New guy here, advice appreciated

Hi.

Since childhood years spent watching Robot Wars I have wanted to build a fighting robot, and now that it is back on TV I have decided now is the time to do it. Slight catch though, I have absolutely zero experience with building something like this. I have experience building stuff in general, being a hobbyist woodworker and a builder by trade, but my electrical experience ends at plug sockets and light fittings.

Through searching the internet and browsing this forum I have garnered some basic knowledge about where to begin and plan to have a practice run by making a featherweight wedge bot, this experience should teach me the basics about RC transmitters/receivers and ESCs (which I had never even heard of before a few days ago).

For this practice bot I want to try and keep costs to a minimum, I don't plan on entering any competitions with this bot, it's more to just show myself that I can make something that drives around to prove to myself that this is something I'm capable of learning how to do.

So far I have ordered a couple of cheap drills for the motors ( http://www.ebay.co.uk/itm/131435563121 ) as this seems to be a cost effective way of getting good enough motors. Now I'm into the realms of stuff I know nothing about. I need a transmitter and receiver, batteries and ESC, this is where I need advice.

For an ESC I'm currently leaning towards this one: https://www.technobotsonline.com/sab...er-for-rc.html
it seems a tad expensive to me, but never having bought one before I have nothing to compare it to. From what I can tell it should do what I need it to, but if anyone can recommend an alternative that might be a better option I would be appreciative.

As for transmitter and receiver I have no idea what to go for so any suggestions as to a good entry level purchase would be very helpful.

Batteries are again an area I require advice as to what to buy, I get the impression LiPo batteries are the way forward but after having a browse and being totally overwhelmed by the many different types with lots of different numbers and letters in their names I have no idea what to get.

If anyone could advise me on what to go for here I would really appreciate it, so far my foray into robot building has been halted by simply not knowing what to buy, once I have parts that I can start putting together I hope to be able to pick up the pace.

Many thanks,

TJ

Can't post a lot (have to go to work soon), but others are better qualified anyway.

Do go to an event.
Make sure to put your electronics really safe, since you'll want to reuse them in your "real" bot, it's likely you'll want to do major changes to the chassis afterwards, anyway.
i'm new to this, too, and had my first event last weekend. also tried to get just something that drives together.
And honestly... what i've learned there (just from looking at others, them helping me putting it back together and stuff like that) was worth more than months of internet searches.

Hi, Welcome.

The Sabretooth 12a dual esc you linked is too light for use in a feather. Your motors will happily pull 20a and upwards. For reuseability I'd recommend looking into a tz85 Botbitz controller. These will run just a single side (but can handle two motors per side) so you'll need two.

TX/RX wise. I'm very happy with my spektrum dx6i and Orangerx 620 receiver. Not the cheapest option but not crazy money either. This combo will do all the safety features and can be used with 10 different model settings should you end up with several machines.

If you can wire a plug and understand the difference between positive and negative on a battery you know enough to build a bot! As Niels says the Tz85s are great controllers. They are actually not made to control brushed motors like drill motors by standard but have to be reprogrammed. You can buy them reprogrammed from a few sources.

Another speed controller option that I've used in a heavyweight but would be well suited for a featherweight is the ragebridge speed controller. A little more expensive and they have to be imported from the US but if you look after it, it should run any featherweight you come up with.

For radio gear the standard go to these days is the spektrum DX6. Again it may seem pricey but radio gear is another thing that can move from robot to robot easily. Others have had success with cheaper sets from hobbyking but I can't comment on how good or bad those are.

There are a few figures with lipo batteries to pay attention to. The cell count, usually denoted by a number then "s". This tells you the voltage of the battery pack. So a 5s pack will have a voltage of 4.2v (cell voltage) x 5 = 21v

The capacity of the pack tells you how much energy it can provide. A 3000mAh pack will provide 3A constantly for an hour, 6A for a half hour, 12A for 15 minutes etc. For featherweights, packs around the 3000 to 4000mAh size will be ideal.

There are two other figures for lipo packs and these refer to charging and discharging rates. These are denoted by a number and "C". So a 3000mAh pack with a discharge rating of 30C will be able to discharge 90A. You also find that there will be a constant rating and a short discharge rating. Essentially the short term discharge is what can be given for a few seconds whereas the constant discharge rate is what can be provided without damaging the battery pack. The charging rate is also given in C. Typically it will be around 2 or 3C. This means for our 3000mAh pack, you can charge it at up to 9A. This would give a full charge from dead in around 20 minutes. Useful in the pits when you are needing a quick turn around. Slower charging is recommended when you can do it though as it's better for the batteries.

Brand wise, I like optipower and we get a sizable discount with FRA membership. Zippy and nanotech have also been used and are cheaper but people have had cell failures with these before. For a first go machine, these should do the job fine. Just make sure to get a lipo sack (search ebay) to charge them in.

I would also recommend attending a live event even as a spectator. Get chatting to the roboteers and they will be only too happy to show you what they have put together and why. It will give you a much better idea of the forces and sizes of bits and pieces involved.

Phew that's a big post!

Thanks for the advice everyone, I'll do a bit of shopping when I get back from work and keep you posted as to how it's going.

As far as live events are concerned there's a couple coming up near me that I'm hoping to go to, one in portsmouth and one in Guildford.

So, got a bit more time on hands now:
Another idea for an esc would be the ones most german roboteers use for brushed drives:
http://www.ib-fink.de/
Either the 4_5 for drive only, or the 4_3 if you also want to use a brushed weapon motor (hopefully a version with brushed drive and brushless weapon will be out some day, but not yet).
Can drive both sides at once (would take the XXL-version (80 amps) if you want four motors), if it says 80 amps, it is more likely able to handle 100amps or more if you cool it. and you can configure more things than i even knew existed...

might be twice as expensive than the botblitz, but you just need one, not one for each side. Also got a mixer included, if you want to drive with just one stick. And if space is tight, they are handmade for you when you order them. for example i got one with the fuse of the XL-version, but only cooling from the standard version to make it flatter. Used it with two drill motors (combined 40 amps stall current minimum), burned one motor while trying to free me from lying on the side, but ESC not even warm.



Also, you should always look after:

Voltage: Motor should be labeled same volts as battery (motor having more would mean not using its potential, motor having less meaning overstressing it. can be done with most motors to some extend, but too much and it will burn out.)
ESC fitting to that. Most have some range of voltage labeled, just stay inside that.

Amps: Provided with their right voltage, motors will take the amps they need. If the ESC can't handle that, it'll get hot and possibly burn out (or its fuse, if it has one). Same with battery, you'll have to look at the C-rating to see how much it can handle (as typhoon mentioned). Really... never use motors stronger than you can handle. it doesn't do good, but expensive smoke and flames. better use smaller motors and possibly even burn them, they are the cheapest part of the main electronics.

If you use multiple ESCs, you'll have to cut one of the small wires to the receiver on each esc except one. But i always forget which colour, you'll find it here multiple time if you search for "BEC". The receiver gets its power from the ESC, and with multiple power sources it will likely missbehave. So cut one of the three small wires, it will not get power from those but still send signals to the receiver, problem solved.

For radio gear ebay can be a good source, if you don't mind it being used and don't have to rush.

Don't forget a link (and a LED) in your design, and make sure it has a failsafe. Even if you don't want to go to an event, it is really good to make sure if the bot will move or not when transporting it or wanting to open it. Got a nasty accident with an RC car as kid, when it somehow suddenly started to drive while i had it in my arms walking up a stair. and that was just one of these small buggies, you don't want that with 13.6kg of robot. And you also don't want your batteries in the radio to fail and your bot driving amok down the streets where you possibly tested it.

I feel like I should say something here because after an 18 month lay off I've been building a new feather and so speedo's are something I've been looking at a lot.

I've been using Sabertooths for ages but they are too dear now and I won't be buying any more.

Back in the day I bought a few for around 30 quid each, and to be honest they've been alright. All of them still run ok-ish but the 2x12 will overload on drill motors. 2x25 would be better. I just looked and a 2x25 controller is about £140 and I nearly fell off my chair. They are great, easy to use, literally do everything you need in that the cables screw in easily with no soldering, they supply power to your receiver, and have basic jumpers so you can set them up without needing a laptop. They have overload protection so are pretty much impossible to cook and showed me that even though I've gone off those ESC's, the features they came with are what I would want going forward as building a robot with them is effortless.

So going forward, I will be looking for a cheap dual motor controller that has mixing built in, easy connections for batt and motors, powers a receiver, and is simple and robust. There are a few people that swear by using single controllers because they're cheap and have high current ratings for the money, but from experience they are a ball ache if your a bit lazy like me. For starters you have to mix on the handset which some of the single controllers struggle with. Some you need to start cutting receiver cables because they supply too much current and blow it up. Some need new software before you can use them with drills. Some have naff cabling that crumbles when you try to solder it.

That is not to say they aren't good controllers, but I feel strongly about something being simple and easy to use, and I think a dual motor controller with all the features works a lot better for newish builders.

Final advise is read all the build threads and go and watch a couple of events before you build anything or buy anything. Can't stress this enough. You will learn a ton. Make a note of what everyone uses and how they build, and you will start to see patterns of what works and what doesn't. Then once you've sussed the basics you can get creative.

Davimi, then the IBF's do a great job. Connections are Industrial screw terminals, so connecting it all is as easy as possible.
Rating is at least 20a per channel continous, and those are German conservative amps, not Chinese optimistic ones.

Mixing is build in, and it's fully programmable with a simple USB converter and the freeware downloadable at Reiners site. Even has options to fit a gyro direct to the board.

Pricetag is about 2 TZ85's.

OK so I've bought a cheapish tx and rx from Ebay, will probably upgrade to a Spektrum in the future but this will do for now.
( http://www.ebay.co.uk/itm/232108142107 )

I'm looking at batteries right now, my motors can take 18v, so should I be going for a 5S battery? I've seen some 4S I like but I feel like 14.8v wouldn't be getting the maximum potential out of my motors.

Back to ESCs, for running just the two front wheels (will consider 4WD in the future but want to keep things simple for now) with my drill motors, would two botbitz 30a ESCs be suitable? I'm really trying to keep cost at a minimum here.

Thanks for all your help so far everyone :)

Depending on your design, powering the back wheels could be more effective.
If someone gets under you (absolutely possibly, even if you try to stay low to the ground) front wheels are off the ground almost instantly, so you don't have any control left. Depending on size, positioning etc. you might still have back wheels on the ground, allowing you to drive backwards down from your enemy before you get shoved into the pit or such.

Anyway, 5s battery for 18v motors is what is mostly done, i think. the motors should have no problem to handle that, at least not with the right gearing (which you will have on drill gearboxes and standard sized wheels. just don't use absurdly bih wheels like i did and land on the side...^^ remembers me i should upgrade my build diary)
I don't know what motors exactly you are using, but 30A botblitz per side for drill motors sound okay, but only just.
If you gonna push a lot (stall amps are way higher than usual amps) they might get hot, but i didn't use them, so better wait for someone who did.

The main question for me here is: do you want to put this practice bot, after it's done its job into a shelf or such, or do you want to reuse (internal) parts for a "real" bot later?

first option: take the cheapest parts you can, even if you drive on the street and try to do tests, those tests will likely be softer than the arena, so no big risk to burn anything. and even if: it was just practise.

second option: take something good right away, better buy good once than to buy cheap a bazillion times.
At least on the esc and battery, which will likely be the most expensive reusable parts in your first bot.

I advise using NiMH batteries for a beginner. They are easier to charge, simpler, safer and cheaper than LiPo. They don't have the density of LiPo, but are so much safer. You don't want to end up like Chompalot, do you? Hobbyking have a good range of well priced NiMH batteries, two 7.2v packs would work nicely. The Botbitz 30A would work with featherweight motors, I think, and ranglebox sells the brushed version of it for a reasonable price, or get a FeatherTwo from Rory, though I think he's quite busy since robot wars came back.

Thanks Runsler, I hadn't even considered going for rear wheel drive but that makes a lot of sense.

My my logic regarding cheap or expensive is right now I need to buy everything, so it's less of a strain if I try and stay low cost right now and then I can upgrade to better parts one at a time at a more steady pace, effectively spreading the cost out over several months instead of one big payout right now.

If you want safe, go for LiFePo4 cells.
NiMH is not up the task, unless you want an absolute low power machine or have a kilo of batteries in there.

I'm happy enough using lipos, as long as I follow the safety precautions and don't do anything stupid I should be safe enough. I have a balance charger and I'll be ordering a lipo sack with the batteries.

I've got a small wiring question, I've decided to go for a removable link and an LED power light, so that should I get the opportunity, the robot will be legal.
I know what I'm doing for the removable link, but I need some advice for the LED. I thought I probably wouldn't be able just wire the LED straight into the 5s battery, but seeing as I had two LEDs i decided to test that hypothesis. brief flash of light, funny smell, theory confirmed. So my question is, how do i power the LED from with the 18.5v current I have? Do I need a resistor? If so what type?
Many thanks.

Your ESCs should have a battery eliminator circuit built in. The red wire in your connectors (those three-pin cables with orange, red and brown) should be at about 5V. If you connect your LEDs to this, or one LED and a resistor, and the other side to the ground/negative rail, you should be fine. If you want, you can pop the red wire out of the connector to secure it to your LED.

As for what resistor, you just need to make sure your LEDs aren't getting more of a voltage drop across them than they're rated for. LEDs' voltage rating goes up roughly along with the energy of the wavelength they emit, so red LEDs only need around 1.8V, while blues usually need around 2.2-2.4V. So either put LEDs in series until their ratings add up to roughly 5V, or put a resistor in (330 Ohms is usually fine for supplies 9V and under) with fewer LEDs. If your LEDs seem dim, just try lowering the value of the resistor a little. But if your blue/green LEDs start to glow red, that's when you know you're giving it too much juice.

Thanks for the reply. I think i understand but I have a couple of follow up questions. I understand that I need to cut the BEC wire on one of my ESCs so as not to fry the receiver, should this be the BEC i use for the LED? Secondly what do you mean by the ground/negative rail? and where would i find it?
If it helps at all I will be using Botbitz 30A ESCs, just waiting for Ranglebox to get some more in stock.

Yes, ideally you need to use one of the BEC wires you've removed as the positive for your LEDs. By ground, I mean any negative wire. It might be easiest to just connect it to one of the spare ground pins on your receiver (that's the one that normally takes a brown wire). You can do this if you have a jumper wire with a female connection at one end - you can just plug it straight in.