P08205: RP 1 Motor Module First Generation
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Gomez Interview 20070928

Normally when I talk about these motor modules I usually you know go over the electrical just because that’s what we actually dealt with now as far as the mechanical perspective is concerned, I think, the main concept was surprisingly good because it did what it was supposed to, and it’s super versatile then what we encounter more is that is the young design that it need more improvement so for example one of the this things that is always a big thing is how high this thing was I think if we were to take a ratio of the distance from the floor to the end of the (wheel) and then from there up we get a find that (EH) you know for height/ for each inch we have to the wheel shint than can be translate 2 or 3 inch on the tope, so they when you actually do some center of gravity calculation and dynamic calculations you find that actually ends up playing a huge role on how stable this platform can be. So that one/the after one of course is shape round shape on wells or the wells end up being pretty big so in order to count you know all those detail that when you final put everything together you go oh OK you know this didn’t go there because they were perhaps too big and then you say OK let me make this hole alot bigger so we can (23â€17) allow for that Suppose to this screw […] in the rite place. So then again that is suspected to/for young design also they […] if you look at the lower shaft we have two main positional shaft. One / I think it is half an inch and it is held togesser by this spring it is some sertify washer with spring on it. that makes difficult for her to come […] and I think that could be good […] however when you actually use the technology if I […] that you need a lot more. […] in place also these is lot washer where a single washer proper size could be used. so you can have / so some point we had larger washer when I […] he was oviously too big for the job then another washer was put in place to accommodate for that difference and yet another washer put in there used to […] washer to keep in place so if only the write washer was you know […] used to begin with […]. Some other part, there were to many part in the module so it could be good to bring this part down to a basic engineering principle the less parts you have the less that can go wrong . now they […] that not to say that / also they, some of they […] turning table / first of all that turning table, it does […] suppose to do, but think we can do something else about that, it is so happen that turning table is excellent for action/ force and to deal with that type of load but it is not really great to the […] any size low or any momentum and given that the cross section (25â€22) of the […] I think it is 20 or 18 gage (HE) steel it why made of a mix […] very susceptible to those type of loads. Also they […] , In order for the lower part of the motor module to rotate there is an inner gear and an outer gear that are meshed together it is so happen that this two gear are 20° pressure angle and the other has a 14 degree pressure angle so when you actually (mesh these two gears together)they actually appear to mesh correctly but they don’t so and what happens is eventually it will work within a range after that is gone a stock get stock so that […] especially because it so happen that the driving motor was linked to this inner gear by means of a shaft it was put together and that not exactly the beefiest of connections. (26â€44) So let me know draw a picture to explain you have this, (stirling motor) yes so you have this, this is essentially it could be an inner gear they are attached permanently to the lower portion of the motor module. Right so I noticed for this to spin I need to hold it at the axis and apply a force so we can do that by getting the shaft in here , conveniently the driving shaft which is quite clever and there are an other gear, here, that’s an outer gear to drive OK and we have actually have an other shaft here so we have two motors one is it driving and this little guy and the cool thing about this is that this can rotate. Pretty much indefinitely now the problem would be in here so the (matching) of these two gears it is the pressure angle and so they didn’t match up completely and so eventually they get stuck and as soon as they get stuck(28â€04) this guy stalled meaning that the […]so this shaft here broke and the reason why the broke it is because if you look at the coupling in here it should be the actual driving, oh excuse me, they turning motor and the other motor actually was attached to the rest of the shaft was actually attached in here I think this was the whole and there is turning down so it could fit inside and then there was a pin (28:45) going through just like a spring a shear pin and then this failed about four times and that meant given that this is of the heart of the module and we have to take apart the entire thing to replace that little shear pin (any accessibility of components is an issue also) innovation too something like that because if you look at the conception then you have something like that. This is the main shaft this is the secondary shaft. And then this is the (shear) pin going right through it now the funny thing about this is that these guys here about (a quarter inch) and these guys here it is about 16,5 inch across so there is very small component not to mention this is the spring pin so it is only on the outside […] material […] now I mean from a visual perspective it might seem that it’s going to work but it is just turns out that this thing gives out enough torque to break the thing and then which to be expect if you know if you’re playing with these things and they’re still in development things will break. And then on top of things to access that is just almost impossible. I mean if you need to demonstrate the technology at 11 you think that working at 10:30 all of a sudden the thing breaks its gonna be 11:45 its gonna be 12 before you can put a new one in place (30:35) So that’s one also putting wiring inside the module can be quite frustrating. So once we have this there is a cover that goes over it and then you (gonna) have 1, 2, 5 14 wires coming out of there so two of them are gonna be quite big […] ok then those go to the main motor for the turning motor you get have some anywhere from some 16 or 18 and then you have the actual signal of the encoder (31:21) so that actually two line or 5 conductors (each) and they ought to be shielded OK so and then what makes this funny is that this conduct a lot of current so they are beefy at least to get the power from the battery to the module we used I think 6 gauge wire and that just if you look at the battery cable in your car that is 10 we use 6 which is two numbers larger than that so this thing are pretty big and with this small compact design it is really difficult to deal with in addition to that these things are turning so there are false signals and then everything is made out of metal that mean there is a lot of noise so on this motor one (that’s why it was shielded) the encoder which is just a low current signal that can potentially it’s also a high frequency signal that can get dirty because of interaction and what we had was a different connecter […] so we have one type of connecter for the (high current) […] current connector then we had molex for the driving motor connectors and we had some little connecter for the encoder so essentially we have 4 connecters on each module that mean that every time you change it you have to changed 4 connecters instead of have just one unified connecter and I think that was one of we actually said this a really good idea to try to put every thing in one connecter. Now for small robot I think it is an awesome idea I don’t know how could be dealt with for a larger robot other than the gauge of the wires but I think that something we […] mechanical aspect of thing it could be improve in addition to , you know reduce some part […] make the thing more accessible better usage of the volume of the module to be more careful with couplings (do you think motor selection and other component selection drives down the gauging of the wire that will overall improve the usefulness of the volume available) yes if by component you mean if […] OK if the motor module was sine so we had an 8 to 1 gear ration we had a 20 or 80 to 1 gear ratio[…] that mean that the motor didn’t have to deliver so much torque and therefore draw too much current. Now there’s pros and cons to that to that mean you have a gear box in there first of all are you going to actually make that gear box, it takes a lot of machine expertise to make and go right or if you buy something else it might be expensive […] and also there are more volume, more components added to the overall design so I guess that’s something along the point of trying to reach the optimum point we actually draw down the current to something more reasonable and you know we could actually sacrifice […]I believe that could be an approached to do that. And also you know mechanical connection I think is actually […] I think are udge safety issue. I mean I don’t know […] for a smaller robot but […] big dill (35:30) but if you have a smaller robot likely […] to be used […] battery could be expensive don’t be another pressure […] because robot […] less courant […] you know […] the electrical safety […] because I mean the electronic […] and the battery are sensitive so […]. One single plug could be great. Anything else? hen (professor E. told me that originally […] team […] a circular mechanical interface between the platform and motor module and platform team […] square one.

Summary

Mechanical concept was good. And we can use it. But there are some things that we must modify for example the interface between shaft and gear. To create the link between shaft and gear they used a pin and it was this pin which broke. This pine broke because the size is note very big and because there is a pressure angle which is not appropriate. The couple hangs on is very important. We must change this link by another or modify the pressure angle. It is important to say that there is not a lot of place and component is very small.

There are a lot of washers where a single washer proper size could be used.

The turning table is excellent for “acio†or force but it is not realy great to the […]

There is also a lot of consumption about motor. And we can try to reduce this consumption. (We can compare this one with a car) that it could be hard for us is to find a compromise between consumption and number of part used. Because if we want reduce the consumption we must add some new part and the pries increase. We must find the good compromise. It is important to say that buy new battery is expensive.

We can see for different connection with platform, round, square, rectangular … it depend of the geometries of platforms. We can see different technique to put motor module on the platform, for last project it was easier to incorporate motor module by one side because it was for 100 or 10 Kg platform team. But for us it could be different. To him circular or rectangular interfaces are good idea. To do our choice we must know who the platform could be used. We must adapted the technology.

Now for 100 or 10 Kg motor module there are 4 connectors for motor and it could be interesting to have just 1 plug. He thinks that is important to put just one connector.