Beefy Remote Controlled Tea Table

[ThreeWatt]

My TD wants me to create a remote controlled "magic" tea table for a childrens play for one of our neighboring theaters. Although he excels at scenic design, when it comes to common sense he could use some work. He bought this little RC toy car to facilitate movement, but it can barely take the weight of the table without snapping its axles in two, much less move the load under its own power. Has anybody here had do something similar? Did you use a really big (like 1/10 scale) RC car? Or something custom made?

I'm a little out of my element here, I have some experience repairing electronics but I mostly do board programming and lighting maintenance. I have 5 days to get this working.:neutral:

 

[headcrab]

Could you tie tie line (or similar) to each leg and have stagehands pull on it, thus moving the table?

 

[ThreeWatt]

I thought of that, but I think it'd be too awkward a spectacle, the table has to steer as it moves along and tie line would limit that pretty badly. I'm wondering if there's something like a heavy-duty RC chassis kit that I could buy and mount to the table. I'm not sure what my budget is, maybe $500?

The table weighs about 25 pounds. The local hobby shop said they don't have anything that can move that much weight.

 

[Footer]

You don't need an RC car, you need an RC fighting robot.

DIY Combat Robot - Systm

That should have enough power to do this. Obviously you don't have to go as far as they did, but the control system would be the same.

 

[ThreeWatt]

That video was really helpful, I'm going to try to shoot for this if I can get the parts and get it built in time. The worlds first RC fighting tea table.

It gonna serve rage tea.

 

[Van]

You CAN use the guts of the car you have already and modify the motor somewhat. Pickup an old makita or Dewalt drill and use the motor from it as a final drive motor. You can do this a couple of different ways; Sophisticated or Van ways. Sophisticated would be to build or have made a custom gear case to assist in going from the motor to the axle on the tea cart and then driving the motor via a realy hooked into the existing r/c cars drive motor circuit. the Van way would be to rig the drill under the teacart. remove the trigger and replace it with leads running to the r/c cars motor supply install a DPDT relay which is driven from the existing r/c cars motor control.
Steering could be acomplished the same way by using a hevier duty motor to drive something like an Acme Screw rod which runs through a central pivot axle on the front wheels this makes the cart, on a whole a little more unstable, but as long as you're not doing donuts it should be fine. Does this all make sense ?
I did this same thing with a bed for Scrooge once, only there I had to adapt even larger motors, but the r/c car guts, and acme screw drive steering were all the same.

 

[ThreeWatt]

Well, it looks like my TD over-estimated my buget, so no fancy PWM speed controllers for me. I'll give The Van Way a shot.

 

[Les]

LOL this reminds me of a trick we played on our director in high school. We were doing Peter Pan, and for one of the first flight scenes, he wanted them to "fly" over Big Ben. So we built this 7' tall Big Ben replica to roll under them as they were swooping back and forth (via Foy). The director wanted to see if we could motorize it to eliminate the need for a stage hand, so we had the same idea. Get an RC car. Well, our Big Ben weighed about 100lbs, so after the first test, we quickly decided it wasn't going to happen. So, we put our friend Marc inside Big Ben with a DeWalt drill and had him roll around in the shop while pressing the drill's trigger at varying speeds. We called the director in and said "Hey look at this!" while my tech friend pretended to be controlling the thing with the RC remote. He was pretty amazed by us until Marc stuck his arm out of the side and yelled "Hey Bailey!" to our director (his name was Eric Bailey, RIP).

Needless to say, we just used our smallest cast member to walk it across the stage. Honestly, the effect looked fine with the lighting and the fog we used. You couldn't see him at all.

I know this doesn't help you, but I thought I'd share this funny story from years past!

 

[ThreeWatt]

We did something like that during one of our Wizard of Oz productions, our twister sequence had two techs out on stage pushing and pulling a 12ft tall tornado on a caster base and making it spin with a rubber belt and a DeWalt drill. Apparently no one ever saw them.

Anyway, I went to Harbor Freight and got two cheap 18v drills for movement, the way I figure is that I can make a plywood platform and mount the drills chuck-side-out on the center sides of the platform, and then put one small swivel caster on each corner to keep it stable. Then I'll mount the whole thing to the underside of the table. Having one drive wheel move forward and the other one stay off should make the table pivot on the stationary wheel, if it stays stationary. The RC guts from the toy car put out 10vdc and 6vdc on the forward/reverse and left/right motor circuits respectively, so I think I'll use two solid state relays that can accept multiple control voltages to keep it simple. Has anyone here ever used a solid state dc-to-dc relay that can handle 8 amps or so? Granger has a big selection but most are dc-control-ac-output I don't know if I can use them or not.

 

[headcrab]

Certain AC SSRs can't switch DC because they use SCRs as the switching elements. The SCR will latch on and since the voltage never goes through zero the load won't turn off. An AC SSR can only switch DC if it uses IGBTs or something similar to switch the current.
What's wrong with a mechanical relay? They're cheaper, slightly harder to kill, and will switch any current up to their rating. (DC AND AC)

 

[Van]

I gotta agree with Headcrab a straight mechanical relay is going to be easiest. Now, that means no variability in start-stop, but you wanted cheap and fast. remember the Production triangle " Cheap. Fast. Good. Pick Two." Also you might need to put a shaft with a pulley and a belt that then runs to the wheel depending how fast you want this thing to go and how heavy it is. If You're driving tea cart sized back wheels < 14 - 18" diameter> then you'll have a lot of rotational momentum/resistance to over come.

 

[ThreeWatt]

I'd love to get a few Victor 884's but my boss can't spare that much. I'm also having trouble finding a 6v and 10v mechanical relay that can handle a sufficient amount of amps.

 

[jwl868]

A comment about my experience remote control toys. We used a radio controlled car to “power” an effect, and it worked fine for years at several venues, until we used a different venue. There, another device (I never knew what) activated the effect multiple times during the rehearsals (but not during the show). (And my fix was to have a performer switch the device on a few minutes before I activated it.) I suspect that it’s a very low potential problem, but something to be aware of.

Joe