Featherweight Recommended Speed / Output Shaft RPM

[Triceratop]

Hi all,
Looking at building Featherweight number two as first (Tricerabot Jnr) was a bit of fun / prototype. The problem I have there is an abundance of motors / gearboxes etc, all having different output speeds. Can anyone suggest a happy medium speed I should be looking for please? I will be running on 4" wheels so either output shaft rpm or Km/hr will be a great help.
I have found a couple of very high torque drill motor/gearbox assemblies but the output shaft is giving 650rpm which equates to 12.250km/hr on 4" wheels (seems slow)....
Finally I cannot increase wheel size due to construction of robot.
Thanks for the help.

[Ocracoke]

650rpm on 4" wheels is OK, that is about 7.7mph. The Honey Badger 2.2 used 4.33 inch wheels with a motor/gearbox giving about 844rpm at 19.8v meaning about 11mph and if you watch some of the videos of it at Manchester 2018, that was petty fast.

If you wanted 9mph, you'd want about 770rpm for example which I imagine is achievable with the motors you are looking at by overvolting slightly.

[Triceratop]

Hi Michael,
Thanks for the reply, I intend to over volt using 6s Lipo battery, so yes should get a little more than the specified rpm out put. The torque on the output shaft is running around 40 n/m ea, so should have plenty of umph to stand it's ground.
Regards

[Eidg]

My FW Spinner makes 20km/h, especially in bigger arenas is speed important.

[Al_]

Whats the nominal voltage of the motors and what are you planning on running them at? It would be good to get a more precise figure of the overvoltage and therefore the theoretical new rpm. FYI both mine are geared for the 10-12mph range which I find plenty fast enough. Being able to control them and drive accurately is another matter....

[emisnug]

I'm running 4" wheels on the feather that I'm building at the moment, but geared more for speed and silly traction than anything else - so take my numbers with a pinch of salt as I'm one of the crazier people here.

Mine is geared for 20MPH - which is over the top, but what I have space for. Shaft input of 8600RPM with a 5:1 reduction. A good middle ground is the 10MPH mark!

[Triceratop]

Hi guys, thanks for the input, just for clarification I shall be running 18v motors with a 650rpm on the output shaft @ 22.2v so I should see a slight increase of speed, I am guessing approx. 800rpm. This in mind I shall be running 4" wheels so theoretically I should get 15km/hr (9mph). With the current design of the new bot I cannot increase the wheel size, but if speed is a problem then I will have to redesign for 5" wheels .

[Ocracoke]

I honestly don't think it'll be an issue. Whilst speed is nice, control is often better.

[grant_ploughbot]

9mph is a nice speed for a featherweight that won't be uncontrollable.

[James Williams]

9mph should be quick enough. Keep in mind at live events you'll be thrown in with at least 15 other bots (sometimes more than twice that) so you there will always be an opponent less than 4 feet away.

[Triceratop]

Thanks for all the comments and advice, I think I shall stay with the 9mph and keep the high torque which should help in close combat.
Regards