Mechanical tips for rookies

[Anne Shade]

After reading some of the pit tips listed in another thread, I thought it would be a good idea to list some tips for mechanical design. I think this would be a good handout for rookies before or at kickoff to help them out. I'll combine these and make up a one pager. Here are some I came up with so far:

1. Know your limitations. Innovation and new ideas are great, but trying to do more than your team is able to handle doesn’t help anyone. It is much better to do one thing really well than to do a lot of things badly.

2. Keep track of weight. Having an overweight robot is the number one problem of robots at their first competitions. To avoid this, assign someone the job to keep track of the weights of each part going on the robot. This person can also perform weight estimates during design as well.

3. Think about maintenance during design. Some parts will require more maintenance than others (like gearboxes, motors, etc). Make sure those parts are easily accessible and that you have spares.

4. Keep the center of gravity low. There is a lot of interaction between robots on the field. Many robots get tipped over. To avoid this, try to keep the CG as low as possible and distribute weight on your base accordingly.

5. Prototype ideas. Test ideas with simple prototypes with materials like card board, wood, etc. Helps to find problems early in the design phase and give visual people a better idea of what’s going on.

6. Create design drawings. The best would be full 3D CAD models but at a minimum have hand drawn scaled drawings or 2D CAD. This helps avoid mistakes during manufacturing.

7. Standardize hardware. Have one or two types of nuts and bolts. Makes it much easier since only one or two tools are needed for building and repairs. At the very least, choose either metric or English.

8. Make spares. The easiest time to make spares is at usually at the same time as the original piece. Taking some time to do this will save you a lot of stress during competitions.

9. Get a base and drive train done soon. Not only is this a big moral booster, it gives drivers more practice and gives you more time to debug this most vital system of your robot.

10. Don’t forget about pneumatics. Pneumatics are sometimes an easier solution than a motor for simple applications. Their advantage increases when they are used in several locations on robot (weight).

11. Avoid set screws. Robots have a lot of vibrations and they tend to shake the set screws loose. Use pins, welding, keyways, etc to attach parts to shafts.

12. Too much traction can be bad. With too much traction, your robot won’t go anywhere or will be jumping all over the place when you’re turning. This is another good reason to have the drive train up and running early, to test out your wheels.

[RoboMom]

Anne, these are great. Make sure you post in the white papers so they are easy to find.

[SpaceOsc]

you forgot about BATTERYS and keeping someone on them at all times, check before matches, keep them charged during build for testing moments or when that Powered rolling skate board you come up with first is ready for moving.

its STUPID for the team to send a robot on the field without at lease someone knowing its voltage... then see it CHOKE and die

hmms heres another, when you mark something for cutting dont do it with a WIDE print dry erase marker... hmms use a flat head screw driver or dark .5mm pencil or ball point pen.

[JVN]

Originally Posted by Billfred

Oh, and remember that while it is important to keep your batteries juiced, you may not have to charge them every match...

BAD ADVICE!
DANGER!

Bill,
I'm gonna come right out and say you're wrong.
You ALWAYS want to put the freshest battery you have on the robot. Brownouts/lowvoltage can KILL you at a critical moment in a match.

Every team should implement some kind of battery management system (ours is a senior named "Aaron"). Trust me, you don't want to die at that critical moment because your battery died.

Charge every match.
Charge constantly.
Keep multiple batteries on charge.

Also, be familiar with your chargers. The ones that take 8 hours to fully trickle charge a battery are NOT going to cut it during the heat of competition.

John

[JVN]

Anne,
This is AWESOME. You're selling yourself short though...

Rookie teams? I bet there are lots of veteran teams who could probably use a reminder of some of these principles from time to time as well.

This is just good advice for ALL teams to take to heart.

Thanks for posting!

John

[Anne Shade]

Very true John, this is advice for all. I'll keep that in mind when I put the final list together.

As for the batteries, I didn't put them on this list since it is the mechanical list. Look at the electrical list and you will see it on there. Please keep the suggestions coming, the more info on this list the better.

[Doug G]

After a bit of chaos last year, our team was / is determined to have a full-functional prototype robot for the 2005 season. Maybe have it completed by the Third or Fourth week. It could be made from 80-20 or Bosch extrusion or even wood. There are some obvious increase in costs associated with this - but hopefully will allow for a more functional and tested robot in the end. Any idea how many teams are out there that already do this? Maybe 10%?

[SpaceOsc]

how about a tip on loctie and whats shouldnt be and what should be

always cut long , but never short (as in extra materail vs making short and useless)


(One of Ours mentors really stress this)
Tight Means Tight , Not how tight you could get it , and not striping and destroying parts, and not leaving it loose


PVC Can be your friend


ALWAYS Clamp it Down


Right tool for the right job


more to come... maybe

[greencactus3]

weeelll, remeber, bungee is your friend, but always do the math to figure out if the cylinder you wanna use has enuf force to lift w/e. even if it works at 100psi, it doesnt matter if it doesnt at 60.

[Al Skierkiewicz]

All,
The top of my list is to get a working/driving base finished first. It is needed for electrical to work on part placement, drive team needs practice and autonomous team needs something to mount prototypes on.
Open gear transmissions produce metal flakes (grindage) so protect electrical circuits from fallout.
Be aware of robot systems when drilling or machining parts on the bot. A square tube makes as good an electrical conduit as it does a support member. Your electrical team may have passed motor wiring through the tube you are drilling!
NO GRINDING IN THE PITS! Besides it causing incredible noise, the flying hot bits are a real fire hazard.
When a motor or other shaft does not have enough bearing (most do not) you must add bearings that can take the stress. You cannot hang a sprocket or wheel on the end of the chalupa motor shaft and expect it (the motor) to survive.
Motors do draw "stall current" when you stop them. Avoid stalling motors or running them in near stall in your designs. The currents are extreme and the motors will run very hot. Stall current on the drill motor is 129 Amps or over 1500 watts.
Grindage and flakes from ferrous metals are attracted to the magnets inside motors. This is a big concern for open frame motors like the drill and FP motors and fans, where the flakes will jamb between magnet and armature or short out the brush assembly or armature windings. Compressed air will not dislodge these flakes. The speed controllers are not sealed and many have died from metal flakes falling into them.

[Anne Shade]

I've posted the updated list in the white paper section. If anyone has any other suggestions, let me know and I'll update the document. Feel free to use it as a handout for your team and for new rookie teams. Hope it helps.