Screaming Mimi

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TOU
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Re: Screaming Mimi

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Hey Randy,

AMAZING CAR and very Innovative!

I am very interested in further details for the electronically uneducated. Funny thing is we have an unlimited race coming up and I heard there were some that were considering Mouse trap type cars, CO2 cars and one guy was talking about a ducted fan motor.

Well coincidentally I bought one of these EXACT planes about 18months ago and it has sat in the closet ever since. So I was thinking about tearing it apart and somehow adopting it for this race....then I came across this post. TOo cool. We have two weight classes, a 5 oz & an 8 oz class...I'm thinking the last in order to use pine. Can you give me more details on the build? More of the gotchas and how to's?

Okay, I have already gutted it...no I didn't even fly it once. (We have another and figured we'd use the rest for spare parts on it.) First question, did you you the two top motor cowlings for the top and bottom of the motors sandwiching with a piece of wood?

Is the wood piece in the middle pine or balsa?

Can you give me more detail on how you actually attached the motor snugly? Post? TO? and then to?

It has two motors attached. Did you just cut one motor off? Doesn't that "over-power" the other one ? Did you just leave the antenna wire inside the car?

Anything more you would do differently?

Thx so much in advance for any details and help youcan lend.

TOU
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gpraceman
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Re: Screaming Mimi

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TOU wrote:First question, did you you the two top motor cowlings for the top and bottom of the motors sandwiching with a piece of wood?
I used both halves of the cowling from one of the motors. Of course, I had to cut up the wing for the bottom half.
TOU wrote:Is the wood piece in the middle pine or balsa?

Between the two halves of the cowling it is a balsa piece shaped into a mini wing, which conforms to the shape of the cowlings.
TOU wrote:Can you give me more detail on how you actually attached the motor snugly? Post? TO? and then to?

I glued a post to the base platform and then used two small screws to secure the bottom motor cowling to the post. I think I put a dab of Gorilla glue on there for good measure. The post is also glued to the back of the body housing the electronics.
TOU wrote:It has two motors attached. Did you just cut one motor off?
Yes, just the one.
TOU wrote:Doesn't that "over-power" the other one ?
Not sure what you mean. There is only one motor on the car.
TOU wrote:Did you just leave the antenna wire inside the car?
No. There is a small hole in the back of the body where a few inches of the antennae is sticking out. The rest is coiled inside of the body. If found that I needed some sticking out in order to get a good enough control signal to the motor.
TOU wrote:Anything more you would do differently?
Maybe mounting the cutoff switch to the body. As it is now, you have to remove the body's lid to set that switch.
TOU wrote:We have two weight classes, a 5 oz & an 8 oz class.
We still had a 5.0 oz limit for our Outlaw race, which was definitely a challenge due to the weight of the motor and battery pack. The post and the thin sliver of a platform base were the only things made from pine. Some of the platform was cut out and replaced with balsa. The rest of the body is balsa. The razor wheels also helped reduce weight.

If you can, try to make the 5.0 oz class. It would likely be the most competitive in that division. I would think that you would see more powerful cars (like CO2, direct drive, and ducted fan) in the heavier division.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
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Re: Screaming Mimi

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Hey Randy,

Thx so much for taking the time to give such an excellent and quick response...I appreciate it.
gpraceman wrote:
TOU wrote:First question, did you you the two top motor cowling's for the top and bottom of the motors sandwiching with a piece of wood?
I used both halves of the cowling from one of the motors. Of course, I had to cut up the wing for the bottom half.


Okay...that's kinda what I thought, but was trying to avoid that if I could. I was thinking about using the two top cowling pieces from each motor but I think you're right it will probably fit better your way.
gpraceman wrote:
TOU wrote:Is the wood piece in the middle pine or balsa?

Between the two halves of the cowling it is a balsa piece shaped into a mini wing, which conforms to the shape of the cowling's.


In your pictures it looks as though you used the OEM screws to screw it to the balsa. I can't imagine that they bite strong enough into thwe balsa to hold it tight, did you just glue this together as well and the screws are for looks? Or screws only?

Image
Image Image
gpraceman wrote:
TOU wrote:It has two motors attached. Did you just cut one motor off?
Yes, just the one.
TOU wrote:Doesn't that "over-power" the other one ?
Not sure what you mean. There is only one motor on the car.


I just figured (in my non-electronically knowledgeable mind) that with it only using one motor instead of it's intended two motors...but with all four batteries that this might be too much voltage? and maybe burn up the motor. Obviously it has worked for you to just cut the other wire and motor off. Cool, thx.
gpraceman wrote:
TOU wrote:Did you just leave the antenna wire inside the car?
No. There is a small hole in the back of the body where a few inches of the antennae is sticking out. The rest is coiled inside of the body. I found that I needed some sticking out in order to get a good enough control signal to the motor.

Totally makes sense.
gpraceman wrote:
TOU wrote:Anything more you would do differently?
Maybe mounting the cutoff switch to the body. As it is now, you have to remove the body's lid to set that switch.

Agreed, I was thinking the same thing...and maybe also thought about marking the "off" & "on" on on the outside that were easily visualized so you can see at a glance if someone has "sabotaged" you. LOL

gpraceman wrote:
TOU wrote:We have two weight classes, a 5 oz & an 8 oz class.
We still had a 5.0 oz limit for our Outlaw race, which was definitely a challenge due to the weight of the motor and battery pack. The post and the thin sliver of a platform base were the only things made from pine. Some of the platform was cut out and replaced with balsa. The rest of the body is balsa. The razor wheels also helped reduce weight.
Makes sense...just don't know if I can come up with some Balsa in time. It also seems it would be much more fragile. But...5 oz. Oh...and yeah I got a nice set of razor wheels waiting for just such an occasion.
gpraceman wrote: If you can, try to make the 5.0 oz class. It would likely be the most competitive in that division. I would think that you would see more powerful cars (like CO2, direct drive, and ducted fan) in the heavier division.
Makes total sense...I think that they will end up making another class...super modified that is all encompassing no matter what the weight so long as it is not over 8 oz.

Thx again!

TOU
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Re: Screaming Mimi

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gpraceman wrote:
TOU wrote:It has two motors attached. Did you just cut one motor off?
Yes, just the one.
Sorry, another couple of dumb questions, does it matter which one?

Also, did you go with standard one wheel raised?

Thx,

TOU
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Re: Screaming Mimi

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TOU wrote:In your pictures it looks as though you used the OEM screws to screw it to the balsa. I can't imagine that they bite strong enough into thwe balsa to hold it tight, did you just glue this together as well and the screws are for looks? Or screws only?
Since I used the top and bottom of the engine cowling, the OEM screws are all that is needed to hold the motor and mini wing in place.
TOU wrote:I just figured (in my non-electronically knowledgeable mind) that with it only using one motor instead of it's intended two motors...but with all four batteries that this might be too much voltage? and maybe burn up the motor. Obviously it has worked for you to just cut the other wire and motor off. Cool, thx.
Hadn't had any problems. There is less drain on the battery pack only running the one engine, so the charge will last longer.
TOU wrote:Makes sense...just don't know if I can come up with some Balsa in time. It also seems it would be much more fragile. But...5 oz. Oh...and yeah I got a nice set of razor wheels waiting for just such an occasion.
You can get balsa at Hobby Lobby, regular hobby stores and some craft stores. Wal-Mart might even have a balsa variety pack in its craft section.

The important parts of the car are regular pine, the chassis and the motor post. Those are what take all of the stresses. The body is one chunk of balsa, hollowed out for the electronics, shaped and then glued down to the chassis. The floor under the electronics was cut out and replaced with balsa to trim weight.
TOU wrote:does it matter which one?
Either motor will work fine.
TOU wrote:Also, did you go with standard one wheel raised?
It is a 4 on the floor. With all of that foward thrust, being as high up on the car as it is, having a raised front wheel would likely end up resulting in it running on both fronts and one rear.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
TOU
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Re: Screaming Mimi

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gpraceman wrote:Since I used the top and bottom of the engine cowling, the OEM screws are all that is needed to hold the motor and mini wing in place.
Yeah...after I wrote this last night I went back and played with it and I can see it makes MUCH MUCH easier to do that. I just liked the thought of symmetricalness of the two upper cowling's rather than having one side look hacked. I think with using the softness of the the "balsa" wing one can take care of it no problem though.
gpraceman wrote:
TOU wrote:I just figured (in my non-electronically knowledgeable mind) that with it only using one motor instead of it's intended two motors...but with all four batteries that this might be too much voltage? and maybe burn up the motor. Obviously it has worked for you to just cut the other wire and motor off. Cool, thx.
Hadn't had any problems. There is less drain on the battery pack only running the one engine, so the charge will last longer.
Makes sense now, thx. Also last night I read a bit more on another one that was using 2-9V batteries (18V total) on a 12V motor. (MaxV?) The comment was that so long as one did not run it too long that way the motor did not get hot and overloaded and hence did not burn out. Even if it ever did...I have the spare motor...LOL.
gpraceman wrote:You can get balsa at Hobby Lobby, regular hobby stores and some craft stores. Wal-Mart might even have a balsa variety pack in its craft section.


Gotcha...I will see what I can do. BTW, weighing it a bit roughly...the motor, battery, propeller, wiring and servo chip set weighed about 3.6-3.7 oz. Soooo...not much left for the car design, wheels & axles. BTW, I'm thinking about wrapping the motor post in a circular pattern with the antenna wire..."Thinking" to get better reception if needed.
gpraceman wrote: The important parts of the car are regular pine, the chassis and the motor post. Those are what take all of the stresses. The body is one chunk of balsa, hollowed out for the electronics, shaped and then glued down to the chassis. The floor under the electronics was cut out and replaced with balsa to trim weight.
I'm convinced that you are right...for a 5 oz weight limit, this is the only way to go....especially if the OEM pine is some of the more dense variations.
gpraceman wrote:
TOU wrote:Also, did you go with standard one wheel raised?
It is a 4 on the floor. With all of that forward thrust, being as high up on the car as it is, having a raised front wheel would likely end up resulting in it running on both fronts and one rear.
EXACTLY...that's what I was wondering about. Hmmm..."having a raised front wheel would likely end up resulting in it running on both fronts and one rear."...maybe not a bad idea. I had worried about it contributing to torquing the car to one side. I'd also think if the mounting to the motor post was too high it might lead to the same scenario but more significantly. Either way, it looks like you have the right ratios as that thing just sings right along with out error.

Thx again for the input and feedback as well as the original thoughts. It may not be as pretty as yours, but I will post a picture when I get'er done.

All the best!

TOU
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gpraceman
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Re: Screaming Mimi

Post by gpraceman »

TOU wrote:BTW, I'm thinking about wrapping the motor post in a circular pattern with the antenna wire..."Thinking" to get better reception if needed.
It is worth giving it a try, but make it so you can easily reconfigure it if it doesn't work out.
TOU wrote:I'd also think if the mounting to the motor post was too high it might lead to the same scenario but more significantly. Either way, it looks like you have the right ratios as that thing just sings right along with out error.
The other thing to factor into your design is the height of the timer bridge. You want to make sure the prop will clear; otherwise, you might have a spectacular crash. :shock:
TOU wrote:It may not be as pretty as yours, but I will post a picture when I get'er done.
I'm looking forward to it.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
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Re: Screaming Mimi

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I was just thinking about something related to cost. Yes, I spent $30 on the plane and never even flew it. BUT...to put it in perspective, I previously spent $18+ on a 3.5 oz tungsten weight. They both weigh approximately the same. A bit more for the plane kit BUT I still have many spare parts for other projects left over from it. For it's application I think it may be a huge bang for the buck.

Hmmm...may have to pick up a couple more kits. LOL
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Re: Screaming Mimi

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Hey Randy,

I was trying to decide what kind of design. All the ones I was coming up with just don't lend them to:
  • a) Storing the gear
    b) Easy access to the gear as needed.
    c) Push the wheels as far apart as possible.
    d) Still look like something but maybe different than yours
About the only thing I could think of was a Yellow School Bus. :lol: But...I'm thinking I may have settled on a design that should lend itself well also....kind of a hybrid between your "Screaming Mimi" and one of Nitro Dan's designs.

Image

So...What do you think?


TOU

P.S. Went to 2 Wally's, 1 Michael's, 2 other craft stores, Home Depot and two hobby stores before I could come up with a solid block of balsa. (Lots of basswood but it is too heavy I think.) Even then I had to special order the blocks....should be in on Thursday evening. (FYI: It was a 2x2x12 for $4.50 at Hobby Town USA..) It should work nicely and not too badly priced.

TOU
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Re: Screaming Mimi

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I finished my version...here is a write up on it:

"My Midnight Deuce and a half..."
viewtopic.php?f=19&t=4932" target="_blank

Thx for the help!

TOU
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Re: Screaming Mimi

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gpraceman wrote:Now, here is another cool prop car. It's a pretty funny video too.

Though, I don't know about the claim to the "world's fastest". I think Screaming Mimi would give it a run for its money. :mrgreen: They are about an hour North of me. Maybe We need to do a local prop car race and see.
After racing my version this past weekend, I think I would agree with you. Of interesting note, his car was 14 ounces! Yours was 5 oz & mine ended up around 5.75 oz. (best I could bring it down to was around 5.3 oz...just gave up trying to get it less and ran it in the 8 oz class.) I wonder what his time and speed was? (BTW, mine was similar to yours.) I bet he spent a bit more $ on that set up than we did on ours. ;) Thx again for the inspiration.

TOU

P.S. I took some video, just need to figure out how to upload it.
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