ANTWEIGHT.CO.UK

 

Parts

In this section I will go over the basic parts required to build an antweight and list the various options available. I will also give links to parts suppliers.

 

Transmitter (Tx)

The Tx will probably be the highest initial payout needed to get into antweights, get a good one and it will last you a good number of years. In the UK we are limited to 2 ground frequencies, 27 and 40MHz. 35MHz is a reserved frequency for aircraft/helicopters so this cannot be used for antweight robots. 27MHz tends to be a 'cheaper' frequency and most Tx now use 40MHz.

Tx come with a different number of channels, the minimum required is 2 (1 for each wheel). To get a future proof Tx go for 3 or 4 channels. This will allow you to have a spare channel for a weapon.

When you buy a transmitter you tend to get a receiver, servos, NiCad battery and charger bundled. Depending on the store you can get a bare transmitter with just the NiCad battery and charger, this will save money (normal receivers and servos are too heavy for use in antweights).

The last choice is mainly down to cost, either a basic Tx or a computerised. With the computerised Tx you can store multiple model memories, this allows you to keep settings so you can easily switch between your ants which is very handy between rounds. A computerised Tx also allows inbuilt mixing functions (I will go into details later), this saves about £13.

I used to use a basic Futaba Skysport 4 and had no problems with it. I then moved onto a Futaba 6EXA which is far superior but double the price.

Receivers (Rx)

As mentioned above standard Rx are too heavy for antweights, they can weigh 30-40g. Considering the antweight weight limit is 150g you can see this is pretty heavy. A number of companies produce micro receivers varying in weight from 3g, however at this weight the cost is fairly high. A good compromise as aiming for a sub 10g Rx, an old favorite used is the Hitec Feather Rx weighing 10g (with crystal). I use these all the time and have had no problems whatsoever. The downside is Hitec appear to have replaced them with the HFS-05MS, this looks to be roughly the same, weighing 8g (without crystal). On the good side it is £16 from SMC www.sussex-model-centre.co.uk

Crystals

Crystals are used in both the Tx and Rx and control the exact frequency they communicate with. With the base frequency of 40MHz you have a number of sub-frequencies, for example 40.825, 40.835, 40.845 When you buy crystals you need a matching pair of Tx and Rx, it is good to have at last two different sets to prevent clashes.

There are mainly two types of crystals, single and dual conversion. With the micro Rx they tend to use single conversion so when you buy the crystals go for single conversion.

There has been a lot of talk about mixing Futaba/Hitec crystals with Hitec/Futaba Tx and Rx. Personally I haven't run into any issues using a Futaba Tx and crystals and a Hitec Rx, bear in mind there maybe compatability issues.

 

Mixers

If you have standard Tx and use servos for drive a mixer is a nice thing to have if you have £13 and 5g spare.

Shown is a GWS mixer.

As mentioned below modified servo's can be used to drive an ant. With a wheel at each side of the ant the type of drive is called 'independant drive' or tank drive, this means both wheels are being driven independantly. As a contrast RC cars have 1 drive motor and a servo controlling the steering, the bad point of this is the turning circle. With independant drive the turning circle is 0, turning on a coin is possible.

Now for that mixer explanation.

This is how a basic ant would be driven, the Rx is connected to the drive servos.

This means on the transmitter (Tx) you need 2 sticks, one goes forward and back and the other goes forward and back. Not many Tx do this and if it does it normally has a ratchet on one channel so it won't return to 0 when the stick is let go.

For a RC car Tx this can be very confusing. You have to either swap one of the sticks round on the Tx so it goes forward-back or you have to learn to drive so left-right goes back-forward.
By including a mixer driving is made easier. The mixer takes the 2 forward-back channels and 'mixes' then into a forward-back and left-right channel.

So on the Tx when you press forward on the stick the ant goes forward and the same with reverse.

When you go left the clever bit kicks in as one motor goes clockwise and the other goes anti-clockwise so the ants spins on the spot.

This is very good if you have a RC car remote as it will control an ant without modification or confusion.

The only bad point about mixers is if you push forward 100% and turn it won't turn as you expect due to the way the mixer handles the inputs. You have to decrease the 'throttle' to say 80% and turn, this will allow the ant to turn as you want.

 

If you plan to use motors rather than servos and something like one of the Sozbots controllers then a mixer isn't required. See the drive section for more about this.

 

Batteries

Over the past few years battery development has come on a huge amount. When Antweights started in 1999 the only choice for rechargeable batteries was NiCad (Nickel-Cadmium). This then progressed to NiMh (Nickel-MetalHydride), which could store more charge for the same weight. Now both these types have been replaced by the newest LiPo (Lithium-Polymer) type of batteries. These are lighter than the earlier types and can store more charge allowing the ant to run longer.

The downside is that LiPo batteries are dangerous when pierced and require a special charger (NiCad and NiMh batteries could be charged from the Tx charger). LiPo chargers are a lot cheaper than they used to be, they vary from £15 to £55. I use a simple charger and have no problems. You can also buy balancing chargers, with 2 cell packs (see below) this balances the charge between the cells.

Battery packs: NiCad and NiMh batteries each have a voltage of 1.2V, battery packs are typically 4.8 or 6V for antweights. With LiPo batteries each pack contains either 2 or 3 cells, each having 3.7V. This means the pack produces 7.4V or 11.1V, you have to be carefull with higher voltages as some servos and Rx are only meant to run at 6V rather than 7.4V (11.1V will most likely kill them). I have put together a rough list of whcih servos are happy at 7.4V here.

Capacity: Each battery pack has a capacity and current rating. The more the current rating the longer the ant will run before needed a recharge. The higher the capacity the more current it can discharge, for spinners a high discharge is essential. The discharge capacity is listed on the pack as C, this means how much of it's current it can discharge, I have a number of LiPo battery packs, for example:

Kokam 640mAh 27g 2C 7.4V

Litestorm 300mAh 19g 20C 7.4V

E-Tec 450mAh 25g 10C 7.4V

For the first battery the current rating is 640mAh (milli Amp hours), this means the batteries will discharge that amount or current for 1 hour. The discharge rating is 2C, meaning its maximum discharge is 2*640mAh so 1280mAh (or 1.28 Amps). For spinners 1.2A is a small current, you really need a 10/20C battery. I use the 640mAh batteries in ants where I don't need a high discharge but have space weight, this allows me to have a number of fights before I need to charge them.

300mAh 7.4V 20C 640mAh 7.4V 2C

 

Two suppliers of LiPo batteries are www.overlander.co.uk/ and www.robotbirds.com/

 

Drive

Servos:

When antweights started the only method available to drive the ants was to use 360 degree modified servos. My favorite was the SD200s, I still use these on Odyssey but they are proving a bit old now so need replacing. A desciption to 360 degree modify a SD200 can be found here. Another modification to the SD200 is to 'speed mod' it, this involves removing a gear and cutting the servo body. I won't go into details as the SD200 is an old servo and several servos have come along and been better suited for antweights. One is the GWS Park HPX series. These servos are very easy to get running at 360 degrees, are very fast as standard and run fine at 7.4V A list of recommended servos is here. For a rough price/weight comparison the SD200 are £14 each and 16g, the GWS HPX/F is £13 and 19g.

Motors:

In the past year the move has been away from using servos as drive and more to using geared motors and speed controllers. This is more like a smaller version of RobotWars. Part of this is due to the US antweight scene (US ants weiging 1lb or 454g as opposed to 150g UK ants). An online shop selling US antweight parts is www.Robotmarketplace.com

The favorite type of motor appears to be the Sanyo or Sanyo clone, these are geared motors and weigh approx 8/9g each. They are very powerfull and easily suited for ants. A cheaper supplier in the UK is www.fastcomponents.co.uk/ which sells the motors for £5 each.

There are 2 slight downsides to the geared motors, the first is that the output shaft is just a plain 3mm shaft, the second being an expensive speed controller is required. With servos you can attach wheels to the servo horn (bit of the servo that turns round), but with the gearbox you just have a small output shaft. There are two ways round this, first is to use wheels that fit onto the output shaft, the second is to use a 3mm shaft adapter that a wheel can be attached too. Both of these solutions are available from www.Robotmarketplace.com

Yellow servo horn from an SD200 servo connected to deodorant tops make good wheels.

 

Next is the speed controllers, again we go to www.Robotmarketplace.com. There are 3 manufacturers of antweight speed controllers, Sozbots, Barello and Scorpion. At least 1 person has had issues with the Barello speed controllers and come across a lack of support, so far no-one has complained about the Sozbots controller. As mentioned above one of the Sozbots controllers has mixing built in, all have BEC (battery eliminator circuit).

A BEC means you can connect a 7.4/11.1V LiPo battery to the controller and the Rx gets 6V from the servo connector lead, this prevents the Rx dying.

The Sozbots controller are $60-65 and 14g so roughly £40. With motors that means £50 (without postage). As you can see this is higher than £28 for 2 servos, servos do burn out however so you need to look at the long run.

Armour

You can use almost anything as armour, well almost. In the rules it states 1mm is the maximum armour thickness, and that the body can't be machined from a single piece of metal or made from a single bent piece of metal.

Armour can include the following:

Cardboard, cheap, easily available, takes damage fairly easy, easy to replace. 2mm mounting card is good

Plasticard, available from model shops, easily bent and shaped, semi-cheap, easily cut

Polycarbonate, 1 step up from plasticard. 1mm polycarb is normally sufficient as armour. Easily cut and bent

Steel, heavy and hard to cut without tools

Aluminium, lighter than steel, easier to cut and bend. Can take damage fairly easily

Titanium, harder than steel, ideally need tools to cut and machine it. Easily blunts jigsaw blades. Breaks if bent in a tight bend. Fairly expensive. Used for spinner weapons.

Spring steel, I obtained a sheet of spring steel from an ESD screen (Electro-Static Discharge) and used this as amour. It is thin enough to cut with strong scissors and is strong against spinners as it is meant to 'spring'. No-one else has used this, just me.

 

Weapons

This is the section everyone wants to read. Depending on your building ability and amount you have to spend, weapons can be added to your ant. I will try to briefly list the various weapons available.

Pushers:

Pushers rely on just pushing your opponent around and out of the ring. Ideally you need lots of traction and that the ant works both ways up if it is flipped. They may seem boring but pushers have become popular recently, for example Dynamould has just won AWS21, the almost identical Dynamite won AWS19 and Defiant has always been near the top.

As you can see from the pictures all have lots of grip (4 wheels and tracks) and armour (polycarbonate and titanium).

Lifters:

Lifters tend to be lighter versions of flippers, the extra weight being used for a lifting servo. A lifting ant is fairly easy to build and drive and is a good start for an antweight builder. There have been a few good lifters in the past few years, Odyssey is one of them.

If you are using servos for drive you want want to use a different weapons servo. For example the GWS Park HPX servos are good for drive but the BMS 380Max is a good weapons servo. It has metal gears and lots of torque, it can't be 360 degree modified but is ideal for a lifter.

Crushers:

There have been a few crushers in the history of AWS and have been semi successfull. With the weight it is hard to get the crushing power required to do any damage, what crushers are good at however is pinning the opponent so they can be driven to the edge and pushed off. Recently however the move has been to make lower wedge shaped ants, this makes it very hard to grip your opponent.

My ant Anteater shown below is an example of a crushing ant.

Axes:

With antweights axes don't tend to do too much damage due to lack of weight. If you look at Anticide the axe is used to pin the opponent robot so it can be driven off the arena. Damage is negliable but the axe is very usefull.

Spinners:

I could almost do a whole page on spinner, they look good and can cause a lot of damage. Due to this all spinner battles are done in a polycarbonate arena due to safety, in antweights safety comes first, fun 2nd.

First off I need to explain about motors, there are 2 seperate types. The conventional motor with 2 wires, connect a battery and the motor turns (brushed). These type of motors were used on spinners until brushless motors came down in price. Typically type 280/300/electric slot car motors were used. The motors were fairly cheap from £5-20, a simple speed controller was also required at under £15.

The speed controller is required to connect to the receiver, battery and motor. This allows to to vary the speed of the motor which is usefull at some times.

More recently brushless motors have come into their own and are becoming cheaper by the month. Whereas a brushed motor is controlled by a varying voltage to the motor a brushless motor has 3 wires and is controlled by rotating pulses between the wires. Brushless motors have a lot more torque than previous motors, the downside being the cost as they are still fairly expensive at about £30.

As well as the motor a brushless speed controller is required, these can cost upto £60. If you shop around you should be able to get a decent brushless speed controller for under £20.

Once you have the motor and speed controller you will need to have a spinning blade. From experience blades are a bad idea, a scalpel blade travelling at 28,000 rpm (revs per minute) easily breaks when it hits something. It is better to have something like a small circular cutting disk (minicraft for example). Another way is to cut a blade from a sheet of metal, titantium works well as it is doesn't bend too easily when hit.

The cutting disk can be connected to the motor in a variety of ways. It can be screwed to the motor itself as some of the brushless motors allow this. Otherwise you will need a shaft adapter, something like an aircraft prop shaft adapter works well in these situtations. www.robotbirds.com sell 3mm shaft to prop adapters, all you need to do is to make the hole in the cutting disk so it can be attached to the shaft adapter.

When you have the cutting disk spinning it may wobble, this is due to it not being balanced. The ideal way is to balance the blade on a point and you can see which is the heavy side, file this until it doesn't tilt too much. This is painfull but if balanced correctly the weapon will work a lot better.

Again www.sussex-model-centre.co.uk www.robotmarketplace.com and www.robotbirds.com sell motors and speed controllers.

 

All of the above is just meant as an overview of the parts used in antweight robots.

If you have any questions look at the Robotwars101 forum Have a look in the question and answer section first then post your question. Normally the question should be answered within a day or quicker.

 

A few years ago I made an example of how to build an ant, to see it go here:

 

Howto build an antweight

 

 
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