www.robowars.org

RoboWars Australia Forum Index -> Builders Reports

Total Recoil - Chunkulator - NSW
Goto page Previous  1, 2, 3, 4, 5, 6  Next

Post new topic   Reply to topic
  Author    Thread
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  

It's now fully assembled and has a flipping blade. It's 32cm wheel-to-wheel so the flipping blade is 7cm wide to comply with the "less than 1/4 of the width of the bot" rule.


I spent a bit of time driving and flipping today and a few issues came up I need to deal with. The main one is that firing the flipper without a payload causes enough of a jolt to shake some of the connectors loose from my microcontroller board. I'm 3D printing a connector-retaining cover at the moment to try to keep everything plugged in.

It doesn't drive that well I have to say. It really needs more gearing to have enough starting torque and it's kind of an awkward shape to skid steer. These issues will have to be sorted out in V2.


Last edited by chunkulator on Sat Jun 03, 2017 8:26 pm; edited 1 time in total

Post Fri Jun 02, 2017 9:32 pm 
 View user's profile Send private message
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW


 Reply with quote  

If there is a bit of spare weight, you could maybe fix the driving. Adding a HDPE or UMHW skid pad under the flipper can reduce friction and improve turning and top speeds. It only needs to be thin and a relatively small surface area. Place it on the centre line and as far forwards as possible to give the bot three points of contact.

You can probably increase wheel traction by cutting up a bike tyre and gluing & screwing it to the Bunnings wheels. Most builders use a chunky BMX tread but I think a soft indoor racing tyre will have more grip - check out eBay and a local bike store.
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Fri Jun 02, 2017 9:46 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  

Unfortunately the issue is more baked in than that. I'm using 270kV brushless motors with sensorless ESCs with only 2:1 gearing to a 5 inch wheel. At that low gear ratio, the ESC can't reliably get the motor spinning if the bot is pushing against something. Needs more gearing and/or a Sensored ESC or brushed motor to resolve.

That's what happens when you go experimenting with untried drivetrain configurations I guess. I had to fit the drive system into a tricky space where there wasn't room for a gearbox, so was hoping this would work. It does, but it's less than ideal.

I think V2 will be wider with room for proper motor drives and made of laser cut steel plate.

Post Sat Jun 03, 2017 6:41 am 
 View user's profile Send private message
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW


 Reply with quote  

2:1 gearing is very low for brushless motors. I have seen 3:1 gearing with sensored motors but around 20:1 and a higher KV motor generally works better.
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Sat Jun 03, 2017 8:55 am 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  

Yes. I've learned my lesson on that. I think after Vivd I can probably hack a jackshaft in there to up the gearing, but will need to shed weight elsewhere to do so. I don't think it's wise to attempt that now. This is effectively my last build day before Vivid I need to do a little work on the other bot to get it ready. I will have to see how it goes as is.

Post Sat Jun 03, 2017 11:04 am 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  

After more troubleshooting on the drive I'm feeling a lot more positive about it. I found a couple of places where things were slipping and rubbing which a fixed with some grinding here and some beefier set screws there. Now that I've sorted that out and had a bit more driving practice I feel like I'm a lot more in control of the bot. It's definitely not going to win any pushing match from a standing start but if you give it a short runway it's extremely quick and with some practice you can keep it somewhat pointed in the right direction.

Post Sat Jun 03, 2017 2:22 pm 
 View user's profile Send private message
pilleya



Joined: 31 Mar 2016
Posts: 91
Location: Sydney


 Reply with quote  

What size are the gears you are using? You should be able to fit a decent reduction in the space that you have, I'm running 12-48t 20DP reduction in mine mainly just because that was the maximum that I could fit in a single stage and in the available space.

Post Sat Jun 03, 2017 6:25 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  

I am not currently using any (the 2:1 ratio is the chain and sprocket drive), but generally I use metric 1 module gears. I spent a long time in the CAD phase trying to fit 1 module gearing in but I need the motors quite far away from the axle in order to not interfere with the spring mechanism and I'm right on the weight limit, which is why I ended up with chain and sprocket. It might look like a big robot but the insides are pretty tightly packed full of spring flipping mechanism!

Post Sat Jun 03, 2017 8:25 pm 
 View user's profile Send private message
Philip
Experienced Roboteer


Joined: 18 Jun 2004
Posts: 3842
Location: Queensland near Brisbane


 Reply with quote  

Can you put up some details on your latest build?
_________________
So even the rain that falls isn't actually going to fill our dams and our river systems

Post Sat May 26, 2018 2:46 am 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  

Thanks for the prompt Philip. Here it comes...

Post Sat May 26, 2018 11:58 am 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  
Total Recoil 2

Total Recoil 1 showed a spring flipper could kinda be effective so I set out to make a second version learning from the mistakes of the first version. The key differences:
- Proper planetary gearboxes in the drive system (BaneBots P60s)
- CAD designed in Fusion 360 and lasercut from Hardox 450
- Snail cam to tension and release the springs instead of the leadscrew design I used in the first Total Recoil.

Post Sat May 26, 2018 12:02 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  

I started out doing a lot of CAD work in Fusion 360:



Before I got the metalwork laser cut I cut two prototypes from 3mm MDF using my CNC router:


Nick helped me cut keyways in some of the 1/2" 4140 shafts:

I made sure everything fit properly (a few things didn't and I made some tweaks to the CAD design before sending it out for the laser cutting). Here you can see the BaneBots P80 gearbox which drives the snail cam through a #35 chain and sprocket drive. You can also see one side of the drive. I used NTM PropDrive 35-42 motors on BaneBots P60s (16:1) with 3" Colson wheels. The shafts are supported both sides of the wheel with the BaneBots bearing blocks. To reduce ground clearance to 5mm I CNC cut risers for the gearboxes and bearings from 5mm HDPE.

Post Sat May 26, 2018 12:08 pm 
 View user's profile Send private message
Philip
Experienced Roboteer


Joined: 18 Jun 2004
Posts: 3842
Location: Queensland near Brisbane


 Reply with quote  

Thanks, Richard. Do you have any video of it flipping a robot or equivalent weight? How many kilograms of weight does it take to force the tip to the ground?
_________________
So even the rain that falls isn't actually going to fill our dams and our river systems

Post Sat May 26, 2018 12:23 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  

I cut a custom P80 gearbox backplate from 12mm 6061 on my CNC machine. You can see my big CNC router's not really rigid enough for doing aluminium, but if you go slow you can almost get away with it:

Here is the backplate on the gearbox:

This allowed me to mount a large 5060 brushless for a longboard on the P80:

I started out with 256:1 gearing but bought the 64:1 ring gear as well. Once I had the whole thing together I found 64:1 was plenty of gearing. Here you can also see the rotary encoder which I mounted on the snail cam shaft so the micro (Teensy 3.2) can determine the snail cam position:


Last edited by chunkulator on Sat May 26, 2018 9:45 pm; edited 1 time in total

Post Sat May 26, 2018 12:25 pm 
 View user's profile Send private message
chunkulator



Joined: 27 Jul 2016
Posts: 219


 Reply with quote  

Here is a prototype of the snail cam which I cut from plywood:

The real one was cut from 8mm hardox. The cam was welded to a hub which Nick turned and keyed for me from 4140. Here is the prototype cam mounted in the prototype frame. Not mounted here is the cam follower which is a piece of 1/2" 4140 shaft that runs in FR8 bearings pressed into the large holes you can see in the arm.

These are the springs with lobster for scale. I bought them on ebay from a supplier of porch swing mounting hardware in the UK. They are each designed to support a 250kg porch swing and are made of 6mm diameter spring steel (that's a lot of force to try to contain):

Post Sat May 26, 2018 12:31 pm 
 View user's profile Send private message
  Display posts from previous:      

Forum Jump:
Jump to:  

Post new topic   Reply to topic
Page 5 of 6

Goto page Previous  1, 2, 3, 4, 5, 6  Next

Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

 

Last Thread | Next Thread  >
Powered by phpBB: © 2001 phpBB Group
millenniumFalcon Template By Vereor.