magnethead

I'm studying to me an ME/minor AE. However, I'm working on my generation 2 robot (which may also turn into a college project, if it lasts all the way to my senior project) and would like somebody to look over my schematics for the steering system.

Also, I want to use limit switches [and diodes if needed] to limit the travel of the stering system, so the motor will shut off in the repsective direction at 20° of steering angle. With a diode, can't I rig the limit switch so that C-NC is a straight shot, but C-NO has a check valve rectifier diode?

Like say, I make it turn left. At 20° (or wherever I set it), the tie rod activates the switch. So instead of having direct flow, the motor will now only receiver reversed flow because of the rectifier diode. Would this work if put immediately before the motor terminals?


Here's the drawings as I have them now.

Log2

Love to help, but really... I don't understand your schematics at all, you need to help out a bit more, with labeling and better drawings, use a schematic program for it, so it lets you enter values and what not

magnethead

I can't supply a whole lot more than i put as text on the slides, because everything else is yet to be compiled. all i can tell you is:

motors: http://www.superdroidrobots.com/shop...asp?itemid=722

battery: http://www3.towerhobbies.com/cgi-bin...?&I=LXULN3&P=0

It's a centering and crab/counter steer steering selection system. Turning means when counter-steering, locked is while turning, centered is when the wheels are set straight center, reversed is for crab steer.

I'm concerned most about backflow and diode direction/placement. The diodes I intend to use are these: http://www.radioshack.com/product/in...entPage=search

Log2

ok taht cleared up a bit, but when you say SW, or switch, are you referring to a switch, or a "switch" aka a transistor? if you're not referring to a transistor, what type of switch are you using?

magnethead

micro-limit switch

joycejose

Glad to help, but really... I don't understand ...

magnethead

Also, if you can't tell from the drawings, the switches are SPDT. But the ones I have put common in the center instead of on the end. I'm going to bend the lever on the unsuspended end a little so that the cam shaped lobe on the steering arm will actuate it (SW2).

SW1: Do I want motors to stop when centered or have free range of motion

SW2.n: Shuts motor n off when the steering arm's lobe actuates the switch, unless SW1 is still supplying power to it

SW3.1 & 3.2: in a stacked arrangement, do I want the motor to rotate forward or reverse

SW3.3: Do I want any power to flow to middle motor, or do i want it out of the circuit

magnethead

OK, i'm hoping i have everything right, because i'm now working on the steering stop switches (4 more switches per motor). Should have those schem's done around wednesday or thursdayish.

Stu_computer

quick look at the drawings..

if red indicates positive(+) then diodes are backwards.

sw1 diodes are blocking/protecting branches, what cross-talk?

sw3.1,3.2 reversing motor will short circuit if one switch fails, use a single DPDT microswitch for reversing motor circuit or add blocking diodes on sw3.1,3.2 NO to motor leads.

magnethead

if you can find a DPDT micro lever switch, do let me know. I'm yet to find any.

The diodes are to prevent cross talk if one of motors are centered while 1 or more are not- there would be a power flow through the lines which would bypass the other centering switches

I hand drew a sketch of how i'm going to do the steering engle limit switches. When i go home this weekend, I'll scan it. It's also got cleaner layout of the schematic, not so messy.

magnethead

I finally just went and looked, thanks for being able to read diodes ;).

I'll flip them around on my hand-written schem.

Everything i see talks about electron flow (neg to pos), not neccesarily power flow. I had to go look in a basic circuit and figure out that the triangle points in direction of blockage.

magnethead

Here's the version I hand drew, digitized and animated. You may have to right click > pause to review it.

Because the rear axle will be backwards compared to the front two, I'm not expecting the steer stops to work on the rear axle under crab steer, though it would be nice if they did. If nothing else, i can reverse the 2 diodes and/or motor leads on the rear axle, and see if that fixes any issues. But crab steer really doesnt need steer stops, because I dont think i'll ever need the full 20 degrees to crab walk, though would be nice. Guess i'll have to wait and see once it's built.

http://magnethead794.com/self-steer2.swf

The easy thing to do would to use a pair of 4PDT relays to replace switch sets 1 and 3 (the center one I forgot to label is a switch 3).

Switch Set 1 is the center lock/unlock. Having seperate switches eliminates the needed diodes and completely prevents voltage cross-talk in case of unsyncronized centering. Could also use 3 poles of a 4PDT relay.

Switch Set 2 is the centering switches- when Switch Sets 1 and 2 are activated, they cut power to their respective motors. When Switch Set 1 is left engaged and Switch Set 2 are tripped, the motors still receive power.

Switch Set 3 is the reversing and center activation switches. An Alternative would be to use 3 poles of a 4PDT relay

Switch Set 4 is the steering angle lock switches. They cut power to their respective motors in the direction of lock, but allow power to flow in the reverse direction.

In all switches, center is Common, bottom is Normally Closed, and top is Normally Open.

magnethead

GR12V10A4P

http://www.futurlec.com/RelGen.shtml

20 dollars for 2 relays, optional bases are 10 dollars more. They would replace 6 micro-switches, at 3 dollars each, for 18 dollars. Then use a http://www.superdroidrobots.com/shop...asp?itemid=828 to actuate each relay- they cost about the same as a new retract servo (which is the only kind you can really use for switching things solid state). This would make everything be nice and compact below the frame as well- both relays, both ESC's, the lights switch circuit (already have), and everything else that I could think of could be put below the chassis. All I want in the electronics bay between the cab and cargo bay are the bettery, receiver, bay door servos, and the winch motor (already have) for the roll-back bed.

Stu_computer

JQX-115F-12 http://www.futurlec.com/RelDip.shtml
etch a board instead-more compact and easier to enclose, and can use cheaper pcb relays-those motors don't need much juice.

magnethead

They're rated 1 amp at 12 volts- I'll be running them at 7.2 volts, and all 3 will be on the same source circuit. And I havent done PCB's before, though i do like the thought.

magnethead

shite! idk how a PCB relay could be so much cheaper, but now you're got me thinking!

It would actually be the 9 volt version, the 12 doesnt relay below 8.4V it says, steering will be on 7.2V.

So I could put a good chunk of the steering system on a PCB...or even a breadboard (like i said, i've never etched, wouldnt know where to start).

edit 4: I guess I could always direct-solder the wires to the relay leads, and zip-tie the relays to a mounting board, which would screw into the platform in the electronics box. Everything needs to be removable ;).

magnethead

My choices are 30 bucks for a pair of relays and sockets, or 5 bucks for the relays (they're only DPDT), plus the whole kit and kaboodle to do the circuit. I think i'd be more willing to pay more for the 4PDT set, likely be easier to work with. All the electronics are going to be under the chassis, so not alot of space. And i want it to be a minimum of wire, hence the servo switches, even though they're 20 bucks each, thats same as equivelent servo setup with less wiring

magnethead

Relays actually cut down a good bit on the involveness of the circuit. I don't think it can be any more simplified...which is a good thing.

Stu_computer

you know a good source for free small parts?

old floppy drives, cd drives, and hard drives are good for microswitches, motors, screws, gears, fastners, etc.