How would you spend £500?

Last night I was given a £500 grant to run a robotics club in school. I want to make sure the money in the right way so thought I'd open it up and see what people think I should buy.

My idea is to build a number of control boxes that take care of all the complicated electronics. These armoured boxes will have threads cut into the bases so they can be easily moved between machines allowing 10+ robots to be built and run with 3 - 4 shared boxes. The boxes will have a number of female connectors around the side to plug in motors, weapons, removable links etc.

So the question is what goes inside the box? and what drive units should I buy?

My main concern is reliability. These unit probably wont face too much abuse, I'm imaging an after school club will mostly produce rambots and simple weapons (spikes, drills etc) But they need solid electronics and drive if this is going to work.

Here's are my initial thoughts:

1 x OrangeRx T-SIX Transmitter (Although I think the Tx85a's code was written to work with HK's own 2.4ghz TX so maybe those instead if they'll make the ESC's work properly)

1 x Orange Rx

1 x Battery (Probably NiMh over LiPo)

2 x Hacked TX85A ESC’s

1 x Weapon controller, either another hacked TX85a, a relay/switch set up or maybe one unit with a brushless output.

2 x GR02 motors

2 x Robochallenge Wheels

Nylon and Lexan for the housing

None of that is set in stone so any thoughts, ideas, additions, sponsorship deals ;) welcome.

Also worth noting I'm going to be donating my kit to this, I've got one complete set, I'd like to produce 3 more with this money but will settle for 2 if it wont stretch far enough.

That sounds bang on personally. How you got £500 out of your school I have no idea. Neither my secondary or Uni would part with anything what I tried to do this.

I personally would swap the Nylon for HDPE or even MDF simply because its much cheaper. This will free up money to get the ESC's and the other more expensive parts. Also you could make your own wheels for much less and that also means people can pick their own diameters giving a little more design variation; unless you can do some kind of deal with the RC guys.

Out of interest where are you planing to fight the machines just in case someone comes up with something that exceeds your expectations in terms of lethality?

It was a uni bursary, I could spend it on anything I wanted as long as it would increase my employability.

DIY wheels is a good idea, I've just bought some Banebots wheels with 1/2" hex's and they need some modification so making them myself wouldn't take too much longer.

I'm planning on providing MDF template chassis that they can build whatever they want on. I'm hoping to spark their creativity with the basic bots and if they want to make something more dangerous they I'll point them in the right direction.

Use flanges instead of threads as threads will get worn out over time for the boxes

A few things:
Are you hacking the TZ85's yourself?

Have you considered a few argos drill motors in permanent housings?

You can get a bunch of wheels cheaply from bearing boys then using a drill press (or even a pillar drill) heat up nuts and press them in.

Just a few money saving ideas from me. :D

Good idea with the wheels, I'll free up nearly £30 making them myself!

Yes I'll be hacking the TX85a's, the last 2 I did weren't too difficult after I got my head around the programming software. My only concern is the mixing problem lots of people seem to be having. If I can guarantee they'll work with the cheap HK RX I'll use them.

I had thought about going down the Argos drill route, but I want the kits to look fairly professional. I could fabricate some housings but that's more time and material, the drills are £13 + say £5 for ali housings is £18, the GR02's are £32 but Ewan mentioned discounts for bulk orders and I think investing in GR02's should pay off as they're unlikely to get damaged. It might be the difference between having 2 or 3 kits though in which case Argos it is!

Gary I'm not familiar with flanges could you elaborate please? I've got some threaded inserts left from Splinter that would help. Ideally I'd like to use fixings that can be quickly undone so the units can be swapped between machines quickly, a bit like the half turn fixings on Ikea furniture, not sure how well and Ikea table would stand up under full combat though!

take a piece of angle steel. Drill holes in it in both faces of the angle. Screw or bolt one side on to the boxes and then the other mounting hole is available to mount the box to a chassis.

Best image I could find is here,

http://www.bigassfans.com/onlineguid...n_Brackets.png

Take one of those and put it on either end of the box.

No need to worry about wear or cross threading. This will happen. I know how useless university students are with anything practical

This might be the third copy of this post but I still can't work this new Forum layout!

I think I'm going to use NiMh instead of LiPo's, but I know very little about NiMh. I'm planning on running the control units at 12v, so should I get one 12v pack (thinking Vapextech) or run 2 x 7.2v in series?

Also what sort of mAh do people recommend ? Does the mAh rating effect the peak current a pack can deliver like LiPo?

Finally would this be a good purchase for charging them?

http://www.hobbyking.com/hobbyking/s...i_Charger.html

Cheers

Well, some of the reviews on Hobbyking seem not to suggest it, with it seemingly going up in flames. Yet, they gave it 4 stars?

Though I can't say from personal experience, but wouldn't it be very stressful for the board/s inside? I wouldn't trust it, IMO, but I've not really had experience with chargers outside the B6AC, and I'm no super Electrician.

I would recommend a "Turnegy Accucel 6" for charging. You can get them with an adaptor on Ebay for about £35 each.

There is nothing that can go drastically wrong with a NiMH as far as I know unless you really abuse it. Though one thing I have been told is don't over charge them as they will go bang (Well pop 95% of the time but its still bust)

Personally I would buy some large capacity SLAs as they are cheap, not much an go wrong, and will provide a much longer running time which for a group of students, I think is important as they don't want to have 3 mins of driving before having to stop and wait for am hour to charge.
You could however just get larg capacity NIMHs but those would be expensive.

I wouldn't run smaller cells in series, just more packs to charge.

NiMH batteries are expensive for their performance. For the best run time/cost/power output ratio for this you're probably best looking into SLA. A typical car charger should charge them, too, which saves money on needing a fancy charger to do the job.

Granted they weren't off the shelf, but the two 2.5Ah 18v NiMH packs Component-Shop made for us cost more than 60 quid undelivered. You can get a far superior LiPo in terms of power to weight for much less.

Though LiPo charging brings its own risks, understandably, so I'd return to thinking about SLAs. Scotbots use them, and from what I can tell, they work well for them.

I have used Slas for ages, and they work well. and as a bonus you pretty much treat them awfully and there still fine. And you cant damage them from Discharging at a to high current because they simply wont give out more than they can handle, which also means they save stalled motors!

But how ever unlike other batteries, the AH changes depending on the current you discharge at, so you need a high AH for higher currents but for your application 7Ah would last many many battles. Bruiser would last all day on one!

For students, SLAs. For a combat machine, lipo

Have people any experience of these ESC's?

http://cgi.ebay.co.uk/ws/eBayISAPI.d...:X:RTQ:GB:1123

They've said I can have 12 for £140 saving about £15. Because of the low voltage of the kits these seem ideal, just wanted to check and see if anyone had experience with them, specifically if they'll have the same mixing issues as the TZ85a's?

I hope the dimensions are wrong. Also. With 14awg wires and 320 amps... Then the wire acts as a fuse.

i use them in both my bots on a 4s lipo after a battle the motors are warm but the esc are still cool

Quote:

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Originally Posted by Dan-27

specifically if they'll have the same mixing issues as the TZ85a's?

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I THINK I've cracked the mixing issue but I'll confirm hopefully by the end of the week. Seems to work on the bench anyway but I need to give the code a +3 minute run in a bot to confirm that the mixing works and the temperature cut out has been disabled.

Quote:

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Originally Posted by maddox10

I hope the dimensions are wrong.

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Good point I hadn't spotted that they're a foot and a half long! I'm hoping it's a translation error.

Great news Danjr1, I'm going to be using TZ85a's in at least one maybe two of them so keep us posted on your progress. As these are half the price and I don't need more than 12v I think I'll go with these.

oh also o found a uk seller of the 320a esc i can post the link later if you want as im on my phone at the mo

Quote:

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Originally Posted by Dan-27

Good point I hadn't spotted that they're a foot and a half long! I'm hoping it's a translation error.

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I think you are reading the dimensions as cm not mm.

Quote:

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Originally Posted by Danjr1

I THINK I've cracked the mixing issue but I'll confirm hopefully by the end of the week. Seems to work on the bench anyway but I need to give the code a +3 minute run in a bot to confirm that the mixing works and the temperature cut out has been disabled.

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Good news - is this something releasable (is there such a word?) to the wider community if it works? (have mixing issues on my tz85's that I hacked)

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Originally Posted by Shakey

I think you are reading the dimensions as cm not mm.

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The dimensions on the picture are in cm.

That's the plan. Give it a good test then the plan is to post online for others to use. Completely at their own risk obviously but the signs at the moment are good!

Quote:

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Originally Posted by Dan-27

The dimensions on the picture are in cm.

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Made a similar mistake the other day sizing up wood for my shed. They're listed as mm in the item description further down so it's just a typo, although I would have loved to have seen a 1.5 foot tall ESC :lol:

Quote:

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Originally Posted by Dan-27

The dimensions on the picture are in cm.

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Heh I was looking in the item description. :P

The code is open source I believe, so as long as there's a credit to the original author you should be able use and edit freely. Check the licence it's distributed under though.

I thought I'd post an update on this. I spent all the money I was given, and then some, and spent about a month assembling all the control units. The design changed a little due to time and money constraints. The electronics are now housed in 5mm acrylic boxes, it's not ideal but it's a start. I have been teaching since September and was able to take 2 lesson with a year 7 class to test the kit out. A couple of technical issues but on the whole it went really well.

We had a robot sumo competition in the last lesson and most of the class came back at lunchtime to keep using their robots. Ill try and add some photos, I was really impressed with their outcomes considering they had 90 minutes.

Attachment 4206Attachment 4207Attachment 4208Attachment 4209

That is brilliantly done, excellent! One thing I would say though is you could probably do with a bigger space for the fights.
Still very cool :)

Harry.

I wouldn't mind a go at that! Nice job on the kits, they look very nicely done. :)

Looks awesome! I think those electronic boxes with the esc's all wired up would make a great component for a new person to robotics as all the have to do is plug battery and motors in!
Just a thought