pic: Team 948 Shifting Transmission Version #2

A CAD drawing of the new, improved NRG 948 two speed, ball shifting transmission.

Very nice, have you guys built it yet? =)

Working on it - the gears have been ordered at least. The whole gearbox casing (w/ the pneumatic mounting) is only 3 inches thick, the gearbox is around 8 lbs.

Out or curiosity, did you order gear stock for the gears? And of you did, from where? (See my signature)

Looks nice,:slight_smile:

Are those spacers next to the gears? or the hubs of the gears. If is the hubs I would suggest putting some spacer in between the two gears to reduce friction since they will spin at different ratios.

Just my $0.02
David G.

Looks good! Just remember to give yourself enough time to get the output shaft and gears heat treated.

Why do you say they have to heat treat them. I dont think there is a need, not for FIRST uses. But then again I am not an engineer. Do you mind explaining.


David G.

We have always hardened both the output gears and shaft for two main reasons. Hardening both parts means no wear on parts and also reduces the chances of galling. The gears definately will need to be hardened if you plan on shifting under a full load condition. Testing before hardening the slots in the gears that the ball bearing pops into has shown a slight wear pattern. This wear pattern maybe due to just run in and not get any worse during the season however our team likes to have a nearly maintenance free transmission. I know teams who used a ball shifter that did not harden the output shaft or the gears and they had no problems, but we’d rather not have an extra part to keep track of on our machine. Build it simple and fool proof. :cool:

I see, :rolleyes:

I designed a ball bearing shifter that is currently being tested but i did not take into a count hardening the gears. However :smiley: I used 6 holes on the gears and 3 balls so there is not as much friction while shifting. But either way do you think you could describe the process for hardening the gears?:confused:

I would appreciate it.


David Guzman


We have a local company harden the gears and shaft for us. I don’t know much about the process :o Maybe someone with more mechanical knowledge could explain the process of case hardening.

Dave Lavery made two very informative posts about hardening stuff here and here.

One inch diameter A2 tool steel is what we make the shaft with. The shaft and gears were hardened to between 55 and 62 Rockwell C.

Whatever you do, just keep them lubricated as with any transmission!

In 2003, we had a gearbox for our four-bar lift. We hit the bar across the field wrong two days before ship at a practice event and broke two teeth on one gear (non-treated). We exchanged it for a heat-treated gear and had no problems later.

Those are 1/16 in spacers.

For the gears, we ordered standard gears from smallparts.com - GSS 1435 and GSS 1460 are the part #s.


Does anyone have thoughts on using a servo to drive this, without modifying the center spool to include a spring?

I pitty the little servo about to die. :ahh: All joking aside, I think you might run into problems if there is no spring in the system. Remember for a short period of time every time you shift, there will be binding while you’re waiting for the balls to line up with the slots in the gear. These transmissions are more friendly than others towards their shifting actuator, but I would seriously suggest having some spring in there. The plunger shaft doesn’t have to have springs on it as long as the device actuating the plunger has some sort of shock absortion either in the unit or the connecting linkages.

Yeah, after thinking about it for awhile this makes a lot of sense… mainly we are trying to get rid of the pneumatics weight - but, according to my calculations, we should be able to get 28 shifts each on 2 gearboxes before we run one tank down from 120 psi to 40 psi, so we may run our bot without a compressor onboard which would make this work.