Has anybody ever tried opposing magnets principle for an electric flipper? Had done some research and experements on the subject but the results were not so good...in theory should work tho
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Has anybody ever tried opposing magnets principle for an electric flipper? Had done some research and experements on the subject but the results were not so good...in theory should work tho
I'm interested in what Dale did in a 1 or 3lb machine in the US. In short, he used a massive capacitor to dump 60v+ into a motor, and the torque produced when geared down was used on a flipper arm. Completely different approach, and probably very unreliable, but interesting.
That's pretty much my plan, the amount of Torque fan motors produce at 24v should be enough for a very small gearing reduction (like 4:1 on a 15cm arm) with still more then enough power to throw opponents and of course selfright.
Given how little travel a 4 bar mechanism actually goes through it should also be fast.
Was hoping to use the same Li-Po but it may limit me on amps.
The risk isn't losing power at the motor end, it's killing the LiPo due to discharging it way too hard. There's a C rating for a reason!
But that shouldn't happen. You're not discharging direct from the battery, but from a capacitor. Be interesting to see what the charge-time on the capacitor would need to be restricted-to so that the battery is safe, but it's probably not gonna be ridiculous.Quote:
Originally Posted by Ellis
I assumed that Li-Pos would just top out if you want more amps than they can give? I thought the discharging danger came from letting them drain too low.
The amp draw is going to be very short and very powerful.
If you exceed the rated discharge rates of a lipo you end up putting alot of heat into the cells internally, and that will start to cause problems with the packs balance and life. It's certainly not a good idea to expect that a lipo will just top out and not have any issues. You are however likely to not be able to pull the max current from a lipo due to inefficiency in the wiring and added resistance through connectors etc.
I've spotted a *thing* here, which may purely be chance-happening from the particular threads and post's I've seen. But there does seem to be lots of talk about mild-steel.Quote:
Originally Posted by typhoon_driver
According to all common sense, spring-steel should be the better material for almost everything. So is that in fact not the case where combat is concerned? Or is it the price difference?
For me it's just an availability thing, mild steel and stainless steel sheet is readily available. Don't even know if you can get spring steel in sheet.
Guilherme uses spring steel teeth on his drum.
Cheers Grant, being fan motors from a scrapped car I'm unsure what they'll draw. In their previous applications we didn't even blow 60a fuses but flicking a robot up may demand more.
Does anyone know if possible and how I can reverse the timing of fan motors? Currently advanced and want to mount them facing eachother.
I found this:
http://redneckrobots.com/ev/mod.htm
The motors 'look' similar, and I've read it a few times but it's just not sinking in :s
Sorry for the rather wordy long post, but I've been doing a bit of research into 4 Bar lifters and thought I'd post my findings.
I don't know of a single competing 4 Bar in the UK, which strikes me as odd since they look like a very effective and simple design and have great proven success in the US with Biohazard and the Ziggys.
But this is a good thing because I always want to make something a bit different, except this time it may actually be effective! Downside is I've no one to copy...
Anyway! To my findings.
Firstly I discovered that 4 Bar actually refers to a standard 4 bar linkage, the maths behind which is just engineering gobledeegook to me, but I did teach me that the 4th bar is actually the base (always wondered about that one!)
I then set about finding a way to design the system. The length of each arm is important, plus I needed to know what sort of power I would need.
So I did 2 things;
I did research into Biohazard, by looking at photos of it from the side I could surmise the ratio of each bar length. The base and top arm (same length) are twice that of the front bar, which is twice that of the rear bar. Figuring out where the linkages sat on the bars thought wasn't so easy.
The second thing was I found this:
http://www.totalinsanity.net/tut/mec...arfrontbar.php
It's a tutorial on designing a 4bar, not very indepth but does come with a little app you can run to calculate arm lengths.
By putting in Biohazards ratio it didn't work.... I think the linkage locations are pretty important.. But what I did give me an idea of was what sort of torque I require at my arm end to lift a FW.
Works out I need 200 Kgf*cm of torque to hold 13.6kg at the arm tip, at the most taxing part of the stroke. Now that doesn't account for lifting (only holding) nor additional friction or forward movement in the stroke, only vertical movement. Plus I want to make a flipper, not a lifter.
So how does that translate? Well I figured it wise to aim for 2/3 times that resultant torque in my setup from stalling motors. Since motors produce Max torque at 0rpm and 0Torque at Max rpm if I put too much emphasis on speed in the setup then it will just struggle and become slow. To much torque and I just have a lifter.
So depending on how easily I can obtain 400-600kgf*cm dictates my speed.
Originally I wanted to use a dual Fan motor setup. According to the EV Warrior stats on RMP they produce 82kgf*cm stall torque each at 24v. The only stats I can find for my fan motors, have 'nominal torque' and that's 10kgf*cm. Double that to 24v you have 20kgf*cm. How realistic is it to expect 4times the power at stall from nominal?
Anyway, fan motors are big (110mm discs) and heavy (1.6kgs each!) and I would need a 4:1 reduction on them which would give me 656kgf*cm torque which is more than enough.
Then I realised that Ewan has accurate stats for his drill motor setups!
So I went over to Gimson Robotics and found that 1 GR02 at 24v produces 197kgf*cm torque at stall. 2 of them instead and I am at 400kgf*cm already. Add my own additional 1.5:1 reduction and I have 600kgf*cm and saved a lot of weight. The Gimson gearboxes may struggle with all the torque.
Well that's the theory anyway. The alternative would be to look at this from the RPM side and decide what torque I can get based on a revolution speed that I know is fast.
Why not make use of the linear actuator we've got? It's designed to output loads of torque, and you wouldn't have to worry about stopping the motor as it's got the micro switches built in. I don't know quite how you'd use it to power a 4 bar lifter but think Bio Hazard used an actuator successfully so it's got to be possible.
You could use it either to power a crank connected to the axle of the front bar (which is how Biohazard and Griffon did it, both using two actuators) or just have the actuator act on the front bar (a la Flick, Suren Balendran's pneumatic 4 bar flipper thing from a while ago). You could probably use both of those on the rear bar too but more torque would be needed I think?
I don't think the actuator will be quick enough, I could most likely use it to make a lifter but I want more speed.
Biohazard used 2 x 12v actuators overvolted to 24v pushing a bell crank which lifted the front arms.
The system worked well and satisfied his design to keep the robot on a very low profile but the amount of stress acting on that bell crank is well beyond anything I could engineer.
Making 2 pivot points and having an actuator acting on one of the upright bars does seem the simplest option though.
As for rear bar vs front I don't know which I better. I just assumed rear was since you're acting on the shorter bar, meaning a greater lever advantage, but I would be wrong. Plus I wanted as much weight at the back of the machine so that when full extended the rear of the robot doesn't lift up.
You could do a really simple real-world test, whereby you stick a length of something onto your motor's shaft and see how much it can lift at the tip of it. From there it's easy to roughly calculate the ratio you'll need, knowing what it could lift and the length of the bar you put on. That's how we designed Tormenta 2's ratios (in about 10 minutes with the drill itself and a 7" allenkey stuck in the chuck), and it has easily enough speed and power to leave the ground when selfrighting.
I'd work backwards from RPM figures anyway, not torque figures. Work out how fast the tip of the lifter must move to launch a robot a realistic amount (obviously not so it theoretically goes 50 feet) and calculate the ratio you need from the motor from that. At 4:1 I very much doubt the motor will have enough power to be satisfying. Depending on its RPM I'd expect more like 15 or 20:1. In a perfect world 4:1 would result in a ballistic flipper, but in reality such a huge mechanical disadvantage for the motor will make it turn slowly, and so it'll probably struggle to even lift a target, even if the torque figures say it should.
Interestingly in pneumatic flippers people tend to go with huge amounts of power (like more than half a tonne of force to flip a fw) which will make the flipper slower as it takes longer to fill up.
I assume there is a good reason for this which I can't really explain, but clearly you need lots of power rather than just a high speed.
in pneumatic flippers a lot of "power" is used because you need the flipper arm to move a long distance in a short time, the best way to do it is a large force close as possible to the fulcrum of the flipper arm. The large force is required as the closer the force applied is to the hinge point, the larger the mechanical disadvantage becomes.
lots of power alone is useless, take for example a flipper using a hydraulic system. You can easily get 3000psi on a ram with an equivalent force of in excess of 3 tons, but it will just lift the load not make it fly as the hydraulic ram will not extend as quickly as a pneumatic ram....
I was rereading the topic, and I itch to add a bit about drive.
Satanix is bloody fast, but does it with a single stage gearing.
The Z12 mod 1 steel gear is welded to the axle of the Speed 900 and drives a Z72 aluminium gear inside a 130mm wheel.
Simplicity has its advantages.
I'm all up for simplicity!
I figured aiming for 100rpm output speed after reductions would be a good speed. So that's more like a 5:1 after the drill gearbox of 36:1.
As for power transfer I figured the simplest way would be to attach a gear to the centre of the rear arm pivot point and put a 2nd gear on the output shaft of the drill motor gearbox.
It would work, just that big question mark over whether the average argos drill gearbox would last. Why have you moved away from the car fan motor? In the right setup, that really could be ballistic.
I am looking through old footage for various reasons. One of which is there was a bot, name of which I can't remember. I am pretty sure it had one of the few successful pneumatic rams and was really low psi but high cfm. Sent bots flying oota sometimes.Quote:
Originally Posted by Max
was it m2 theirs was powerful
http://m2robot.com/
That definitely rings a bell! But the bot shown there has a lifter/flipper, not a ram. Hmm.
Slightly pointed upwards, helping it occasionally act as a flipper?
the early ripper had a lp flipper
Anyway, the point I was making is that it was one of the few successful spear/ram jobs due to high CFM rather than high PSI.
I've shy'd away from the car fan motors because they are so big and heavy, plus didn't seem to offer a huge power advantage over the drill motors and gearboxes.
We have a couple of spare all metal Dewalt motor/gearboxes, so hoping to put them to good use. I think they have 700 size cans.
They sound good. Ours is an 885-size can. Also, unless I'm missing something, surely the torque figures for a 550 are dwarfed by those of a good fan motor? Are you sure you weren't looking at motor figures for the fan motor and after gearbox figures for drills? Of course if the power to weight of a fan motor+gear reduction vs a drill motor is in favour of the drill then that makes sense. Either way, I look forward to what you build!
Spawn Of Scutter had what I think was a low/full pressure (I can't remember but I know they tried to run a low pressure ram at full pressure in series 7 and blew the end cap off the ram when they fired it unloaded) spike pointing upwards in series 4 - it was very good at flipping opponents over, but not very good at all at putting holes in them even with the extra gravitational assistance...
The only other robots I can think of that had *serious* spike weapons were 101 and Pain - 101 kept running into the problem of pushing its opponents away instead of doing damage even on full pressure CO2, and Pain's weapon was banned due to the fact it involved barely controlled explosions and the robot didn't work!
Apologies for hijacking thread, I'll go back to lurking ^^;;
@Joey no worries! Spear weapons are an interesting area.
@Ellis, Oh yeh the fan motors are way more torque-y. In terms of stall toque though, drill motors after the gearbox should be sufficient.
My main consideration is the weight (1.6kgs each) and size (110mm Dia, about 60mm deep) for fan motors, and that's without any sort of gearing. They'll also stall at 200a each at 24v, drill motors shouldn't get above 100a (which is the rating SSRs I have).
What reduction did you say you were running? 5:1? It seems pretty quick and can obviously lift other robots fine.
We're running 4:1 after the drill, but of course the drill is pretty big. Size isn't everything (shh! Lol), but it's quite punchy. If you have a smaller motor (885 can or less) you may want to gear higher. That said if you're powering the rear "leg" in a four-bar there's a ratio so you may be fine.
I don't actually know what ratio our drill has in low speed, only that it is about 400rpm at nom. voltage. We're overvolting to where that rpm is theoretically around 580rpm. Take 4:1 from there and the weapon would do about 145rpm. We just kind of round that down, allowing for load and losses, to about 120rpm on the weapon. If you aim for something along those lines you should topple other machines over nicely.
One thing I'll say, though, is that make sure the transfer from the drill to the weapon business is up to it. You may remember we had a real struggle to contain the torque when T2 came into being. Keep the torque limiter if those dewalt gearboxes have one, on its near-max it shouldn't slip when lifting but should when the weapon can't move. It's awful to hear and look at when it kicks in but I think it has saved us more than once!
Using the torque limiter is a good idea! I think Mike who built a lifter on here bought a dedicated one for his system.
Using 2 drills should help me share the load hopefully.
Having a bit of trouble deciding lengths for the 4 bar arms. Simulating the movement is proving tricky so thought I'd look at other 4 bar bots to see what they used.
At which point it occurred to me that I had never considered looking at Storm 2, d'oh!
So has anyone got any decent side on pictures of some 4bars with the arms up so I can deduct ratios, or better yet the actual measurements!
Cheers!
I know its a little tricky to simulate in 3d but if you have any measurments I can quickly do a few mockup animation tests in maya. Sorry I havnt read the past 12 pages but is it electric of pneumatic?
There's this, if it helps:
http://i1088.photobucket.com/albums/...2032012327.jpg
You can see the lower pivot point for the rear "leg" of the lifter glinting towards the back of the machine, at top panel height. That's the very top of an m10 bolt. You should be able to fairly accurately deduce the dimensions from that.
We designed the weapon as we did because it gave us the greatest lift height achievable in the space we had inside the machine.
Attachment 3783
Found this online years back (I think it was the Aussie forum). The sizes are specific to that robot but I seem to remember the user saying that this was the optimum ratio he'd deduced and it would be easy enough to transplant your sizes in keeping the same ratios. Although obviously you can vary it if you want more power or travel.
http://www.totalinsanity.net/tut/mec...arfrontbar.php - Finds the torque to hold a load at each point in the travel of your lifter, find the maximum and spec a bigger motor so it will actually lift things.
isnt there somthing on storm 2 in the real robots books with pics of the arm
An alternative use for our 50x100mm cylinder is a 4 bar lifter. I have been examining Ziggy, the US Superheavy weight. That makes things fly! Though the whole thing is built from Titanium and has 2 massive buffer tanks to insure a constant thrust which you cant really do in a feather but its worth a look!
Thanks for the responses everyone, a great help!
@Marco, that would be a great help thanks!
I found Biohazard to have:
Top Bar is twice the length of Front Bar
Front Bar is twice that of Rear Bar
Where they attach is a differebt matter.
It's electric. The tricky parts are designing so that the thing will lay flat (at at least ear flat) when retracted, and have decent reach when fully extended. I figured to be decent at this scale the tip of the arm should be at least 30cm from the floor and from the robot.
@Ellis, cheers! Deciding height over reach is a tricky one.
@Jamie, that's a great help. Ignoring the right angle in the front bar it's length is 210mm, so;
Top Bar 360mm
Front Bar 210mm
Rear Bar 135mm
Lower Pivot Distance 235mm
Upper Pivot Distance 160mm
@Marco, could you possible animate this?
@Daliad, that's a great tool I used a bit to calculate how much torque I would need, but it's quite buggy and difficult to set up.
@Plargen, I believe Jamie has them all online, I'll have to trawl through.
@Alex, Ziggy is something else! Have you seen it self right?