Crusher, why not?

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Lowtech
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Re: Crusher, why not?

Post by Lowtech »

This is my first time building a 4wd robot. It turned out pretty well I think.

https://www.youtube.com/watch?v=35g5rlx ... mbatechist
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Re: Crusher, why not?

Post by Dazmund »

Reminds me of a bite-sized World Peace. I like the look!
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Re: Crusher, why not?

Post by Lowtech »

Dazmund wrote: Fri Feb 26, 2021 11:19 pm Reminds me of a bite-sized World Peace. I like the look!
Thank you. I'm sad to say I may have to remove some of the plates if it comes in over 150g :(
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Re: Crusher, why not?

Post by Lowtech »

https://www.youtube.com/watch?v=dNHP3JD ... mbatechist

The claw test was quite disappointing. Are Duracell batteries not capable for putting out enough power?

What kind of improvement can I expect to see when I hook it up to the BEC of my receiver powered by a 7.4V 25C lipo?
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Re: Crusher, why not?

Post by EddieJ »

AA batteries are 1.5V. You are using a servo to power it? Which will be on the 5V of the BEC? I think you will get a better result
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Lowtech
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Re: Crusher, why not?

Post by Lowtech »

https://www.youtube.com/watch?v=JaRCb4F ... mbatechist

I modified a servo ESC to power the claw using the BEC. This was the result, much better!

Still, I was hoping for more. Can someone with a better knowledge of electronics than me please explain what my limiting factors are?

I'm aware I'm forcing the motor to stall every time I use the crusher, what would increase the stall threshold if you will?

Could the BEC or my ESC be limiting the current in anyway? If so what can I do?
Last edited by Lowtech on Sun Mar 07, 2021 3:01 pm, edited 1 time in total.
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Re: Crusher, why not?

Post by Lowtech »

EddieJ wrote: Sun Mar 07, 2021 10:57 am AA batteries are 1.5V. You are using a servo to power it? Which will be on the 5V of the BEC? I think you will get a better result
I went out and did it today. You can see the result through the link.
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Re: Crusher, why not?

Post by EddieJ »

Whats the internals looking like? It might be you want a mechanical solution rather than an electronic one. If the servo is designed for 5V, and you are running it like that. Instead maybe you could add some gearing?
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Re: Crusher, why not?

Post by Lowtech »

EddieJ wrote: Mon Mar 08, 2021 10:39 am Whats the internals looking like? It might be you want a mechanical solution rather than an electronic one. If the servo is designed for 5V, and you are running it like that. Instead maybe you could add some gearing?
Hi Eddie,

The claw is powered by a pololu geared motor with an extra reduction stage.

The mechanical advantage is about 3000:1. The claw should have 41N of force (4.2kg) at 6 volts and the motor should have a stall current of 0.36 amps.

Assuming the receiver is 5 volts, and that torque is linear, then that becomes 3.5kg of force.

I don't know exactly what 3.5kg of force should look like, but I suspect I'm not quite hitting that right now.

Do we think a spektrum receiver can output 0.36 amps?

Of course, at 7.4 volts, the claw should be crushing with 5.2kg force. I may be looking to run a direct line from the battery, but that won't change anything if the receiver can't supply the current.

(The only other thing I can think of is that the battery may be flat, but then again I think Lipos are quite consistent)
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Re: Crusher, why not?

Post by EddieJ »

Have you got some electronic scales it can bite down on? Perhaps measure what force you are getting now, to see if you are far off the 3.5kg?
Im not sure what amps the Rx will output.
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