Hi, quick question. To build an electric axe capable of self righting what sort of size of motor would I need to look at to power it?
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Hi, quick question. To build an electric axe capable of self righting what sort of size of motor would I need to look at to power it?
Depends on the gearing! A scooter motor will have the beans at a high ratio, but a standard drill size 550 motor will too at a low enough ratio.
Can you give any idea what sort of motor you had in mind?
Speed 900, 6S, 30-1 gearratio, 300mm long arm. Does the job very aggressively.
Erm, my fav robots are Little Hitter, Tiny Toon (not relevent lol), b-e-t-a, basher
I have a nearly finished robot at circa 6kg. Was umming and arring about building another for a cluster or armour this more and going with a big hammer, although then it won't be invertable.
So was looking into it and most are pneumatic, but would rather go electric and wanted to see if I'd be able to sort out a big enough motor with a 6kg allowance. To be honest I don't know what ratio to be looking at, I think it'd depend on the motor. I'd hoped it would be manageable with something like a pair of wiper motors etc. But if it needed something like a wheelchair motor in I'd never do it in the weight I don't think.
Sorry, forgot to say,
So I was just looking for an indication of the power it needs in the first place to self right if i move towards a better more rounded shape etc.
If you want to build a 6 kg machine, you should have a look at the German Raptor rules.
But to make the search shorter.
No brushless ,no brushed larger than speed 700 size and no rare earth magnet motors allowed.
12V SLA, 10S NiMH, 3S LiPo or 4S LiFePo4 batteries.
Voltage boosters or extra batteries allowed for valve control.
The rest is classic featherweight rules.
I didn't deliberately end up with a 6kg robot, its just the way it's ended up, hence either building a second as a cluster or trying to build a hammer to go on top. Sorting the hammer won't be that bad, I'm just not sure of the size of motor and torque that I'll need to be able to self right.
Avenger has a 300W scooter motor on 22.2V, a 80:11 reduction and a 300mm axe and it manages to get a bit of air while self righting. A quick guesstimation while looking at the motor power graph (chinese, so don't trust it) and guessing the rpm, I'd say it gets 30Nm at the axe. Can't decided if that's too high or low, so I guess its close.
Do you mean a scooter as in an electric wheel chair type of thing? Do you have any pictures of Avenger?
The motor Daniel mentions is a large, heavy motor, on the edge of usability of feathers. Also called EV warrior.
Most we see now are Chinese clones.
I do happen to have one in my spare box.
The most recent pictures I have are on this page http://www.robowars.org/forum/viewto...=asc&start=435 Videos from its fights at our Nationals are on youtube too.
1.5kg for a motor is a bit heavy, but I find the lower rpm makes up for needing extra reduction. But I've broken all my scooter motors at our last national championships and have now discovered that my local supplier has put his prices up. So I'm currently redesigning my two scooter motor powered robots to use HK brushless motors instead
Funny Daniel, that is exactly the motor I have in my spares box.
So something like a pair of Gimson GR02's wouldn't give enough of a kick to throw it back over?
So its all in the gearing (I suspect)
So I toyed with one of thoe scooter motors and have one in my spares box
Instead I went the 2 GR01 route
Been busy at work but plan to weapon test over Christmas
http://i1184.photobucket.com/albums/...ps672cbbea.jpg
Well why not do the sums and work out what will be able to self right?
Lets assume a 30cm long axe with worst case the majority (say 10kg) at the axe head end of the robot. Torque is simply distance x force so that would be 0.3m x 10*9.8 (to get the mass into newtons) = 29.4Nm. Call it 30 to keep the numbers simple.
Now looking at the gimson GR02 18v. That will give you 1.41Nm at peak efficiency. So in theory you would need a ratio of 21:1 to get a flip back over.
Now of course I have assumed that all the 10kg mass is on one side of the axe mechanism and is only balance by very little mass on the other side. So what I would do is roughly work out the mass distribution of your machine and then work out the imbalance that the axe mechanism has to self right. You will probably come out with a figure somewhere between 5:1 and 10:1.
I would always advise doing the sums and work out what you will need adding a little bit more for the real world rather than going down the route of yeah that should work, spending the cash and time on it then realizing it doesn't.
Certainly looks the business! Here's hoping it has the goods.
Here's a quick video of it self righting
The battery is 4s with low charge but will be changing this up to a 5s
It also self rights with the axe extended
http://i1184.photobucket.com/albums/...ps43137a78.jpg
Stripped the bot down to do some welding and tidying
That's really cool!
Very tidy looking machine.
Very nice machine, what motor are you using behind the axe?
2 Gimson GR01's
Previous page, man.Quote:
Originally Posted by mattsdragons
http://i1184.photobucket.com/albums/...ps672cbbea.jpg
Edit: Mario beat me to it!
That's nice, didnt look at the other page, just the video
Very nice, have u any plans to stop it getting stuck on its side?
Havent tested yet as I did a complete strip down to do some welding
Its not too obvious but the side panels are not vertical
I'm banking on that plus the axe changing the centre of gravity will force the bot upside which I can self right from.
If that doesnt work then some spikes on the side (I liked the look of the kebab skewers that someone else posted) look fun and would make it more unsteady
http://i1184.photobucket.com/albums/...ps5bfe40c2.jpg
Still pondering a scooter motor. Those buggers are heavy though (MY1016 are 2Kg) - I know the Aussies use them
MY6812 are quoted as 0.42 Nm @ 24V
MY1016 are quoted as 0.61 Nm @ 24V / 2932 rpm [max efficiency]
These would really need a 2 stage reduction
Gimson's are 1.41Nm at peak
My main problem is packaging. The battery is higher up than I want it to be. [it fits but feels too vulnerable]
Might move the motors up to allow the battery to be packaged in the guts of the machine and moving the electronics (TZ85A's) to one side.
I can save weight by moving from pillow bearings (convenient but heavy) to simple bushing. For now its a runner (well, once its all bolted back together :) )
Much more than 1.41Nm 'at peak', I think you're quoting the maximum efficiency torque.
Don't forget you need to get the li-po out for charging and in the stress of the pit having it buried deep in the robot is the last thing you want.
A couple of videos just to prove to can get a scooter motor powered axe into a 5mm steel chassis and get it under 13.6kg
Not the best camera angle and you should ignore the fact that the drill gearboxes fell out of the robot :oops:
http://www.youtube.com/watch?v=VIOxQtQbXqQ
nice find on the videos, I like Avenger and Huntmans axe bots
Good write up at http://robowars.org/forum/viewtopic.php?t=734
I will be sticking with the current design and making the battery well package and accessible (something to ponder over Christmas)
As I said before, do the sums and work out which motor will work best for you. Then design the machine around it.
Would a normal cordless drill motor do the job as a axe motor if it is geared correctly?
There is only so much power in a batterydrill motor. Gearing won't amplify it at all, just make it a tad more efficient.
I used a cordless drill motor as an axe motor on a 5:1 ratio. In short, no. There are small steel pins inside the drill gearbox that keep the small pinion gears in place, and the forces from a weapon like that just cause the pins to fail (basically falling out of the holes in which they're mounted).
If you want to go for an electric axe, have a look at electric scooter motors on eBay, specifically around 300-350W power rating. I changed my drill motor on the axe to one of these and they are vastly superior. On the same ratio the axe hits a lot harder and faster, and the motor can definitely take it. Sam also uses one for his robot Hatchet and has it working well for him.
I see, what exactly does the 5:1 ratio mean? I would guess small gear to big gear type of set up.
Yep, the drill motor had a sprocket on it with 8 teeth, and the axe had a sprocket with 40 teeth on it, connected to each other by a chain. So for every five rotations of the drill motor shaft/sprocket, the axe arm only rotated once, thus the 5:1 ratio. It reduces the speed but increases the torque (or turning force) so that it isn't as much of a struggle for the motor to turn the heavy arm.
Oh good, I guess there will be some modding to fit the small sprocket to the motor.
Quote:
Originally Posted by RogueTwoRobots
something like this?
http://www.ebay.co.uk/itm/24-VOLT-30...AAAOSwBLlVcco6
Yep.
As someone who's concrete garage floor has been attacked by Jamie's axe I can say that the scooter motors are indeed well suited to this application :)