Team Bitza

[Liftoff]

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

[Ellis]

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.

[PJ-27]

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.

[Ellis]

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!

[Bacon Wizard]

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.

[PJ-27]

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.

[grant_ploughbot]

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.

[Bacon Wizard]

I wouldn't be so negative. You learned a valuable lesson. Don't build a spinner from cast iron! It's too brittle and it failed right at the threads that you tapped in it (stress raisers). If that disk has been made from mild steel it wouldn't have had the same issues. My advice is to keep going with what you have and chalk this down to a lesson learned.

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.

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?

[PJ-27]

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

[PJ-27]

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.