FeatherW help/parts

*This is also posted in wanted section, but post also includes FeatherW questions. Apologies for double post.*

Hi there, my names Jon. This is my first post on these forums, but as long time browser though i've read and learnt allot of really useful tip and tricks already from this site and would like to take chance to say thank you for the wealth of information stored here and the willingness of users to provide it.

Back to the post, i'm a final year student studying at brighton uni. one of the projects i'm working on this year is the design and production of a Feather weight fighting robot, its run by Ian Watts, whose one of our lecturers as well, best lecture i've had at the uni.

Weapon
Were looking to make a crusher, and are having difficulties sourcing a liner actuator. at the moment were still in the design stage so were open to suggestions on spec, (around say a 100-150mm stroke, low weight with decent pushing power), however were going to have to make a decision pretty sharpish. I've found several on ebay however they tend to be completly the wroung spec, I have spoted one today that is close (15mms 800n 100mm stroke), however after contacting seller he wont sell direct, so i'm going to have to bid. Was hoping someone may have one for sale or know of a company that sells cheap items. We really cant affort to pay £80 which is what ive been quoted for the linak la22.

Power
I have a 30v drill bat that were going to cannibalize to power the weapon along with the 18v drill batteries. However would there be a way to combine the batteries for the drive and the actuator? or would this have detrimental effects on drive while the weapon was in use? Also how would the voltage normally be controlled if it is possible to combine power source.

Drive
we've sourced some cheap 18v drills from ironmongreyonline.com, but were in need of some wheels. would the suggested Robo Challenge €˜Blue wheels€™ still be the best choice?

Electronics
the RC unit is provided by the uni, however we need to either make the motor controller or we can buy one. Would anyone have a circuit diagram for one? my apologies if its already posted i had a look but couldn't find one. also would it be best to integrate the weapon into the same controller as drive or use a separate one?

for the body were thinking of using a tubular steel frame with a thin 1mm welded plate shell.

If anything i've suggested sounds stupid or wishful thinking please pull me up on it. I built an ant weight about 5 years ago for school, but its not that relevant to this build.
Thank you sincerely four your time =)
Jon A

I've PM'ed you an Ebay link that I consider to be worth while.

You may already have spotted it on Ebay.

Woody

You could always build your own linear actuator. Attach a drill motor to a threaded rod and run a nut along it.

Yeah you can run all your power from a single set of batteries. Makes wiring up a lot easier.

Robochallenge wheels are going to be your easiest bet

Speed Controllers are best just bought. You can try and make your own but it's a bigger pain in the proverbial than it's worth. There are a number available. Everyone has their preference. I like the series that electronize does. Nice and robust.

Is the machine for show or for actual combat? I'd recommend dropping the 1mm steel shell and using some HDPE. Better at absorbing impacts and far easier to work with as it can be machined with wood working tooling.

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JonA321Weapon
Were looking to make a crusher, and are having difficulties sourcing a liner actuator. at the moment were still in the design stage so were open to suggestions on spec, (around say a 100-150mm stroke, low weight with decent pushing power), however were going to have to make a decision pretty sharpish. I've found several on ebay however they tend to be completly the wroung spec, I have spoted one today that is close (15mms 800n 100mm stroke), however after contacting seller he wont sell direct, so i'm going to have to bid. Was hoping someone may have one for sale or know of a company that sells cheap items. We really cant affort to pay £80 which is what ive been quoted for the linak la22.

Power
I have a 30v drill bat that were going to cannibalize to power the weapon along with the 18v drill batteries. However would there be a way to combine the batteries for the drive and the actuator? or would this have detrimental effects on drive while the weapon was in use? Also how would the voltage normally be controlled if it is possible to combine power source.

I'd prefer ONE battery..You may get voltage sag when both the weapon and drive are on... depends how good or bad your bats are.

Drive
we've sourced some cheap 18v drills from ironmongreyonline.com, but were in need of some wheels. would the suggested Robo Challenge €˜Blue wheels€™ still be the best choice?

Good choice ...have you calculated the robots potential speed?

Electronics
the RC unit is provided by the uni, however we need to either make the motor controller or we can buy one. Would anyone have a circuit diagram for one? my apologies if its already posted i had a look but couldn't find one. also would it be best to integrate the weapon into the same controller as drive or use a separate one?

Building a speed controller can be a knightmare!.. I'd not bother with speed control on the weapon.



for the body were thinking of using a tubular steel frame with a thin 1mm welded plate shell.

If anything i've suggested sounds stupid or wishful thinking please pull me up on it. I built an ant weight about 5 years ago for school, but its not that relevant to this build.
Thank you sincerely four your time =)
Jon A

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Can i just add jon.....your very polite. :)

Many thanks for the quick responses =)

to typhoon_driver
I was thinking about making the actuator but wasnt sure how much force would be generated. I imagine the pitch of the thread could be changed to increase speed.
Any idea how i could calculate the Load in N generated from the drills tourque? (will also look on google so may be a pointless question)

as for battle it will be in a compotion vs the other teams robots, but we were thinking full out destruction minium defence =) thought carbon tempered steel would be best for weight and price ratio. As hdpe we would have to source it, the uni can provide steel, alu and mig/tig and metal working equipment. will definatly have a look though, theres a local plastic shop that does me discounts will see what he charges (thinking around 8mm, that about right?)

To Woody and typhoon
The bats are second hand drill bats from a boot sale. However not very confident on how to assemble and ensure i dont burn out the drive.

I havnt worked out the speed, good shout tho will try and work it out.

for the speed control. we would get more marks if we make it ourselves so would be worth giving it a shot if you have any tips. if it goes horibily wroung we will have it to show as an attempt.


Cheers had to finish post quick didnt get chance to spell check, sorry for typos
Jon

you are probably all ready aware but ian makes his own speed controller the wooty series for combat robots, not sure if you can/cant have help from him for this ??

also for the robot speed use this :

http://www.technobotsonline.com/robot-s ... lator.html

i think the typical 18v drill rpm is 775rpm not 100% on that though

alex

I have a bunch of equations somewhere in my piles of notes from uni that cover it.

If you are getting free steel from the uni then by all means use it. Most people here use directplastics for HDPE or you could ask around to see if anyone has any spare kicking around. 8mm will happily protect your machine but do the calculations to work out the weight of the armour etc to check that it will be within weight.

If the batteries are second hand they may well be junk. You could disassemble the battery pack and make up a pack with a suitable voltage. There are many guides on the internet that cover making up battery packs. Basically you need a big soldering iron (100W+) and a bit of patience.

Speed controller....don't bother. It's an entire university project in itself. Ask Ian how many versions he has had to go through to get a working speed controller that didn't blow itself up, bearing in mind the experience he has in the field. If you are set on building on I have seen several based on a pic controller, H-bridge controller chip and H bridge with MOSFETS that have worked after several doses of the magic smoke.

Ian gives us a few lectures on the motor controller (not for another 3 weeks), however this module is normally taken by the robot engineers and mechanical engineers, working in mixed groups. Who do large amounts of pic and hbridge work in lead up to final year. Being a product design student we only do one small pic project just to get an understanding. Its good because it means were not marked as highly on the controller compared to everyone else so if we try and fail horribly then have to buy one, we should still get ok marks. Unfortunately Ian wont just show me how to do it =(. Also we can get some of the circuit components from the uni so could save some money.

I was just having difficulties finding circuit diagrams, and even more with the pic coding.
There are a few articles I€™ve found but can€™t tell myself its right for the job.
http://www.mcmanis.com/chuck/robotics/p ... servo.html has a diagram and code. Would need someone that knows what a board and code should look like to say if it€™s good or not.

So if I have a 24V bat pack to power weapon and drive. What would be the best way of controlling the power supplied to 18v motors?
Cheers

Jon

So if I have a 24V bat pack to power weapon and drive. What would be the best way of controlling the power supplied to 18v motors?

Give the 18v motors 24v.

Speed control diagram.
http://imgs.xkcd.com/comics/circuit_diagram.png

Hi Jon,
I don't know if you have sorted your weapon yet, but Gary makes a very good suggestion. If you wanted to use a screw thread, you could consider a car jack. About the easist and cheepest thing to get hold of and it has suitable thread type (and obvious rated to reasonable forces [for a feather anyway]). I used one for the original Tiberius (heavyweight). Only down side is you only want to use the threaded bar in tension, whereas linacs are ok in either so it depend if this fits with your your design.
Working out the 'ideal' axial force of a screw thread should be fairly straight forward.
U'll need to know the pitch of the thread (usually roughly 3mm) and input torque to the threaded bar.

good luck
Sam

ah thats good to know about the bat, something i know very little about to be honest =). I was thinking I would need two packs, but I imagine the two new bats supplied with the drills, broken down would give a 36v pack, wouldn't need that much would I? (apologies if these are simple stupid questions =)
lol love the circuit diagram =P

To sam, yeah i was looking at using a jack, was playing around earlier today at uni with some threaded bar and a N test gauge got a 44N pull of a 18v drill before it started spinning in the chuck, was told 'under pain of death do not damage the chuck' by our tech guy =). Copying the idea on a smaller scale or getting a small jack would defiantly provide more than enough force.

Hopefully however I think the search for an Actuator is over. should know by tomorrow which is great!

Would anyone happen to know the width of the robo challenge wheels was looking on google but could only find dia. Also if anyone is selling a set of 100mm let me know will be very happy to take them of your hands =)

Sounds like a pretty mundane piece but was wondering if there are any caster ball makes/types that people would recommend?

Cheers
Jon

hi, the blue wheels are 30mm diameter i beleive :)

Yeah.....they're more like 30mm wide :crazy: :)
That's for the 100mm diameter wheels anyway, and I believe the 75mm ones are around 23-25mm wide

oops! meant to say width :crazy: thanks jamie

Yeah I figured it was just a typo :)

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Sounds like a pretty mundane piece but was wondering if there are any caster ball makes/types that people would recommend?

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Hi Jon. To be honest, I'd recommend going for none. With castors, unless they're pretty industrial (therefore heavy) they won't really survive robot combat and will likely get damaged beyond useability (did I just make that word up? :shock: ). Ball transfers units are a more robust alternative but they can get clogged up with bits of crud from the arena, or dirt and gravel (if you test/run your robot outside) which results in them becoming much rougher and, generally, crap.

I've always found that a simple skid pad or two, fitted near the leading edge and made from a piece of low-friction plastic or similar, does a sufficient job and is easy to mount and replace if damaged. Cost is almost zero, just requiring a small offcut of material and a bolt or two to hold it on.

You get to this in uni? Man, the nearest I got was a remote control power switch...

Anyway. Advice:
Print out all the rules- you'll refer to them a fair bit.
Skim through the Rio bot tutorial. Good advice if a little long winded

As for the controller, surely you'd get the similar amount of marks if you just explained WHY you chose not to attempt to building your speed controllers (with the knowledge of how it works) compared to spending the building something that will just blow up and take money with it. It's not the best engineering decision I grant you but it is the best project management decision you could make. If possible, have a quick chat with Ian - he can't make your decisions for you but even his evasive efforts should tell you where the marks lie.

I'll keep reading- good luck!