Is One Parallel Capacitor Enough for Small Tamiya Motor?

Mikerocontroller

· I'm·wiring up a pair of small Tamiya motors for 5 volt use.·· ·I see different noise filtering configurations using up to three capacitors.· I'm using a Pololu Dual Serial Motor Controller.· Has anyone out there found a single .1 uf. capacitor mounted between the each pair of motor terminals to be sufficient?· I don't really want to run to Radio Shack for extra capacitors if I can help it.· I will do what it takes to make sure the motor noise doesen't interfere with the Stamp I am using (including walking to the Shack ........if I must).· Anyone out there running this combo with just one capacitor per motor?

agfa

I've tried the same motors and controller combo.· I ran with single .1s across·each motor.··I also ended up putting·.1s across the motor outputs on the controller to keep the controller from doing strange things.· I didn't have any problems with the stamp though.

I did have a lot of controller thermal shutdowns·with those motors if I ran them full tilt.· I think I read on Pololu's web site that the motors were more than the controller could handle.

edit:· I had to put the caps across the logic and motor supplies near the controller,·not the motor outputs.

Post Edited (agfa) : 3/5/2010 4:03:18 AM GMT

erco

Mikero: Depends on motor load & current, so we can't say for sure, too many variables. Which Tamiya motor, which winding, which gear ratio, your bot weight, wheel size, etc. One cap may work OK, 3 in a delta config is usually best. Try it and see. Wire them right on the motor tabs, not on your board.

0.1 uF caps are very useful for may apps, stock up and keep them handy. Hosfelt sells them for about a nickel each. Buy a hundred!

Curious that the new Stingray robot has no motor filter caps at all.

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·"If you build it, they will come."

Mikerocontroller

·· @agfa...have you also used tried the Tamiya twin-motor gearbox as well? ·I'm driving 56mm wheels and I'm using the "C" output section of the gearbox. It is a three-speed box but ·is configured for one speed only during assembly. I want to load the motors as lightly as possible and maybe that might reduce electrical noise.· I lost the documentation and dont know the ratios of the "A", "B", and "C" configurations. Do you know them?· Each selected ratio changes the location of the axles so I have to sort that out before I go any further.

·· ·I also had some problems with the motor controller when I first tried it last year.· I remember doing away with the reset line for some odd reason.· I'm sure·it had to do with noise issues from the motors.·· I might agree that these motors may be drawing too much current under some conditions.

·· ·I wonder if ramping-up the motor current will help?· I'm stuck with this wheel and gearbox/motor combo because my chassis has been designed around it.· I've taken steps to protect the exposed gears from debris and muck because I saw this as a problem in my early prototype.· A rock or wound-up carpet fiber in the gearbox would definitely overload the controller.

· Sorry erco..did'nt see your post.· Is there enough info provided?· The bot uses a PS2 mouse shell, 4-AA cells , OEM BS2x board, Pololu Micro Dual Serial Controller, and no caster installed.· Does this give you a ballpark weight?· I need a scale...· Do you know the available ratios for the Tamiya Twin Motor combo (not to be confused with the Tamiya Dual Motor Gearbox which is beefier).?

· I really should not complain...the Radio Shack is ONLY A BLOCK AWAY!

Post Edited (Mikerocontroller) : 3/5/2010 4:41:44 AM GMT

Mikerocontroller

@erco..when you say delta do you mean across the motor and a series (-) and series (+)?· Or do you mean across the motor and· from each tab to the motor housing?

agfa

I·thought we·were talking about the same gear box.· I have the double gear box.· It sure looked like the same one you posted in another thread.· Heres a pic of mine.

The unusual behavior I experienced had nothing to do with motor or load.· I used single caps because I was afraid of damaging the motors while soldering to the case, and there wasn't enough of the case exposed without modifying the gear box.· I believe ramping helped,·Pololu did·recomend it, in fact I wasn't ramping when I experieced the shutdowns.· If you think it·will help I can scan·my copy of the·instructions for you, just pm me an email address.

Post Edited (agfa) : 3/5/2010 1:08:20 PM GMT

Mikerocontroller

·@agfa... Actually· there are two different gearboxes: Dual and Twin.· Yours is the Dual and has·wider (stronger) gears.· I don't know if the motors and ratios are the same.· I agree about soldering on the case.· I'm thinking about potting the motor/gearbox into the chassis·with expanding insulation foam.· I'm hoping this will quiet the gearbox·and help to position it·.· I have another motor in case this gets messed up.· I think I liked servos better in some respects: no noisy external gearbox and no unintended acceleration when things go haywire.· I just want to make sure I do the "building" part of my project as few times as possible.· Thanks for the replies.· PS· I found my gearbox and controller docs.

erco

"across the motor and from each tab to the motor housing"--perfect!

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·"If you build it, they will come."

Mikerocontroller

Thanks erco (aka Father of the Poor Cousin).·· I suppose the other configuration I proposed would have blocked ·DC!

Whit

erco said...

Curious that the new Stingray robot has no motor filter caps at all.

Yes, wonder why that is? Are it's motor's less noisy (electrically speaking?) or does the Stingray's motor control circuitry have something to take care of this?

I saw that you had added these to poor cousin. I know they are also present on the Scribbler. I know this is often done.

What exactly does it do? And how does the configuration aid this?

@Mikerocontroller - thanks for asking this. I meant to PM erco and ask about it after I saw the pics of the Poor Cousin (aka RetroBot) in Robot Magazine.

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Whit+


"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

Whit

Hey guys,

I think I answered my own question - see here http://www.beam-wiki.org/wiki/Reducing_Motor_Noise

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Whit+


"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

Roy Eltham

Could the reason the Stingray doesn't have them be that it has the power to the motors seperate from the power to the rest of the board?

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Check out the Propeller Wiki·and contribute if you can.

erco

That's a wonderful Wiki, Whit! Say that 10 times fast.

The Stingray motors are standard Chinese brushed DC gear motors. They make the same electrical noise as any other small DC motor, even if they have their own seperate power supply (is this really how the Stingray is set up, Roy?). At that low 30:1 gear ratio, there's a lot of current flowing there under acceleration: more current is more noise. It's generally good practice to put 1-3 filter caps on all DC motors to reduce unnecessary electrical noise & spurious emissions. It prevents some problems and head-scratching. Sure couldn't hurt to add them to a Stingray.

As you saw, Whit, Retrobot does use three filter caps per motor. Those are gigantic mylar ones in the photos, but they're still 0.1 uF. First ones I grabbed off my bench. Small ceramic 0.1 uF units are fine, too. I think I needed the extra weight for traction!

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·"If you build it, they will come."

Whit

erco said...
·I think I needed the extra weight for traction!

Good call!

@Roy - the Stingray comes standard with a single power source for motors and electronics (Six AA rechargables).

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Whit+


"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

Roy Eltham

erco & Whit: The battery input (vin) goes directly to the L6205 dual full bridge chip where the motors are connected and it also goes into the L3501 based switched power supply circuit that has filter caps and produces the 3.3v and 5v power for the rest of the board. So the power for the rest of the board is sort of isolated from the motor power via the power supply circuit and the L6205.· The datasheet·for the L6205 chip says that its cmos logic side is isolated from the dmos motor power side, so I assume that would block power noise from the motors getting into the control pins hooked up to the Prop.

In any case, I've had no issues so far·running the stingray with the motors going full speed.

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Check out the Propeller Wiki·and contribute if you can.

Whit

Thanks Roy! I will take a look at this.

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Whit+


"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

Martin_H

Whit that link to the BEAM wiki was great. I always figured the capacitors were some kind of low pass filter, but seeing that circuit broken into components really cleared things up.

GWJax

Here is a diagram that I use as a general purpose when using motors that are not grounded to the frame. I have not had a problem with noise to a MCU after doing this to each motor no matter the size in respect to hobby motors. Now large current drawing motors use the diodes as well that are in the above link that was posted.

Jax

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If a robot has a screw then it must be romoved and hacked into..

Mikerocontroller

Thanks for the replies.· I tried out the vehicle today using the 58:1 gear ratio.· Wow!· The thing shot across the room and slammed into the wall before I could stop it.· I'm going to have to ramp the motor current just to keep this thing under control.· The vehicle skids on its belly just fine so a caster will not be used.· Now it's time to splice up a bunch of wires.