Building animatronic gauntlet blades

Honus

Blooded
So I started working on a design for some animatronic gauntlet blades. After looking at several options for motorizing the mechanism I decided on a servo system- primarily for its versatility, light weight and low power requirements.

I obtained a super low profile linear slide to base this on. It has very little friction and is really light weight. The drive servo (an old servo I had sitting around) has been modified to continuous rotation and the internal potentiometer has been retired in favor of a multi turn external pot that will be geared to give position feedback. I modified a servo wheel and turned it into a drive gear to speed up the final drive, otherwise it would be way too slow since most servos are designed for high torque instead of high rpm. The average servo turns around 50 -60 rpm while the fastest digital servos turn around 160 rpm. This particular servo is rated at 94 oz-in. torque and .13 seconds to turn 60 degrees @ 6V. This translates to roughly 77rpm.

In order to speed things up I'm gearing the servo 2.91:1, which gives a rotational speed of 224.07rpm. The final drive will be rack and pinion using a drive gear that is 1.75" diameter (5.495 in. circumference.) If we take 5.495 in. x 224.07 rpm we get a drive speed of 1231.26 in/min, or 20.52 in/sec. This gives an 8 in. blade extension a time of .39 sec. without dropping the torque rating too low to move the blades with some authority. It can always be faster and stronger but this will be a good first test.

The only other option was to make my own servo. I found a small geared motor that turns 350 rpm at 35 oz-in torque @6V. I'd just need to add some control circuitry so time will tell if that proves to be a better solution- at least for light weight blades. I could probably shave .1 second off the extension time using this setup.

Here's what I've got so far-
WristBladeMech1.jpg
 

Ei luj

Hunter
Honus,

You're off to a good start, the servos you picked out are a good balance between speed and strength....

not easy to find just the right one... have you heard of a place called All Electronics; they're in California.

---
Ei'luj
 

fyhninfo

Unblooded
Excellent work!
I'm working on a similar setup :)
Looking forward to more pictures from you, perhaps I'm able to "borrow" some of the design :lol: Will post pictures of my blades when I get the parts.
 

Honus

Blooded
And cost! Cheap is neat but free is for me! :)

I'm familiar with All Electronics- they get some pretty good deals on surplus stuff every now and then. There's a really great electronics surplus store near me- I could spend hours in the place. Sparkfun is also about 15 minutes from my work which is really nice.

Picking a servo isn't easy. I tend to use Hitec because there's a lot of accessories for them. Servocity sells gears that fit directly on the servo output shaft as well as all kinds of inexpensive gears and gear racks. The Hitec HS965MG would be a good choice for strength and speed but it's a bit expensive for me. That's why I started looking at geared motors and essentially building my own servo. The problem with most motors is current draw vs. speed and torque. I wanted to keep the current draw minimal so I could still use an inexpensive servo board to drive it as well as extend battery life.

I think this little gem would work really well, provided you kept your blades light and tried minimize friction. Using this motor you could build a decent little servo with very high speed for under $50. Since it turns 350 rpm you could couple it directly to the pinion gear to really minimize frictional loss. Using a slightly smaller pinion would improve torque at a small decrease in speed. A 1.75 in diameter drive gear would give an 8 in. blade extension of .25 seconds and a 1.50 in gear would give a time of .29 seconds. Of course these speeds are "no load theoretical" so real world times will be different since you lose nearly 10% efficiency just in the rack and pinion....
http://www.pololu.com/catalog/product/1091

If you need more torque than that then you're probably going to be in the $75+ range to get good torque and speed and you still have to add the external pot and gears- at the very least you need a rack and pinion for the final drive no matter what power source you choose. The latest and greatest high speed digital servos have really high current draw as well. If you've got heavy blades then you're going to spend big $$$ to get rapid acceleration no matter what.

To get an 8" blade extension in under .3 seconds you have keep the blades light, you need a decent amount of torque and at least 300 rpm final drive speed with a decent sized final drive gear- a pretty tall order, especially if you're on a tight budget.

Jerome
 

Usurper

Veteran Hunter
Jerome.....................



i can NOT wait to see this. :)

I do hope you will consider a commision of making me one for my P1 guantlets in the near future :lol:
 

Elkman

Blooded
Interesting setup you've got going there. I should probably figure out how to use servo motors in my own projects. I was talking with someone at Crypticon about using servo motors, and he suggested using a single-turn servo with a linkage that would throw the blades all the way in or all the way out. I'd still have to figure out where to put the motor and everything, though, so I haven't investigated it. Even with a single-turn servo and a linkage system, I'm not sure how I could place a linkage in there and still fit into a gauntlet, so your multi-turn system is probably the way to go.

Where do you plan to put the servo in your gauntlets? Will it be mounted between the blades on a traveler mechanism or something like that? And are you still using an Arduino board for the controller?

Also, using a rack and gear system for the final drive is the way to go. That's what I've been using for the gear mechanisms I've been building lately. I'm not cutting up old CD-ROM drives these days because I've been building smaller-profile mechanisms to fit into other people's gauntlets. I don't remember offhand where I was getting my gears and racks, but it's a robotics shop on the Web.

Oh, and I love Sparkfun as well. I've been buying Arduino boards and LED display drivers from there. They've got a lot of cool stuff that I'd like to check out.

Thanks for sharing your knowledge! I'll keep my eyes on this topic.
 

Honus

Blooded
Yep, I looked at all kinds of linkage setups and came to the conclusion that rack and pinion is the way to go. It's really compact, easy to build and it's more efficient than any other system that will fit. The problem with an arm/linkage system is generating enough travel. For short travel it'll work great but for anything like 8 in travel it just isn't practical. I've designed more than my share of suspension mountain bikes and I have linkage software that will allow me to analyze different systems so I'm no stranger to designing a linear travel linkage system.

There are two ways I considered using a servo- first as a moving sled/drive and second as motor for a belt drive using a miniature timing belt. The advantage of a timing belt is you are reducing the accelerated mass since the belt is only moving the blade carrier and it can be a pretty compact mechanism. A timing belt system is more complex to build and belts can be a bit of a pain to keep secured- it's not as robust as rack and pinion. So a rack and pinion with the servo attached to the moving sled is what I chose. Servocity.com sells the gears and racks in both 32 and 48 pitch.

It is still Arduino and will plug into my existing controller. Controlling servo position with Arduino is easy and only requires a few lines of code- just let me know if you need help with it.

Since I don't have a gauntlet to measure it'll be interesting to see if it will actually fit in one. :)

Jerome
 

Uratz

Hunter
There are two ways I considered using a servo- first as a moving sled/drive and second as motor for a belt drive using a miniature timing belt. The advantage of a timing belt is you are reducing the accelerated mass since the belt is only moving the blade carrier and it can be a pretty compact mechanism. A timing belt system is more complex to build and belts can be a bit of a pain to keep secured- it's not as robust as rack and pinion. So a rack and pinion with the servo attached to the moving sled is what I chose. Servocity.com sells the gears and racks in both 32 and 48 pitch.

It is still Arduino and will plug into my existing controller. Controlling servo position with Arduino is easy and only requires a few lines of code- just let me know if you need help with it.

Since I don't have a gauntlet to measure it'll be interesting to see if it will actually fit in one. :)

Jerome

HI Jerome

Belt drive thing do you mean something like this?

Small-WristBlade-Mech.jpg


This one uses a motor in between the blades and also hides small AA batteries in the center of the gauntlet to maintain good weight balance.
The trick is to make the housing fit on top a gauntlet with the battery holes underneath. The gray rectabgles are stop switches which cut off power to the motor
when it tripped. There are 2 of these.
The Blue is the sliding rack. The Green is the blade holder that slides across the entire housing.

I've also designed another system with the pulleys/ slider tray in the rack and pinion but its in theory and gotta figure out the length of the ropes to pull out the blade holder
all the way out.

Blade-Mechanizem.jpg


I've designed these like a year ago and haven't found anyone that could make them. Perhaps We can collab on these so feel free to use the plans to develop something
kick ass for the Lair~!
 

Honus

Blooded
That's somewhat similar to what I had in mind as far as the belt drive goes. There are a couple of potential issues I see with your design. It looks like the belt is acting as a retainer to keep the blade holder in place and there will be a lot of friction due to the height of the blade holder and the large surface area. You would also need a very high speed final drive- probably around 500 rpm due to the pulley diameter.

The way I envisioned it the motor would sit perpendicular to the belt at the end of the slide (or underneath it) so it would directly drive the belt pulley and a potentiometer would be geared to the motor shaft to give position feedback. I'll have to do a sketch to explain it but it's super simple.

Jerome
 

Uratz

Hunter
Jerome - I know you gonna do it justice. I've scrapped mine. I hope I can get your mechanism ASAP. Let me be the first on your list!
 

carlart

Hunter
I elect Jerome to the position of science officer! Great stuff as always, amigo. Can't wait to see how the rest of this comes out.
 

Honus

Blooded
I elect Jerome to the position of science officer! Great stuff as always, amigo. Can't wait to see how the rest of this comes out.
Ha! Good one. :) I think it's more like Engineering Staff member... So you're going to sculpt some gauntlets for me right? And then after that we need to talk about the animatronic head I have planned... The backpack is just the beginning! :lol:

Jerome
 
My 2 cents. I placed video here a while back of a similair idea. The motor sits perpendicular and it drives sprockets and a nylon chain. Here is the video. I have recently changed the blade arrangement as they sat with to high a profile. I am actually working on the sculpt of the housing currently. Ok I'm trying to ad the video. Seem to be having issues.
 
I used a motor from a power window. Small and powerful. I am designing my own housing. Like I said above, I reconfigured the blades and it has a much lower profile now. I'll get some new pics up soon.
 

REYALS

Elite Hunter
*scratches head*- I don't understand all the spec's language, but that video pretty much summed up how freaking sweet this Gaunt is going to turn out.

[sup]KICK ASS JOB!!![/sup] ;)
 
Last edited by a moderator:

ksj

Young Blood
Did you ever get this up and working or have any pictures of this. Sorry for the thread necromancy on this.
 
Top