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So starting work on a new HW. Might take a while as I'll be doing it on free weekends.
Wondering if anyone could recommend a speed controller- the stall current of my motors is around 230A. I'm looking to keep it cheap if possible (student budget) but prepared to fork out a bit.
Possible designs uploaded soon.
A Wotty.
What are the max amperages on the 360?
Enough to survive your motors.
360amps, don't scrimp on the speedo you will suffer down the line if you do. Wotty is the best bet yes.
A good speedo is an investment for years. Especialy a speedo with good support.
Cool, I'm happy with Wottys. Do second hand 360's come up for sale often? Or would it be better to get the 360EVM new from Ian?
Also, are burkets worth buying second hand or is it best to buy new?
Not often that they turn up second hand, and in most cases, those need some TLC like replacement seals. If the solenoids ain't AC .
I don't own a pneumatic based robot, but I would have thought from a safety perspective new valves would be a must.
Ok thanks. Where is the best place to get them?
We buy our Burkert 5404 1/2bsp 24V DC coil 2/2 valves with RS components.
But there is a less expensive way, if you're willing to go Chinese. 2 disadvantages. No warranty whatsoever, and except the body, not compatible with the Burkerts (means you can use an original burkert body, but have to replace anything else if you want to mix and match). You can buy 5 "Churkerts" for the price of 3.5 originals. And that's including import tax. (why 5, because that's the minimum)
Thanks for the info. Very helpful.
I'd like to understand before I buy- this valve (the 5404- I assume the same as the one you are referring to?) says it is good for pressures up to 50 bar. I thought the fire extinguishers produced about 60-70 bar? Am I being stupid here?
(link to valve: http://www.buerkert.com/COM/buerkert...e=5404&sk_id=2)
The firm "Burkert" garanties that the valve will work constant and dependable @50 bar with a working voltage of 19-24V, what a standard PLC voltage is.
In the 13 years I use those valves, and a lot of roboteers with me, we learned that the pressure isn't a factor, and that the valve can withstand 200 bar(thanks to Mike Lambert, who spend the money to have them certified). The point is that it won't work always unless you feed it 24V+.
That is why we use a voltage booster in our feathers, meaning we don't have to lug around a 24V battery.
In the heavies we run 36V, so there it isn't an issue whatsoever.
The only disadvantage of 36V on the 24V coil is that it will run hot. But with a working time of 5 minutes max, the solenoid , ment for permanent powering, won't care.
Things that will ruin a 5404 are swarf and age.
Getting this back on track again- I'm wondering what batteries people use? I dont think I'm ready to go full LiPo yet, but I think I need to finally upgrade from SLAs.
So-
What NiCads do/did people use? I'm hoping they will provide me a middle ground...
Don't think you're allowed NiCad's anymore, would have to be Nimh.
New NiCd isn't cheaper or safer than LiFePo4.
If you can find them. In theory it's old stock that's being sold.
Oh right- good thing I checked! Any idea why they were banned?
Do NiCads come with a C rating like Lipos do?
I think nicads are banned from sale under EU law because of the harmful chemicals (cadium I think). Nimh sprang up in their place and are pretty much identical. Think they even work with the same chargers etc.
If you can get old Nicad packs, then you can use them as far as I'm aware (haven't read the rules recently) but yes they are no longer allowed to be sold commercially. There are packs that come up for sale now and again on here but they're old packs that will have been used. Yes they might be fine but they'll have seen battle in most cases.
Nimhs are the next progression. Similar in size & stats but I don't think they are/were as good at providing as high a discharge current as Nicads. For the money, you'd be as well using Lipos. If you're unsure, just ask the right people lots of questions on them, read all the rules regarding them, and have a look at how other HW users have fitted them. If you follow the right procedures and treat them properly, they'll just be like any other battery.
The EU did ban NiCd due the cadmium in it. Rightfully so. It's a very harmfull heavy metal.
This is a stupid question but did you build the original Leveller 2 etc. ?
Getting this project back on track now I've got all the parts together. I was wondering what pressure relief valve people use?
Also, where do you source shutoff valves? Is there a high flow option that would eliminate the need for buffer tanks? I assume there isn't otherwise people wouldn't still be using buffer tanks!
Ta
I could add an hydraulic ballvalve with a build on burst disk ,as mandatory on CO2 bottles, to an excisting extinguisher.
That would be high flow. But getting that certified, forget it.
PRV's, the search function here will give you several sources.
Having a higher flow valve on the end of your main tank is likely to cause issues with sending alot of liquid CO2 through your solenoid valve. A low flow bottle valve and buffer tank seems to be fairly critical in giving any liquid that goes through time to expand into gas before having any major issues.
Ah of course- I forgot the liquid CO2 factor.
Is the burst valve from a fire extinguisher too highly rated to be used as the safety in a bot (190 bar vs 69)?
The burst disk will prevent the bottle reaching its critical pressure. You need the pressure relief valve to protect the rest of the system from over pressure. I.e. a valve rated to the pressure of the weakest component in the system.
The Pressure Relieve Valve has as main function to protect from overpressure or a too high working pressure (max1000psi/69bar).
The burst disk just protects the surroundings from exploding bottles.
About any modern industrial CO2 bottle is actualy a simular bottle as argon or such, therefor the test presure is 300 bar, and the working pressure 200 bar. This gives the reason for the 195 bar burst disk.
Paintball or Sodastream bottles sometimes have 135 bar burstdisks.
Cheers guys. That's what I thought, just wanted to check.
Regarding buffers, is there any benefit in having a buffer volume of 8000cc versus 4000cc if my ram is only 943cc? I know the rule of thumb is no less than 3 times your ram volume, I'm wondering if the increase in pressure from 4L to 8L would be enough to justify the weight.
Some progress, waiting for bullet connectors to come from China so I can get the batteries wired up. Then it's solenoid wiring and fabrication.
Attachment 5112
The advantage from 4 times to 8 times buffer isn't in relation to the weight and space used. In short, keep it 4 times.
Thanks Mario. I have started with 8 times now so I'll see how that goes. Weight and space don't seem to be an issue at the moment but it's nice to know I have a buffer (no pun intended) if they become an issue.
Thinking about battery boxes- I was thinking of making a little polycarb box to contain them, but I realised I have no idea what I'm doing when it comes to working with polycarb.
How do others secure their batteries? Do the batteries make contact with a baseplate- or would people put something in between to absorb some impact? Is arena fire (at RW events) an issue with LiFe batteries?
Cheers
There are voices that want to mandate a metal battery-support-baseplate, but for now anything is ok.
For team RCC.
LiFe's are no firehazard. We had in the 7 years we use'm 2 mishaps.
1) Recharging a 4S pack on 6S. Result, a bit of smoke and bulged packs.
2) Drilling a hole trough them. Result, a lot of smoke.
The raptors Nebelwerfer and Perun use a bend and HDPE box that gets closed up when the armor goes together.
Hannibalito 3.2 uses a steel plate with bend sides as part of a support frame, and a piece of heavy duty RC velcro strap.
These 3 machines use a Zippy 3S 4000mAh LiPo hardcase pack.
Bullfrog has a shockmounted ali box containing the 2 5S 5000mAh LiPo's.
Kan Opener has shockmounted open framed Titanium support structures to keep the 4 Zippy 4S 8000mAh packs in place.
So just don't drill through the batteries... got it! :D
Thanks for that- you don't happen to have any pictures of the on in Bullfrog do you (or any others, just trying to picture them)? Dont trouble yourself taking any if you don't.
Drilled and tapped the holes in the buffer tank and got all the pneumatic parts put together today.
Current problem is that the ram goes up very slowly. Am I doing something obviously wrong? I'm worried the flow rate through the valve is too low.
If I remove the ram from the system and connect the ram up to with 2 closed burkets and leave one port open the piston moves up and down with ease. However if I now plug a 3rd burket into the open port and open the valve I can push the ram down but it is stiff. Am I getting a normal amount of flow through my burkets?
Cheers. Video attached.
https://www.youtube.com/watch?v=6Gez...ature=youtu.be
It's normal with all the ports closed that the ram moves very slow and stiff, it shouldn't move at all even.
But I guess there are some small losses in unpressurised Burkerts.
Now, how did you connect it all up? Any restriction in flow will make a large ram like that move slow.
The ports in the ram are 1/2bsp.
If you use 2 Burkerts 5404's to feed the ram, there should be 2 hoses or pipes between those and the buffertank. Internal diameter of hose/pipe should be at least 12mm.
If these conditions are fullfilled, there is another possible reason to have a "limp ram". The shuttles not moving in the main valves.
Option 1)
The pressure is over 50 bar, some Burkerts need more than 24V to open the solenoid fast enough to have the shuttle move, otherwise it's just the 2mm assist hole in the Burkert that feeds the ram.
2) Foreing matter in the valves ( swarf or sticky iccy stuff)
I explained it very badly- I meant with one of the ports open the ram only moves slowly.
The burket needing 24V to open sounds like the most likely thing at the moment- I'll up the voltage and try again tomorrow!
Also- when the ram is at full extension, I can hear air escaping from inside the ram. Is this intentional or a problem?
Cheers,
Tried it again with 24v, no change.
I guess that means I'm down to swarf in the burkets- but all 3 of them?
How would I clear this out if it is the problem?
open the valves is the first part of that.
Some slow but steady progress. Havent had chance to look at the valves yet, that's the next job for when I've got time to sit down with them. Also need some spacers on the wheels- they move laterally quite a lot at the moment.
Attachment 5163Attachment 5164