Dual motor Axe bot

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Jonathan J
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Dual motor Axe bot

Post by Jonathan J » Mon Mar 25, 2019 6:48 pm

Hi all so I was wondering how I could go about making a anywight axe bot with two geared motors so it could be powerful i know people have done it before so I’m just curious about it because I’ve always liked the idea of making and axe bot and the dule geared motors seems to be the most affective method for one any help and tips would be much appreciated
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MarkR
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Re: Dual motor Axe bot

Post by MarkR » Mon Mar 25, 2019 7:14 pm

Yes that sounds like a great idea. Derek Dudge also did something similar with one motor on Manticore, an overhead bolt which bashed the crap out of the other robots, it was very popular with the audience.

I would also recommend using a higher voltage, maybe a 3S pack or a voltage boost circuit, to maximise damage! Or use Pololu high power N20 motors (they are quite expensive) for total carnage (maybe cause a lot of damage to the speed controller too though).

Also, maybe you will need a programmable transmitter, or a programmable element in the robot (Arduino, etc?) to fully automate the carnage, so you don't get a sore finger wiggling the stick and can bash the opponents faster.
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Re: Dual motor Axe bot

Post by LimaHotel » Mon Mar 25, 2019 8:17 pm

The simple way it's done is just by running the motors off the rudder channel, as the rudder stick is self centering. The N20s are stalled for the time between contact and you releasing the flippy flappy rudder stick, but they don't seem to mind being stalled. It largely depends on the kind of axe you want - are you thinking Axiom or Axe of 8 wheels? End of the day, an axe at Antweight won't be damaging (excepting maybe cutting exposed wires if it's REALLY sharp). By no means does that mean it won't be fun though!
If you just want to get a functional axe going Axiom-style, then the only thing that you need to do differently to using a servo is you need to get a speed controller for the N20s. You can run multiple N20s off a single channel speed controller so long as it's rated to enough current to handle 2 stalled N20s. As for getting them to both spin in the correct direction, just cross the wires on whichever one is going the wrong way. They're really beautifully simple things.
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Re: Dual motor Axe bot

Post by Kyro » Mon Mar 25, 2019 9:20 pm

having never built an axe bot, take my tips with a pinch of salt... i would say that at ant level, speed is far more important than power so try and find the fastest rated n20's you can...

blunt force seems more effective in an axe bot than its penetrating ability... however the more weight swinging, the more unstable your bot is likely to be during use...

as for control of the axe, maybe a pair of switches that the axe shaft presses at each end of the throw to reverse polarity so it would keep running back and forth until you cut the power with the transmitter
that would save a lot of thumb waggling and instead would allow for one motion to start the axe and one to stop it... this should also minimise stall... but this is just speculation and there's probably a reason this approach has not been taken in axebots before as far as im aware...


sadly axes just aren't effective enough at antweight but i would love to see one built that can actually cause the kind of damage we saw in robot wars...
that said, they are extremely fun to watch and everyone seems to enjoy watching a little ant hammering away...

ants are generally tough little things... far tougher it seems than back in robot wars where axes were effective in the heavyweight class...

maybe some kind of rat trap spring powered axe could hit hard enough to cause real damage, its just working out how to reset it during a match...

best bet would be to experiment and see what works best... hopefully the advice you get here will help with experimentation...

good luck...
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Re: Dual motor Axe bot

Post by voorsk » Tue Mar 26, 2019 10:35 am

GeorgeR's axebot is dual motor - there are pics in his build diary, so you can see how he did it. Using two motors means that they'll fight each other a little bit, so they have to be well secured. You also have to consider the torque reaction of the axe, as it's possible to make an axebot that flips itself around the axe instead of hitting someone. It does look really cool, tho! :D

From my limited experience, I made a single motor axe with a stanley blade as the axe, so it has hardly any weight to it initially. Extra weight can be bolted on post-build, depending on how much there is to spare. It's got a 50:1 non-pololu motor, so not as powerful as it could be.

I'm not really sure how much to worry about trauma damage. I don't think any ant axe can do much trauma - a good flip or ram probably does more damage. Falling in the pit probably does more damage, come to think of it. :P I don't really care about that, tho. As Mark says - it's more about being fun! :D It does double-up as a self-righter and grabber, which is very handy!

Don't forget you'll need a speed controller for the axe. I use a Vex 29, but I guess any 2S dual direction controller will be okay.

For control, I took the tensioner out of the throttle control on my Devo 7E, so it springs back to centre instead of staying in position. Seems more natural than using the rudder. I'm not sure if the same is possible on other controllers. The Devo had instructions on how to do it, which is cool.

Good luck with the bot!
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Re: Dual motor Axe bot

Post by GeorgeR » Tue Mar 26, 2019 1:59 pm

I wouldn't worry too much about power, there's simply no way to make a damaging antweight axe, but don't let that stop you - axebots are great fun.

As others have said, it can be done by simply wiring both motors to a single channel esc, and running off of the rudder channel for control. For Axiom I use 2x pololu high power motors with pololu universal hubs to mount the axe, and a vex 29 esc.

Good luck!
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Re: Dual motor Axe bot

Post by Jonathan J » Wed Mar 27, 2019 9:29 am

Thank you for all your help! i will be sure to give it a go once i've finished my current robots for aws 58.
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Re: Dual motor Axe bot

Post by LimaHotel » Wed Mar 27, 2019 3:03 pm

I have a query regarding the Vex29 esc. Vex reckons they weigh a whopping 9g each! I'm assuming a significant part of that is the horrible plastic they insist on surrounding it with - roughly how much do they weigh once you've shelled them?
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Re: Dual motor Axe bot

Post by GeorgeR » Wed Mar 27, 2019 3:51 pm

Not sure of the exact weight, but without the case they are pretty much the same size as a no-pin lemon rx, or a dasmikro, so will be in the same kind of range as those.
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Re: Dual motor Axe bot

Post by LimaHotel » Wed Mar 27, 2019 4:57 pm

Oh nice - I might put in an order for some of them!
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Re: Dual motor Axe bot

Post by Retroman » Wed Mar 27, 2019 7:17 pm

Literally just had my vex29 on the scales, with shell it's 9/10g (resolution on the scales isn't the greatest), but shelled I got 7g with standard length wires, you could possibly shave a g or 2 by trimming them down depending how neatly you can join them.
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Re: Dual motor Axe bot

Post by razerdave » Sat Mar 30, 2019 12:03 am

For Baby Hell I use a fingertech tinyESC. Expensive, yes, but at 3g it’s best for weight and will handle 2 HP motors easy (I use them to drive a beetle with no issue).
Control wise, I have a spring-centred Double pole, double throw switch attached to the rudder control. Basically, if you take the leads from the rudder stick and put them at the 3 pins of the switch (middle wire to middle pin), you get a full power shot from the axe in an instant (no going through the range on the normal stick), and it’s such a quick click, the N20’s don’t have time to stall before the spring switch clicks back to neutral.

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Re: Dual motor Axe bot

Post by Jonathan J » Sat Mar 30, 2019 8:19 pm

Ah okay that’s really good to know thanks Dave
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