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a few design questions...
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Glen
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you could definitely stand to move those wheels a few cm inboard, just incase the sidewall gets mashed into them.

as for the spacing it looks okay with those dimensions. it really depends on the drive power. old plan g had far larger spacing than that and ran well enough with two mini ev size motors.
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Post Sun Apr 08, 2007 3:07 pm 
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Karmond



Joined: 16 Jun 2004
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quote:
Originally posted by Philip Taylor:
You can always start building your design and find out how it handles. Some builders have made prototypes from MDF and the like. This will allow you to test your theories and find if you are happy with the result without spending lots of money on purchasing specialized materials, cutting and welding.

Good luck.
Well first I'd like to be confident I can build it in the first place. :p I'm not going to get parts until I'm sure I can do the actuators.

quote:
Originally posted by Glen:
you could definitely stand to move those wheels a few cm inboard, just incase the sidewall gets mashed into them.

as for the spacing it looks okay with those dimensions. it really depends on the drive power. old plan g had far larger spacing than that and ran well enough with two mini ev size motors.
Yeah, there's pleanty of space to move them inwards, There's already 5mm infront and back of the rubber and there will be the outer shell running around the bot. I drew up aluminum strips to go inbetween the belts to help strengthen that space up also.

Just for fun I reshuffled the gearbox to see how it would look. It freed up some space. I got the spaces from the center of the wheels to be 230 mm (left-right) by 240 mm (front-back) this did put extra weight behind the rear axles though (I'm guessing those gearbox setups will be around 1kg each). I'm not sure how much that would effect driving.


Post Sun Apr 08, 2007 3:24 pm 
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Glen
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assuming the motors are at the rear i think thatll be a much better setup Smile
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Post Sun Apr 08, 2007 3:34 pm 
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Valen
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dude diagonals
otherwise you will end up with the "singularity effect", where one sideways impact means your robot is now diamond shaped.
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Post Sun Apr 08, 2007 3:35 pm 
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Karmond



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quote:
Originally posted by Valen:
dude diagonals
otherwise you will end up with the "singularity effect", where one sideways impact means your robot is now diamond shaped.
But, but, but squares are easier. Sad

Post Sun Apr 08, 2007 3:58 pm 
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dyrodium
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I strongly agree with Jake, he helped me out putting diagonals and triangulation into snak masheen and results in a way stronger frame. And that singularity hit was messy... Laughing
Get some cardboard and pretend it's your frame, if its aluminium it'll bend as easy as cardboard to spinners anywho. Razz
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Post Sun Apr 08, 2007 4:30 pm 
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Nick
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Trianulation is good - you can get it by using a strong baseplate and well attached sidepanels
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Post Sun Apr 08, 2007 5:28 pm 
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kkeerroo
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Nick do you know what a triangle is? I can lend you a structural engineering textbook if you want. It has lots of triangles in it.
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Post Sun Apr 08, 2007 7:47 pm 
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Nick
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Confused Pardon? Confused I'm pretty sure I know what a triangle is and you get two nice ones by drawing a line between opposite corners of of a rectangular baseplate Laughing I might not have a degree in engineering, but I DO have a load of experience - you might notice that none of my bots have ever bent from a lack of triangulation!
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Post Sun Apr 08, 2007 8:09 pm 
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Daniel
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My robots flex a lot, but that is just how different people design things.

I told my brother that his post made no sense, but he still hit the submit button.

Post Sun Apr 08, 2007 8:16 pm 
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Totaly_Recycled
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you get 4 nice triangles if you draw a line from the other two corners Very Happy

Post Sun Apr 08, 2007 9:09 pm 
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Nick
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So true - a base plate is just 4 large gusset plates welded together Smile
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Post Sun Apr 08, 2007 9:26 pm 
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Karmond



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Um, where abouts could I put some triangulation... I could reinforce areas like putting some aliminium horizontally in those empty boxes next to the wheels. Maybe put some more aluminium next to the outer walls (like the rear wall, infront of the front wheels [the top and bottom corners] and where the sides meet the front and rear walls.

Post Sun Apr 08, 2007 10:13 pm 
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Karmond



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Could anyone confirm/deny if the following sounds right:
http://www.nookindustries.com/acme/AcmeInchAvailability.cfm

in the same time and distance...
a 1/4" screw with 4x4 threads per inch with a motor geared to do 4 RPM, and having 1lb-in of torque will be able to move 17.9lb.

a 1/4" screw with 20 threads per inch with a motor geared to do 20 RPM, and having 0.2lb-in of torque will be able to move 10lb.

A 3/8" 8 thread, 100 RPM motor with 50lb-in of torque moves 1190.5lb.
A 3/8" 16 thread, 200 RPM motor with 25lb-in of torque moves 806.5lb.


Edit: I've edited out the stupid in my post after realising there's a typo on that page.

Post Tue Apr 10, 2007 3:05 pm 
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Karmond



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Well now that I've fixed the problem in my previous post, these are some calculations I came up with some different acme threads thread sizes (using the more efficient threads & the bronze nut) and an RS550 at 125:1 ratio runnning at 14.8v.

RS550 125:1 (3 stage)
190 RPM @ 14.8v
= 3.2 RPS

10876 oz-in stall torque
= 679.8 lb-in stall torque
= 783200 g-cm stall torque
= 783.2 kg-cm stall torque


Acme Thread
6.4mm (1/4") = 3x4 per 25.4mm (3/in)

9312.3 lb force
4224 kg force
27.09 mm/s

Acme Thread
7.9mm (5/16") = 4x2 per 25.4mm (4/in)

11522.0 lb force
5226 kg force
20.32 mm/s


Acme Thread
9.5mm (3/8") = 2x4 per 25.4mm (2/in)

6353.3 lb force
2882 kg force
40.64 mm/s


Does something like this sound like a good idea? Is going for a low RPM high torque gearbox setup a good way to go? Biohazard's actuators are the other way around, high RPM low torque. The 12v motors for it's actuators are running at 24v, with a ratio of about 9:1.

Post Wed Apr 11, 2007 4:05 pm 
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