Using RC car/truck to mobilize a robot prop ??

Discussion in 'Replica Props' started by DR4296, Aug 5, 2015.

  1. DR4296

    DR4296 Active Member

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    Just looking to see if anybody's done this sort of thing before:

    A little over a week ago, I took on the project of building a replica of Dr. Who's K-9 (robot dog)...within ONE MONTH. It will be used as a prop at ... well... it's kind of like a convention kind of event.

    So, I found some Pepakura files for K-9, printed those off onto cardstock, cut them out, and now I'm currently using them to cut out pieces of Sintra to form the body.

    Now, it'd be really cool if I could make him mobile. But I've only got a little over two weeks left to finish this and I don't even have his body assembled yet. I'd found a brief build-log for someone's K-9 build from years ago... where they talk about using a Radio Controlled TANK that they had lying around to make K-9 mobile. There was a photo that showed that this person obviously knew their way around the internal workings of such a tank better than I do.

    But I was thinking: What if I went out and bought an RC car, truck, or tank? How could I mount a Sintra K-9 onto such a thing.... and create a tight-enough, yet removable "bond" between the two units? I'm sure a lot would depend on how the RC vehicle is put together.

    I'm hoping that this Sintra K-9 will only be a couple of pounds, so a large RC car / truck / tank... something with as wide a wheel base as I can find... would probably be able to support the Sintra. But I'm still going over in my mind how I might be able to attach the two together.

    Just wondering if anybody's tried this sort of thing before and can speak from experience?
  2. Teddz

    Teddz Sr Member RPF PREMIUM MEMBER

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    I would assume attaching the two portions (sintra body to R/C tank) would be the easiest part since you're just replacing the existing tank body with a different "tank" body, in this case Dr. Who's K-9.

    You'll obviously need to modify the lower 1/2 of the tank to have some sort of mounting bracket that would mate up to the corresponding mounting bracket in the sintra body and then screw them together. This would be the best way to have a non-permanent bond of the two parts.

    If you can post up some pics of what you have to work with, maybe we can help with working out some sort of mounting system that would work.
  3. nomuse

    nomuse Sr Member RPF PREMIUM MEMBER

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    Did it: EV-E01.jpg

    I used a cheap RC car -- stripped off the body and hot-glued it inside. The weight of the robot was almost too much for it and the speed made it difficult to control, but it made it (mostly) through a four-week run.

    Used it for Willy Wonka. Besides the LEDs in the eyes, one eye held a cheap wireless video camera that was played back live on stage. The actor driving the prop from the wings also provided vocalizations on microphone.

    I would strongly suggest paying for speed control, and looking into a tank as Tedzz suggests; otherwise it is just too zippy to control. Unfortunately, although there are a lot of nice robotics chassis out there, they tend to be crawlingly slow, and once you get above the footprint of a paperback book, unfortunately expensive. The main advantage to a full modern R/C car rig (costing around $400 to put together) is controllability, power, range, and the ease in adding on additional channels for tricks like eye lights, ear servos, K9's head bob -- as if you had time to do any of that on your schedule!
  4. DR4296

    DR4296 Active Member

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    Thanks for the info, guys!

    I can't post anything yet because I'm still cutting out Sintra pieces and haven't started actual assembly / gluing yet. I hope to get started on gluing by late tomorrow (as I have the day off). However, this weekend is my wedding anniversary and.... shhhh.... I haven't bought or planned anything yet (yikes!), so I'm sure that will cut into my time.

    I'm at least glad to hear that somebody's gone this route. How "cheap" was that RC car, nomuse?

    I was looking at RC trucks yesterday on Amazon, especially ones where the "main body" seems to "ride up above the wheels", as it seems to me that it may be easier to attach / detach the truck from K-9 with the wheels effectively "out of the way". Here's one I've been eyeballing:,p_72:1248963011,p_36:1253561011

    I don't really need the "off-roading". I don't see me operating K-9 on anything other than indoor flooring material... carpeting at worst.

    I'm hoping the Sintra's going to be light enough where a foot-long RC vehicle valued at $50 or less will be able to handle the additional weight.

    But I'll post some pics here once I get the basic form assembled. Keep in mind: K-9 is 29 inches long. Not quite sure on the width, but I'm sure it's on the order of 18 inches. But then again, the only "innards" I plan on putting inside (other than internal structural supports of some kind) would be some sort of LED's with batteries or tiny flashlights for the eyes.... and then the control panel on his back will probably contain LED's and a couple of batteries as well.

    (Hmmm... that reminds me... I was going to run over to the hardware store on my lunch hour today and look for plastic that I could use to help provide internal support. A good portion of the "internal angles" between sheets are NOT 90 degree angles, so some plastic L-brackets aren't going to be all that useful. But I thought maybe I could find some light hollow plastic square-ish bars... where maybe I could custom-cut the angles on the ends or something.)


    -= Dave =-
  5. DR4296

    DR4296 Active Member

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    Say, I was going to post another thread on this, but I thought I'd ask you guys first:

    I vaguely recall seeing build threads (but I can't seem to find them again)... where folks use some sort of .... (and here's my problem... I don't know the right terminology) "spackling material" to fill in the edges where, say, two pieces of Sintra meet at a 90 degree angle, so as to give the illusion that it's all one piece.

    I'm assuming that NOT doing this will result in a K-9 that looks not-so-good. So, I'm wondering what sort of material I can use for this?
    (Trying to get all my ducks in a row / have all my materials purchased very soon.)


    -= Dave =-
  6. Gixxerfool

    Gixxerfool Well-Known Member

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    Bondo, an automotive body filler, is used for such an event. Although never having worked with sintra I'm unsure of the rigidity. Most body fillers aren't flexible and will crack and break out with any impact if used on flexible surface. Aves Apoxie Sculpt is a great product that may work for you. If sintra is anything like styrene, can you fill it with Zap-a-Gap and then sand and finish from there?
  7. Teddz

    Teddz Sr Member RPF PREMIUM MEMBER

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    Using bondo will attack the sintra and release toxic fumes. I thought of this too, but a quick google search said it was a bad idea.

    You can try wood filler, vinyl spackle, mod podge or paper clay & gesso. If you use gesso, you'll need to cover the exposed foam with paper clay first then use the gesso.
  8. DR4296

    DR4296 Active Member

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    OK, here's an update.

    I'm attaching some photos I took on Monday night. These are simply showing how I've taped a lot of the body parts together, just to see how things line-up.:

    2015-08-10 15.36.30.jpg 2015-08-10 15.36.41.jpg 2015-08-10 15.36.47.jpg 2015-08-10 15.36.54.jpg 2015-08-10 15.37.04.jpg 2015-08-10 15.37.11.jpg 2015-08-10 15.37.23.jpg

    Now, I've assembled this stuff after printing off the Pepakura files onto cardstock and then only cutting out the larger pieces, tracing them onto sintra, and then cutting them out. I've included photos showing that there are some minor problems with the Pepakura plans: Two sides end up with a thin bar on the outer bottom edge. Two sides do not. There are a few gaps where some pieces, roughly an inch or so wide, are missing. I know two of them are missing because they're a part of a much, much larger piece that I have not printed off, as it became apparent to me that within the Pepakura plans, they sort of repeat the entire bottom piece a second time, plus I think there's another horizontal layer they shove inside it that seems to be unnecessary. So, I'm going to have to measure and custom-cut a few odds and ends.

    My big concerns.... keep in mind I have until August 20th to complete this:

    a) Mounting the head. Sorry, I haven't included any head photos yet, as it's still half-assembled. I have to take a heat gun to a few key head pieces, in order to curve them, before I can continue much further on that. BUT, I did purchase a "Lowe's Flex Drain Downspout Adapter" that has a 4 inch diameter. I'm thinking that should just be an outer piece "for show", while inside it, I use a piece of PVC pipe to do the actual support. My concerns are how to connect it at "both ends" so that the head stays up. Yeah, maybe just an adhesive connection between the base of the head and the PVC pipe will suffice there, but I'm not sure how I'm going to connect or support the other end that's inside the body.

    b) Overall structural support. I feel like I should be gluing in some sort of supportive plastic beams inside, as the top half of the body seems very flimsy. I did a brief look around my garage and the only thing I had on-hand was two plastic rods... the kind that come attached to window blinds and act as "turners" for them. They're hex-shaped, actually. I think I need to spend a good 30 minutes running around at Lowe's and using my imagination... see if I can come up with some lightweight plastic beams to use on the inside.

    c) Buying a car to motorize this. I went to Walmart before running off to work yesterday morning. I looked at the $30-40 price range cars, which were similar in size to the one I posted from Amazon in my previous post. However, on the shelf underneath those were larger $60 cars. They didn't seem to have a prominent brand name, but they WERE larger than the 12 inch long ones I was looking at. But I just can't justify plopping down $60 at this point. (You see, in addition to materials and tools for this K-9, I've also spent $60 on a pair of maroon Converse shoes... plus another $100 on a 10th Doctor coat.... and then there's the $20 on the Sonic screwdriver... and I still have to buy a dress shirt that fits. <sigh> The costs just keep climbing. (Ideally, I'd wanted to buy a digital photo frame to use as K-9's side display screen as well, but very few of those are battery operated... plus it seems like I'd be looking at spending another $40 on that.)

    And I'm still looking for a stupid red suction cup / dart tip. (You'd THINK I'd have spotted one in a dollar store by now!)

    So, that's where I'm at. If anybody has any advice for me, please post!!

    Tonight, I won't be around the house very much, so I won't get much gluing done. But I hope to be cutting out K-9's mesh ears and the red acrylic that covers his eyes. I will be ordering about 15-20 white LED's later today.


    -= Dave =-
  9. DR4296

    DR4296 Active Member

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    20150816_181119.jpg 20150816_163122.jpg 20150816_163110.jpg 20150816_163100.jpg

    Well, I'm almost done with assembling the main structure of K-9. I need to recut and refit the back piece, plus I'm hoping to attach it with magnets. A few issues:

    I had purchased some white wood filler to smooth some borders /edges and fill some gaps. But it came out so chalky, it was hard to it was basically unusable.

    I'm also not sure how to attach the PVC neck into the hole in the head in such a manner that it doesn't drop below a certain point....and yet, it sure would be convenient if I could detach it again, if I needed to.

    If anybody has any thoughts on that, please let me know! I have to have this ready by early Thursday.

  10. ElectroDFW

    ElectroDFW Active Member

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    The best advice I can give from my experience with cutting things so close such as this, is to forgo the way you would prefer to make it *if you had the time*, and go for the way you can make it *in the time you have.*

    I am notorious for working on things up til 3am the day of the con, and believe me, I want all my props and costumes to have all the bells and whistles I can muster.
    I am still learning the lesson of weighing what I want done against the time I have in which to get it done.

    My advice is to forgo all accoutrements that take more time to get it done. The magnetic back, the side video display, detachable head, light-up gizmos you haven't already built or wired, etc.
    With the short time you've had available, and limited budget, you now need to focus on getting the body and head together, securely assembled and attached, and mounting it on the RC platform.

    Plan for this one to be the 'trial' or 'prototype' K9 for you. Use it as a learning tool. Be okay with its limitations. Start putting together a timeline and a budget for the next con. Whatever function you find yourself regretting not having on this one the most, make sure that's first on your list for next time. Then work your way down the priority list.
    Believe me; not having something ready the way you want it to be is frustrating, but not having anything at all to show for your time, is disappointing.

    Just some words from someone who's been there.
    Your Friend In Time,
    Marty McFly Dallas Cosplay
    aka David M.
    DR4296 likes this.
  11. DR4296

    DR4296 Active Member

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    Thanks for the advice, David M.!

    I decided to give up on...or at least delay...on the idea of making K9 mobile.

    And I definitely chucked the idea of a video display, since I wasnt finding any digital photo frames that were battery operated.

    So, with tomorrow being my deadline, here's what I've got:

    20150819_205720.jpg 20150819_205825.jpg 20150819_205730.jpg 20150819_205849.jpg

    Hot glue turned out to be my best friend, as the plastic adhesive I was using for the body just wouldn't stick to other materials....and even that E6000 adhesive didn't work on a lot of things.

    The so-called "warm white" LEDs I bought off of eBay really were "not very bright" LEDs. I used them in K9's 12 control buttons, but I'm not exactly thrilled with the results. So when it came time to do the two big red control lights and the two eyes, I wanted some other solution. So, just this morning, with one day to go, I bought 4 of those hockey puck closet lights and raided them for their LEDs and switches. I wasn't looking forward to using electrical tape to make the various connections, but I recently learned that ine can use hot glue to do it! That sped things up considerably.

    A cheap but long string of bright LEDs I bought off of eBay make for a nice glow effect. And as for the gaping hole where the display will be, well, I need that hole to turn on and off the under-chassis LEDs, so I'm just going to try to tape in a good photo from the TV show.

    Gotta run!


    -= Dave =-

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