Cheap components for an antweight class

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EpicentrE
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Cheap components for an antweight class

Post by EpicentrE » Thu Jul 07, 2016 11:30 am

Hi All,

We've just had a new "FabLab" open up in Coventry, and I've been in talks with the owners to run an antweight building class one day over the summer. The intent would be that people pay a fee, build a robot during the day, have a small competition with them at the end of the day, and then get to keep everything at the end.

I'm looking for suggestions for components for this. My main goal is to keep the price as low as possible, which isn't something I'm historically good at, as I tend to spend far more money than I need to!

My thoughts so far are thus;

TX: Blade or similar
RX: Whatever is cheapest on eBay; lemons/oranges?
ESC: Maybe a bulk discount deal on Roryboards :P? Otherwise I'm a bit stumped as to other low-cost options here. Servo boards would work but would require work to dismantle and modify all of them in advance.
Batteries: The cheapest option would probably just be some standard AA or 9v batteries, but I'm concerned about the weight. I guess we could use these during the class, with an increased weight limit, but provide links for LiPo information and stuff for those who wanted their machines to be competition legal after the class?
Motors: Cheapy eBay gearmotors, I was thinking a couple of different ratios, provided with a couple of different sized wheels, to give people options.
Wheels: As above, a few different sizes. Would see if there's anything that's cheap in bulk from Pololu, or could look at printing them.
Servos (for weapons): Whatever is cheap and a reasonable spec, need to spend some time researching for this.

I'd appreciate any suggestions or advice, especially if anyone has done something like this before!

Thanks,

Scott
Scott Fyfe-Jamieson, Captain of Epic Robotics. Champion of AWS38/41/42.
http://www.epicrobotics.co.uk

Roboteernat
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Re: Cheap components for an antweight class

Post by Roboteernat » Thu Jul 07, 2016 1:05 pm

Sounds like a good idea,
Having common parts that could be used for legal battles would be beneficial, such as the motor controller, RX, commonly used motors would inspire attendees to continue in the competition fields.

Using servos as drive controllers would be ok, perhaps a load of 9g servos, about £5 a pop,
I would use the lemon RX as they are very cheap from china, and happily come under the tax bracket ;)
wheels can be 3d printed, mounted to the servo or to the servo.
batteries could be a couple of aa batteries.
You could have flippers, axe, claws/grabbers easily with a servo
Lots of card/plastic/cable ties and hot glue for building and it would be great.

Transmitters, you could get a few spectrum types cheap, blades would be ok but not often on ebay. however make sure it matches that of the rx, dsm2 or what ever, Coul;d even reduce the cost if they bring their own rx kit if they have a blade heli or simular.
Some projects done: Wirelessly controlled mechanical hand/arm
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Antweight robot : in production
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Shakey
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Re: Cheap components for an antweight class

Post by Shakey » Thu Jul 07, 2016 2:07 pm

http://www.hobbyking.co.uk/hobbyking/st ... de_2_.html
I've been eyeing these up as blades are getting expensive and unreliable to source.

SG90 servo boards may work nicely for drive controllers (As nice as servo drive is anyway), i think some get used with micro gearmotors.

A good PP3 battery can work nicely in these bots: Image
I say good as this bot had trouble originally because had a super el cheapo one in that would brown out whenever current was drawn, the duracell one made it work though.

Motors can be sourced from aliexpress pretty cheaply if you're bulk ordering.
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BeligerAnt
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Re: Cheap components for an antweight class

Post by BeligerAnt » Thu Jul 07, 2016 6:28 pm

I'd steer away from 9V PP3 batteries, they are only meant for low-current applications such as smoke detectors. Decent branded (ie expensive!) PP3's might be OK, but cheaper ones will almost certainly struggle.
I'd suggest 4 x AA or 4 x AAA and modify the weight limit. You could go for, say, 140g plus batteries or 200g including batteries. Back in the "old days" we used to be able to build competitive robots with 4 x 2/3AAA battery packs!
Remember that 4 alkaline cells give 6V (not 4.8V) so you would need a receiver and servo(s) that can cope with the voltage.

I wouldn't go for 9g servo boards to drive gear motors. They will work but their life expectancy won't be good. The motors draw more current than those boards can cope with for extended periods of time. Boards from standard servos work OK and they are often even cheaper than 9g servos!

Good luck with it!
Gary, Team BeligerAnt

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Re: Cheap components for an antweight class

Post by peterwaller » Fri Jul 08, 2016 7:32 am

As I mentioned some where else on the forum 3D print world held a slot car racing event last Tuesday for schools who designed and printed their own body shells.
I took the arena and robots along and got a lot of interest but like you I realised getting reasonably priced parts would be the key to success.
These schools were looking at it from the 3D printing point of view so body parts and wheel were not a problem but the electronics and transmitters would be.
So far I have just had a quick look and there are some cheap controllers on ebay which look usable such as:
http://www.ebay.co.uk/itm/Useful-10A-Br ... Sw5ZBWPFm4
http://www.ebay.co.uk/itm/RC-ESC-10A-Br ... 1924138649
On the transmitter front I had been wondering about using one of the tiny DelTang transmitter boards and building one but thats about as far as I have got so far.
http://www.deltang.co.uk/tx2.htm

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Re: Cheap components for an antweight class

Post by AntRoboteer » Fri Jul 08, 2016 8:15 am

We used 4 AAAs in ur first Antweights and they actually came in under the weight limit as well with a bit of careful tinkering.
I wouldn't go for 9g servo boards to drive gear motors. They will work but their life expectancy won't be good. The motors draw more current than those boards can cope with for extended periods of time. Boards from standard servos work OK and they are often even cheaper than 9g servos!
You'd be surprised actually. The SG90 boards run gear motors frighteningly well and due to the poor efficiency of the motors they come bundled with, they are actually built to deal with quite a current draw in practise so they run gear motors flawlessly and often have larger controller chips than the large boards! :D

Tashic
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Re: Cheap components for an antweight class

Post by Tashic » Fri Jul 08, 2016 11:51 pm

I'm also interested in some cheap components!
Today I met a person which is a teacher and wants to make an antweight tournament (a sportsman/no damage type), ironically while I was in the fablab of my city.
Has anyone used those ESCs that Peter linked?

Also remember that I'm situated in Italy and some components that are easy to get in the UK, might not be for me.

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Re: Cheap components for an antweight class

Post by UserFriendly » Mon Jul 11, 2016 8:18 am

AntRoboteer wrote: You'd be surprised actually. The SG90 boards run gear motors frighteningly well and due to the poor efficiency of the motors they come bundled with, they are actually built to deal with quite a current draw in practise so they run gear motors flawlessly and often have larger controller chips than the large boards! :D
Thanks for this tip! I had a play last night, and clipped out the driver boards from a couple of SG90s I had, wired and hot glued them to the Lemon, and got myself another controller. Seems to work ok, will still have to test output power etc., and still haven't quite worked out how to correctly mix channels on the DEVO 7E transmitter yet - just 'tank drive' atm!

Image
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ozcoder
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Re: Cheap components for an antweight class

Post by ozcoder » Sun Jul 17, 2016 3:56 am

If you have a cheap transmitter that doesn't mix channels you can use a V-Tail mixer to do that for you, when you use those 10A Brushed controllers.
Example https://www.hobbyking.com/hobbyking/sto ... duct=46730

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Re: Cheap components for an antweight class

Post by ozcoder » Mon Aug 01, 2016 8:39 am

Has anybody tried using a flight control board as an ESC?
This one has a DSM2 receiver and 4 x ESC, but I don't know if it would work in a robot.
http://www.hobbyking.com/hobbyking/stor ... ouse_.html

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Re: Cheap components for an antweight class

Post by Shakey » Mon Aug 01, 2016 9:26 am

ozcoder wrote:Has anybody tried using a flight control board as an ESC?
This one has a DSM2 receiver and 4 x ESC, but I don't know if it would work in a robot.
http://www.hobbyking.com/hobbyking/stor ... ouse_.html
Those ESC's look like simple single FET channels so would have no reversing. Plus it'd probably need a firmware reflash.
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Re: Cheap components for an antweight class

Post by EpicentrE » Mon Aug 01, 2016 3:39 pm

Thanks for all the help everyone. I'm putting together a price list for this at the moment to be shown to the Fablab this week. I'm currently coming in at about ~£40 per robot including transmitter, excluding the bits we'll be making (wheels. chassis, etc). The only component I haven't decided on yet is a weapons servo. Does anyone have any suggestions of anything around the ~20g range which would be good for a variety of weapons, and can be got nice and cheap on eBay?
Scott Fyfe-Jamieson, Captain of Epic Robotics. Champion of AWS38/41/42.
http://www.epicrobotics.co.uk

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Shakey
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Re: Cheap components for an antweight class

Post by Shakey » Mon Aug 01, 2016 3:44 pm

That servo sounds like a job for the MG90. A bit lucky dip in the exact specs of what you get but cheap and metal geared. (I wouldn't quite stoop down to SG90 levels as they strip a lot and as soon as one does it becomes more expensive than a mg90).
Nuts And Bots - For all your components and ready built antweights!

Alex Shakespeare - Team Shakey / Nuts And Bots / Team Nuts:
AWS 44, 45, 49, 51 & 55 Winner - Far too many robots!

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Re: Cheap components for an antweight class

Post by EpicentrE » Mon Aug 01, 2016 4:01 pm

Thanks Alex, that's great. I'll take this list to them later in the week and see what they think :).
Scott Fyfe-Jamieson, Captain of Epic Robotics. Champion of AWS38/41/42.
http://www.epicrobotics.co.uk

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Re: Cheap components for an antweight class

Post by UserFriendly » Tue Aug 02, 2016 3:48 pm

ozcoder wrote:Has anybody tried using a flight control board as an ESC?
This one has a DSM2 receiver and 4 x ESC, but I don't know if it would work in a robot.
http://www.hobbyking.com/hobbyking/stor ... ouse_.html
Yeah, I have, used a heli board before. Pretty useless as I had it. As Alex says, no reverse. I would try something else first.
Andy B - Team UserFriendly
Reading Cybernetics Graduate 1996
Trying not to take Antweights too seriously. I think I'm failing.
First AWS was 46.

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