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Speed Controller
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Spockie-Tech
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Joined: 31 May 2004
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Location: Melbourne, Australia


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The Medium Motor Controller is mostly the same as an O.S.M.C. controller ( http://www.robot-power.com/products/osmc_info.html with heatsinks and a switchmode regulator added.

It should handle around 200 amps fairly reliably, and several prototypes have been built and tested,, but we havent gone into production with it, since the arena's for heavyweights and larger dont exist yet, so we (or anyone else) havent needed them..

Its not going to be cheap though, since it has 4x the amount of fets, heatsinks etc of the IBC, and its a single motor controller, so you need one per drive channel (side) of your bot. At a very rough guess, I'd expect them to be around $700-$750 for a set of two, with the uMOB needed to drive them

(the uMOB is built into the IBC, its the micro brain bit that converts the radio signals to PWM drive for the H-Bridge Fets)
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Post Mon Aug 16, 2004 11:06 pm 
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Spockie-Tech
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I've never heard of a "36mhz speed controller"...

Different speed controllers do run at different frequencies, but they usually refer to the "Pulse Width Modulation" (PWM) frequency, which is the rate at which the controller pulses power into the motors at.

IFI controllers (Victors, Thors etc) run down around 300 Hz (pulses per second) IIRC, which gives the motors a deeper "hum" sound when at part throttle. The IBC, OSMC and most others run at around 2000-4000 hertz which gives them a higher "singing" sound (supposedly more efficient operation)..

This has nothing to do with the radio receiver operation however, the controller shouldnt care about that, since all it sees are the servo-motor signals well after the radio stuff is all over and done with.
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Post Mon Aug 16, 2004 11:12 pm 
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timmeh
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Joined: 20 Jul 2004
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The speed comtroller that marto was building is that on off driving with the relays or dose it have vareable speed?
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Post Thu Sep 02, 2004 6:18 pm 
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Totaly_Recycled
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The speed controler Marto was makeing is from a deshigh i sent him that i got of the net and added a few mods to with the help of Brett(Spockie) it uses servo circute boards with out the servo motor ,to drive fetts for full speed control . I used rotary switches on my first atemt controlers but made the circute also for useing relays .. Steve and marto were haveing a bit of trouble with the relays chattering but i havent heard wheather they got the problem fixed or not .

Post Thu Sep 02, 2004 7:51 pm 
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marto
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Nah i gave up one trying to get the servo controller working. If i had some decent fets and more time it would work.

BTW im only one person.

I am steve
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Post Thu Sep 02, 2004 10:01 pm 
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marto
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OK I have had enough of trying to make the one's using the servos work so i've decided to try a PIC. My team mate johno can program in C but i was just wondering how i go about it.

I think to start off with i might just get it to drive the darling to switch relays to start off with and then move up to FETs.

Also which PIC should i use?
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Post Fri Sep 03, 2004 9:35 pm 
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Spockie-Tech
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Hi-Power Motor controllers are a bit like Race-Car engines. the more power you want them to deal with, the more everything has to be spot-on or they will break..

Driving a full H-Bridge of Fets (so they can reverse) at high currents and (PWM) Pulse Width Modulating them on and off hundreds to thousands of times a second without getting "Shoot Through" (where the upper and lower Fets on the same side of the bridge are on at the same time) is quite an art.

It seems like it should be simple enough at first glance, the Fets should only do what the micro tells them to shouldnt they ? So if there's no shoot through in the micro-code, then the fets should be fine ? Uh-Uh.

They behave capacitively and take time to start and stop their huge surges of power, so require either a lot of theoretical work to figure out the current flows in and out of the gate capacitance to charge and discharge their switching, or a fair bit of "practical experience" (read blown up Fets) tuning the drive circuit until you hit the sweet spot.

Do a google search for the "miller effect" as an example of one of the unsuspected areas of complexity that can bite you.

If you want to save yourself a lot of trouble and benefit from the experience of others rather than remaking the same mistakes, read through the OSMC group (on Yahoo groups) archives and you will get a running start on making your own controller.

Other than the Fet-Drive bit (which is the important one), A controller is fairly simple in basic concept.. Time the width of the servo-drive pulse (1ms - 2ms long) with your micro, scale it and turn it into a bi-directional variable Pulse Width Output to drive the output stage.

Adding features like mixing and failsafe takes a bit of extra work, but they can be added after you get it moving.

Remember though, if your primary goal is to battle reliably, bite the bullet and buy a controller, I guarantee it will save you a lot of time, money and frustration in the not-too short term while you debug your own design (and get your bot beaten up in the process). If you are interested in learning "just cause you want to know", then read up on the OSMC group and ask myself or them any questions you would like an opinion on..

Which PIC should you use ? If you are just building one controller, get the beefiest, fastest one you can. preferably with multiple hardware PWM outputs.

The more hardware grunt you have (for a few $ extra), the less time you will have to spend getting the code to do things which will minimise your development time. If you are building for a high-volume production environment, then you always use the micro that has *just* enough to do the job (With a safety factor). just like most engineering.

I cant give you specific model #'s though, since my PIC experience is limited to 16f84's and the Pic-Axe range, and they bring out new ones all the time. Jake/Valen might be able to.
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Post Sun Sep 05, 2004 12:39 am 
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Valen
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Joined: 07 Jul 2004
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i'm going 16f877A
(well specifically 16LF877A (low voltage part) to interface with my radio)

2 HW pwm chans
10MHZ/4 instruction cycle
8 A/D inputs
$13+ from RS in ones

Post Sun Sep 05, 2004 10:33 am 
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Totaly_Recycled
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Ok Here is a circute that was sent to me last night by Randel (mytqik).
As i dont know a lot about chips and stuff mabe Jake or Bret can check it out and see if its any good . http://www.bobblick.com/techref/projects/sv2pwm/sv2pwm.html

Post Sun Sep 05, 2004 1:43 pm 
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Spockie-Tech
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That Bob-Blick circuit looks like it would work, but its way too complicated given that the whole thing could easily be replaced by a $5 single 8-pin microprocessor.. (or maybe I'm just biased towards micro's rather than discrete analog circuitry ?).

Also, its only a part of a speed controller. you still need the high-power section described at http://www.bobblick.com/techref/projects/hbridge/hbridge.html

the first circuit is just the single-channel RC servo to PWM converter, however it only has low-side-of-the-H-bridge outputs, meaning the seperate H-Bridge circuit would need additional drive, logic and timing circuitry in it to control the high-side of the bridge.

It looks like the hard way of doing things to me though.. Confused
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Post Sun Sep 05, 2004 2:36 pm 
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Totaly_Recycled
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Ok i wont add it to the good bot building links then

Post Sun Sep 05, 2004 4:38 pm 
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Totaly_Recycled
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Ok i had a god read and the circute is not good for curents over 5 amps also he doesnt recomend useing it for driveing fetts he links to some where else iff you are looking at useuing fetts

Post Sun Sep 05, 2004 5:01 pm 
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marto
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Yeah i'll end up buying a controller eventually when i run out of ideas to do it myself.

I don't think i'll try and get FETs to work initially just get them to switch some relays
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Post Sun Sep 05, 2004 10:46 pm 
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bigjimmy



Joined: 18 Jun 2004
Posts: 40
Location: New South Wales


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hey spokie(brett) i sent an email to you about a week ago about wheather you had any of those pre programmed PIC-AXE 18A micros for the relay speed contoller you described in the abbl forum and the 75477 chip for the ibc.

I have all the parts for the realy speed contrller so im just waiting for the pic-axe 18 micro (if you have any)
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Post Tue Sep 07, 2004 12:53 pm 
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Spockie-Tech
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Wow, that was a while ago I mentioned the Pic-Relay-Controller, I didnt think anyone else had bothered to build one of those, so I didnt bother to program up any micro's for sale at the time..

I still have the code for it though, and have to build a couple for our PC-Bots, so I can probably make you one without too much trouble.

I was fiddling around with it working on adding some other features though, so it might take me a few days to return the code to standard and test it before I send you one.. Give me about a week and hassle me some more then..
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Post Tue Sep 07, 2004 6:30 pm 
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