Author Topic: solenoid duty cycle with step-up circiut / dc to dc conveter  (Read 2378 times)

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Offline Jak24Topic starter

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solenoid duty cycle with step-up circiut / dc to dc conveter
« on: August 16, 2010, 09:57:18 AM »
HI

I Am looking for a new solenoid for my robot(i need to kick this ball :
http://www.acroname.com/robotics/parts/R194-ROBO-BALL.html)
, previously i used a 10%(pulse) duty cycle solenoid and i activated it with a relay, no extra circuitry. I got a OK kick, but for my new solenoid i need it to kick the ball for min 4 meters
at 4m/s and to do this i pretty sure i need a dc to dc conversion chip, however unfortunately,
i don't know what kind of chip/circiut i need to achieve those specs :P
and further more i don't know what kind of duty cycle i require, cause as far as i know a 10% duty cycle x volt solenoid has a maximum possible voltage of x(it's assigned voltage)and so i don't know if i should get a 10% or 25% or 50% or 100% duty cycle solenoid 
any suggestion are welcome

Thanks

Regards

Jak24

Offline Jak24Topic starter

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #1 on: August 17, 2010, 12:21:04 PM »
Hi

Any ideas?......
or at least point me at some dc to dc converters, and tell me the duty cycle i would need.....  ?

Thanks

Regards

Jak24

Offline waltr

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #2 on: August 17, 2010, 02:27:49 PM »
If the solenoid is only energized to occasionally kicking the ball then I don't think you need a high duty rating.
As to what will actually work I think you will need to do some experimenting.

What would be the input and output voltages for the DC-DC converter? What output power or current is required?
One possibility is to use a large cap that is charger by a lower current DC-DC converter but then gives a huge current into the solenoid coil to kick the ball.
If the excitation pulse is fairly short you may be able to use a much higher voltage (current) than what the solenoid coil is rate for.
The magnetic field strength in the coil is proportional the the current times the number of turns.  The stronger the magnetic field the stronger the pull on the plunger. Again some experimenting is in order.

The accelerate a 0.7lb (300gm) ball to 4m/s in a distance of the solenoid plunger travel distance, say 2cm, would engage the ball for 10msec. Or have an average acceleration of 400 m/s/s. This requires 120 Newtons of force on the plunger/ball or 480W of power.
[I think these last calculations are correct. A check would be appreciated.]

Offline Jak24Topic starter

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #3 on: August 18, 2010, 08:23:33 AM »
Hi!

These are the Solenoids i would consider:
http://www.electromechanicsonline.com/product.asp?pid=26
http://www.electromechanicsonline.com/product.asp?pid=849
http://www.electromechanicsonline.com/product.asp?pid=39
the input v would be from a 18.5v li-po battery
the output i don't know :P
and i  don't know the duty cycle i need :P
Feel free to give suggestions on dc to dc converter

Thanks  

Regards
Jak24

Offline waltr

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #4 on: August 18, 2010, 09:21:17 AM »
The rated duty cycle is the: on_time/(on_time + off_time). How often will you need to kick the ball?
I'll guess maybe every 10 seconds at the maximum, does this sound reasonable?

From my post above the solenoid only needs to be energized for a 1/100 of a sec so that would be a 0.1% DC if it kicks every 10 seconds.
I also calculated that 120N of force will be required to kick the ball with a 4m/s velocity. The conversion is 1N = 0.2278lb force, so the solenoid needs to have 431 oz force. The none of solenoids look to have the required force according to the data. The third solenoid is the strongest and may be a starting point for tests. This one is rated for 100 Watts and the additional data shows a coil resistance of 6.1 Ohm if wound for 24V. That will be 4 Amps of current.
But I calculated that 480 Watts of power is required to accelerate the ball in a stoke length of 2cm. So my guess is that this solenoid will not get you the desired ball velocity.

I understand that you already have a solenoid ball kicker so run some tests and measurements with that system to check on my calculations. Then you will have a much better idea as to what is required for the new ball kicker.

What specs do you need for the DC-DC converter? Input voltage of 18V (LiPo). Output voltage? Output current? Duty cycle of power demand?

Is this a school/team project? It does sound like it and it sounds like it is a fun, challenging project that is doable.

Offline Jak24Topic starter

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #5 on: August 18, 2010, 01:54:26 PM »
HI
The rated duty cycle is the: on_time/(on_time + off_time). How often will you need to kick the ball?
I'll guess maybe every 10 seconds at the maximum, does this sound reasonable?

From my post above the solenoid only needs to be energized for a 1/100 of a sec so that would be a 0.1% DC if it kicks every 10 seconds.
I also calculated that 120N of force will be required to kick the ball with a 4m/s velocity. The conversion is 1N = 0.2278lb force, so the solenoid needs to have 431 oz force. The none of solenoids look to have the required force according to the data. The third solenoid is the strongest and may be a starting point for tests. This one is rated for 100 Watts and the additional data shows a coil resistance of 6.1 Ohm if wound for 24V. That will be 4 Amps of current.
But I calculated that 480 Watts of power is required to accelerate the ball in a stoke length of 2cm. So my guess is that this solenoid will not get you the desired ball velocity.

I understand that you already have a solenoid ball kicker so run some tests and measurements with that system to check on my calculations. Then you will have a much better idea as to what is required for the new ball kicker.

What specs do you need for the DC-DC converter? Input voltage of 18V (LiPo). Output voltage? Output current? Duty cycle of power demand?

Is this a school/team project? It does sound like it and it sounds like it is a fun, challenging project that is doable.

Yes i would need it to shoot every 10sec(roughly)
And i didn't find any (small)solenoid that is 480W
or did you mean:100W solenoid that is boosted to a high voltage it would give 480 w?
I found this website:
http://www.nomad.ee/micros/mc34063a/index.shtml
that helps design a circiut for the MC34063A dc-dc converter
but that's about all i found dc-dc converter circuits
.... i don't know how much Output voltage, Output current, in need cause i don't know much about
dc-dc converters.
and i did even pick a solenoid yet :P
I guess if i boost 18.5v up to 100 or so then I'll get a fairly good kick
i don't know what my output current should be as i guess as the voltage grows the current becomes less?
capacitors would be the best(i would need the same voltage cap as the out put voltage?)
i'll run some test and keep you posted.... i have a MC34063A i try it out,
this is the solenoid i have : http://www.electromechanicsonline.com/product.asp?pid=24
what is the max voltage if the on time if 0.05 s and the of time is roughly 10 sec?
Is this a school/team project? It does sound like it and it sounds like it is a fun, challenging project that is doable.

I'm building robots for robocup junior soccer :P
and sorry i ask so many question's, i don't know much about dc-dc converters :P

Thanks
Regards

Jak24

Offline waltr

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #6 on: August 18, 2010, 03:41:51 PM »
Quote
And i didn't find any (small)solenoid that is 480W
or did you mean:100W solenoid that is boosted to a high voltage it would give 480 w?

That is the general idea but you must do testing and work up to that power lever to determine if the solenoid coils will remain intact.

Quote
i don't know what my output current should be as i guess as the voltage grows the current becomes less?

This is true only if the power is held constant. Refer to Ohm's law and the power equation: E = I*R and P = I*E.
For a given solenoid the coils resistance is constant ( to first approx) so then as the voltage increases the current also increases and so does the power and heat. The trick is to not melt the wire in the coil while getting the most powerful kick out.

Quote
sorry i ask so many question's
As long as you work on understanding the answers given then keep asking.

Offline Soeren

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #7 on: August 24, 2010, 07:58:56 PM »
Hi,

i don't know what kind of chip/circiut i need to achieve those specs :P
You could buy (or get an emptied one at a photo lab) a single use film camera with a flash and use the converter and the capacitor (perhaps a couple or more caps in parallel) for a good some-hundred-volt jolt.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline cyberfish

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #8 on: August 26, 2010, 10:46:59 PM »
Is this for RoboCup?

I am actually part of a RoboCup team, too, but we play in the small sized league.

We use a flyback converter to charge a 1F cap bank to ~220V, and was able to get it to kick near the maximum legal speed (forgot what it is). We use an FPGA for control, but a microcontroller will probably work also (if you have a big enough inductor, so the switching frequency doesn't need to be crazy high).

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

We use a 4 cells lithium. Takes about 5 seconds to charge the capacitors.

Offline Jak24Topic starter

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #9 on: August 27, 2010, 12:28:37 PM »
HI
Is this for RoboCup?

I am actually part of a RoboCup team, too, but we play in the small sized league.

We use a flyback converter to charge a 1F cap bank to ~220V, and was able to get it to kick near the maximum legal speed (forgot what it is). We use an FPGA for control, but a microcontroller will probably work also (if you have a big enough inductor, so the switching frequency doesn't need to be crazy high).

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

We use a 4 cells lithium. Takes about 5 seconds to charge the capacitors.

Yes it's for Robocup junior soccer A primary to be more specific :P
i understand small league uses a golf ball, which is quite heavy, but i don't how it would kick my ball :
http://www.acroname.com/robotics/parts/R194-ROBO-BALL.html
cause if it's far to powerful, then i wight get banned from competition :P
and i also understand the any/most kind of dc-dc converters require lots of current,
maybe it would just be a better solution to use a 6v solenoid and power it with a 12-or higher v battery.
cause i only need to kick the ball for 2m min at an acceleration  of 2-4 m/s
and i know in small league you need to kick it for 4m+
What kind of solenoid did you use for the Flyback converter, also what duty cycle was it?
and i probably don't have that much experience the build Flyback converter circiut.
if you could maybe suggest a chip that is easier to operate it may be better for me.

Thanks

Regards
Jak24

Offline cyberfish

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #10 on: August 27, 2010, 01:35:50 PM »
The kicking speed limit for small sized league is 10m/s, and I think we had to scale it down to stay within the limit.

How hard it kicks would depend on the inductor and how high you charge the capacitor to (if you use a flyback converter).

We used a 1:10 flyback transformer so the MOSFET won't need to block 200V+. I'm not sure which one we are using specifically (I didn't build the circuit).

Actually, do you mean the inductor for energy storage (in flyback converter) or for kicking (electrmanget)? We made the kicking inductor ourselves.

I am not aware of any flyback converter controller chip (if they even exist), since we built our own on an FPGA.

Offline waltr

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #11 on: August 27, 2010, 06:15:24 PM »
I'm glad Cyberfish has stepped in with his experience with the robo soccer kicker.

There are quite a few controller chips that can be used for a fly-back DC-DC converter (power supply). Check Linear Tech's web site for ICs and app notes. In general the design is nor trivial but for this application it should be too difficult to design and build since that output does need to be tightly regulated and/or supply a large current.

 

Offline Soeren

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #12 on: August 29, 2010, 06:14:16 PM »
Hi,

There's no need for IC's, a transistor will do for a flyback converter.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline cyberfish

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #13 on: August 29, 2010, 06:23:59 PM »
How would you do that?

Offline Soeren

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Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Jak24Topic starter

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Re: solenoid duty cycle with step-up circiut / dc to dc conveter
« Reply #15 on: October 13, 2010, 06:24:18 AM »
Hi!

I have deiced that i am probably going to use this solenoid:
http://www.electromechanicsonline.com/product.asp?pid=26
6v/ 10% duty cycle
and power it with a 11.1 Li-PO battery
activated by a relay, the on time will be like 0.05 seconds so it shouldn't heat up that much.
I am wondering though how much more power in the kick would i get, as i am giving it almost 2x more Volts?
And how much current would it use if the time between kicks would be minimum 5 seconds?

Thanks
Regards

Jak24

Offline Jak24Topic starter

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To cyberfish
« Reply #16 on: October 19, 2010, 12:09:44 PM »
HI!

I got my answers for my previous questions my contacting the solenoid company :P
I have a question for cyberfish:

I was wondering if you could tell me what kind of motor you used as your main and dribbler motor on your
Robocup small size league robot,
And what kind of omni wheels did you use ?

Thanks

Regards

Jak24

 


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