If you are using IPD/PCM or FS1 failsafes this may be of concern for you:-
The only check carried out by the scrutineers at Robot Wars is to switch off the transmitter under full stick conditions.
BUT if you’re really concerned about your safety, try this further check:-
Switch off the receiver battery (or simulate a cut wire between the receiver and it’s supply).
Does the weapon & drive system stop?
No,
should you be concerned?
Not for your entry but for your safety?
Combining IPD failsafes and a ‘Ken Hewitt' designed switch will cause the systems to fail safe in either of these situations!
If you are happy your motor switching can live with the current spike at start up then it’s time to check it can live with a stalled motor…
If you are running motors above their normal rated voltage then the stall current will be massive – can your relays handle it?
IT WILL HAPPEN.
Most robots use a drive ratio of between 3:1 & 5:1.
This will vary depending on the motor torque and speed and on wheel diameter.
It is unlikely this can be done in a single stage if you choose to use
a drive chain because the sprockets will either be too big or too small
to be sensible. I figured that bicycle chain would be sufficiently strong
since the torque generated by a human is without doubt more than I needed.
I didn’t really consider the chain speed though:-
Since the robot moves in both directions chain tensioning was done by moving sprocket centres. Bicycle chain is by necessity flexible, this is achieved by using slack pins and plates. When running at high speed the chain whips axially and is likely to jump the sprocket. I tried to prevent this by using nylon chain guides in the middle of each run but it became difficult to assemble, adjust, and was noisy.
IF YOU WANT TO USE A CHAIN DRIVE SYSTEM I STRONGLY RECOMMEND YOU DON’T USE BICYCLE CHAIN.
In addition to the rules could I add that the link really should be at the back of the robot. The stage setup means the robot is loaded into a sealed cell (pig pen) before the link is added from outside. (Lean over the wall). It's only possible to reach the back of the robot.
Ruf Ruf Dougal's link was unfortunately at the front so under protest he was allowed to compete but had to enter the arena backwards!
You will have to be able to switch off the receiver battery because the completed robot may have to wait in the 'pig pen' for an hour, if you load up before lunch. Don't forget you'll only be able to reach the back of the robot.
Ken Hewitt Radio Controlled Switch
OK, so you bought a tiny bit of strip board, assembled the components and tried the switch..............
It doesn't work:-
Don't despair the answers here.
Instead of using wire links everywhere, in one place he linked two tracks by running solder across, but he didn't tell you! Look at this picture and then go and put it right.
Problem solved.
You can find a link to Ken's projects on the links page but in case he deletes the switch I've copied the file here:-
rcsw.zip (240kB)