wheelchair motor question

mikea

Hi, i have an r/c "buggy" driven by two wheelchair motors. i finally got it working and drove it around for 3 or 4 minutes. there are "cups" on the end of these motors that got twice as hot as the rest of the motor. after this short time i could touch the motor for maybe a second, but couldnt touch these cups at the end they were so hot. there are 2 wires to the motor and 2 to the cup. i thought it was a brake or encoder. this buggy is a scooter chair pretty much without the seat. the controller was bad so i took it off and controlling the motors with relays. does anyone have some info about these end caps im not sure if this is normal or not and dont want to damage anything.-mike

W9GFO

A picture would be really helpful.

If they are like mine then they are electromagnetic brakes. I removed mine and installed encoders in their place.

You should be able to remove them without affecting the rest of the motor.

mikea

Cool, thank you W9GFO. I will try to upload a picture....it says 10 watts on them and would like to keep them so there is no coasting but not sure if there is something abnormal going on to make them get so hot. Did yours get super hot when they were still in use?-mike

jdolecki

Take the 2 screws out that hold the "cups" on

If its a stock motor then those are the brakes.

You can easily remove them by taking out a couple of screws.

W9GFO

If you leave them on you will need to control them. When energized the motor will turn freely, they do not get hot at all. I would guess that yours get hot due to them being in the "brake" condition and the motor is forcing it to turn which will quickly build up a lot of heat from the friction.

In an electric wheel chair - when the joystick is moved you will hear a click. That is the electromagnetic brakes releasing. When the joystick goes back to center it will click again when they engage.

mikea

Thanks jdolecki, took it off definately a brake. Now that i think about it, it slows down to a crawl usually before those are applied when the chair controller worked. they are getting so hot now because im using relays and going full speed to stop. what do you guys use for speed control for the wheel chair motors? -mike

W9GFO

If you use 12V you can use HB-25s to control the motors. I have Jaguars to run mine at 24V. Dimension Engineering has Sabertooth controllers that work at 24V too for a pretty good price.

mikea

Mine are 24V. I definately need some sort of speed control. i took the brakes off which have apparently been braking 100% of the time and it goes really fast now. Thanks again.mike

mikea

I would like to try to build a controller. i found a diagram but cant figure out the cap values. the one on the regulator is 100 nanofarad i think, but cant tell if the rest are ultra or micro farads. its a picture 1/2 way down the page if someone could take a peek and see what they think i would appreciate it.-mike

http://www.hvlabs.com/hbridge.html

W9GFO

Haven't heard of "ultra" farads.

Generally they are micro (μ), nano (n) or pico (p).

http://en.wikipedia.org/wiki/Metric_prefix

mikea

ok, thank you couldn't tell if it was a u or m, and wasn't sure if "ultra" was used.-mike

jdolecki

Do the motors have the gearboxes still on them?

I use the Sabertooth 2x25 drive with a Spectrum RC controller.

http://www.youtube.com/watch?v=OQn5SD7UQgw

wheel chair motors with snow blower tracks.

GordonMcComb

W9GFO wrote: »

Haven't heard of "ultra" farads.

Hehe, but there *are* ultracapacitors, which somehow sound better than sooper-dooper supercaps. These are the ones with, for example, 500-3000 **Farads**. Frankly, I can't even imagine that. They used to say a 1F cap would be the size of a city block. Somehow city blocks got a lot smaller!

-- Gordon

idbruce

@mikea

Thanks for posting the hbridge link. I collect those

kwinn

mikea wrote: »

I would like to try to build a controller. i found a diagram but cant figure out the cap values. the one on the regulator is 100 nanofarad i think, but cant tell if the rest are ultra or micro farads. its a picture 1/2 way down the page if someone could take a peek and see what they think i would appreciate it.-mike

http://www.hvlabs.com/hbridge.html

I see two 680uF, one 1uF, and one 100nF on the schematic. (uF = microfarads, nF = nanofarads)

mikea

@jdolecki , there are no gearboxes. i hooked them through an ammeter and seem to remember they drew 20-25 amp? at no load. i really like the snow blower tracks idea, i would like to couple this buggy to a mower in the summer and put a plow on it in the winter. the scooter chair tires are bald and spin too easily.
does anyone have tips on homemade tracks? Also i was wondering if anyone has built their own motor/speed controller. i was going to try the one on the diagram i posted and wondered if anyone had some tips for stuff that may usually go wrong. im relatively new to this stuff and smoked a hip4081 and some mosfets on my first attempt. -mike

erco

25A no load? Wait until you put a load (and tracks) on 'em...

You'll need huge batteries, booster cable wiring and starter relays for those motors...

Maybe parts from http://www.tncscooters.com will work for you.

mikea

Ha Ha ...maybe i should double check the current before i go much further. Thanks for the link erco.-mike

jdolecki

All my robots have 20 amp fuses on the battery leads and on the motor leads

The only time i ever blew a fuse was when i started the motor with one of the brakes on.

That track robot has 20 amp fuses on it and i only used 12 gauge stranded wire for the hook up.

I believe the motor with no load draws less than 1 amp.

I can check it this weekend

mikea

I was way off... no load per motor was 3 amps. Is there a rule of thumb as to what that might go up to if the motor was really dogged down? The sabertooth 2x25 i think was around 125$. If it would normally be less than 12 amps even loaded up heavy there was a 12 amp version that was 1/2 the cost.-mike

Falcon

W9GFO wrote: »

A picture would be really helpful.

If they are like mine then they are electromagnetic brakes. I removed mine and installed encoders in their place.

You should be able to remove them without affecting the rest of the motor.

W9GFO,

Do you have additional info on the encoder you used, and how you interfaced that with the motor controller?

I have two geared motors from a Jazzy 610 power chair and a Sabertooth 2x25. The motors have that cap on the end with the brake inside. I removed the brakes and think that will be a perfect location for an encoder. I want to incorporate encoders to help with straight-line stability as I will besetting up a bot with differential steering.

Thanks,

falcon

W9GFO

I used the Parallax Position Controller(s). I had to make an adapter so that the encoder wheels would fit onto the shafts.

We encountered a problem using the Position Controllers to control the HB-25s. The PID values that are hard coded into the Position Controllers are tuned for the smaller wheels of the Motor Mount and Wheel kit like is found on the MadeUSA or Eddie robots. The massive 13" wheels of my wheelchair based robot would go into oscillations and there was nothing that could be done to fix it. I think it was Kevin (Wood?) at Parallax that spent a couple hours one night during UPEW 2010 trying to get it to work.

The solution is to use the Position Controllers as encoders only - rather than task them with directly controlling the motors.

Falcon

W9GFO wrote: »

The solution is to use the Position Controllers as encoders only - rather than task them with directly controlling the motors.

I did find this place with a selection of encoder wheels . http://www.encodergeek.com/EncoderReaders.html I suppose I could use one of these wheels (since they're cheaper) and find an encoder that would read it.

I've also seen some motor controllers with connections for encoder feedback. Since the 2x25 doesn't have this feature, would I just have to connect the encoder directly to the Propeller and modify the PWM signal based on that feedback? Is that what it boils down to?

Question: I see the wheel-type encoders used in many situation but I haven't seen the rotary encoders like the Parallax P/N 27805 [url] http://www.parallax.com/tabid/768/txtSearch/encoder/List/0/SortField/4/Default.aspx[/url] I'm sure it could be mounted and coupled to the motor shaft under that cap. Is it just not the right type of encoder electrically?



falcon

W9GFO

That rotary encoder would work, but I am pretty sure that it uses physical contacts inside. It would wear out fairly quickly. The common encoder uses a pair of IR LEDs and detectors. Either the encoder disk has slots to break the IR with the detector on one side and the LED on the other, or it reflects of the slots (or stripes) with the LED and detector on the same side. There is no contact so nothing to wear out.

BTW, if there is a pair of detectors then it is quadrature, if just one LED and detector then it is a tach. The difference is that quadrature gives you four times the number of "counts" per revolution as the tach, and it can tell you the direction it is rotating. A tach only can tell you the speed, it has no way to tell when the direction changes or which direction it is turning.

There are some good quadrature encoder objects in the Obex. Use one of those to have the Propeller monitor the wheel position and speed and then drive the motors accordingly. You'll want to learn about PID (Proportional, Integral, Derivative). You can probably do well just using the "P" (proportional) part so don't think that it is too complicated.