a little more difficult.  We would recommend using either cobalt drill bits or bosch all purpose drill bits.  Best to use a pillar drill with as slow a speed as possible.  All of the wear plate materials can be laser cut, water cut and plasma cut.  We used a mixture of laser and plasma cutting in PP3D.  We will discuss manufacturing in more detail in a future post.

Titanium is a great material when used in the right application.  It is exceptionally expensive but very strong.  The easiest way to tell if you are working with a piece of titanium is to touch a grinding disc to it.  Titanium will give you a characteristic bright white spark whereas steels give a yellow orange spark.  With experience you can also tell due to the weight of the piece.  Titanium has a density just over half of steel. 

There are a number of grades of titanium.  The most useful to us is grade 5 titanium.  This is the grade that the majority of titanium is manufactured in worldwide.  It has great strength characteristics and is well suited to armour applications.

It can and has been used for armour in the past but sourcing it without breaking the bank can be a real issue! 

Machining it is an interesting affair.  You can use an angle grinder to cut and shape but just be aware that the sparks are hotter and will set materials on fire more readily.  We have in the past had titanium fires from excess material when turning it on a lathe.  The only thing you can really do is to walk away as a titanium fire creates it's own oxygen and will keep burning intensely.  When drilling use sharp HSS bits and flood the area with coolant.  Titanium tends to gum up when drilling if your drill bits aren't sharp.  If you want to tap a thread into it, use a high quality spiral tap.  Otherwise you will likely snap the tap.  We will discuss this further in a future post and how it nearly ruined our chances of getting on Robot Wars!

Aluminium is an excellent material to use in the construction of combat robots.  It's exceptionally light, easy to work with, strong and it won't break the bank.  It's best used in internal applications.  Everything from bulkhead supports through to pneumatic components can all be made from aluminium.  It shouldn't be used as armour as it is far too soft for that application.

Aluminium can be found in a large number of grades.  Some are easier to machine, others are easier to weld and some are stronger than others.  We would recommend researching the various grades before purchasing.

In PP3D we used aluminium in the custom bearing block housings that we machined up to support the disc shaft. 

It can be machined with a wide range of hand tools and is very easy to drill, turn and mill.  It can be welded but you will need special equipment to do so.  Aluminium can be tapped and will hold a thread which makes it easy to use bolts in the internal construction of a robot. 

Plastics are an interesting topic in combat robots.  They can be very useful due to their very low density resulting in lightweight parts but they have to be used in the right ways.  Nylon is a material that is very good for structural applications.  It is a slippy plastic that is very difficult to bond with adhesives but will hold a thread and so can be bolted together.  You can also "weld" it with special equipment which melts the plastic to bond it together. 

Nylon has been used successfully in featherweight robots for years however it has still to be fully proven in a heavyweight robot.  We wouldn't recommend it for armour.

HDPE is a softer plastic which works well in armour applications.  It's lightweight but very good at absorbing huge amounts of energy which makes it good against spinners.  It is easy to machine with basic woodworking tools and is very cheap.  It won't however hold a thread for bolts and so insert nuts should be used or it should be bolted together onto another structure. 

This was the material that Gabriel was made from in the recent series of Robot Wars.

A clear plastic that was used a lot in the old days of Robot Wars.  There are various reasons why but essentially we wouldn't recommend using it in a new build.

In summary there are a variety of options available when it comes to chassis design.  All have good points and bad points.  The design of the chassis that you use will depend on what experience, tooling and equipment you have available and also the weapon you plan to incorporate.  With materials again there are a huge range available but you don't necessarily have to have a huge budget to build a competitive machine.  The chassis on PP3D was one of the cheaper elements and was assembled using a stick arc welder!  If you have any questions about a design idea then by all means drop us a line and we would be only too happy to discuss through your options.

Want to support PP3D and get your name on our new discs for a second series of Robot Wars!?  Then check out our kickstarter

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Time for part 2 of our "So You Want To Build A Robot For Robot Wars" blog looking at the insides of a Robot Wars robot.  Previously we looked at the batteries and speed controllers.  Now we will look at the remainder of our schematic.

Electric motors are again a topic that we could spend an entire blog discussing but we will look to give you the most important information.  The motors we are discussing here are those we will use for a drive system.  They tend to have different characteristics from those you would use in a weapon system.  We will also focus entirely on DC brushed motor options as the brushless option is still very experimental with some of the most experienced teams and is therefore not recommended for the new builder. 

If you are not experienced with the general workings of a DC electric motor then we would highly recommend carrying out your own research on this topic.  There are dozens of websites that do a far better job of explaining this than we could do.

Traditional options
In the older series of robot wars the go to motor for 90% of teams was the 24v bosch 750GPA motor.  This motor was used in truck refrigeration systems and would produce 750w or roughly 1hp.  The motor could have several modifications made to make it battle hardened.  Unfortunately this motor is no longer manufactured and finding them is almost impossible although they do pop up from time to time.  We would recommend avoiding it simply because replacements are difficult to come by. 

Another traditional option that is actually still in production is the Iskra 24v 800w motor.  These were used by a few teams including Team Typhoon.  Slightly smaller than the bosch 750w they were also completely sealed so didn't have to worry about getting dirt inside.  They are typically used in hydraulic systems.  Again we wouldn't recommend using them these days purely based on the price increases that have seen new versions of this motor cost upwards of £200.  There are other more cost effective motors available to the robot builder nowadays.

Other options previously used include wheelchair motors and engine starter motors.  Whilst these can be picked up cheaply, we wouldn't recommend using either.  Wheelchair motors are typically geared to no more than 4 or 5mph on an 8 to 10 inch wheel.  Modern robots need to move much quicker than this around the arena.  So the only options are to use exceptionally large wheels like chimera did in the 2016 series or accept that you will be run around by every other machine in the arena.  Starter motors draw huge currents and are not designed to be run for more than a few seconds at a time.  Speed control on these is therefore exceptionally difficult.

Modern options
There are mainly options available to the modern roboteer although a few require importing from the USA which obviously increases the price a little.

The motors that we use in PP3D are the NPC T64 motor and gearbox (we will look at gearboxes and gearing in a separate post).  These are made for wheelchairs however they are designed for use in wheelchairs for bariatric care.  This means that they are more powerful and robust than your typical wheelchair motor.  They also come in a T74 variant that is slightly more powerful.  The T64 version is more than adequate for heavyweight use.  There are also a number of bolt on options to connect to the output shaft although be aware that the threads are imperial.  Suitable bolts can be found easily on ebay. 

Another well used option are the ampflow series of motors.  These come in many variants.  The main differences in the various models being the type of magnets used in the motors.  Some variants use cheaper ferrite based magnets whereas the real expensive powerhouse motors use rare earth neodymium magnets.  These are incredibly powerful producing several horsepower in a tiny package however they can get quite pricey and all version require additional gearing.  There are bolt on gearboxes available for these from both ampflow and team whyachi which can be handy for a quick set up. 

If you are on more of a budget and looking for options in the UK then there are a few available.  These include 36v 800w and 1000W scooter motors which are available on ebay and can be bought cheaper if you ship them from china although this comes with a longer delivery time.  Some teams have been recently buying these to experiment with and have found them to work well.  Just make sure you don't get anything below 750w in terms of power rating as it will struggle to move your robot. 

Another option is from an Italian manufacturer called Movimotor.  They have motors available that are essentially drop in replacements in terms of power and fitment as a bosch 750 GPA however they are a bit heavier and again need some battle hardening but have been used in the heavyweight robot Brutus successfully.  Movimotor provide a whole range of options so it would be best to contact them directly for specifications and pricing.

Traditionally roboteers were stuck using the 40Mhz frequency radio band for ground based vehicles.  The 40Mhz kit meant that you had to have a huge aerial sticking out the transmitter and robot (obvious when you look at the old fights on youtube) and they were very susceptible to interference.  In the old series, radio problems were a major problem for a lot of machines.  The old sets were also very expensive with a decent setup costing upwards of £200 plus.

You will have noticed that watching the new series, radio issues were never a problem.  This is because we have all switched over to the 2.4Ghz radio frequency.  The radio equipment now uses tiny aerials that can be tucked away behind panels and wiring without fear of losing control of your machine.  We rarely worry about the location of the receiver in the robot.

There are two parts to your hobby radio gear, the receiver (the bit in the robot) and transmitter (the bit you hold to control the robot).  On 2.4Ghz the transmitter and receiver bind to one another so that they will only ever response to each other and not another set. 

 You can see on the receiver on the right in the picture above that there are a series of pins.  These pins are the sockets that your speed controller plugs into.  From these pins the speed controller gets it's signal to let it know when to drive the motors and by how much.  They use a standard servo plug which has three lines, a positive, a negative and a signal line.  The colours used for each of these lines can change from manufacturer but they are always the same three connections.  In the image below, the negative is black, positive is red and signal is white.

Each set of 3 pins on the transmitter is known as a channel.  Each one of these channels corresponds to a control on the transmitter.  So for instance, the sticks in the middle each have two possible movements (up and down, left and right).  Each of these movements is a channel.  So that's 4 channels.  You can have extra channels which can correspond to extra switches on the transmitter shoulders.  The Dx6 shown in the image above has 6 channels which is more than enough to control a robot and weapon.  This is a decent set which won't break the bank but will give you all the functionality you need for most robot designs. 

If you have an old 40Mhz or 35Mhz set that you have stashed away then it is possible to upgrade it and use it legally on the 2.4Ghz frequency.  There are conversion kits available from frsky which require a bit of soldering inside the transmitter but allow you to use your older equipment.  This is what we did for PP3D as we had some old futaba 40Mhz radio gear that was still perfectly usable.

There are dozens of other sets available but the most important thing is that they failsafe when signal is lost.  During the tech check that will be carried out on your robot before the competition you will be asked to demonstrate that the robot failsafes by running it's wheels and then turning off the transmitter.  It must stop within a few seconds to pass this test.  If it doesn't then you won't be allowed to compete.  Some cheaper radio sets won't failsafe properly.  Best to ask around on the FRA forum if the set you have in mind will be any good.

The rules state that each robot MUST incorporate a removable link.  This link should remove all power to the robot.  It should be removable by hand and without the use of tools.

You will have seen in the latest series that a problem in a few matches was the removable link coming loose.  While this may be a frustration for both builder and viewer it highlights a very important fact about the removable link.  That when it fails, it fails to a safe condition.

Typical removable links are made from a connector such as the anderson 175A or EC5s.  The connector has to take all the current that will pass through the various systems on the robot.  For the large spinners this can be many hundreds of amps. 

One half of the connector has a loop of wire connected to both terminals in the same connector which gives you a loop of wire you can grab to pull it out.  The other half is placed on the positive line (preferably) just after the battery and before the various elements of the robot that use the battery (as shown in the diagram at the start of this post).  Placing the loop in completes the circuit and pulling it out kills it disabling the robot. 

There have been a number of individuals on the FRA forum that have suggested a custom link of some description to stop the link falling out.  The big issue with this is, if you happen to misplace your link just before your battle (believe me, it happens) then you can still grab another robots link and run your machine as you are running with the same removable link.  A strip of duct tape over the link is generally more than good enough to keep the link in place.

If your robot is invertible you have to make sure that the link is accessible regardless of whether it's upside down or not.  If you have multiple links, such as one for your drive and another for your weapon system, these have to be located together on the robot so that the crew can deactivate your robot quickly and safely.

That's us come to the end of our basic diagram describing the internals of a basic rammer bot.  Hopefully the inner workings make sense as we have described them!  If you have any questions, comments or ideas for future blog posts then please put them in the comments below.

We are also running a kick starter to help us with upgrades to PP3D for a second series of Robot Wars.  If you have enjoyed our blog then please consider pledging.  Any help you can give means a huge amount to the team.

https://www.kickstarter.com/projects/583580427/pp3d-upgrades-for-series-2-of-robot-wars

You've had a play with some CAD packages and have sat through some tutorials.  That's all well and good but you need to know what parts need to go into a robot.  In this post we are going to look at the most basic of setups to keep things simple.  A simple rammer with no weapons.  Now of course this wouldn't be allowed on the show as you have to have an active weapon (it's in the rules) but we will build up to looking at weapons in later posts.

Please excuse the simplicity of our schematic below but it will give us a basis to talk through a basic robot.

No matter what battery chemistry is used, only batteries that are non spill are allowed in the arena.  This is to stop any accidents involving acids if the robot is tipped upside down.  Therefore the car battery that you thought was ideal to use I'm afraid will have to be put to some other use.

Older battery chemistries
Traditionally sealed lead acid (SLA) batteries, nickel metal hydride (Nimh) or Nickel Cadmium (Nicad) batteries were all that was available the robot builder.

Sealed lead acid
SLA batteries are very heavy however using batteries such as the hawker odyssey gave the potential for huge current draws.  If you used these in your robot you were typically looking at either the 13Ah or 18Ah versions which would give you anywhere from 12kg upwards of batteries in your machine to run on 24v which is a huge percentage of the weight limit.  This means less weight for weapons and armour! 

Amp hours
This seems like as good a point as any to talk about Ah or amp hours.  Essentially this is a measure of the capacity of a battery.  This is the number of amps that the battery should be able to give you constantly at the batteries rated voltage for an hour.  In a perfect world the battery would be able to give you double this current at 30 minutes and four times the current in a 15 minute window.  So for a 13Ah battery you would get 26A for 30 minutes and 52A for 15 minutes.  This isn't strictly true in the real world but it gives you an idea of how much current you can expect to get for a period of time out of a battery.

Nicad
Nicad batteries are no longer sold in the EU and so we won't even consider them as an option here.

Nimh
These batteries are still used by a select few machines.  They provide 1.2V per cell.  These cells are then linked in series to form larger batteries with typically 10 cells giving you a 12v battery.  Nimh can provide moderate current draws and require a charger with the ability to charge them.  They are however an outdated battery technology and not one we would recommend investing in.

New battery chemistry
Newer battery technologies relying on lithium are the go to choice nowadays for the robot builder.  The actual technologies available can get a little confusing due to the differences in chemistry and cell voltages.

As stated in the rules, lipo batteries need to have a fuse which is rated to below the burst current for the pack.  In the above diagram this would be located on one of the main lines coming out of the battery pack.

A123 or LiFePO4 (3.6V per cell)

The A123 systems were some of the first to come along when it came to lithium technology.  The first robots experimenting with them appeared in the arena around the 2006 to 2007 time.  The best source originally for these cells was from dewalt 36V lithium battery packs.  John Reid, the builder of TerrorHurtz does a great write up of the cells and how to put together a pack yourself here.

The other picture shows a modern equivalent pack.  The cells in these packs are long and flat. You will notice there are two thick leads coming out the top along with several smaller leads that all hook up to a plug.  The large leads are the positive and negative sides of the battery with the smaller leads being hooked up to each individual cell.  With lithium cell technologies it is important to balance the cells to make sure they are all charged within 0.05v of one another.  If they start to unbalance then you can end up with the entire battery pack at best reducing it's effective use quickly or at worst go up in flames.   Whenever charging lithium batteries they must be charged in a lipo sack.  This is a special sack that is designed to contain any fire if something should go wrong during the charging process.  These can be picked up cheap from RC stores and ebay.

The advantage to these cell chemistries in particular is that they are more stable than some of the other lithium based batteries.  The majority of the teams in the USA prefer to use these cells with tombstone using them to great effect.  They however can't provide quite as much discharge current as some of the other technologies below.  For this reason, PP3D robotics sticks with Lipo technology.

Lithium Polymer (Lipo 4.2V per cell)
These cells are the go to cells for PP3D robotics.  They have a higher discharge rate than the LiFePO4 cells and are typically around the same size for a given capacity.  You will notice these batteries also have main leads and balancing leads.

When it comes to all lipo cells, the discharge rates are typically given using the unit, C.  The same goes for the recommended charging rate for the cells.  To figure out the charge / discharge, you multiply the capacity figure by the C figure.  So a 8000mAh pack with a 30C discharge will be able to supply, 8000mA x 30 = 240,000mA or 240A discharge.

The cell count tells you the voltage of the pack.  By multiplying the number of cells (generally given the units "s") by 4.2V for lipo, you can figure out the pack voltage.

They also require balanced charging and must be charged in a lipo sack.  The downside to these cells is that they are more volatile than the other lithium chemistries.  This means you can end up in a chompalot situation if you aren't careful.  Thankfully this has never happened to us as we always ensure that we pad the batteries using foam (a £5 argos camping mat cut up works well) and ensure they are well secured with appropriately rated wiring. 

Speed controllers are a  complex topic that an entire blog could be devoted to.  However for the majority of roboteers there are a few things that you should know which we hope to cover here.

What is a speed controller?
Essentially a speed controller is the electronic interface between your radio receiver and the motors it will power.  They allow for variable control of motors rather than simple on / off control.  This is the part that people most worry about when it comes to robots but they are single housed units that require hooking up to a few inputs and outputs and you are good to go!

Selection
To keep things simple, there are a number of tried and tested speed controllers available for heavyweight robots.  We will stick to heavyweights as that's what Robot Wars is focused on.  Controllers that have been used successfully include,

- Vantec RDFR47E or RDFR36E (Dual channel)
- Roboteq (various models available including single and dual channel)
- Wotty (Dual channel custom controller made by Iain of Bigger Brother / Orte)
- Ragebridge 2 (Dual channel)
- Robot Power Vyper 120A (Single channel)

There are various other controllers available and by having these here it shouldn't be taken as an endorsement of any controller over another. 

When selecting a speed controller there are a number of things you need to be aware of,

- It's physical size - will it fit in my design?
- Will it run at the voltage my motors will run at?
- Can it withstand the current that my motors will draw?  Some controllers come with current limiting, some don't.  We can go into more detail on this in a future post.
- How will I shock mount it?
- How may channels does it have?  Channels on a speed controller essentially refer to the number of independent motors that the control is able to control.  A single channel controller can control a single motor whereas a dual channel can control two independent motors.  If you plan to have a motor either side of the robot which is the standard set up then you will need either a dual channel controller or two single channel controllers.
- Does it have a BEC (Battery eliminator circuit)?  Traditionally you needed a separate battery to power your receiver.  Nowadays it's much easy to either have a speed controller that will power the receiver or a separate BEC circuit.

All of the controllers on this list come with standard servo wires that will plug into any conventional hobby radio receiver which is what the majority of roboteers use.  We will go into more depth on the radio side of things in a future blog post

We are going to end this post here so that we can get it out and keep to our plan of one a week.

TO BE CONTINUED......

Like what you've read?  Want to support PP3D Robotics?  How about getting your name on the new discs for PP3D?  How about owning part of the robot that appeared on Robot Wars 2016!?  Then head over to our kickstarter!

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