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DIY speed controller
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andrew12



Joined: 09 Nov 2006
Posts: 19


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DIY speed controller

Hi,

I was looking through the forums and noticed that someone mentioned a DIY speed control found at these sites:

http://www.mcmanis.com/chuck/robotics/projects/servo.html

http://www.mcmanis.com/chuck/robotics/projects/esc2/index.html

My question is: Has anyone built this speed control and actually gotten it to work?

Some of you might ask why Im bothering to build my own speed control...the reason is its for a competition that our school is entered in and we cannot afford a commercially produced speed control.

Thanks for any feedback or comments,

Andrew

Post Fri Nov 10, 2006 7:59 am 
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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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now class repeat after me..

"You will *not* save money making your own speed controller !"

---

Hoenstly.. the parts you need are 3-5 as expensive in small quantities than they are in bulk (100 controllers worth) price that is available to the commercial manufacturers.

There is also the high likelyhood of an assembly error causing half the speed controller to go up in smoke and cost you the parts over again, and quite likely the fight.

If your budget is tight, look for a cheaper commercial speed controller, (Scorprions, Electronize's), or hunt around and find what you need second hand. Most ESC's are regularly traded on the for sale sections of the various forums.

I'm not being difficult, I'm a very do-it-yourself kinda guy do.. the difference is.. I've *done it*. I designed and built the IBC prototypes and I can tell you they worked out far more expensive each than just buying a production unit would be now.

You will find that applies to all ESC's. They do not use parts that are available from your local Dick Smith or Jaycar at a good price.

For example, the IRF1405 FET has just been started carried in stock by jaycar (so I read) for `$5 per FET. (An IBC uses 16 of them). Jason buys them in 1000 packs for around $2 each, so your $50 behind the commcerial unit cost already, and youve just started.

Sorry. There are plenty of plans on the net for simple and cheapo (Transistor bases) speed controllers tht can handle a maximum of 5-10 amps.. beyond that, powerful speed controllers need big $$ and time to make work.

Seriously, look at the Robot Power Scroprion, the English Electronize and shop 2nd hand, thats as cheap as it gets.
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Post Fri Nov 10, 2006 8:17 am 
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andrew12



Joined: 09 Nov 2006
Posts: 19


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I understand what you are saying and it makes complete sense. However, all the parts aren't as expensive as u think. For the ESC on that website the cost is less then $50....for a 72amp system that runs off of 12v. The only draw back is that its only tank style steering and there is no flip function and all the niffty things. Yet thats all programming. Also there is only a need for 4 mosfets not 16...and the mosfets are IRFz48....60v and 72amps....it should handle 50amps continuous per channel easily with a fan...the only problem is stalls...thats why the motors we are using only draw 10amps peak(windshield wiper motors). Without the mods I plan on adding the total should be about $18 and with the mods about $35-45. The parts are not that hard to find either most can for the DIYer be ordered as samples. The main problem with the design is the highside driver which Im goin to use a more robust and powerful IR21844 to switch on the MOSFETS fast. Other then that I see no real expensive things. The fact also that the board is going to be made as a favour like commercial boards is a bonus.

So again I ask has anyone tried this design mentioned previously or does anyone think it will/won't work?

I do not want to come across as being mean or anything of that sort....its just our school is supplying no funding whatsoever and the money is coming out of the few students in the groups pocket and we believe that if its done carefully it will work. Also, like you yourself I love doing things myself and challenging my electronic and programming skills.

If you still do not think this can be done would it be possible to give us some kind of deal if we pitch in and by an IBC?

Thanks,

Andrew

Post Fri Nov 10, 2006 9:16 am 
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Knightrous
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Joined: 15 Jun 2004
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For windscreen wiper motors, you might as well use use some bang-bang micro switch controllers. You will find speed control on those motors are nearly never used because the motors are so slow to begin with that you can just wing it.

If you want to try building some speed controllers on the cheap, PM Andrew (totaly_recycled), he has built PWM drill trigger controllers that have been very effective. Cost about $10 in parts if you have your own servo's and drill triggers from an XU1 cordless drill...
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Post Fri Nov 10, 2006 10:28 am 
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andrew12



Joined: 09 Nov 2006
Posts: 19


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Thanks for that tip. Suprisingly the motors we are using are pretty fast when using the high function on the wiper motor. To top it off we plan on using a chain drive becuase the fact that they have a massive amount of torque and can spare some of it for more speed. Also they respond well to a standard PWM signal.

Andrew

Post Fri Nov 10, 2006 10:32 am 
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DumHed
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Joined: 29 Jun 2004
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My cheapo custom PicAxe PWM stuff worked pretty well, it was just the radio link that didn't...
(the radio worked fine everywhere except in the arena Razz)
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Post Fri Nov 10, 2006 10:39 am 
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Knightrous
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Drill triggers are for you then Cool

If you PM Andrew, he might still have his spare set there that you could buy from him.
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Post Fri Nov 10, 2006 10:40 am 
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andrew12



Joined: 09 Nov 2006
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I'll look into that.

Thanks

Post Fri Nov 10, 2006 10:41 am 
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Rotwang
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Joined: 15 Jun 2004
Posts: 1586
Location: Vic


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http://robotcombat.com/marketplace_speedcontrollers.html

The Scorpion HX deals look good value to me and they would run wiper motors fine. Gives you weapon channel and legal and reliable fail-safe.

The Buddy deals are tempting.

I bought a couple of XL’s a while ago for testing, there very good.

I understand completely your do it yourself attitude, your not going to last long in Robot combat otherwise.

Just wondering where you go to school. We have had a few SC contact us and I am wondering if its one of them.

Post Fri Nov 10, 2006 11:24 am 
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Fish_in_a_Barrel



Joined: 30 Sep 2006
Posts: 673
Location: Perth, Western Australia


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I had a look at this design a few weeks ago, and one interesting part was the power dissapation information.

http://www.mcmanis.com/chuck/robotics/projects/esc2/FET-power.html

My $5 60V 100A FETs can only put out 71A max, while putting out 300 watts of heat. And to get rid of all that heat for a 3 phase H-bridge will cost me around $300 in fans & heatsinks.

For your situation, presuming your drive motors (2) are stalled (10A each) and your using a H-bridge driver (4 FETs per motor, 2 in use at any one time), you need to find a heatsink that will dissapate 9* degrees/Watt, not too hard, as long as there is some air movement. (If your bot is fully sealed then it will have thermal capacity and there will be a time limit before the air inside the bot gets too hot to cool the FETs.)
*I think this is right but it's getting late.

If for some reason you go all out on you motors and find some with a stall current of 50 amps then you need to get a 0.35 degree/Watt heatsink, which will total ~$80 from jaycar. (This would require fans venting outside the bot.)

Since it is low power, perhaps you could save some heat by doing PWM with one or two FETs and forward and reverse with relays.

Back to your first post: I haven't built it, but i haven't noticed any technical errors in his site, I looks like it should work fine. Good luck if you decide to build it.

Post Sat Nov 11, 2006 1:23 am 
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andrew12



Joined: 09 Nov 2006
Posts: 19


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I live in Canada and go to a school close to Toronto. I have the DIY attitude because when things break I'll atleast know how to fix them and I can modify things easier if I make it myself. Also, I just find it alot more enjoyable of a sport when u can turn around and say I built that whole thing.

Thanks for the info on FETs. I have read through the whole site and like you said to me there seems to be no technical errors. I am still not sure whether to make it or not, but Im trying to keep our options open. I have been trying to raise money to buy a already built speed control, but I would still like to try and build my own.

Post Sat Nov 11, 2006 6:25 am 
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Spockie-Tech
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Chucks website is full of good information, you wont go wrong following the principles of his design.

Thigs that'll get you in real life ESC design are the practicalities caused by things like PCB track Layout, EMI caused spikes, power supply filtering and hidden parasitic capcitance, and inducatance altering the H-bridge timing and causing shoot through.

Little things like having the FET gate drive tracks too long can trip you up (long tracks hanve solf inductance which is bad when you are trying to shove amps of gate charge current through them in microseconds)

Enjoyment and Learning is the only reason to consider building your own speed controller in *small* quantities. You will learn a lot about power electronics and if learning is enjoyable and more important to you than winning, go for it.

Just be prepared to be let down by your ESC on occasion while you iron out the wrinkles in the *impleementation* (not the design).

Thats why I said its cheaper to buy commerical. If you take into account a couple of likely smoke-bangs to repair that happen under combat stress, and the damage that will likely happen to your bot from being immobilisied mid-fight, then home made ESC's start to look very expensive against a proven reliable unit.

Especially seeing as how most people let time run away from them and are usually committing the sin of trying to finish their bot in the days before the competition. Having an unproven and untested component in there is almost guaranteeing a first round out, which doesnt please event promoters (like me) either. We want to see you put up a good fight throughout the event, not go out with a whimper first round - which is why I reccomend proven components to first time competitiors.

If you *want* to learn all about ESC's and how they work, and the primary motivation is not just to save a few $$ on a one-off unit (you wont). then by all means build your own.

Its a very rewarding process and you do learn a lot of stuff you probably never suspected (I had 10+ years of electronics experience and I found that *power* electronics encompasses a lot more subtle effects the become major ones under the influence of 50+amps that you just never see in <1amp circuits).

Just make sure you test your home brew ESC *thoroughly* before you jump into the arena with it. and try to build it in such a package shape that if it does all go haywire close to the event, you can drop in one of the commerical ESC;s to replace it and still go a fighting.

you should also join up to the OSMC (Open Source Motor Controller) yahoo group and have a read of the archives and follow the discussions for a bit. Thats where most of the friendly ESC design guru's hang out.
http://tech.groups.yahoo.com/group/osmc/
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Post Sat Nov 11, 2006 8:41 am 
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WiperMotor



Joined: 04 Sep 2006
Posts: 301
Location: SA,Australia


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I think I was trying to make my own speed controler at some stage but I decided that it was better just going with an IBC (with fan)

Post Sat Nov 11, 2006 9:21 am 
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andrew12



Joined: 09 Nov 2006
Posts: 19


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Thanks for the info on testing and making sure I take my time. I already plan on doing that. Im in no real hurry to get it done at this point in time. We have raised $360 and plan on buying an IBC for use if the homemade one fails and for future robots we design.

Is the IBC programmable and if so what is the original code that it is programmed with when you buy it?

Has anyone also reprogrammed their IBC then?

Post Sun Nov 12, 2006 2:21 am 
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Spockie-Tech
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THE IBC is reprogrammable. It uses an Atmel AVR Micro and the source code is available on request. You need a little programmer widget you can make for about $10, or buy from Jaycar for about $30 as a kit.

Jake/Valen gave theirs a brain transplant by using on off-board processor to replace the Atmel wth a faster one so he could do his packetised spectrum link radio control system
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Post Sun Nov 12, 2006 8:43 am 
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